third workshop on size-dependent effects in materials for

Third Workshop on

Size-Dependent Effects in Materials for Environmental

Protection and Energy Application

Bulgarian Academy of Sciences

Institute of General and Inorganic Chemistry

September 12 – 15, 2021

Pomorie, Bulgaria

Third Workshop on

Size-Dependent Effects in Materials for

Environmental Protection and Energy Application

Bulgarian Academy of Sciences

Institute of General and Inorganic Chemistry

September 12 – 15, 2021

Pomorie, Bulgaria

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Workshop on Size-Dependent Effect in Materials for Environmental Protection and Energy Application

Pomorie, Bulgaria | September 12-15, 2021

Workshop Topics

Topic A. MATERIALS AND THIN FILMS FOR ENVIRONMENTAL PROTECTION

Topic B. MATERIALS FOR CLEAN ENERGY STORAGE

Topic C. CERAMICS/BIOCERAMICS AND GLASSES FOR BETTER LIFE

Workshop Organizers

Chairs of the workshop:

Radostina STOYANOVA (Bulgaria)

Konstantin HADJIIVANOV (Bulgaria)

International scientific committee:

Alfonso CABALLERO (Spain)

Helmut EHRENBERG (Germany)

Peter David HAYNES (United Kingdom)

Tony SPASSOV (Bulgaria)

Local organizers:

The local organisation is undertaken by Institute of General and Inorganic Chemistry, Bulgarian

Academy of Sciences.

Ivelina Georgieva

Albena Bachvarova

Genoveva Atanasova

Delyana Manasieva

Elena Ivanova

Kristina Chakarova

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Plenary lectures

Topic A

A. CABALLERO - Instituto de Ciencia de Materiales de Sevilla, Spain

An in situ characterization of Ni/SBA-15 catalysts: how to elucidate if metal is confined in the

mesoporous channels

P. HAYNES - Imperial College London, United Kingdom

In situ quantum-mechanical simulations of nanomaterials

P. K. PETROV - Imperial College London, United Kingdom

Transition metal nitride thin films for surfaces with enhanced performance

Topic B

A. R. GONZÁLEZ-ELIPE - Instituto de Ciencia de Materiales de Sevilla, Spain

Porous electrodes prepared by magnetron sputtering: from electrochemical sensing to energy

applications

E.I. KAMITSOS - Theoretical and Physical Chemistry Institute, NHRF, Greece

Ion conducting glasses in thin film forms by infrared techniques

J. MAIBACH - Karlsruhe Institute of Technology, Germany

What can photoelectron spectroscopy tell us about the transition from Li to post-Li batteries?

T. SPASSOV - Faculty of Chemistry and Pharmacy, University of Sofia, Bulgaria

Three-dimensional porous metallic structures by selective dissolution of amorphous and

nanocrystalline alloys

Topic C

M. A. DIAZ - CUENCA - ICMS, joint CSIC-University of Seville Center, Spain

Mesoporous ceramics: applications in biomedical research

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Contents

Topic A

АO-1 AN IN SITU CHARACTERIZATION OF NI/SBA-15 CATALYSTS: HOW TO ELUCIDATE IF METAL IS CONFINED IN THE MESOPOROUS CHANNELS A. CABALLERO 7

АO-2 IN SITU QUANTUM-MECHANICAL SIMULATIONS OF NANOMATERIALS P. HAYNES 9

АO-3 MONOLAYER CATALYSIS: CATALYTIC ACTIVITY OF HYBRID PD MONOLAYERS OVER Γ-AL2O3 AND MONOCLINIC ZRO2 IN DISSOCIATION REACTIONS A. A. RYBAKOV, V. A. LARIN, S. TODOROVA, D. N. TRUBNIKOV AND A. V. LARIN 10

АO-4 TRANSITION METAL NITRIDE THIN FILMS FOR SURFACES WITH ENHANCED PERFORMANCE R. BOWER AND P. K. PETROV 12

АO-5 TAILORING THE SINGLET FISSION PROPENSITY OF ORGANIC CHROMOPHORES J. STOYCHEVA, A. TADJER AND J. ROMANOVA 14

АP-1 STRUCTURE AND PROPERTIES OF KNI–HEXACYANOFERRATE PRUSSIAN BLUE ANALOGUES FOR EFFICIENT CO2 CAPTURE: HOST–GUEST INTERACTION CHEMISTRY

AND DYNAMICS OF CO2 ADSORPTION S. ANDONOVA, S. S. AKBARI, F. KARADAŞ, I. SPASSOVA, D. PANEVA AND K. HADJIIVANOV 15

AP-2 NOBLE-METAL NANOCOLUMNS PRODUCED BY PLD AT ATMOSPHERIC PRESSURE G. ATANASOVA, T. DILOVA, RU. G. NIKOV, A. OG. DIKOVSKA AND N. N. NEDYALKOV 17

АP-3 XPS STUDY OF PURE AND COMPOSITE NOBLE METAL NANOPARTICLES A. BAEVA, T. DILOVA, G. ATANASOVA, RU. G. NIKOV, RO. G. NIKOV, A. OG. DIKOVSKA AND N. N. NEDYALKOV 19

АP-4 HYDROTHERMAL SYNTHESIS OF ZSM-5 ZEOLITE FOR CATALYTIC APPLICATIONS B. BARBOV, T. TODOROVA, G. KARCHEVA AND YU. KALVACHEV 21

АP-5 CATION DISTRIBUTION AND MAGNETIC PROPERTIES OF NI-ZN FERRITES PREPARED BY SOLUTION COMBUSTION TECHNIQUE WITH GLYCINE AS A FUEL G. BURDINA, V. TUMBALEV, N. MARINKOV, D. KOVACHEVA, M. GEORGIEVA AND D. TZANKOV 22

АP-6 ADSORPTION PROPERTIES OF THE MICROPOROUS MIL-96(AL) MOF: IN-SITU IR STUDY K. CHAKAROVA, M. MIHAYLOV AND K. HADJIIVANOV 24

АP-7 STUDIES ON COPPER (II) BIOSORPTION USING A MATERIAL BASED ON THYMUS VULGARIS L L. IVANOVA, P. VASSILEVA AND A. DETCHEVA 26

АP-8 ACETONE-SENSING PROPERTIES OF ZNO–NOBLE METALS COMPOSITE NANOSTRUCTURES AND THEIR IMPROVEMENT BY LIGHT IRRADIATION T. DILOVA, G. ATANASOVA, RO. G. NIKOV, A. OG. DIKOVSKA AND N. N. NEDYALKOV 28

АP-9 SORPTION MECHANISM OF MCPA HERBICIDE ON MINERAL GOETHITE (110) SURFACE IN DEPENDENCE OF PH. THEORETICAL STUDY I. GEORGIEVA, M. KERSTEN AND D. TUNEGA 29

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АP-10 SILVER-CONTAINING ZEOLITES – PREPARATION, COMPOSITION AND ANTIBACTERIAL PROPERTIES G. GICHEVA, N. MINTCHEVA, M. PANAYOTOVA AND O. GEMISHEV 31

АP-11 APPLICATION OF BULGARIAN CLINOPTILOLITE AS CARRIER FOR MN-CONTAINING CATALYST IN VOCS ELIMINATION I. HRISTOVA, S. TODOROVA, H. KOLEV, G. AVDEEV AND A. NAYDENOV 33

АP-12 MESOPOROUS NANOSTRUCTURED IRON-TITANIUM-MANGANESE MIXED OXIDE AS CATALYSTS IN ETHYL ACETATE OXIDATION G. ISSA, M. DIMITROV, R. IVANOVA, D. KOVACHEVA AND T. TSONCHEVA 35

АP-13 NI- AND CU-ZSM-5 ADSORBENTS FOR FINE HYDROGEN PURIFICATION FROM CO V. ZDRAVKOVA, E. IVANOVA, S. ANDONOVA, N. DRENCHEV, M. MIHAYLOV AND K. HADJIIVANOV 37

АP-14 THREE-STEP PROCEDURE FOR PREPARATION OF POROUS SPHERICAL CARBON FROM GRAPHITE D. KICHUKOVA, D. KOVACHEVA AND I. SPASSOVA 39

АP-15 XPS STUDY OF MONO AND BIMETALLIC METAL (CO, MN) OXIDE CATALYSTS H. KOLEV, S. TODOROVA, I. HRISTOVA, P. GAUDIN AND J. L. BLIN 41

АP-16 THERMODYNAMIC MODELLING OF SALT CRYSTALLIZATION IN SURFACE POLLUTED WATER TO PREDICT ITS SELF-CLEANING ABILITY A. KOVACHEVA, S. TEPAVITCHAROVA, R. ILIEVA, R. GERGULOVA AND D. RABADJIEVA 43

АP-17 MNCOFEO4 OBTAINED BY SOLUTION COMBUSTION METHOD FOR LOW TEMPERATURE HYDROCARBONS OXIDATION: INFLUENCE OF THE TYPE OF THE FUEL V. TUMBALEV, D. KOVACHEVA, R. VELINOVA, I. SPASSOVA, A. NAYDENOV AND N. VELINOV 45

АP-18 SYNTHESIS AND PHYSICOCHEMICAL CHARACTERIZATION OF ACTIVE CEO2 MATERIALS O. LAGUNOV, V. ZDRAVKOVA, M. MIHAYLOV, I. SPASSOVA, D. NIHTIANOVA, G. ATANASOVA, D. PANAYOTOV AND K.

HADJIIVANOV 47

АP-19 SURFACE NITRATES ON NANOCERIA: EFFECT OF ZR SUBSTITUTION M. MIHAYLOV, E. IVANOVA, V. ZDRAVKOVA, K. CHAKAROVA, H. ALEKSANDROV, P. PETKOV, G. VAYSSILOV

AND

K. HADJIIVANOV 49

АP-20 FUNCTIONALIZED NANOCOMPOSITES DERIVED FROM NATURAL ZEOLITE AS ANTIBACTERIAL AGENTS N. MINTCHEVA, M. PANAYOTOVA, G. GICHEVA AND O. GEMISHEV 51

АP-21 HDS ACTIVITY OF MO AND NIMO SULFIDED CATALYST PREPARED BY THIOGLYCOLIC ACID ASSISTED HYDROTHERMAL SYNTHESIS R. PALCHEVA, L. KALUZA, G. TYULIEV, K. JIRATOVA, D. GULKOVA, L. DIMITROV AND G. AVDEEV 53

АP-22 STRUCTURAL AND MECHANICAL PROPERTIES OF NI-AND CO-BASED DENTAL ALLOYS OBTAINED BY POWDER-METALLURGICAL AND THERMAL ALLOYING

METHODS D. RADEV AND D. KOVACHEVA 55

АP-23 CARBON-NANOFIBERS ENCAPSULATED FE-CE-NI MESOPOROUS NANOPARTICLES: SYNTHESIS, MORPHOLOGICAL STUDIES AND CATALYTIC BEHAVIOR FOR THE

OXYGEN EVOLUTION REACTION IN AN ALKALINE MEDIUM C. ROSMINI, T. TSONCHEVA, D. KOVACHEVA, N. VELINOV, D. KARASHANOVA, D. SEBASTIÁN AND M. J. LÁZARO 57

АP-24 XPS INVESTIGATION OF ZRO2/TIO2/CARBON STEEL COATINGS BEFORE AND AFTER CORROSION TESTS М. SHIPOCHKA, I. STAMBOLOVA, D. STOYANOVA, N. BOSHKOV AND N. BOSHKOVA 59

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АP-25 SUPPORTED PALLADIUM CONTAINING PEROVSKITE CATALYSTS FOR METHANE COMBUSTION S. STANCHOVSKA, R. STOYANOVA, E. ZHECHEVA AND A. NAYDENOV 61

АP-26 SOLID STATE TAUTOMERISM OF 2-CARBAMIDO-1,3-INDANDIONE N. STOYANOVA, M. ROGOJEROV, TS. ZAHARIEV AND V. ENCHEV 63

АP-27 CATALYTIC COMBUSTION OF METHANE OVER NI MODIFIED PD/AL2O3 CATALYSTS S. TODOROVA, A. NAYDENOV, R. VELINOVA, Y. KARAKIROVA, H. KOLEV AND A. LARIN 65

АP-28 COMPARATIVE STUDIES OF NOBLE METAL CATALYSTS LOADED ON MORDENITE AND ZSM-5 IN CO AND BENZENE OXIDATION REACTIONS T. TODOROVA, YU. KALVACHEV, P. PETROVA, T. PETROVA, B. BARBOV, G. KARCHEVA AND S. TODOROVA 67

АP-29 EFFECT OF PRE- AND POST-TREATMENT OPERATIONS OF ALUMINUM ON THE CORROSION RESISTANCE OF CHEMICALLY DEPOSITED ON IT CONVERSION CERIA

COATINGS R. ANDREEVA, A. TSANEV AND D. STOYCHEV 68

АP-30 SURFACE PROPERTIES AND STRUCTURE OF GLASSY CARBON COATINGS AFTER PROLONGED STAY ON THE INTERNATIONAL SPACE STATION (ISS) D. TEODOSIEV, P. TZVETKOV, A. BOUZEKOVA-PENKOVA, B. TSYNTSARSKI AND A. TSANEV 70

АP-31 A QUANTITATIVE ANALYSIS OF THE BASIC AND MICRO-NUTRIENT ELEMENTS IN THREE AGRICULTURAL WASTES I. UZUNOV, G. GENTSCHEVA AND CH. TZVETKOVA 71

АP-32 TRANSITION METAL CHALCOGENIDES AS CATALYSTS FOR CARBON DIOXIDE REDUCTION – A DENSITY FUNCTIONAL STUDY E. UZUNOVA 73

АP-33 CONGO RED ADSORPTION ON CATIONIZED RICE HUSK CELLULOSE P. VASSILEVA, I. UZUNOV AND D. VOYKOVA 74

АP-34 HYBRID CO2 ADSORBENTS. CONTROL ON THE MATERIALS PROPERTIES VIA NEW SEQUENCE OF ADDITION OF THE SILANOLS N. VELIKOVA AND I. SPASSOVA 77

АP-35

CATALYTIC COMBUSTION OF VOLATILE ORGANIC COMPOUNDS OVER CО-ZSM-5 ZEOLITES 78

R. VELINOVA, B. GRAHOVSKI, H. KOLEV, G. IVANOV, S. TODOROVA, A. NAYDENOV

АP-36 LACCASE IMMOBILIZED ONTO HYBRID CARRIERS AS AN EFFECTIVE BIOCATALYTIC SYSTEM FOR PHENOL DEGRADATION S. YANEVA, N. RANGELOVA AND N. SAVOV 80

Topic B

BO-1 POROUS ELECTRODES PREPARED BY MAGNETRON SPUTTERING: FROM ELECTROCHEMICAL SENSING TO ENERGY APPLICATIONS AGUSTÍN R. GONZÁLEZ-ELIPE 81

BO-2 ION CONDUCTING GLASSES IN THIN FILM FORMS BY INFRARED TECHNIQUES E.I. KAMITSOS 82

BO-3 WHAT CAN PHOTOELECTRON SPECTROSCOPY TELL US ABOUT THE TRANSITION FROM LI TO POST-LI BATTERIES? J. MAIBACH, S. DSOKE AND F. JESCHULL 83

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BO-4 CAPTURE AND CONVERSION OF CO2 USING MOF-BASED COMPOSITE MATERIALS D. PANAYOTOV, M. MIHAYLOV, AND K. HADJIIVANOV 84

BO-5 CATION DESOLVATION ON A MODEL ELECTRODE SURFACE: A STORY OF COMMITMENT AND BREAKUP H. RASHEEV, R. STOYANOVA AND A. TADJER 86

BO-6 MACHINE-LEARNING-AIDED DISCOVERY OF EFFICIENT ORGANIC PHOTOVOLTAIC MATERIALS L. BORISLAVOV, M. NEDYALKOVA, J. STOYCHEVA, A. TADJER AND J. ROMANOVA 87

BO-7 THREE-DIMENSIONAL POROUS METALLIC STRUCTURES BY SELECTIVE DISSOLUTION OF AMORPHOUS AND NANOCRYSTALLINE ALLOYS T. SPASSOV, E. VASSILEVA AND L. MIHAYLOV 88

BO-8 MOLECULAR MODELLING OF COMPONENTS FOR RECHARGEABLE METAL-ION BATTERIES A. TADJER, H. RASHEEV, Y. DANCHOVSKY, L. BORISLAVOV, N. ILIEVA AND R. STOYANOVA 89

BO-9 SIMPLE SYNTHESIS AND EFFECT OF THE PARTICLE SIZE AND SURFACE AREA MODIFICATION ON ELECTROCHEMICAL PROPERTIES OF LI4TI5O12 ANODES M. FABIÁN, M. ŽUKALOVÁ, L. KAVAN AND M. SENNA 90

BO-10 COMPUTATIONAL MODELLING OF METAL COMPLEXES WITH REDOX-ACTIVE LIGANDS FOR LI-ION BATTERIES Y. DANCHOVSKI, H. RASHEEV, R. STOYANOVA AND A. TADJER 92

BP-1 INVESTIGATION OF LOW TEMPERATURE MODIFIED CARBON BLACK BY XPS I. AVRAMOVA, D. DIMOV, G. AVDEEV AND T. MILENOV 94

BP-2 MACHINE LEARNING AIDED DESIGN OF ORGANIC REDOX MATERIALS FOR METAL-ION BATTERIES L. BORISLAVOV, I. KICHEV, N. ILIEVA, R. STOYANOVA AND A. TADJER 94

BP-3 CHARACTERIZATION OF MG2NIH4 TYPE HYDRIDES BY TEM E. GRIGOROVA, P. MARKOV AND D. NIHTIANOVA 95

BP-4 THERMOELELCTRICAL PROPERTIES OF COMPOSITES BETWEEN PEROVSKITES AND MISFIT LAYERED OXIDES S. HARIZANOVA, E. ZHECHEVA AND R. STOYANOVA 97

BP-5 SYNTHESIS OF NANOSTRUCTURED COPPER OXIDE SUPPORTED ON MESOPOROUS MANGANESE-TITANIUM OXIDES: CHARACTERIZATION AND APPLICATION AS

CATALYSTS FOR HYDROGEN PRODUCTION R. IVANOVA, G. ISSA, M. KORMUNDA, M. DIMITROV, J. HENYCH, M. ŠŤASTNÝ AND T. TSONCHEVA 99

BP-6 IMPROVED ELECTROCHEMICAL PERFORMANCE OF NA2/3NI1/2MN1/2O2 THROUGH STABILIZING THE OXYGEN REDOX ACTIVITY M. KALAPSAZOVA, P.MARKOV, R. KUKEVA, E. ZHECHEVA AND R. STOYANOVA 101

BP-7 THEORETICAL INVESTIGATION ON NITROGEN CONTAINING SINGLET FISSION ORGANICS I. KICHEV, J. STOYCHEVA, A. TADJER AND J. ROMANOVA 103

BP-8 MECHANOCHEMICALLY INDUCED TRANSFORMATION OF NAFEPO4 MARICITE: ANION REDOX ACTIVITY AND HIGH SPECIFIC CAPACITY T. BOYADZHIEVA, V. KOLEVA AND R. STOYANOVA 104

BP-9 THE ROLE OF CONFORMATION IN THE DESIGN OF SINGLET FISSION CHROMOPHORES FOR PHOTOVOLTAIC APPLICATIONS G. KOSTADINOVA, R. LYAPCHEV, J. STOYCHEVA, A.TADJER, M. DE WERGIFOSSE AND J.ROMANOVA 106

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BP-10 FAST METHOD OF SYNTHESIS OF LI2MN(SO4)2 CATHODE MATERIAL AND ELECTROCHEMICAL PERFORMANCE D. MARINOVA, K. VESELINOV, M. KALAPSAZOVA, P. MARKOV AND E. ZHECHEVA 107

BP-11 COMPROMISE BETWEEN STABILITY AND SINGLET FISSION PROPENSITY OF ORGANIC MOLECULES: A THEORETICAL STUDY V. PETAKOVA, L. BORISLAVOV, J. STOYCHEVA, A.TADJER AND J. ROMANOVA 108

BP-12 INFLUENCE OF THE INITIAL COMPOUNDS ON THE SYNTHESIS AND MORPHOLOGY OF BA7NB4MOO20 CERAMIC USED AS ELECTROLYTE IN SOLID OXIDE FUEL CELLS M. TSVETANOVA, D. KOVACHEVA, P. TZVETKOV AND V. TUMBALEV 109

BP-13 CAPTURE OF CO2 BY CEO2 MATERIALS OF DIFFERENT ORIGIN AND CEO2(75%)ZRO2(25%) V. ZDRAVKOVA, O. LAGUNOV, S. ANDONOVA, I. SPASSOVA, E. IVANOVA, M. MIHAYLOV, D. PANAYOTOV AND

K. HADJIIVANOV 111

BP-14 A NEW CLASS OF HIGH ENTROPY AB2O4 SPINEL OXIDES PREPARED BY MECHANOCHEMICAL SYNTHESIS

O. PORODKO, M. FABIÁN, H. KOLEV, M. LISCHNICHUK, M. ŽUKALOVÁ, V. GIRMAN 113

Topic C

CO-1 MESOPOROUS CERAMICS: APPLICATIONS IN BIOMEDICAL RESEARCH A. DIAZ - CUENCA 115

CO-2 EFFECT OF AMINO ACIDS ON THE CHEMICAL, PHASE AND MORPHOLOGICAL CHARACTERISTICS OF WET-SYNTHESIZED CALCIUM PHOSPHATES D. RABADJIEVA, R. GERGULOVA, K. SEZANOVA, D. KOVACHEVA 116

CO-3 ENERGY TRANSFER AND PHOTOPHYSICAL PROPERTIRES OF LUMINESCENT [EU(PHEN)2]

3+/SIO2 - BASED COMPOSITES: THEORETICAL STUDY T. ZAHARIEV, N. TRENDAFILOVA AND I. GEORGIEVA 118

CP-1 CRYSTALLIZATION AND LUMINESCENCE PROPERTIES OF 50ZNO:40B2O3:10WO3:XEU

3+ GLASS-CRYSTALLINE MATERIALS

L. ALEKSANDROV, M. MILANOVA, R. IORDANOVA AND I. KOSEVA 120

CP-2 SYNTHESIS, CRYSTALLIZATION AND PROPERTIES OF TEO2/TIO2/B2O3 GLASSES A. BACHVAROVA-NEDELCHEVA, R. IORDANOVA, K. L. KOSTOV AND M. PENEVA 122

CP-3 LUMINESCENT COMPLEXES OF EU(III) AND SM(III) WITH PYROLIDINEDITHIOCARBAMATE LIGANDS: SYNTHESIS AND THEORETICAL DESCRIPTION OF THE ENERGY

TRANSFER MECHANISM B. BORRISOV, M. TZVETKOV, TS. ZAHARIEV, I. GEORGIEVA 124

CP-4 RARE EARTH CONCENTRATION DEPENDENCE ON THE GLASS OPTICAL PROPERTIES IN THE SYSTEM CAO-GEO2-LI2O-B2O3 (RE=DY

3+) I. KOSEVA, V. NIKOLOV, M. GANCHEVA, L. ALEKSANDROV, P. IVANOV, P. PETROVA, R. IORDANOVA, R. TOMOVA 126

CP-5 SPECTROSCOPIC INVESTIGATIONS ON BARIUM TITANATE CONTAINING OXIDE GLASS-CERAMICS R. HARIZANOVA, I. AVRAMOVA, Z. CHERKEZOVA-ZHELEVA, D. PANEVA, R. KUKEVA, R. STOYANOVA, I. MIHAILOVA, I. GUGOV

AND C. RÜSSEL 128

CP-6 NMR AND THERMAL CHARACTERISTICS OF POORLY CRYSTALLINE HYDROXYAPATITE R. ILIEVA, P. SHESTAKOVA, E. DYULGEROVA, D. RABADJIEVA 130

CP-7 OPTICAL PROPERTIES OF THE GLASSES FROM THE SYSTEM CAO-GEO2-LI2O-B2O3 DOPED BY TERBIUM I. KOSEVA, V. NIKOLOV, M. GANCHEVA, L. ALEKSANDROV, P. IVANOV, P. PETROVA, R. IORDANOVA AND R. TOMOVA 132

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CP-8 Luminescence properties of tungsten modified zinc borate glass and glass-crystalline materials doped with Eu3+ ions, obtained by

melt quenching M. MILANOVA, L. ALEKSANDROV AND R. IORDANOVA 134

CP-9 EUROPIUM DOPED GLASSES FROM THE OXIDE SYSTEM CAO-GEO2-LI2O-B2O3 FOR LED APPLICATION I. KOSEVA, V. NIKOLOV, M. GANCHEVA, L. ALEKSANDROV, P. IVANOV, P. PETROVA, R. IORDANOVA AND R. TOMOVA 135

CP-10 STRUCTURE AND ANTIMICROBIAL ABILITY OF COPPER DOPED SIO2/HPC COMPOSITES N. RANGELOVA, L. ALEKSANDROV, T. ANGELOVA N. GEORGIEVA, S. YANEVA 137

CP-11 EFFECT OF THE REACTION MEDIUM MODIFICATION ON THE CHEMICAL AND PHASE COMPOSITION AND MORPHOLOGICAL CHARACTERISTICS OF BIOMIMETICALLY

SYNTHESIZED CALCIUM PHOSPHATE CERAMIC POWDERS K. SEZANOVA, S. TEPAVITCHAROVA, P. SHESTAKOVA, R. GERGULOVA, AND D. RABADJIEVA 138

CP-12 PLANT-MEDIATED SYNTHESIS OF ZNO NANOPARTICLES USING MENTHA ARVENSIS LEAVES: MORPHOLOGY AND PHYSICOCHEMICAL CHARACTERIZATION D. STOYANOVA, I. STAMBOLOVA, P. GEORGIEVA, E. MITKOVA, V. DYAKOVA, Y. KOSTOVA

AND R. MLADENOVA 140

INDEX OF PARTICIPANTS 142

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Topic A

АO-1

An in situ characterization of Ni/SBA-15 catalysts: how to elucidate if metal is

confined in the mesoporous channels

A. Caballero

Instituto de Ciencia de Materiales de Sevilla and Departamento de Quimica Inorganica,

Sevilla, 41092, Spain

E-mail: [email protected]

Keywords: Ni catalysts, SBA-15, in situ characterization, XPS, XAS

Heterogeneous supported nickel catalysts is the main catalytic system for the

industrial steam reforming of hydrocarbons (mainly using methane, SRM) [1]. Alternatively,

the dry reforming of methane (DRM) reaction has been extensively studied in the last years,

especially after the recent and fast development of new gas natural extraction

methodologies, as the fracking processes but also because of the use of CO2 as reactive, a

greenhouse gas often contained in natural gas fields [2]. There are many known factors

affecting the catalytic performance of these catalysts, and the use of mesoporous supports

has been proposed as good alternative for the improvement of catalytic performance. The

mesostructured silica SBA-15 has a high internal area, consisting on hexagonal pores with a

mean diameter from 5 nm and framework walls of about 3-6 nm, presenting a remarkable

hydrothermal and mechanical stability [3]. Considering the harsh reactions conditions

needed for the DRM process, these characteristics make the SBA-15 suitable for the process.

In this contribution we have studied four nickel catalysts supported on two different

mesoporous solids: a high surface area SiO2, presenting a high amount of open mesoporous

surface; and a SBA-15 solid, a silica support with the structure of mesoporous channels

described below. In both cases, we have used two different preparation methodologies: an

impregnation procedure (Ni/SiO2-ImU and Ni/SBA-15-ImU samples); and a deposition-

precipitation method (Ni/SiO2-DP and Ni/SBA-15-DP samples). In this way, we have managed

to get systems with nickel particles located on the outer surface of the support

nanoparticles, but also dispersed in the inner mesoporous surface of both supports. By using

simultaneously two in situ spectroscopy techniques, one of them bulk sensitive (XAS) and

the other one surface sensitive (XPS), we have been able to discriminate between nickel

phases in different locations: a NiO phase supported in the external surface, easily reducible

and presenting a low interaction with the supports; and a second oxidized nickel phase

located in the internal mesoporous structure which in all cases interacts more strongly with

the support, as reflected in their higher reduction temperature. These features have allowed

us to correlate the kind of nickel phase with the different behaviors under reaction

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conditions, with the greater catalytic performance obtained for the nickel particles located

inside the mesoporous of the SBA-15 support.

Results and discussion

Figure 1. XPS spectra of nickel-based systems

The four catalytic systems were

tested in DRM and their catalytic

performances differ drastically depending

on the support and the preparation

method. It is worth pointing out the

excellent performance, both in activity

and stability, of Ni/SBA-15-DP after 40

hours under this harsh reaction conditions

(undiluted mixture of methane and CO2).

The two ImU samples supported on SBA-

15 and SiO2 present a similar behavior,

with a relatively high initial activity (35-

45%) but a high deactivation rate.

Finally, the Ni/SiO2-DP presents a mixed behavior, with initial values similar to

Ni/SBA-15-DP, but quickly declining to conversion values close to that of the ImU catalysts.

To understand these differences in behavior, we have studied the chemical state of these

systems. Figure 1 includes the XPS obtained for the different catalysts under the indicated in

situ conditions: samples calcined and after hydrogen reduction at 350, 500 and 750 oC,

respectively. Spectra of both calcined ImU samples are characteristic of NiO, while the

corresponding two DP samples show spectra attributed to Ni2+ species of a phyllosilicate

phase.

The spectra obtained for both DP samples after a hydrogen treatment at 500 oC show

that virtually all the nickel is reduced to the metallic state, but according to the XAS spectra

obtained after the same treatments only a small fraction of nickel must be reduced.

Considering the bulk sensitivity of XAS but the surface sensitive of XPS, these results are

indicating that the nickel species reducing at the lowest temperature range are located in

the outer surface of the supports [4]. The major fraction remaining oxidized is undetectable

by XPS and consequently, should be located inside the channels of the mesoporous SBA-15

support.

References

1. S. T. Oyama, P. Hacarlioglu, Y. F. Gu and D. Lee, Int. J. Hyd. Energy 37 (2012) 10444.

2. Q. Wang, X. Chen, A. N. Jha and H. Rogers, Renew. Sust. Energy Reviews 30 (2014) 1.

3. J. P. Thielemann, F. Girgsdies, R. Schlögl, C. Hess and J. Beilstein, Nanotechnol. 2 (2011) 110.

4. A. Rodriguez-Gomez and A. Caballero, ChemNanoMat 3 (2017) 94.

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Topic A

АO-2

In situ quantum-mechanical simulations of nanomaterials

P. Haynes

Faculty of Engineering, Department of Materials, Imperial College London, United Kingdom


Keywords: quantum-mechanical calculations, nanomaterials

Through the development of new algorithms, first-principles electronic structure

calculations are now capable of studying entire nanocrystals and molecules comprising

thousands of atoms. Nevertheless, the important influence of the environment on the

properties of materials requires these quantum-mechanical calculations to be embedded

within a classical model or multiscale framework. This talk will demonstrate a number of

different strategies with reference to examples including the structural transformations of

semiconducting nanocrystals under pressure and colour prediction for dye molecules in

different solutions.

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Topic A

АO-3

Monolayer catalysis: catalytic activity of hybrid Pd monolayers over γ-Al2O3

and monoclinic ZrO2 in dissociation reactions

A. A. Rybakov1, V. A. Larin2, S. Todorova3, D. N. Trubnikov1 and A. V. Larin1*

1 Department of Chemistry, Moscow State University, 119992 Moscow, Russia 2 Technology Center Lantan, LTD, 105082, Moscow, Russia

3 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: alumina, zirconia, DFT, catalysis, dissociation, methane, water, ammonia

The importance of the “heterogeneity” of a Pd monolayer induced by interaction

with a semi-ionic support was evaluated for catalytic dissociation of methane, ammonia, and

water. The geometry of Pd monolayer was optimized over the (100) and (110) planes of γ-

Al2O3 and monoclinic ZrO2(001) at fixed unit cell parameters defined by the oxides.

Simulation of deposition of flat Pd(100) monolayer cut from a bulk led to a formation of new

distorted Pd monolayers (Fig. 1a, c) whose favored form depends on the support. The

subsequent chemisorption or dissociation of CH4 or H2O at these Pd monolayers can modify

them (Fig. 1) resulting in new hybrid Pd structures containing alternate elements of the (100)

and (111) planes (as the parallel bands of squares and triangles, Fig. 1d). The stability of

various hybrid Pd layers is compared to those of low index Pd planes and clusters when it is

possible (an example for γ-Al2O3 please see in [1]). The catalytic capabilities of these

monolayer structures have been demonstrated for CH4, H2O [1], NH3, and O2 dissociation at

hybrid Pd(100)/(111) layer relative to those at pure (bulk) Pd(100) or Pd(111) surfaces.

Moreover, moderate exothermic heats of these reactions were calculated instead of

endothermic heats at the Pd(100) or Pd(111) surfaces. The relevance of the model of

heterogeneous Pd monolayer for explaining the maximum of reaction rate experimentally

observed at different Pd coverage is discussed. A transferability of the geometry and the

extent of charge inhomogeneity of the hybrid monolayer without vacancies were also tested

at the same supports for other metals (Pt, Rh, and Ag) [1].

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Figure 1. The upper views of 2×2 unit cells of Pd monolayers over (a, b) ZrO2(001) and (c, d) γ-

Al2O3(100) before (a, c) and after (b) H2O adsorption or (d) H2O dissociation (the atoms of the

supports are omitted). Symmetric fragments are shown by rhombs and squares (a, b). Two Pd

vacancies are shown by ellipses in the (d) structure (only for one unit cell out of total four). The atomic

colors are given in gray (small spheres), red, and gray (large spheres) for H, O, and Pd, respectively.

References

1. A. A. Rybakov, D. N. Trubnikov, S. Todorova and A. V. Larin, Dalt. Trans. 50 (2021) 8863.

2. V. Sadovnichy, A. Tikhonravov, V. Voevodin and V. Opanasenko, in Contemporary High

Performance Computing: From Petascale toward Exascale, ed. J. S. Vetter, CRC Press, Boca Raton,

USA, 2013, pp. 283–307.

Acknowledgements: The authors are grateful for financial support from the Bulgarian Science Fund

through contracts KП-06-RUSSIA-22 and the Russian Foundation of Basic Researches within the grant

20-53-18001-Bolg_а. The research has been carried out using the equipment of the shared research

facilities of HPC computing resources at Lomonosov Moscow State University [2].

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Topic A

АO-4

Transition metal nitride thin films for surfaces with enhanced performance

R. Bower and P. K. Petrov*

Department of Materials, Imperial College London, London, SW7 2AZ, UK


Keywords: thin films, nitride

Plasmonic materials have a wide range of applications, from energy storage and

harvesting to bio-sensing and memory storage devices [1–3]. However, the archetypal

plasmonic materials gold and silver are limited in their applicability, displaying poor thermal

stability, limited spectral tunability, and incompatibility with standard CMOS fabrication

processes.

Consequently, transition metal nitrides (TMNs), including titanium nitride have been

suggested as viable alternative plasmonic materials. In addition to superior mechanical and

thermal properties compared to gold and silver, TMNs also offer spectral tunability of the

plasmonic response, with optical prop-erties dependent on phase, stoichiometry and oxygen

impurities [4,5] Furthermore, TMNs such as titanium nitride are currently used within CMOS

compatible fabrication processes.[6]

In this paper, the mechanism of formation of titanium thin films and their optical

properties with tunable epsilon-near-zero (ENZ) behaviour will be discussed. We will present

the technological conditions for deposition of titanium thin films with unusual double ENZ

frequencies and will show that they can be modified by changing the film deposition

conditions. Thus allowing one to fabricate, control and engineer tunable plasmonic and

metamaterial devices and surfaces, using CMOS compatible technology.

References

1. B. Doiron, M. Mota, M. P. Wells, R. Bower, A. Mihai, Y. Li, L. F. Cohen, N. M. N. Alford, P. K. Petrov,

R. F. Oulton and S. A. Maier, Quantifying Figures of Merit for Localized Surface Plasmon Resonance

Applications: A Materials Survey. ACS Photonics. American Chemical Society February 20, 2019, pp

240–259. https://doi.org/10.1021/acsphotonics.8b01369.

2. S. V. Boriskina, H. Ghasemi and G. Chen, Mater. Today 16 (2013) 375.

3. S. M. Fothergill, C. Joyce and F. Xie, Nanoscale 10 (2018) 20914.

4. M. P. Wells, R. Bower, R. Kilmurray, B. Zou, A. P. Mihai, G. Gobalakrichenane, N. M. Alford, R. F. M.

Oulton, L. F. Cohen, S. A. Maier, A. V. Zayats and P. K. Petrov, Opt. Express 26 (2018) 15726.

5. M. Kumar, N. Umezawa, S. Ishii and T. Nagao, ACS Photonics 3 (2016) 43.

6. V. E. Babicheva, N. Kinsey, G. V. Naik, M. Ferrera, A. V. Lavrinenko, V. M. Shalaev and A. Boltasseva,

Opt. Express 21 (2013) 27326.

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Acknowledgements: The project Д01-272/02.10.2020 - "European Network on Materials for Clean

Technologies", funded by the Ministry of Education and Science under the National Program

"European Scientific Networks" are acknowledged.

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Topic A

АO-5

Tailoring the singlet fission propensity of organic chromophores

J. Stoycheva*, A. Tadjer and J. Romanova

Faculty of Chemistry and Pharmacy, University of Sofia, 1164 Sofia, Bulgaria


Keywords: organic photovoltaics, PAHs, topology, substituent effect

Although the basic principles of solar energy conversion have been known for half a

century by now, the use of photovoltaic devices has been strongly restricted by limitations

invoked by the features of the traditionally employed photoactive material - silicon.

Compared to the inorganic solar cells, the organic photovoltaic materials, being cheap, light

and flexible, hold tremendous advantages for transforming sunlight into electricity. A key

shortcoming of today’s organic photovoltaic technologies, however, is the low efficiency

achieved. The latter could be substantially improved, if the material used can undergo

singlet fission, thus allowing a twofold increase of the number of charge carriers.

Here, we propose an original design strategy for molecules, capable of singlet fission.

The functionalities of the organic chromophores are finely tuned by means of the interplay

of topology, type, and number of the heteroatoms in PAHs. With the help of quantum-

chemical approaches, we identified a set of novel carbon-based molecular materials, which

have the potential to outcompete the widely-used inorganic ones.

Acknowledgements: The study is supported by the Bulgarian National Science Fund, Project КП-06-

H39/2 from 09.12.2019 and by the National Research Program E+: DMC 577/17.08.2018, grant

agreement D01-214/28.11.2018. J.S. acknowledges the support received from the program “Young

scientists and Postdoctoral candidates” of the Bulgarian Ministry of Education and Science, MCD No.

577/17.08.2018.

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Topic A

АP-1

Structure and properties of KNi–hexacyanoferrate Prussian blue analogues

for efficient CO2 capture: host–guest interaction chemistry and dynamics of

CO2 adsorption

S. Andonova1*, S. S. Akbari2, F. Karadaş2, I. Spassova1, D. Paneva3 and K. Hadjiivanov1

1 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 2 Chemistry Department, Bilkent University, 06800, Bilkent, Ankara, Turkey 3 Institute of Catalysis, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria


Keywords: CO2 storage adsorbents, Prussian blue analogues, structural distortions, infrared

spectroscopy

Prussian blue analogues (PBAs) have shown great potential as efficient adsorbents for

CO2 capture due to relatively low regeneration energies, efficient physical adsorption profile,

and low–cost precursors. In particular, KNi- Hexacyanoferrate PBAs (KNiFe-PBAs) offer an

excellent platform for efficient CO2 capture due to their porous nature and accessible

channels. In our work [1], the effect of Ni:K atomic ratio (ca. 2.5 and 12) on the structure and

the CO2 storage capacity was studied by employing KNiFe-PBAs with substantially different

porosity and composition containing high– or trace amounts of potassium, respectively. To

study their application as functional materials for efficient CO2 capture, we performed a

series of measurements and analysis of the adsorption isotherms, the storage capacity and

the isosteric heat of CO2 adsorption. In situ FTIR spectroscopy was employed to elucidate the

host–guest interaction chemistry and dynamics of KNiFe-PBAs with CO2 and H2O. The study

enabled the first direct FTIR spectroscopic observation of the high sensitivity of the material

to structural distortions induced by small changes in the water vapor pressure. Moreover, a

drastic effect of potassium on the adsorption properties was established. The samples were

also analysed by using a series of complementary characterization experiments including

specific surface area, pore volume, pore size distribution, X–ray diffraction,

thermogravimetric and differential thermal analysis, Mössbauer spectroscopy, and energy

dispersion X–ray spectroscopy in conjunction with scanning electron microscopy to establish

a structure & adsorption relationship.

The porous nature of the materials is explained with the presence of Fe(CN)6]3-

vacancies, generated together with the interstitial cations to produce charge balance in the

framework. The porosity of the KNiFe-PBAs was found to correlate with the content of alkali

K+ ions inserted into the framework. Thus, the number of micro-channels and their

dimensions can be tuned by varying the Ni:K atomic ratio in the Prussian blue framework. In

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particularly, the higher K content dictates the formation of a fully occupied cubic framework

enclosing much smaller cavities. In contrast, with the K–trace system the alkali ions

occupancy is much lower and this creates larger cavities in the framework. The kinetics of N2

adsorption and desorption was typical of materials with a mixed type micro– and

mesoporous structure. The enhanced surface area and the pore size in K-trace-NiFe-PBA are

attributed to more accessible channels obtained when a majority of the framework space

volume is free of the alkali component.

The CO2 adsorption isotherms clearly demonstrated that the synthesized K-trace-

NiFe-PBA material offers an excellent alternative as an efficient adsorbent for CO2 capture.

The achieved CO2 adsorption capacity of ca. 3.0 mmol g–1 CO2 at 287 K and 100 kPa is

comparable with other well–established CO2 adsorbents. The isosteric heat of adsorption

can be modulated and optimized via changing the Ni:K ratio and thus, covering the

thermodynamic criterion for capture and release of CO2 with acceptable energy costs. At low

CO2 coverages, the heat released during the storage for K-trace-NiFe-PBA is estimated to be

significantly lower (≈ 23.8 kJ mol–1 ) compared to that of K-rich-NiFe-PBA (≈ 56.2 kJ mol–1),

indicating that the presence of K+ cations inserted in the PB framework may act

synergistically to generate highly basic binding sites for strong trapping CO2.

The FTIR spectroscopy studies revealed the presence of two main coordination units

building the structure: Fe(III)–C≡N–Ni(II) and Fe(II)–C≡N–Ni(II). The changes in the

composition via increasing the Ni:K ratio reflects mostly in a noticeable decrease of the

fraction of Fe(II) at the expense of Fe(III) ions. In contrast to the K–trace containing system,

the CO2 adsorption on K-rich-NiFe-PBA is much more suppressed and the bands

corresponding to CO2 adsorbed species (Fig.1) appeared with considerably reduced intensity.

The analysis of the vibrational ν(C≡N) modes also indicated that the PBA network containing

trace amounts of K+ ions undergoes slight distortions upon H2O adsorption. As a

consequence, the lattice expands, leading to an increase of the framework space volume.

The CO2 adsorption when majority of the framework space volume is water–free starts with

the formation of physically adsorbed CO2 species similar to that on almost fully hydrated

material without any significant differences. This behaviour showed that H2O hardly affects

the CO2 adsorption and therefore, these types of materials are perspective for CO2 capture

in the presence of water.

References

1. S. Andonova, S. Sadigh Akbari, F. Karadaş, I. Spassova, D. Paneva and K. Hadjiivanov, J. CO2

Utilization (2021) 101593, accepted; https://doi.org/10.1016/j.jcou.2021.101593

Acknowledgements: This work was supported by the Bulgarian Ministry of Education and Science

(Contract No. DO1-214/28.11.2018) under the National Research Programme “Low-carbon Energy

for the Transport and Domestic Use - EPLUS”.

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Topic A

AP-2

Noble-metal nanocolumns produced by PLD at atmospheric pressure

G. Atanasova1*, T. Dilova1, Ru. G. Nikov2, A. Og. Dikovska2 and N. N. Nedyalkov2


1113 Sofia, Bulgaria 2 Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria


Keywords: nanostructures, Au-Pt, Au-Pd, PLD, OAD geometry, atmospheric pressure, XPS

The growing interest in nanomaterials is related to their unique and promising

properties. Moreover, a strong dependence of the physical and chemical properties of these

structures on their surface morphology makes them very attractive for a wide range of

applications. One special class of materials fabricated in nanoforms is borrowed by noble

metals. Noble metal nanomaterials show strong absorption bands in the ultraviolet or visible

region due to the surface plasmon oscillation modes of conduction electrons that are not

observed in the corresponding bulk metals. Thus, the optical properties of Pt, Pd, Ag, and Au

nanoparticles (NPs) have received considerable attention. The location of the surface plasma

resonance (SPR) peak of Pd and Pt nanoparticles in the UV region not only gives them an

atypical black color but it also makes their SPR characteristics much more difficult to probe

because of the absorption of light at this wavelength by most materials and solvents.

Bimetallic nanoparticles or composites of different noble metal NPs can exhibit special

electronic, optical, and catalytic properties that are absent in the corresponding

monometallic nanoparticles. Their optical and physical properties are reported to be tunable

by varying their structure and/or their composition.

In this work, we present a fabrication of nanocolumns composed by noble-metal

alloy nanoparticles. The nanocolumns were produced by pulsed laser deposition (PLD) at

atmospheric pressure in a different gas environment. The technology applied leads to

formation of NPs due to a fast condensation of the ablated material close to the target. The

PLD process was performed in oblique angle deposition geometry. This specific experimental

setup allows the growth of column-like structure due to the shadowing effect. We focused

our attention on the surface composition, morphology, and optical properties of the AuPt

and AuPd nanostructures. The influence of the gas environment used during fabrication

process on the sample’s morphology and chemical composition was also discussed. It was

found that monometallic Au, Au and Pd, Au and Pt NPs compose the nanocolumns. The

morphology of the nanostructure is influenced by the noble metals used for fabrication. The

gas environment is substantial for the surface chemical composition of the samples.

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Acknowledgements: This work is financially supported by the Bulgarian National Science Fund

under Project KP-06-N37/20. The authors are also grateful to the project Д01-272/02.10.2020 -

"European Network on Materials for Clean Technologies", funded by the Ministry of Education and

Science under the National Program "European Scientific Networks" to present the obtained results

in the SizeMat3 workshop.

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Topic A

АP-3

XPS study of pure and composite noble metal nanoparticles

A. Baeva1, T. Dilova1, G. Atanasova1*, Ru. G. Nikov2, Ro. G. Nikov2, A. Og. Dikovska2 and N. N.

Nedyalkov2


1113 Sofia, Bulgaria 2 Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria


Keywords: nanoparticles, nanocomposite, PLD in open air, XPS

Metal nanostructures attract considerable attention from a scientific and industrial

point of view due to their possibility to be used in applications such as catalysis, devices,

transistors, and optoelectronics. Nanoclusters and colloids of noble metals attracting a great

deal of interest since they exhibit characteristic optical and physical properties substantially

different from those of the corresponding bulk metals. They show strong absorption bands

in the ultraviolet or visible region due to the surface plasmon oscillation modes of

conduction electrons. Thus, the optical properties of platinum, palladium, silver, and gold

nanoparticles (NPs) have received considerable attention. While the optical properties of Au

and Ag nanoparticles have been widely studied from years, the optical properties of Pd and

Pt nanoparticles remain relatively unexplored. The location of the surface plasma resonance

(SPR) peak of Pd and Pt nanoparticles in the UV region not only gives them an untypical black

color but also makes their SPR characteristics much more difficult to probe because of the

absorption of light at this wavelength by most materials and solvents. A new challenge

appears in front of scientists in face of bimetallic nanoparticles. Core/shell and alloy

bimetallic nanoparticles can exhibit special electronic, optical, and catalytic properties that

are absent in the corresponding monometallic nanoparticles. Their optical and physical

properties are reported to be tunable by varying their structure and/or their composition.

In this regard, a technology used for NPs fabrication is essential for the physical

properties demonstrated by them. The efforts for the development of easy-to-implement,

cost-efficient, flexible, and time-saving nanofabrication technologies still continue. Recently,

pulsed laser deposition (PLD) in air at atmospheric pressure (in open air) was established as a

successful technology for production of the NPs. In the base of this technology lays a

complex phenomenon that is still under investigation. Due to the high density of the

ambient atmosphere, the nanoparticle formation is realized close to the target by the

condensation of the ablation material.

Here, we focused our attention on the XPS study of noble metal and alloy NPs

produced by PLD in open air. The optical properties of the NPs were experimentally

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investigated based on the sample’s transmission spectra. A theoretical study of

electromagnetic field interaction with noble metal nanoparticles was also performed. The

absorption, extinction, and scattering cross-section of Au, Ag, Pd, Pt and PdAg alloy

nanoparticles in the air was numerically determined by Generalized Multiparticle Mie theory

software. It was found that the surface of Pd, PdAg, and Pt NPs oxidized during fabrication

and a thin oxide shell is formed. The experimental and numerical results show that the SPR

of alloy (AuAg and PdAg) NPs is obtained between SPR of corresponding monometallic

nanoparticles.

Acknowledgements: This work is financially supported by the Bulgarian National Science Fund under

Project KP-06-N37/20. The authors are also grateful to the project Д01-272/02.10.2020 - "European

Network on Materials for Clean Technologies", funded by the Ministry of Education and Science

under the National Program "European Scientific Networks" to present the obtained results in the

SizeMat3 workshop.

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Topic A

АP-4

Hydrothermal synthesis of ZSM-5 zeolite for catalytic applications

B. Barbov1*, T. Todorova2, G. Karcheva2 and Yu. Kalvachev2

1 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 2 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: hydrothermal synthesis, ZSM-5 zeolite, post-synthesis treatment, NH4F and HF

This study reported on the hydrothermal synthesis of ZSM-5 zeolite from systems

containing tetrapropylammonium bromide (TPABr) as an organic structure determining

agent. By varying of crystallization condition (molar gel, temperature and heating time) were

obtained two type ZSM-5 analogues: aluminium and gallium containing structures. The

AlZSM-5 was synthesized from a system 50SiO2 : Al2O3 : 5.0Na2O : 5.0TPABr : 2000H2O after

72 hours at a crystallization temperature 170 oC. Pure GaZSM-5 was obtained from an initial

gel 30SiO2 : Ga2O3 : 4.4Na2O : 18TPABr : 1000H2O after 114 hours and crystallization

temperature 150 oC. Post synthesis treatment was applied in order to increase the specific

surface area and providing easy access to the active zeolite centres. Secondary pores in

crystals were formed by etching at room temperature with solution of NH4F and 0,25М HF

acid, varying the time of treatment.

All samples have been characterized by X-ray diffraction analysis (XRD), scanning

electron microscopy (SEM), infrared spectroscopy (IR), solid-state nuclear magnetic

resonance (NMR) spectroscopy and physical absorption-desorption of nitrogen.

Acknowledgements: This work was supported by the Bulgarian National Science Fund (Contract No.

KP-06-M39/2) and Bulgarian Ministry of Education and Science under the National Research

Programme “Young scientists and postdoctoral students” approved by DCM 577/17.08.2018.

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Topic A

АP-5

Cation distribution and magnetic properties of Ni-Zn ferrites

prepared by solution combustion technique with glycine as a fuel

G. Burdina1, V. Tumbalev1, N. Marinkov1, D. Kovacheva1*, M. Georgieva2 and D. Tzankov2


1113 Sofia, Bulgaria 2 Faculty of Physics, University of Sofia, 1126 Sofia, Bulgaria


Keywords: Ni-Zn ferrites, SCS-method, magnetic properties, XRD

The global use of communications technologies gave rise to extensive

electromagnetic emissions. Thus, in recent years, the term “electromagnetic pollution”

became a part of the environmental pollution. Moreover, the potential risks to human

health exist, as the microwaves interact with all biological systems with consequences that

are far from being well understood. That is why, during the past decade, materials that

absorb efficiently electromagnetic radiation were developed. Ni–Zn ferrites are well-known

dielectric and soft magnetic materials belonging to the structural class of spinels. Spinel

ferrites Me2+Fe2O4 are complex metal oxides with unique properties due to the different

combination and distribution of Fe3+ and Me2+ ions along the tetrahedral and octahedral

interstices in a cubic close packing of oxygen ions. Since Ni2+ has very strong preference to

the octahedral site and Zn2+ - to the tetrahedral one, Ni-ferrite and Zn-ferrite are models for

inverse and normal spinels when prepared in a bulk form. However, in the nanosized form a

cation mixture occurs and both Ni- and Zn-ferrite are known to exist as a partially inverse

spinel. From this point of view the physical properties of the Ni–Zn ferrite are very sensitive

to the synthesis method. Among various synthetic procedures the solution combustion

synthesis (SCS) is one of the most attractive. It needs simple laboratory equipment and

provides high purity and homogeneity of the final product. In our previous work we have

shown that the type of fuel influences the structure, morphology and the properties of

spinel ferrites prepared by SCS [1, 2]. The aim of the present study is the investigation of the

crystal structure and magnetic properties of nanosized Ni–Zn ferrites prepared by SCS

method using glycine as a fuel.

As starting reagents glycine and metal nitrates were taken in a stoichiometric molar

ratio. The final products were thermally treated at 400, 600, 700 and 800°C for 2 h in air. All

samples were characterized by powder XRD and Scanning electron microscopy. The

magnetization curves were measured at room temperature using vibrating sample

magnetometer in magnetic field up to 6 kOe.

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The results show that unit cell parameter (resp. the cation distribution achieved at

the synthesis) do not change with the increase of the temperature of thermal treatment.

This distribution is in excellent accordance with the theoretical one described with the

formula (Zn2+x Fe3+

1-x)[Ni2+1-x Fe3+

1+x]O4. The mean crystallite size increases in a nonlinear

manner with the increase of the temperature.

Figure 1. a) unit cell parameters, b) mean crystallite size thermally treated at different temperatures

and c) magnetization curves of samples of Ni-Zn ferrites, obtained by solution combustion with

glycine thermally treated at 400°C for 1h.

Since the net magnetic moment of the whole lattice is the difference between the

magnetic moments of the tetrahedral and octahedral sublattices, with the increase of the Zn

content in formula unit, the content of Fe3+ ions on B-sites increases, thus increasing the

total magnetic moment on B-site and decreasing the magnetic moment on A-sites.

Therefore the net value of maximal magnetization increases. On the other hand, coercitivity

in the Ni-Zn ferrite samples decreases with increasing the Zn content which shows that

samples are moving towards the softer ferromagnetic behavior.

References

1. Ts. Lazarova, M. Georgieva, D. Tzankov, D. Voykova , L. Aleksandrov , Z. Cherkezova-Zheleva and D.

Kovacheva, J. Alloys and Compounds 700 (2017) 272.

2. Ts. Lazarova, D. Kovacheva, M. Georgieva, D. Tzankov, G. Tyuliev, I. Spassova and A. Naydenov,

Appl. Surface Science 496 (2019) 143571.

Acknowledgements: The authors thank Project Д01-272/02.10.2020 - "European Network on

Materials for CleanTechnologies", funded by the Ministry of Education and Science under the

National Program "European Scientific Networks".

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Topic A

АP-6

Adsorption properties of the microporous MIL-96(Al) MOF: in-situ IR study

K. Chakarova*, M. Mihaylov and K. Hadjiivanov

Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria


Keywords: IR spectroscopy, metal-organic frameworks, gas separation, CO2 capture

Metal-organic frameworks (MOF) are hybrid porous crystalline materials composed

of inorganic structural units and organic multifunctional ligands linked in periodic

coordination structures [1]. The growing interest in this class of materials is due to the huge

variety of chemical compositions, porous structures and topologies, allowing targeted fine-

tuning of their physicochemical characteristics for certain applications, such as gas

separation and gas storage, catalysis, biomedicine, sensors and more.

The rigid metal-organic framework MIL-96(Al) (MIL denotes Materials of the Lavoisier

Institute) is built of two different structural units, an oxo-centred trimmer of Al octahedra

and a 2D hexagonal network (containing 18-membered rings built by sinusoidal chains of

aluminum octahedra) connected by 1,3,5-benzenetricarboxylate ligands in 3D structure. The

zig-zag channels formed between two types of cavities (denoted as A and B) form a 2D

porous structure (the third type C of cavities remains isolated). The A and B cavities have a

size of ca. 11 Å [2].

MIL-96(Al) micropores include various potential adsorption sites that have been

studied by in situ IR spectroscopy towards different adsorbates. First we studied the stability

of adsorbed water upon degassing at different temperatures. Most of the water in the

pores, including H-bonded to structural OH groups, is easily removed under vacuum at room

temperature. Degassing at 423 K leave only H2O molecules coordinated to Al centres which

can be completely removed at 488 K. Upon dehydration the presence of several types of

structural hydroxyls has been established: different terminal and bridging hydroxyl groups,

as well as strongly H-bonded hydroxyls (most probably localized in the so-called C cavities).

In addition, some dehydroxylation is taking place with the increasing of the evacuation

temperature affecting mostly terminal groups.

To check the availability of the MIL-96(Al) cavities for gas sorption and to evaluate its

Brönsted and Lewis acidity, CO and N2 adsorption at cryogenic temperatures was studied.

The results revealed that the pores of the MOF evacuated at room temperature are not

available for these probe-molecules. However, the accessibility of the inner surface gradually

increases with increasing of the activation temperature. The shift of the OH modes as a

result of the formation of OH···CO complexes corresponds to a very weak protonic acidity. In

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addition, the results show that the hydroxyl groups of different types differ only in the

degree of H-bonding to the framework. Several types of coordinatively unsaturated Al3+ cites

were also detected.

Finally CO2 adsorption at room temperature was studied. Even on a sample activated

at room temperature, the adsorption of CO2 leads to formation of CO2 complexes with both

Al3+ sites and OH groups. The amount of the former increases with the evacuation

temperature due to the removal of coordinated water, while the amount of OH···OCO

species decreases due to dehydroxylation. It was also found that CO2 can displaces aqueous

ligands from the Al3+ sites, which presupposes that this material will preserve its adsorption

capacity towards CO2 in presence of certain amount of water vapour.

In conclusion, the rigid structure of MIL-96(Al), its high thermal and hydrothermal

stability and relatively small pores involving various adsorption sites, such as hydroxyl groups

and Al3+ cations, reveal the potential of this MOF for selective CO2 capture in the presence of

some moisture, usually present in industrial gases. In particular, the nanoparticles of this

material can be used as porous fillers to improve the performance of polymeric membranes

for post-combustion separation of CO2.

References

1. S. Kitagawa and J. H.-C. Zhou, Guest Eds., Chem. Soc. Rev. 43 (2014) 5415.

2. M. Benzaqui, R. S. Pillai, A. Sabetghadam, V. Benoit, P. Normand, J. Marrot, N. Menguy, D.

Montero, W. Shepard, A. Tissot, C. Martineau-Corcos, C. Sicard, M. Mihaylov, F. Carn, I. Beurroies,

P. L. Llewellyn, G. De Weireld, K. Hadjiivanov, J. Gascon, F. Kapteijn, G. Maurin, N. Steunou and C.

Serre, Chem. Mater. 29 (2017) 10326.

Acknowledgements: The authors thank to the Bulgarian National Research Program EPLUS

(approved by DCM # 577/17.08.2018) and project Д01-272/02.10.2020 "European Network on

Materials for Clean Technologies", funded by the Ministry of Education and Science under the


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Topic A

АP-7

Studies on copper (II) biosorption using a material based on

Thymus vulgaris L

L. Ivanova, P. Vassileva and A. Detcheva*




Keywords: Thymus vulgaris L., characterization, biosorption, copper ions

Environmental pollution of heavy metals is increasingly becoming a problem and is of

great concern due to the adverse effects it is causing around the world. These inorganic

pollutants are being discarded in our waters, soils and into the atmosphere due to the

rapidly growing agriculture and metal industries, improper waste disposal, fertilizers and

pesticides [1]. The tendency to bio-accumulate, non-degradability, and persistency are some

of the major attributes of heavy metals. Among heavy metals, copper [Cu(II)] in trace

amounts is essential for the normal growth and development of human beings. But in high

amounts, Cu(II) ions can be very harmful to living organisms. Due to the detrimental

consequences on human health strict regulation have been imposed by various countries for

limiting their levels in waste effluents and in drinking water supplies.

A number of abundant, inexpensive materials have been suggested as potential

biosorbents [2]. Among them, medicinal plants are of great interest because they contain

numerous active phytochemicals which are prone to metal binding. They are low-cost and

non-hazardous materials, abundant in nature, require little processing and are specifically

selective for heavy metals, including Cu(II) ions [3,4]. Thymus vulgaris L., commonly known

as Thyme, is a widely used culinary herb but also has medicinal uses due to its antioxidant,

antiseptic, antibacterial and antimicrobial properties [5]. The aim of the present study is the

characterization of a material based on Thymus vulgaris L. and the investigation of its

efficiency in the removal of Cu(II) from aqueous solutions.

For the characterization of the studied material XRD, TGA, FTIR and SEM analysis

were used. Texture parameters and slurry pH of the investigated sample were also

determined. The estimation of optimal parameters influencing the Cu(II) removal such as

solution acidity, contact time, temperature and initial metal concentration was studied by

means of the batch method. Optimum pH value was found to be about 4. It was established

that the adsorption equilibrium is achieved within the first two minutes which suggests an

excellent affinity of the investigated material towards Cu(II) ions in aqueous media. It was

proved that temperature does not influence the adsorption process. Equilibrium

experimental data were fitted to linear Langmuir, Freundlich and Dubinin-Radushkevich

https://en.wikipedia.org/wiki/Herb

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27

models. The calculated isotherm constants and the correlation coefficients for the three

models mentioned above are presented in Table 1. From the correlation coefficients r2

(greater than 0.97) it is clear that Langmuir model is most adequate in describing the

adsorption processes.

Table 1. Isotherm constants and correlation coefficients for the three models for Cu(II) adsorption

Langmuir parameters Freundlich parameters Dubinin-Radushkevich parameters

Q0

(mg g-1)

K1

(L mg-1) r2

kF

(mg1− nLn g-1)

n

(L mg-1) r2

Qm

(mg g-1)

E

(kJ mol-1) r2

38.93 0.015 0.9735 1.27 1.61 0.9365 21.94 0.133 0.7735

The maximum adsorption capacity for studied material was found to be 38.93 mg g-1.

The results showed high adsorption capacity of the investigated biosorbent towards copper

ions, hence it has good potential for the removal of Cu(II) from contaminated wastewaters.

Desorption studies were also performed.

References

1. J. Briffa, E. Sinagra and R. Blundell, Helyion 6 (2020) e04691.

2. J. He and J. P. Chen, Bioresour. Technol. 160 (2014) 67.

3. L. Ivanova, A. Detcheva and P. Vassileva, Anal. Lett. 52 (2019) 2650.

4. L. Ivanova, P. Vassileva and A. Detcheva, Cellulose Chem. Technol. 54 (2020) 1033.

5. S. Hosseinzadeh, A. Jafarikukhdan, A. Hosseini and R. Armand, Int. J. Clin. Med. 6 (2015) 635.

Acknowledgements: This work is supported by the Bulgarian Ministry of Education and Science

under the National Research Programme "Healthy Foods for a Strong Bio-Economy and Quality of

Life" approved by DCM # 577/ 17.08.2018 and the National Programme „European Research

Networks“, Project TwinTeam, Д01-272/02.10.2020.

https://www.researchgate.net/profile/Jinsong-He?_sg%5B0%5D=5XAhxDi7cKTab4edKY2AlBF5dSD177_A-ZMOs6-YgoLcKpkfCbMWqercgt2hr0xceUfaHfI.6jekpd1T72kes6uwHM2I9dcEzVpxjNT1fP7iZ1W9InT7gozCxRhx2H0ZyjkB6U4Y71dqs85CPTjZql7VpcI7lw&_sg%5B1%5D=EFlPU1ChVtSM4Lk5lVMufcy0Jmp6QK3tGEdIu_zg7a1Bvn9CCFLtKpavrc_13o9XEYizVh4.TjlVNalcm6ZTQBc34eD6Fhf8mTahw3fxiPiXckyfUf1j9BRHqW3lCLc8PcPkDPmnvao5dsAprqkPbEyVdt5pjw

https://www.researchgate.net/profile/Jinsong-He?_sg%5B0%5D=5XAhxDi7cKTab4edKY2AlBF5dSD177_A-ZMOs6-YgoLcKpkfCbMWqercgt2hr0xceUfaHfI.6jekpd1T72kes6uwHM2I9dcEzVpxjNT1fP7iZ1W9InT7gozCxRhx2H0ZyjkB6U4Y71dqs85CPTjZql7VpcI7lw&_sg%5B1%5D=EFlPU1ChVtSM4Lk5lVMufcy0Jmp6QK3tGEdIu_zg7a1Bvn9CCFLtKpavrc_13o9XEYizVh4.TjlVNalcm6ZTQBc34eD6Fhf8mTahw3fxiPiXckyfUf1j9BRHqW3lCLc8PcPkDPmnvao5dsAprqkPbEyVdt5pjw

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Topic A

АP-8

Acetone-sensing properties of ZnO–noble metals composite nanostructures

and their improvement by light irradiation

T. Dilova1*, G. Atanasova1, Ro. G. Nikov2, A. Og. Dikovska2 and N. N. Nedyalkov2


1113 Sofia, Bulgaria 2 Institute of Electronics, Bulgarian Academy of Sciences, 1784, Sofia


Keywords: ZnO nanostructures, PLD in open air, gas sensors, light irradiation

Semiconductor oxides are among the most widely studied materials because of

application such as gas sensors, transparent electrodes, catalysis, etc. due to their

remarkable physical and chemical properties. The main drawbacks of the metal-oxide gas

sensors are a relatively high operating temperature and a low selectivity to different gas

compounds. The effective strategies for improving their sensor performance include surface

modification, doping, and light irradiation.

In this work, highly porous composite nanostructures consisting of ZnO and noble

metals were produced by pulsed laser deposition in air at atmospheric pressure in view of

gas sensor application. The response was studied of pure (ZnO) and composite sensor

elements (Pd-, PdAg- and Ag-ZnO) to acetone under irradiation with UV light. The effect of

simultaneous UV and red light irradiation was also investigated on the sensor elements’

response and response and recovery times. It was found that the alloyed-doped ZnO sample

exhibits a significantly enhanced gas-sensing performance to acetone under simultaneous

UV and optimized red light irradiation. This enhancement of the sensor response was

associated with a local heating effect of the PdAg nanoparticles in the ZnO medium. Such a

sensor element demonstrated the capability of detecting concentrations below 1 ppm of

acetone, which we consider as opening possibilities for simple and low-cost fabrication of

acetone sensors suitable for diagnosing diabetes.


Project KP-06-N37/20. The authors are also grateful to the project Д01-272/02.10.2020 - "European


under the National Program "European Scientific Networks" to present the obtained results in the

SizeMat3 workshop.

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Topic A

АP-9

Sorption mechanism of MCPA herbicide on mineral goethite (110) surface in

dependence of pH. Theoretical study

I. Georgieva1*, M. Kersten2 and D. Tunega3


1113 Sofia, Bulgaria 2 Geosciences Institute, Johannes Gutenberg University, 55099 Mainz, Germany

3 Institute of Soil Research, University of Natural Resources and Life Sciences, 1190 Vienna,

Austria


Keywords: environmental pollution, density functional theory, goethite, MCPA herbicide

The extensively usage of modern herbicides based on phenoxyalkanoic acids might

be a potential risk of contamination of groundwater sources. For that reason, it is important

to trace and understand the fate and behaviour of herbicides after their release into

environment until their final mineralization in soil. The mobility and fixation of herbicides in

soils are determined mainly by adsorption–desorption processes which can vary with

amount, distribution, and properties of soil constituents, and with the chemical properties of

herbicides. Detailed, molecular scale characterization of mechanisms of interactions of these

pollutants with soils or soil components is difficult to achieve from the experiment or

spectroscopic data. In this context, methods of molecular modeling represent an effective

tool to obtain details how pollutants interact with soil matrices. The present theoretical

study reports detailed explanation of surface complexation of 4-chloro-2-

methylphenoxyacetic acid (MCPA) herbicide on the most populate mineral goethite surface

(110)1. The sorption mechanism between MCPA herbicide and goethite is studied by

molecular modeling of the full set of possible surface complexes using density functional

theory with periodic boundary conditions for the structural surface models. Our simulations

reflect the strong pH effect on MCPA adsorption by including the anionic form of MCPA and

the protonated goethite surface into the calculations. Acid–base properties of MCPA and the

goethite surface OH groups lead to creation of several pH ranges (3–4, 4–9, 9) for combining

neutral/deprotonated MCPA with neutral/protonated goethite surface. The stability of

complexes is evaluated on the base of the relative and interaction energies. The most stable

arrangements of the MCPA species are predicted taking into account the type and topology

of the surface OH groups, protonation states (pH effect), the structure of

carboxyl/carboxylate group of MCPA, and the binding type (outer- or inner-sphere

complexes). The calculations show that the basic mechanism for the formation of the outer-

sphere complexes is the formation of hydrogen bonds of a different strength, depending on

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30

which moiety is proton donor or acceptor, respectively. The predicted strongest adsorption

(physisorption) for the complexes in the pH 4–9 range (of the MCPA anion on the protonated

goethite surface, interaction energy in a range of − 124 to − 145 kJ/mol) is followed by

largest solvent destabilization of the outer-sphere complexes due to the high solvent energy

of the MCPA and surface hydration of the hydroxylated goethite surface. For the pH values

close to the pKa value of MCPA (pKa ~ 3), the neutral MCPA molecule interacts weaker with

the protonated goethite surface (interaction energy of about − 80 to -100 kJ/mol), however

its lower solvation energy can produce more stable complexes in solution than that of

anionic MCPA in pH 4–9. Thus, adsorption of MCPA should increase with decreasing pH. This

conclusion is in agreement with the experimental observations reported earlier, in which the

highest adsorbed amount was achieved for the pH ~ 32. The formation of the inner-sphere

chemisorbed surface complex contributes significantly to the overall adsorption of MCPA at

acidic pH range. In the chemisorbed inner-sphere complexes, monodentate binding was

revealed through the formation of a Fe–O–C bridge, Fig. 1.

Figure 1. Most stable chemisorbed complex of neutral MCPA and protonated goethite surface

(FeOH2+ site), reflecting pH bellow 4 (adsorption edge).

References

1. I. Georgieva, M. Kersten and D. Tunega, Theor. Chem. Accounts 139 (2020) 132.

2. A. Iglesias, R. Lopez, D. Gondar, J. Antelo, S. Fiol and F. Arce, Chemosphere 78(11) (2010) 1403.

Acknowledgements: I. Georgieva is thankful to the financial support of Project Д01-272/02.10.2020 -


Science under the National Program "European Scientific Networks".

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Topic A

АP-10

Silver-containing zeolites – preparation, composition and

antibacterial properties

G. Gicheva1*, N. Mintcheva1, M. Panayotova1 and O. Gemishev2

1 Department of Chemistry, University of Mining and Geology, 1700 Sofia, Bulgaria 2 Faculty of Biology, University of Sofia ‘’St. Kliment Ohridski’’, 1000 Sofia, Bulgaria


Keywords: zeolites, silver NPs, nanocomposites, antibacterial properties

Zeolites are one of the most important family of aluminosilicate compounds from

basic and applied research point of view. What defines their importance is not only the vast

natural abundance but also the great variety of the composition and structural diversity.

They are solids with microporous structure which are widely used in water treatment,

chemical catalysis, as ion exchangers, molecular sieves, drug carriers and for advanced

materials production [1]. Zeolites form three-dimensional networks consisting of tetrahedral

SiO4 and AlO4 primary building units and different metal ions as counter ions such as Na+, K+,

Mg2+ and etc.

Essential parameters defining the application of zeolites, both natural and synthetic,

are their chemical composition, thermal stability, pore size and the possibility for surface

functionalization. Zeolite pores and crystals’ surface could serve as templates for formation

of nanostructured metallic and semiconductor nanoparticles, thus forming various new

hybrid materials [2].

In our recent investigations we utilize the natural zeolite clinoptilolite for preparation

of silver-containing composites and examine their antibacterial activity against Escherichia

coli. Aiming to find more active materials, we prepare Ag-zeolite nanocomposites and

compare their composition, morphology and properties. In all cases Ag nanoparticles

(AgNPs) on zeolite were observed that were formed by thermal reduction, chemical

reduction in aqueous solutions with mild (Na-citrate) and strong (NaBH4) reducing agents, so

that the samples Ag-Zeo-1, Ag-Zeo-2 and Ag-Zeo-3, respectively were synthesized. As-

prepared materials were characterized by different methods such as XRD, DRUV-vis, XPS,

TEM (Figure 1). The decoration of nanocomposites with AgNPs as well as co-existence of

immobilized Ag+ ions in zeolite framework was confirmed by microscopic and spectroscopic

results. The maximum efficiency in inhibition of bacterial growth was observed for sample

Ag-Zeo-1, following by Ag-Zeo-2 and Ag-Zeo-3 composites.

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32

Figure 1. TEM images of (a) Ag-Zeo-1; (b) Ag-Zeo-2; (c) Ag-Zeo-3 (inlet: image of different area) and

(c) size distribution of all samples.

References

1. M. Panayotova, N. Mintcheva, O. Gemishev, G. Tyuliev, G. Gicheva and L. Djerahov, Bulg. Chem.

Comm. 50 (2018) 211.

2. M. Panayotova, N. Mintcheva, G. Gicheva, L. Djerahov and N. Mirdzveli, Proceedings of 20th

International Multidisciplinary Scientific GeoConference SGEM 2020, Albena, Bulgaria, 18 - 24 August

2020, p. 77-84.

Acknowledgements: The authors thank the National Science Fund of Bulgaria for financial support

under the grant DN-17/20.

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Topic A

АP-11

Application of Bulgarian clinoptilolite as carrier for Mn-containing

catalyst in VOCs elimination

I. Hristova1*, S. Todorova1, H. Kolev1, G. Avdeev2 and A. Naydenov3

1 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 2 Rostislaw Kaischew Institute of Physical Chemistry, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 3 Institute of General and Inorganic Chemistry Bulgarian Academy of Sciences,



Keywords: VOCs oxidation, Mn catalysts, clinoptilolite, n-hexane

Volatile organic compounds (VOCs) are major pollutants of the atmosphere and

widely known to deteriorate air quality. For VOCs removal, the catalytic oxidation is much

more effective and attractive than conventional combustion. Usually catalytic oxidation

shows good efficiency at lower temperatures without secondary pollutants. The desired

catalysts should exhibit good activity at low temperatures, high selectivity for total oxidation,

and stability to deactivation. It is well known that metal oxide catalysts are of importance in

heterogeneous catalysis, especially chemical processes in industry. The performance of

metal oxide catalysts depends on their nature, size, shape, and surface area, and their

relationship is a critical factor in determining catalytic activity and selectivity. In addition,

active metal impregnation is very important for achieving high catalyst activity and stability

(the type of the active metal is very important for achieving high catalyst activity and

stability). Manganese oxide is reported to be quite promising among the metal oxides used

for preparation of supported catalysts for the removal of VOC. Manganese is an

environmentally friendly active component for many catalyst systems. The heterogeneous

catalysts are commonly supported on a carrier. The carrier is a tool to increase surface area,

optimize porosity, stabilize particle size, and resist poisoning. Such a type of carrier is

clinoptilolite. It is preferred as a support due to its specific microporous structure, high

thermal stability, and possibility of ion exchange. A combination between manganese oxide

and clinoptilolite is expected to result in high catalytic activity. A manganese containing

catalyst involving MnO2 was chosen as the Mn component provides redox functionality,

because among non-noble metal catalysts, those based on MnOx active phase are

characterized by high oxidation activity, low cost, and low toxicity.

The aim of the current investigation was to prepare, characterize, and test Mn-oxide

catalysts using Bulgarian clinoptilolite as support in the reaction of n-hexane oxidation.

Manganese was deposited on the support by wet impregnation with aqueous solution of

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34

Mn(NO3)2.4H2O. The samples were calcined for 3 h at 500°C. Manganese content was 10 and

20 wt.%. Clinoptilolite was modified with nitric acid to clean the pores of various

contaminants and ion exchanged with ammonium nitrate to obtain a catalytically active

form. The obtained materials were studied by the following techniques: XRD, XPS, TPR, and

N2 physisorption. Sample catalytic activity was examined in the reaction of complete

oxidation of n-hexane. In air, n-hexane participates in radical reactions, which are involved in

the formation of photochemical smog. Тhe European Directive 2008/50/EU recommends

such measurements.

Acknowledgement: Financial support by Bulgarian National Science Fund through programme

‘Competition for financial support for projects of junior basic researchers and postdocs – 2020’

(contract No КП-06-М49/2) is greatly acknowledged.

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35

Topic A

АP-12

Mesoporous nanostructured iron-titanium-manganese mixed oxide as

catalysts in ethyl acetate oxidation

G. Issa1*, M. Dimitrov1, R. Ivanova1, D. Kovacheva2 and T. Tsoncheva1

1 Institute of Organic Chemistry with Centre of Phytochemistry, BAS, 1113 Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, BAS, 1113 Sofia, Bulgaria


Keywords: iron-titanium-manganese, catalysts, ethyl acetate oxidation

The negative role of volatile organic compounds (VOCs) such as ethyl acetate,

benzene, ethanol, toluene and acetone as pollutants in the atmosphere is well known. These

compounds can react with other pollutants in the air, such as NOx, under sunlight and

produce tropospheric ozone and photochemical smog, which can be dangerous for human

health [1]. The catalytic oxidation of ethyl acetate to CO2 and water as a method for its

removal has been shown as a promising method for atmospheric air purification. It is an

environmentally friendly technology as it works at low temperatures, causing less NOx

formation in comparison with conventional thermal oxidation, where high operation

temperatures are needed [1–5]. Much research has been done on the application of

multicomponent mixed-metal oxides as heterogeneous catalysts for removal of VOCs [6].

The development of nanostructured mesoporous composites is well known strategy

for the increase of the catalytic activity of the individual oxides via regulation of their

structure, texture and promotion of synergetic effects. Recently, titania based composites

have received much attention due to their superior optical, electronic, mechanical and

catalytic properties, combined with non-toxicity and cost effectiveness. The aim of current

investigation is to study the effect of iron modification of mesoporous manganese- titania

binary oxides on their catalytic behaviour in ethyl acetate oxidation as a member of VOCs.

The effect of binary oxides composition on the state of the hosted in them iron

species is also in the focus of the investigation. The titania-manganese supports were

synthesized by template-assisted technique using CTAB as a template. The iron modification

was carried out by incipient wetness impregnation with Fe(NO3)3.9H2O and further

calcinations at 773 K. The obtained materials were studied by N2 physisorption, XRD, UV-Vis,

XPS, SEM, TEM, Raman and FTIR spectroscopies and TPR with H2. The ethyl acetate oxidation

(EA) were performed in flow type apparatus followed GC analyses. All synthesized

manganese-titania supports exhibit high surface area and mesoporous volume. Among

them, binary oxides represent improved texture characteristics, in the highest extent for

5Mn5Ti. The XRD and Raman analyses for support showed co-existence of anatase, Mn2O3

and Mn5O8 for 5Ti5Mn, while only well crystallized anatase and rutile TiO2 phases were

3RD



36

found for 5Mn5Ti. The slight shifting in the anatase unit cell parameters found for the TiMn

materials did not exclude partial isomorphous substitution of Ti4+ by Mnn+ ions. The XPS

analyses showed stabilization of Ti and Mn ions in lower oxidative state in the obtained

binary oxides. The additives of titania to managanese oxide promote their catalytic activity in

total oxidation of ethyl acetate. After the modification with iron, XRD, Raman and UV-Vis

analyses reveal formation of FexOy nanoparticles of 14-45 nm. XPS spectra demonstrate co-

existence of Mn, Ti and Fe ions in different oxidative state. The amount of ions in lower

oxidative state is higher for the binary supported iron modifications. All iron modifications

exhibit higher catalytic activity in total oxidation of ethyl acetate to CO2 in comparison with

the corresponding supports. The catalytic properties of these materials are determined by

the activity of FexOy crystallites and the facile electron transfer within the “conjugated” Ti-

Mn-Fe redox centres in the interface layer.

Acknowledgement: Financial support from project КП-06-ПМ-39/1/2019 is acknowledged. This work

was supported by the European Regional Development Fund within the Operational Programme

“Science and Education for Smart Growth 2014 - 2020” under the Project CoE “National center of

mechatronics and clean technologies“ BG05M2OP001-1.001-0008".

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37

Topic A

АP-13

Ni- and Cu-ZSM-5 adsorbents for fine hydrogen purification from CO

V. Zdravkova, E. Ivanova*, S. Andonova, N. Drenchev, M. Mihaylov and K. Hadjiivanov




Keywords: adsorption, IR spectroscopy, hydrogen, gas purification, TPD, breakthrough curve

Hydrogen is the most environmentally friendly fuel and is therefore often considered

the fuel of the future. However, some of its technological applications require a high purity.

For example, PEM fuel cells require hydrogen feed to contain less than 10 ppm CO in order

to avoid catalysts poisoning. Adsorption-based technologies for purification of gases have

attracted increased interest because of their energy efficiency. These technologies have the

potential to achieve high selectivity in gas separation processes that need to be further

developed and optimized.

In order to be used for strong binding of CO impurities in H2 matrix, the developed

adsorbents need to have a high enthalpy of CO adsorption and a much lower enthalpy of H2

adsorption. In this work, we investigated Ni-ZSM-5 and Cu-ZSM-5, since stable carbonyl

complexes with exchanged Cu+ and Ni+ ions have been reported for these zeolites. In

addition to in situ IR spectroscopy, adsorption was studied by measuring TPD curves and

breakthrough curves.

The samples were prepared from H-ZSM-5 by conventional ion exchange with

Ni2+/Cu2+. IR spectroscopy showed formation of carbonyl complexes with highly electrophilic

Ni2+ ions in ZSM-5. Although 1+ is not typical oxidation state of Ni, some Ni+ sites are

produced after reduction with CO. In contrast, Cu2+ does not adsorb CO, but most of it can

be converted to Cu+ by CO reduction. Thanks to the facilitated €-bonding Ni+ and Cu+ sites

bind CO very strongly and form multicarbonyls in CO equilibrium pressure.

The zeolites were examined with TPD in order to obtain valuable information about

the energetics of chemisorption and the heterogeneity of the centers. The CO-TPD curve of

oxidized Ni-ZSM-5 contains a complex feature with three components at 107, 160 and 185°C,

indicating the centers are heterogeneous. After reduction of the sample with CO, the

amount of desorbed CO increases and a new desorption maximum appears at 355-380°C.

This can be explained by nickel dispersing and obtaining a certain amount of Ni+ (about 20%

of all centers). In the case of Cu-ZSM-5, a significant amount of desorbed CO is registered

only after a preliminary reduction with CO after majority of Cu2+ has been converted to Cu+.

Again, heterogeneity of the centers was observed for Cu-ZSM-5 as most of CO was desorbed

3RD



38

at temperatures above 300°C, indicating that Cu-ZSM-5 could be more difficult to regenerate

than Ni-ZSM-5.

Figure 1. CO breakthrough curves in presence of H2 of oxidized (blue) and CO-reduced zeolites (red).

The inset shows the subsequently recorded CO-TPD curves.

Finally, CO breakthrough curves in the presence of H2 were measured on oxidized

(treated in O2/Ar at 773 K) and reduced (CO/Ar at 573 K) zeolites (Fig. 1). Hydrogen passes

unimpeded through the adsorbent bed and is not shown. The measured adsorption capacity

of oxidized Ni-ZSM-5 was 3.8 mL/g. Its breakthrough curve is steep, which is an indication of

rapid kinetics. This results in high bed utilization efficiency and high working capacity. The

reduction with CO leads to an increase in capacity to 9.0 mL/g (working capacity 6.4 mL/g)

rather due to an increase in the dispersion of nickel rather than its reduction to Ni+. In the

case of Cu-ZSM-5, pre-reduction with CO plays a crucial role in adsorbent activation, as Cu2+

centers do not adsorb CO. Although the total capacity of the reduced Cu-ZSM-5 (9.8 mL/g)

slightly exceeds that of the reduced Ni-ZSM-5, its working capacity (3.4 mL/g) remains

noticeably lower.

Conclusions. Zeolite ZSM-5 was found to stabilize nickel and copper as isolated

cations in a low coordination and valence state, which favors CO adsorption. As a result, Ni-

ZSM-5 and Cu-ZSM-5 zeolites showed promising behavior as adsorbents to produce high

quality CO-free hydrogen. Activation of the Cu adsorbent required a preliminary reduction

with CO, which converts the Cu2+ ions into Cu+. In contrast, oxidized Ni zeollite captured

good amount of CO under dynamic conditions. Pre-treatment with CO increased its capacity

not only due to reduction to Ni+, but also due to increased dispersion. Dynamic adsorption

measurements showed better working capacity for Ni-ZSM-5, but one can expect more

stable operation in presence of humidity for Cu-ZSM-5.

Acknowledgements: The authors gratefully acknowledge the financial support by the Bulgarian

National Research Program EPLUS (approved by DCM # 577/17.08.2018).

Ni-ZSM-5 Cu-ZSM-5

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39

Topic A

АP-14

Three-step procedure for preparation of porous spherical carbon from

graphite

D. Kichukova, D. Kovacheva* and I. Spassova




Keywords: graphite, spherical carbon, Raman spectra, SEM, BET

Porous carbons play important role in catalysis, environmental protection and energy

storage. The high porosity is achieved by activation of carbon precursors or by a template

method. The activation is usually a chemical or physical and aimed to obtain structural

defects in the carbon precursors. The resulting pore system is formed by the aggregation of

disordered, defect and small size graphite layers. The rise of investigations on grapheme

materials provides an approach for the production of a carbon that has both a high specific

surface area (SSA) and excellent pore accessibility. Single-layer graphene has a theoretical

SSA of 2630m2g-1, while powder-like reduced grapheme oxide (RGO) represent an arbitrary

(random) aggregation of graphene layers, as a result most of the surface of the graphene

sheets is inaccessible, which leads to a relatively low specific surface area. Two approaches

exsist for preparing highly porous RGO, with high SSA: first is focused on producing pores in

individual sheets, which provide transport channels for foreign molecules that have access to

the overlying graphene sheets [1]; second is based on creating of ordered organization,

through linking graphene sheets to three-dimensional (3D) pore systems [2]. Both known

methods require special equipment and procedures. Thus the obtaining of graphene-derived

carbon materials with high SSA and developed porosity by other methods is an interesting

task. The aim of the work is to describe new synthetic method for preparation of porous

spherical carbon (PSC) and to present its basic characteristics.

The oxidation of natural graphite powder (NG7) was performed by modified

Hummers’ method, followed by sonication of the suspension to obtain graphene oxide (GO).

After reduction of GO with ascorbic acid, the produced reduced graphene oxide (RGO) was

dried. Then, the oxidation and reduction steps are repeated and the resulting porous

spherical carbon material was characterized by powder XRD, SEM, TEM, N2-physisorption

and Raman spectroscopy. The SSA obtained for the initial graphite is 2 m2g-1 and for the new

PSC sample is 475 m2g-1. The N2 adsorption isotherm is of type I, typical for microporous

materials with hysteresis type H2, evidencing disordered material. Fig.1. presents the results

from XRD, SEM, TEM and Raman spectroscopy of the initial graphite and the new prepared

PSC samples. It can be seen that the Raman spectra of the initial and final compounds are

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40

completely different. A strong and narrow G band is observed for NG7 while the dominant of

the spectrum of PSC is broad D band. Since the D band corresponds to the sp3 – hybridized

carbon atoms at the edges or defects on graphene basal plane, suggesting that the PSC has

nanopores on graphene sheets and increased defects and disorders. XRD patterns present

typical graphite pattern, while the pattern of PSC is similar to RGO but the 002 peak is

shifted towards lower 2θ. SEM micrograph of NG7 shows typical sheet-like morphology,

while that of PSC shows a ball-like morphology with hierarchical fractal characteristics. TEM

image of PSC confirms that the balls are constructed of graphene sheets.

Figure 1. Raman spectra, SEM photographs, XRD patterns and TEM image of initial NG7

graphite and PSC.

This work reports a new method for preparation of porous spherical carbon material from

natural graphite. This PSC is characterised with hierarchical fractal ball-like morphology, high SSA and

pore volume. The preparation method is simple and does not require special laboratory equipment.

References

1. Y. Zhu, S. Murali, M. D. Stoller, K. J. Ganesh, W. Cai, P. J. Ferreira, A. Pirkle, R. M. Wallace, K. A.

Cychosz, M. Thommes, D. Su, E. A. Stach and R. S. Ru, Science 332 (2011) 1537.

2. Z. Chen, W. Ren, L. Gao, B. Liu, S. Pei and H-M. Cheng, Nat. Mater. 10 (2011) 424.

Acknowledgements: The authors thank to the Project Д01-272/02.10.2020 - "European Network on


National Program "European Scientific Networks" and National Program "Young Scientists and

Postdoctoral Students", module “Young Scientists”, stage III.

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41

Topic A

АP-15

XPS study of mono and bimetallic metal (Co, Mn) oxide catalysts

H. Kolev1*, S. Todorova1, I. Hristova1, P. Gaudin2 and J. L. Blin2

1 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 2 Université de Lorraine/CNRS, F-54506 Vandoeuvre-lès-Nancy cedex, France


Keywords: Co, Mn oxides, catalysts, X-ray photoelectron spectroscopy

Abatement of volatile organic compounds (VOCs) and CO in the waste gases is one of

European Union's main environmental policy tasks since the late 1970s

(http://ec.europa.eu/environment/index_en.htm). In 2013, the EU proposed a Clean Air

Policy Package to further reduce emissions of air pollutants until 2030. The main air

pollutants are Particulate matter (PM), SO2, NH3, NOX, volatile organic compounds (VOCs),

CH4.

Beside many different techniques, such adsorption, absorption, biofiltration and

thermal combustion, catalytic combustion is a cost-effective method for VOCs removal,

especially when the organics cannot be recycled or is present in low concentrations.

Catalysts for the complete VOCs oxidation can be noble metals, mixtures of noble metal and

transition metal oxides, perovskites and transition metal oxides. Transition metal oxides

have shown very good catalytic performances in oxidation reactions and good selectivity.

Moreover, they have a low cost in comparison to the noble metal catalysts, but their main

drawback is the deactivation of the catalysts due to sintering. The problem could be tackled

by applying novel preparation methods and application of supports with new properties.

Mesoporous silica materials have attracted much attention as catalysts support. The

advantage of these materials is that the large macropores combined with the mesoporous

structure give the materials large transport channels accompanied by a high active surface

area, which is beneficial for the catalytic activity of the materials. The mesoporous structure

and morphology of SBA-15 materials with Co, Mn or simultaneously with both cobalt and

manganese type of oxide phases and the size of the oxide particles remain almost

unchanged after tests in reaction of complete n-hexane oxidation.

This work is focused on physicochemical investigation of series of mono component

cobalt and manganese and bi-component Co-Mn catalysts supported on SBA-15 and macro-

mesoporous silica (MMS) before and after catalytic test. The experimental technique used

for this investigation is X-ray Photoelectron Spectroscopy (XPS). XPS is one of the most

widely used analysis techniques due to its extremely surface sensitivity. Beside the

qualitative analysis (identification of all chemical elements except H and He presented on

the surface and determination of their chemical state), it can give a valuable information

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42

about the dispersion of supported nanoparticles presented for real catalytic systems. Using

the power of XPS technique we were able to determine the oxidation state of the surface

cobalt and manganese. Both Co3+ and Co2+ present on the surface of monocomponent Co-

MMS sample. The predominant species on the surface of mono-component Mn catalyst is

Mn3+. The Co2+, Co3+, Mn3+ and Mn4+ ions are observed in all bi-component samples CoMn-

MMS and the ratio between them depends on the concentration of cobalt and manganese.

In the case of mono component CoSBA-15, the clusters of Co3O4 are on the surface and they

are partially located inside the pore system of SBA-15 while for Mn-SBA-15 sample, the Mn3+

and Mn4+ oxide phases preferentially fill up the channels of SBA-15 forming nanowires. The

Co2+, Co3+, Mn3+ and Mn4+ ions are observed in all bi-component samples CoMn-SBA-15

samples. From the XPS analysis it is visible, that with increasing of the amount of manganese

the relative abundance of Co3+ ions sharply decrease and Co2+ is only species in the sample

with highest Mn concentration.

The highest catalytic activity observed for Co-MMS sample in CO and n-hexane

oxidation is related to the predomination of Co3+ species on the surface of Co3O4 and the

more accessible oxide particles located outside the mesopores.

References

1. S. Todorova, J.L. Blin, A. Naydenov, B. Lebeau, D. Karashanova, H. Kolev, P. Gaudin, R. Velinova, L.

Vidal, L. Michelin, L. Josien, D. Filkova, I. Ivanova, A. Dotzeva and K. Tenchev, Catal. Today 361 (2021)

94.

2. S. Todorova, J.L. Blin, A. Naydenov, B. Lebeau, H. Kolev, P. Gaudin, A. Dotzeva, R. Velinova, D.

Filkova, I. Ivanova, L. Vidal, L. Michelin, L. Josien and K. Tenchev, Catal. Today 357 (2020) 602.

Acknowledgements: The authors express their gratitude to the National Science Fund of Bulgaria for

the financial support under the Contract КП-06-Н49/4”. Research equipment of distributed research

infrastructure INFRAMAT ДО1- 382/18.12.2020 (part of Bulgarian National roadmap for research

infrastructures) supported by Bulgarian Ministry of Education and Science was used in this

investigation.

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Topic A

АP-16

Thermodynamic modelling of salt crystallization in surface polluted

water to predict its self-cleaning ability

A. Kovacheva*, S. Tepavitcharova, R. Ilieva, R. Gergulova and D. Rabadjieva




Keywords: natural water, thermodynamic modelling, spontaneous crystallization

Mathematical modelling based on the principles of chemical thermodynamics is

widely used for prognosing, studying and interpreting the behavior of chemical elements in

aqueous electrolyte solutions. Thus, it is a useful tool for calculating solid/liquid phase

equilibria and distribution of the chemical species of elements in natural waters with a view

to solving environmental problems.

Spontaneous salt crystallization, which leads to a reduction in the content of the

pollutants in surface natural waters, was evaluated by the saturation index of the

compounds SI=lоg (IAP/K), where IAP is the ion activity product and K is the solubility

product. The activity coefficients of all possible simple and complex species involved in the

estimation of IAP, were calculated on the basis of the classical ion-association model for

calculating the inorganic metal species and of the Stockholm humic model accounting for the

complexation reactions of trace metals with organic matter. Visual Minteq computer

program, Version 3.1 was used, whose thermodynamic database contains updated and

expanded data for salt solubility products and complex stability constants.

Four hot spots in Bulgaria, characterized by varying degrees of contamination with

trace metals (Al, Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb), were used as case studies. The water

samples were collected from the area around the landfill east of Radnevo town, which is

affected by coal industry in the Maritza iztok complex; from Gabrovshtitza river in the East of

Maglizh town and from Koprinka Dam near the Kazanlak town, affected by developed

agriculture and livestock breeding and several machinery construction factories situated in

the area; and from an area nearby the tailing pond of the lead - zinc pyrometallurgical

factory in Kardjali region.

Results show that 47 solid phases had SI≥0 at the experimental conditions for each

water sample. That means, the waters studied are supersaturated (S>0) or saturated (S=0)

with respect to these compounds and their crystallization is thermodynamically possible. But

only 14 of the calculated salts, namely, Al(OH)3, CaCO3, Ca3(PO4)2(am), CdCO3, CoCO3,

Fe(OH)3, MnCO3, MnHPO4, Ni(OH)2, NiCO3, Pb(OH)2, Pb5(PO4)3Cl, Zn(OH)2 and ZnCO3.H2O

were included in the model as being able for spontaneous precipitation, according to the

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44

literature. The phases displaying a negative SI (solution is unsaturated, crystallization is not

possible) or a positive SI with no spontaneous crystallization to be expected, such as high-

temperature phases, phases obtained as a result of long-term maturation of primary

precipitated phases, phases obtained by oxidation of the solution, etc., were excluded from

the model.

The calculation revealed that, although the water samples are supersaturated with

respect to the above mentioned salts, only some of them (a different number for each of the

water samples) participate in the crystallization process and lead to a reduction in the

content of the trace metal. We discuss this result on the basis of a correlation between the

structural units of the metals in the solution and those in the crystal structures of the salts. It

is known that both the highest crystallization rate and the lowest supersaturation necessary

for nucleation should be exhibited by the salts for which, in the saturated solution, there is a

sufficient concentration of structural entities able to be incorporated unchanged or with

small changes into the crystal structure. We have predicted the chemical species of the

studied trace metals, present in the aqueous solutions, by thermodynamic modelling.

The thermodynamic modelling of the waters under study showed that depending on

pH and composition of the solutions, spontaneous crystallization reduces the contents of Al,

Fe, Mn, Ni and Pb as follows: Al and Fe up to 95% in the form of Me(OH)3; Mn between 42%

and 90% in the form of MnHPO4; Cd between 30 and 60% in the form of CdCO3; Ni between

50 and 98% in the form of Ni(OH)2 and NiCO3; and Pb between 30 and 85% in the form of

Pb5(PO4)3Cl.

Acknowledgement: The authors thank the Bulgarian Ministry of Education and Science for financial

support under project DN 14-7/2017.

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Topic A

АP-17

MnCoFeO4 obtained by solution combustion method for low temperature

hydrocarbons oxidation: influence of the type of the fuel

V. Tumbalev1, D. Kovacheva1*, R. Velinova1, I. Spassova1, A. Naydenov1 and N. Velinov2


1113, Sofia, Bulgaria 2 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: spinels, SCR-method, hydrocarbons, complete oxidation

The catalytic oxidation of hydrocarbons depends not only on the particles size of the

active oxide catalyst but is also structure sensitive. The spinel ferrites offer high activity and

stability during this reaction, due to their high specific surface area and small particle sizes.

The spinel structure favors high resistivity to catalytic poisons, because of the presence of

structural defects, electron exchange between neighboring ions and the possibility for

surface recovery. For spinel oxide ferrites, cations in octahedral sites are mainly exposed to

the surface, and as a result the catalytic activity of these materials is closely related to the

type and octahedral occupancy of the cations. MnFe2O4 and CoFe2O4 are partially inverse

spinels, where only part (around 20%) of manganese or cobalt ions are presented in the

octahedral sites. Thus the catalytic properties of these spinels are mainly due to the Fe3+ ions

[1]. In order to increase the catalytic activity a compositional variation should be made,

allowing more manganese and cobalt ions to be presented in the octahedral sites. The aim

of the present paper is the synthesis of spinels with composition MnCoFeO4 and the study of

their catalytic behavior in the reaction of complete oxidation of n-alkanes - methane,

propane and butane.

Metal nitrates were taken in a molar ratio 1:1:1 as oxidizers and precursors for the

final oxide products. As a fuel in the combustion, sucrose (S) and citric acid (CA) were used.

The final fine powdered products were thermally treated at 400°C for 1h and at 500°C for 1

h. The samples were denoted as MCF(S) and MCF(CA), respectively. All samples were

characterized by powder XRD, nitrogen adsorption at 77K, SEM and Moessbauer

spectroscopy. Catalytic tests were performed in a reactor of continuous flow type. The gas

velocity (GHSV) was 100,000 h−1. The O2 concentration was 16 vol% and the mixtures were

balanced to 100% with N2. XRD results represent single phase spinels showing unit sell

parameter 8.353(2)Å with mean crystallite sizes 6 nm for MCF(S) and 8.386(1)Å with 11 nm

for MCF(CA). The specific surface areas are 93 m2g-1 and 50 m2g-1, respectively. The

adsorption results reveal different pore texture for the investigated spinels. Moessbauer

spectra of both samples are composed of a combination of sextet and doublet components.

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46

The relative amount of the doublet in MCF(S) is higher than that of MCF(CA) confirming that

MCF(S) is more fine crystalline. The results for the complete oxidation of different n-alkanes

are presented in Fig.1.

100 150 200 250 300 350 4000

20

40

60

80

100

MCF(CA)

MCF(S)

Convers

ion, %

Temperature, oC

Propane

100 150 200 250 300 350 4000

20

40

60

80

100

MCF(CA)

MCF(S)

Convers

ion, %

Temperature, oC

Propane+H2O

100 150 200 250 300 350 4000

20

40

60

80

100

MCF(CA)

MCF(S)

Convers

ion, %

Temperature, oC

Butane

300 350 400 450 5000

20

40

60

80

100

MCF(CA)

Convers

ion, %

MCF(S)

Temperature, oC

Methane

Figure 1. Dependence of the conversion degree on the reaction temperature during the

complete oxidation of hydrocarbons on MCF.

The catalysts prepared with different fuels show different morphological and surface

properties. As a result, the catalytic behaviour of the samples is in concordance with their

physicochemical characteristics. The complete oxidation of n-alkanes proceeds at very low

temperatures depending on the type of the catalyst and the n-alkane used. As expected, the

highest temperature for conversion is measured for methane combustion and the observed

decrease of the reaction temperature from methane to n-butane can be correlated with the

strength of the weakest H-C bond of the corresponding n-alkane. The different crystallite

size of the spinel phase influences the number of the active sites on the surface of the

catalysts. The results reveal that structural, surface and morphological characteristics of the

spinels could be tuned by the type of the fuel. The spinels MnCoFeO4 could be successfully

applied in low temperature hydrocarbon oxidation.

References

1. Ts. Lazarova, D. Kovacheva, M. Georgieva, D. Tzankov, G. Tyuliev, I. Spassova and A. Naydenov,

Appl. Surf. Sci. 496 (2019) 143571.

Acknowledgements: The authors thank the National Science Fund, project КП-06-Н29/2, 2018.

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Topic A

АP-18

Synthesis and physicochemical characterization of active CeO2 materials

O. Lagunov*, V. Zdravkova, M. Mihaylov, I. Spassova, D. Nihtianova, G. Atanasova,

D. Panayotov and K. Hadjiivanov




Keywords: ceria, synthesis, XRD, TEM, BET, XPS, Raman spectroscopy

CeO2 and CeO2 - based materials have demonstrated high activity in a wide range of

catalytic and adsorption application. In this respect, nanoparticulate ceria materials offer low

formation energy of defects that can assist a reversible production of reduced materials with

enhanced catalytic activity and selectivity. The redox properties make ceria-based materials

especially suitable for catalytic applications aimed at production of valuable products like

steam reforming, water-gas shift reaction, thermochemical water splitting, and conversion

of CO2 to methane or methanol. Another class of reactions includes the environmentally

oriented oxidation of CO, soot, and hydrocarbons, NOx storage-reduction, selective catalytic

reduction of NO with NH3, etc. The main advantage of CeO2 in the redox catalysis is

associated with its high oxygen release/storage capacity due to the possible easy switching

between the Ce3+ and Ce4+ oxidation states of cerium and creating/filling of oxygen

vacancies. Reducibility of ceria can be modified by the addition of metal ion dopants, like Pt,

Ru, Zr, Ta, Mo or W ions, which substitutes the Ce4+ ion in the CeO2 structure. Zirconium

addition to ceria is found beneficial not only for the reducibility of ceria, but also for the

improved thermal stability and enhanced catalytic activity of pristine ceria. Mixed CeO2–ZrO2

systems can assure better catalytic activity in redox reactions such as methane combustion,

oxidation of propane, reduction of NO, CO2 conversion to valuable products, etc. It was also

shown that the presence of dopants can further tune the surface functionalities, such as the

surface acid–base properties and defect sites, which impact the adsorption behaviour of CO2

on the CeO2 surface.

The active CeO2 materials studied in this work have different origin. Two of them

were commercial nanoparticulate CeO2 powders obtained from two different suppliers, Alfa

Aesar and US Research Nanomaterials. Both samples have comparable nanoparticle size and

specific surface area. The third CeO2 nanoparticulate sample was prepared in our lab by

precipitation with ammonia from of a Ce(NO3)3·6H2O aqueous solution, exposed to

ultrasonic irradiation. The fourth nanoparticulate material was CeO2(75%)ZrO2(25%)

obtained via co-precipitation with ammonia from of a mixed aqueous solution of

Ce(NO3)3·6H2O and ZrO(NO3)2.xH2O, exposed to ultrasonic irradiation. The as

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48

obtained/synthesized samples were characterized by the X-Ray diffraction (XRD),

transmission electron microscopy (TEM), HRTEM and energy-dispersive X-ray spectroscopy

(EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and the N2-adsorption

isotherm BET method. As shown in Figure 1 and Table 1, the samples prepared by

precipitation with ammonia upon ultrasonic irradiation showed enlarged surface area and

more developed pore structure as compared to the commercial samples.

Figure 1. Nitrogen adsorption-desorption isotherms and pore-size distributions.

Sample S

m2/g

Vt

cm3/g

Dav

nm

CeO2-USRN 75 (82) 0.28 15

CeO2-AA 72 (72) 0.23 13

CeO2-son 103 0.29 11

CeO2(75)ZrO2(25)-son 107 0.16 6

Table 1. Texture characteristics, derived by the nitrogen adsorption-desorption isotherms.

Based on the data from HRTEM, XPS and Raman spectroscopy studies, it is concluded

that the two samples prepared by precipitation contain almost twice enlarged number of

defects. On the basis of comparison, it is proposed that the home synthesized samples have

characteristics that make them promising materials for catalytic and adsorption application,

like reduction of NOx and CO2 capture, respectively.

Acknowledgements: The work was supported by the National Scientific fund (project DN19/2) and

the Ministry of Education and Science (National Research Programme “Low Carbon Energy for the

Transport and Domestic Use”) approved by DCM No. 577/17.08.2018 (contract DO1-

214/28.11.2018).

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Topic A

АP-19

Surface nitrates on nanoceria: effect of Zr substitution

M. Mihaylov1*, E. Ivanova1, V. Zdravkova1, K. Chakarova1, H. Aleksandrov2, P. Petkov2,

G. Vayssilov2 and K. Hadjiivanov1


1113 Sofia, Bulgaria 2 Faculty of Chemistry, University of Sofia, 1126 Sofia, Bulgaria


Keywords: ceria, ceria-zirconia, DFT, IR spectroscopy, nitrates, nitrogen oxides

Ceria and Zr substituted ceria are components in many catalysts for NOx conversion,

where nitrates act as important intermediates [1]. Therefore, knowledge of the nature of

surface nitrates on these materials is essential to design new effective DeNOx catalysts. IR

spectroscopy is one of the most convenient techniques in this respect [2].In this work we

propose precise spectroscopic identification of nitrate structures formed on nanosized pure

and Zr substituted CeO2 on the basis of a combined FTIR and DFT study. To reinforce the

assignments, we used isotopically labelled molecules, 15NO and 18O2.

Two commercial CeO2 nanopowders (with different surface area) and series of CeO2-

ZrO2 mixed oxides (with different oxide ratio) prepared by coprecipitation were studied.

Formation and decomposition of surface nitrates were followed by in situ IR spectroscopy.

We identified at least 4 types of nitrate species on CeO2 (Fig. 1A). The thermal stability of the

species increases in sequence B-D-C-E. Based on the literature, one might associate species B

with bridging bidentate nitrates, species C and D, with chelating bidentate nitrates, and

species E, with monodentate nitrates. However, this classification is too simplified and we

offer an advanced assignment based on isotopic studies and comparison with the DFT

results. Very recently we proposed an experimental approach to distinguish between

different nitrate coordination [3]: upon partial exchange with 18O the highest frequency IR

band is shifted to two new bands for monodentate (an indication for two coupled NO

vibrations) and the observed tridentate nitrates and to one new band for bidentate nitrates

(characterized by isolated N=O bond). The high stability of E species impeaches their

assignment to monodentate nitrates and the DFT results indicates they are tridentate

nitrates, although bound to surface more strongly via one oxygen. All other species behave

as bidentate nitrates upon 18O exchange. The C species may be associated with the most

stable modelled structures formed at the surface step where the nitrate ion chelates one

cerium ion and one of the chelating oxygen atoms is simultaneously coordinated to another

cerium cation. The D species are less stable but the position of the HF band is at lower

wavenumbers, as compared to the C species. DFT results suggest that the lower frequency

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50

could be connected with higher symmetry of structures where both chelating oxygens have

multiple coordination. With CeO2-ZrO2 mixed oxides some general decrease of nitrate

concentration is observed, more pronounced for tridentate E structures. New bands are also

noticed (marked with * in Fig. 1A). DFT studies show that nitrate ion may be coordinated

directly to Zr ion or be affected by subsurface Zr. As an example Fig. 1B presents the most

stable structure formed on CeO2(111) surface where the first nitrate O ion is bond to two Ce

ions, the second O, to the Zr cation, and the third O is free.

Figure 1. (A) IR spectra of nitrates on different samples, produced after NO + O2 coadsortion and

evacuation at 573 K (Ce80Zr and Ce60Zr mixed oxides contain 81 and 58 wt% CeO2, respectively). (B)

DFT modelled nitrate structure on Zr-doped CeO2(111) surface.

Conclusions. Based on combined IR and DFT studies we identified differently

coordinated nitrate structures on CeO2 and CeO2-ZrO2 nanopowders. Surface chemistry of

mixed oxides seems to be mostly determined by CeO2. However, Zr dopping of the ceria

surface suppress the formation of stable tridentate structures and may be involved in

bidentate nitrate formation. The tridentate nitrates are with C2v symmetry bound to surface

most strongly via one oxygen. Bidentate nitrates simultaneously bridge and chelate metal

cations. The spectral difference between these species is due to the binding geometry,

symmetry reduction and nature of cations, to which they are bonded. Although subsurface

Zr is not directly bonded to NO3 it may affect nitrate spectra too.

References

1. Catalysis by ceria and related materials, A. Trovarelli, P. Fornasiero (Eds.), Catal. Sci. Ser., vol. 12,

2nd ed., Imeprial College Press, 2013.

2. K. I. Hadjiivanov, Catal. Rev. - Sci. Eng. 42 (2000) 71.

3. M. Y. Mihaylov, V. R. Zdravkova, E. Z. Ivanova, H. A. Aleksandrov, P. St. Petkov, G. N. Vayssilov and

K. I. Hadjiivanov, J. Catal. 394 (2021) 245.

Acknowledgements: The authors gratefully acknowledge the financial support by the Bulgarian

Scientific Fund (project DN 19/2).

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Topic A

АP-20

Functionalized nanocomposites derived from natural zeolite

as antibacterial agents

N. Mintcheva1*, M. Panayotova1, G. Gicheva1 and O. Gemishev2

1 Department of Chemistry, University of Mining and Geology, 1700 Sofia, Bulgaria 2 Faculty of Biology, University of Sofia ‘’St. Kliment Ohridski’’, 1000 Sofia, Bulgaria


Keywords: silver nanoparticles, natural zeolite, functionalized nanocomposites, AgNPs- clinoptilolite,

antibacterial properties

Zeolites are hydrated crystalline aluminosilicates, containing exchangeable cations

(Na+, K+, Ca2+, Mg2+) which compensate the negative charge in Al-O-Si network. Clinoptilolite

is highly abundant mineral in many geographic regions, it is isostructural to heulandite, and

both belong to the framework type HEU. The SiO4 and AlO4 tetrahedral units, linked by

oxygen atoms, form the three-dimensional structure of clinoptilolite, which is characterized

with three types of mutually crossing channels. The typical ion-exchange properties of

natural zeolites derive from a facile exchange of aforementioned cations with many other

metal cations. Silver ions are among the cations that can be easily exchanged to govern the

antibacterial properties of modified zeolites and to widen the area of application of

nanocomposites.

Recently, we have used the natural zeolite, clinoptilolite, and prepared silver-loaded

nanocomposites that were fully characterized by various advanced methods and were tested

for antibacterial activity against Escherichia coli. Furthermore, clinoptilolite was treated with

NaCl and HCl and was converted to its Na- and H-form. The ion-exchange with Ag+ ions in

solution leads to formation of three types of composites: Ag-exchanged natural zeolite, Ag-

exchanged Na-zeolite and Ag-exchanged H-zeolite, that were subsequently heated at 400 oC

to produce silver nanoparticle (AgNPs) containing materials, denoted as Ag-Zeo, Ag-NaZeo

and Ag-HZeo, respectively.

The comparison of structural parameters and composition of these materials revealed the

effect of exchangeable cations in the precursors on the Ag ions load and on the AgNPs

fraction formed on the zeolite. The modification of natural zeolite with HCl and NaCl,

introduces variations in adsorptive and ion-exchanged properties of the zeolite framework,

which allows to control the Ag content and Ag distribution via the change in ion-exchange

capability of the parent zeolite. The highest Ag uptake demonstrated Na-modified zeolite,

followed by natural zeolite, and the lowest Ag content has H-modified zeolite. As can be

expected, Na-modified zeolite provides a large number of specific ion-exchange sites for

immobilization of Ag+ ions and thus ensures higher cation exchange capacity. After heating

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52

at 400 oC in air, evenly distributed Ag+ ions in zeolite channels undergo nucleation to Ag

clusters that aggregate to AgNPs and migrate on the surface of zeolite crystals. In both

samples Ag-Zeo and Ag-NaZeo, nanoparticles with diameter in the range 1-14 nm were

observed, while in Ag-HZeo the AgNPs grew up to 10-42 nm. The UV-vis and XPS data

revealed that in zeolite AgNPs co-exist with significant portion of Ag+ ions which remain non

reduced at elevated temperature and presence of air. The Ag nanocomposites showed

strong antibacterial activity against Gram-negative Bacterium Escherichia coli. The minimum

inhibitory concentration against Escherichia coli for Ag-Zeo and Ag-NaZeo was found to be

0.8 mg/mL, while for Ag-HZeo it is 5.0 mg/mL. The results of this study clearly show that

natural and Na-, H-modified zeolites can be ion-exchanged with Ag+ ions and thermally

stabilized to acquire antibacterial properties, thus such materials can be considered as

promising candidates for antibacterial agents in water treatment.

Figure 1. Antibacterial activity against Escherichia coli of nanocomposites: (a) Ag-Zeo, (b) Ag-

NaZeo, (c) Ag-HZeo, (d) comparison between Ag-NaZeo and Ag-Zeo.

Acknowledgements: The authors thank the National Science Fund of Bulgaria for financial support

under the grant DN-17/20.

(a

) (b

)

(c

) (d

)

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53

Topic A

АP-21

HDS activity of Mo and NiMo sulfided catalyst prepared by thioglycolic acid

assisted hydrothermal synthesis

R. Palcheva1*, L. Kaluza2, G. Tyuliev1, K. Jiratova2, D. Gulkova2, L. Dimitrov3 and G. Avdeev4

1 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 2 Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic,

165 02 Prague, Czech Republic 3 Institute of Mineralogy and Crystallography “Acad. I. Kostov”, Bulgarian Academy of

Sciences, 1113 Sofia, Bulgaria 4 Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: NiMo catalysts, hydrothermal synthesis, thioglycolic acid, HDS of thiophene

The hydrodesulfurization (HDS) process continuously faces strict regulations on the

sulfur content in liquid fuels on one hand and diminution of available low sulfur feedstock on

the other hand. Apart from more severe process conditions or major investments into

plants, ever more active hydrotreating catalysts should be developed to meet the growing

demand for cleaner fuels. Transition metal sulfides have been widely used as hydrotreating

catalysts that are small crystallites of Mo sulfide promoted with Co or Ni supported on

alumina. We have reported optimization of NiMo HDS catalysts prepared on Nb modified

silica mesoporous supports by treating with thioglycolic acid (TGA) [1]. It was found that

simultaneous impregnation by Ni, Mo and thioglycolic acid led to higher HDS activities than

the sequential treatment of the calcined NiMo catalysts by TGA. This observation is due to

formation of a complex of the Mo and/or Ni atoms with TGA.

Now we are reporting synthesis of MoAl and NiMoAl HDS catalysts under mild

hydrothermal conditions with addition of TGA for ex situ sulfidation at 160oC. The dark solids

were analyzed by XRD, FT-IR, SEM and XPS techniques. The reduction patterns of the catalyst

precursors and the sulfidation behavior of MoAl and NiMoAl catalysts were analyzed in TPR

and TPS experiments, respectively. The activity of the catalysts was evaluated in the HDS of

thiophene at 340oC. In the synthesis of the samples Mo-TGA-Al and NiMo-TGA-Al (TGA/Mo =

2 and TGA/Mo = 4), 0.436 g of Ni(NO3)2.6H2O was dissolved in water and the Mo containing

solution was added to reach Ni/Mo ratio 0.3. Then, 1.28 ml and 2.56 ml of TGA were added

to get TGA/Mo = 2 and TGA/Mo = 4, respectively. All reactants were mixed in 100 ml water

and stirred for 40 min. Then, 4 g of γ-Al2O3 was added and stirred for 8 h. The final solution

was sealed into a 100 ml Teflon - lined stainless steel autoclave and heated at 160oC for 22 h.

The product was washed with distilled water and ethanol for several time, and dried in the

air at 40oC for 12 h.

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After re-sulfidation by H2S/H2 at 400 °C, the surface areas of catalysts varied in the

range 160-200 m2/g. The isotherms are of type IV, characteristic for the mesoporous

materials. It was found that SBET and Smeso increases with the loading of nickel and addition of

more amount of TGA. Possibly, there is formation of a secondary mesopores thanks to

formation of molybdenum/nickel sulfides together with re-crystalization of 〈-boehmite

during catalysts preparation. Thioglycolic acid assisted hydrothermal synthesis of Mo and

NiMo catalysts supported on γ-Al2O3 led to high activity catalysts in thiophene

hydrodesulfurization reaction. Almost all deposited Mo and NiMo phase is converted to

highly dispersed sulfidic phase. Traces of thioglycolic acid species remaining in pores and

their decomposition at above 300 °C were determined by combination of FTIR, TPR, and TPS

methods. This part of thioglycolic acid species has positive effect on surface area and

hydrodesulfurization activity. The catalyst prepared with two-fold surplus of thioglycolic acid

(molar ratio of TGA/Mo = 4) resulted in the most active catalyst in hydrodesulfurization of

thiophene.

Table 1. HDS activity at 340oC, TPR-H2, and TPD-NH3 data

Samples HDS activity TPR-H2 TPD-NH3

Charge

mg

Conversion % kTH mmolTH/g.h mmolH2/g

20-500oC

mmolNH3/g

20-500oC

NiMoAl hydroth 10 30.0 32 - -

Mo-TGA2-Al 100 83.2 16 1.71 0.41

NiMo-TGA2-Al 10 65.7 97 1.52 0.52

NiMo-TGA4-Al 10 83.6 164 1.35 0.55

References

1. R. Palcheva, L. Kaluza, L. Dimitrov, G. Tyuliev, G. Avdeev, K. Jiratova and A. Spojakina, Appl. Catal.

A: Gen. 520 (2016) 24.

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Topic A

АP-22

Structural and mechanical properties of Ni-and Co-based dental alloys

obtained by powder-metallurgical and thermal alloying methods

D. Radev* and D. Kovacheva




Keywords: dental alloys, structure, corrosion resistance, biocompatibility, thermal alloying

Here we compare structural and mechanical properties of Ni- and Co-based dental

alloys produced by the conventional thermal alloying and by the innovative method of

powder metallurgy (PM). Biocompatibility, longevity, mechanical and aesthetic properties of

metal ceramic prosthetic restorations depend on the elemental composition and of the

structural properties of the alloy used for the metal framework production. The traditional

production of Ni and Co base dental alloys consists of consequent melting of the

components: Ni, Co, Mo, Cr, W etc. and casting of ingots, weighting 5-10 g. each. Using the

lost wax casting technique these ingots serve to produce the metal framework of dental

bridges, crowns etc., which after veneering with porcelain obtain the final mechanical and

aesthetic properties. The components of dental alloys differ in their physical properties,

which causes compositional inhomogeneity of the melt in the process of classical thermal

alloying. For example, melting points of Mo and W are higher or close to the boiling

temperatures of Ni, Cr, Si, Mn; density values of Si, B, C, which often present in the

compositions of Ni and Co base dental alloys, are several times lower than that of the other

metal components. The elemental inhomogeneity of the melt in the process of thermal

alloying is inherited by the ingots and by the final dental restorations, worsening their

biological, mechanical and aesthetic properties. The innovative method of powder

metallurgy (PM) applied in the production of dental alloys avoids the obstacles of the

traditional high temperature alloying process.

Aim: The aim of this work is to study the influence of the production method on the

structural and mechanical properties of two types of primarily and recasted nickel and cobalt

based alloys obtained by the methods of PM and by the traditional thermal alloying. Phase

and structural peculiarities are investigated using XRD and SEM-methods. The homogeneity

of the elemental distribution in both types of alloys after the first and second casting is

studied by EDX spectroscopy.

Materials and methods: Two types of Ni- and Co-based dental alloys, produced by

the PM and by the classical methods, designed for metal-ceramic restorations are used for

production of four groups of specimens: 1. Marranium FI: Ni-Cr and Marranium CC: Co-Cr

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alloys produced by powder metallurgical methods, producer Sintal MM LTD, Bulgaria; 2.

Wiron 99: Ni-Cr and Wirobond C: Co-Cr alloy produced by conventional methods, producer

Bego, Germany.

Two groups of specimens were produced from each type of alloy – the first group

contained primarily melted and casted alloy and the second one contained 100% recast

without adding “fresh” alloy.

Discussion. When juxtapose the data from the XRD investigations of samples, it is

detected that the 2θ values of the PM-alloys after the second casting are closer in values to

the corresponding peaks of the classically obtained alloy after their first casting. . The PM

ingots have been obtained by sintering of powders, without melting and the completely

alloying of the elements has been finished during the primary casting of the prosthetic

restorations by the dental technician. The picture of the elemental distribution shows that

the processes of phase formation in the classically obtained alloys are in a more advanced

stage comparing to the structure of the PM-alloys. According to the data obtained PM-

technique provides more even distribution of elements and constant composition of any

ingot of the product batch. The comparative analysis of the SEM images indicates that the

elemental fragmentation of the PM alloy is less pronounced. Investigations of the elemental

distribution in the both types of Ni and Co base dental alloys show that the registered

structural differences are based on the technological alternatives of the production

processes. The use of pure metal powders as components of the PM alloy and the exact and

constant composition of ingots lead to excellent mechanical properties of “Marranium FI.

The statistical analysis of the data received from the tensile strength measurements show

that there is no statistically significant difference in tensile strength between the groups of

primarily casted and recasted alloy of the same type. The only factor that matters is the

method of producing the alloys. Data obtained show that the mean values of the PM alloys

are in a narrower range compared to those of the conventionally obtained alloys. This mode

of the result distribution is more pronounced for the recasted PM alloys where the tensile

strength values show smaller deviations from the average value. Except appropriate

mechanical and technological properties, such as castability, limited value of coefficient of

thermal expansion, dental alloys should meet the requirement of high corrosion resistance,

thus to provide the necessary biocompatibility of the final dental restorations. The main

advantage of the echo-friendly PM technology applied in dental alloys production is the

exact and constant elemental distribution in any ingot, thus ensuring the elemental ratio

necessary to maintain a high level of mechanical properties and excellent corrosion stability

of the final dental restorations.

Acknowledgements: The authors wish to thank Project D01-272/02.10.2020 - "European Network on



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Topic A

АP-23

Carbon-nanofibers encapsulated Fe-Ce-Ni mesoporous nanoparticles:

synthesis, morphological studies and catalytic behavior for the oxygen

evolution reaction in an alkaline medium

C. Rosmini1*, T. Tsoncheva1, D. Kovacheva2, N. Velinov3, D. Karashanova4, D. Sebastián5 and

M. J. Lázaro5

1 Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of

Sciences, Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia, Bulgaria

3 Institute of Catalysis, Bulgarian Academy of Sciences, Sofia, Bulgaria 4 Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 5 Instituto de Carboquímica (CSIC), 50018 Zaragoza, Spain


Keywords: carbon nanofibers, iron carbides, Fe-Ni-Ce, methanol decomposition, oxygen evolution

reaction

Two mesoporous supports in Fe-Ce (molar ratios Fe:Ce = 5:5 and 9:1), were

synthesized by hydrothermal template assisted method, and subsequently impregnated with

a quantity of Ni equal to half the moles of Fe (Ni:Fe = 1:2), (called 5Fe5Ce_Ni and

9Fe1Ce_Ni). In order to increase the electro-catalytic properties and reduce the intrinsic

impedance of the metal oxides, two different changes of the metallic phase have been

made, first reducing in H2 (called 5Fe5Ce_Ni_Alloy and 9Fe1Ce_Ni_Alloy), promoting the

formation of Ni-Fe alloys. The metal phase has been further modified into ferrous carbides

and metal alloys encapsulated inside carbon nanofibers (called 5Fe5Ce_Ni_@C and

9Fe1Ce_Ni_@C). For this purpose, the decomposition of methanol vapors was used, a

reaction already widely studied for the production of hydrogen. In fact, this decomposition,

in addition to producing syngas, deactivates the catalysts in use through a chemical vapor

deposition-carbon coating process. This disadvantage has been used by us to demonstrate

how the catalytic residues deriving from these vapor-phase reforming techniques can be

used for electro-catalytic purposes. The various modified phases of the two molar ratios of

the Fe-Ni-Ce catalysts were tested in the Oxygen Evolution Reaction (OER) reaction in an

alkaline environment (1M KOH), showing a satisfactory increase in activity and a surprising

decrease in the overpotential. The samples were also characterized with the following

techniques: XRD, nitrogen physisorption, TEM, EDS, TPR and FTIR, UV-Vis, XPS, Raman and

Moessbauer spectroscopies to evaluate their morphological, textural and chemical-physical

properties.

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Figure 1. OER activity of 5Fe5Ce_Ni and 9Fe1Ce_Ni based materials, in deaerated 1 M KOH aqueous

solution at 1800 rpm at 0.005 V·s-1 scan rate.

Acknowledgements: This project has received funding from the European Union’s Horizon 2020

research and innovation programme under the Marie Sklodowska-Curie grant Agreement No.

813748.

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Topic A

АP-24

XPS Investigation of ZrO2/TiO2/carbon steel coatings before and after

corrosion tests

М. Shipochka1*, I. Stambolova1, D. Stoyanova1, N. Boshkov2 and N. Boshkova2


1113 Sofia, Bulgaria 2 Institute of Physical Chemistry, Bulgarian Academy of Sciences, 1113, Sofia, Bulgaria


Keywords: XPS, ZrO2/TiO2, protective layers, corrosion resistance

The surface composition and chemical state of ZrO2/TiO2 layers before and after

corrosion resistance tests were determined by X-ray photoelectron spectroscopy. Two types

of structures were deposited: the first (13), consisting of three TiO2 underlayers, coated with

one ZrO2 layer and second (31), consisting of one TiO2 underlayer, coated with three ZrO2

layers. The titania coatings were obtained from one non-modified (sol A) and two modified

with polyoxyethylene (20) sorbitan monooleate (sol B) and ethylcellulose (sol C). Zirconium

coatings were obtained from Zr butoxide Zr(OC4H9)4. The final treatment of the samples was

carried out at 500°C. The obtained structures are presented on Figure 1.

The potentiodynamic polarization technique was used to determine the protective

ability of the coatings in a 5% chloride containing model corrosive media.

The film composition and electronic structure were investigated by X-ray

photoelectron spectroscopy (XPS). The measurements were carried out on AXIS Supra

electron- spectrometer (Kratos Analitycal Ltd.) using monochromatic AlKα radiation with a

photon energy of 1486.6 eV and a charge neutralisation system. The binding energies (BE)

were determined with an accuracy of ±0.1 eV. The chemical composition in the depth of the

films was determined monitoring the areas and binding energies of C1s, O1s, Zr3d, Ti2p and

Fe2p photoelectron peaks. Using the commercial data-processing software of Kratos

Analytical Ltd. the concentrations of the different chemical elements (in atomic %) were

calculated by normalizing the areas of the photoelectron peaks to their relative sensitivity

factors.

A comprehensive XPS analysis was performed to evaluate elemental and quantitative

composition of the surface corrosion resistant layer. The C1s, O1s, Zr3d, Ti2p and Fe2p peaks

were registered. The deconvoluted zirconium spectra consist of four peaks, which

correspond to zirconium suboxide and ZrO2. The registered amount of TiO2 in structure 31 is

small because it is deposited under three zirconia layers (Fig.1). The shape of Ti2p and Zr3d

spectra before and after corrosion tests is similar: chemical shifts of the binding energies are

not observable. The quantity of zirconium, titanium and iron remains almost the same after

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the corrosion tests. Based on these observations it could be supposed that the oxide

multilayers cover the metal substrate completely and can be used for effective anti-

corrosion coatings.

Structure 13 Structure 31

ZrO2 ZrO2

TiO2 ZrO2

TiO2 ZrO2

TiO2 TiO2

substrate substrate

Figure 1. Scheme of the both types of oxide structures.

Acknowledgements: The authors are grateful to the financial support by project No.KP-06-H37/16

„New environmentally friendly one- and multi-layer coatings for corrosion protection of structural

materials with wide application” of the Bulgarian Fund For Scientific Researches at the Ministry of

Education and Science of Bulgaria and to the contract “Mono- and poly-component catalytic systems

for waste water and polluted air purification from model contaminants”, which is within the bilateral

cooperation between the Bulgarian Academy of Sciences and the Serbian Academy of Science and

Fine Arts. The authors are grateful to the project Д01-272/02.10.2020 - "European Network on


National Program "European Scientific Networks" for the opportunity to present their research

results.

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Topic A

АP-25

Supported palladium containing perovskite catalysts for methane combustion

S. Stanchovska*, R. Stoyanova, E. Zhecheva and A. Naydenov




Keywords: palladium, cobalt perovskites, methane, complete oxidation

Elaboration of supported Pd-perovskite catalysts for catalytic combustion is,

nowadays, considered as an imperative research task to reduce the emissions of methane as

one of the most abundant air pollutant. This study provides new insight into the effects of

the method of deposition, chemical state of Pd and oxygen storage capability of transition

metal ions on the catalytic reactivity of supported Pd-perovskite catalysts for combustion of

methane. The catalyst with nominal composition La(Co0.8Ni0.1Fe0.1)0.85Pd0.15O3 were

supported on SiO2-modified/γ-alumina and monolithic VDM®Aluchrom Y Hf carrier by means

of two synthetic procedures: (i) aerosol assisted chemical vapour deposition (U-AACVD) and

(ii) wet impregnation (IMP) (Figure 1). The nominal weight of deposited perovskites was 10

wt.% with respect to the support. Irrespective of support type, the average Pd content in the

catalysts was almost the same: 1.7 ± 0.2 wt.% on γ-alumina support and 1.2 ± 0.5 wt.% on

monolithic VDM®Aluchrom Y Hf carrier (Table 1). A uniform distribution of the active phase

was achieved over the γ-alumina support. A comparative analysis shows that a higher

catalytic activity is established for supported catalyst SiO2-modified/γ-alumina obtained by

hot impregnation, where the PdO-like phase is well dispersed and the transition metal ions

display a high oxygen storage capability (Figure 2). The reaction pathway over both IMP- and

U-AACVD-prepared catalysts proceeds most probably through Mars–van Krevelen

mechanism. The supported catalysts are thermally stable when they are aged at 500 oC for

120 hours in air containing 1.2 vol.% water vapour, which is important for their future

exploitation in real industrial conditions.

Table 1. Pd content determined from EDS analysis

support application method Pd, wt %

γ-alumina/SiO2 hot impregnation 1.7 ± 0.2

γ-alumina/SiO2 spray pyrolysis 1.6 ± 0.4

VDM®Aluchrom Y Hf hot impregnation 1.2 ± 0.5

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Figure 1. SEM images of different magnification for γ-alumina (a,c) and monolithic VDM®Aluchrom Y

Hf (b,d) supported catalyst. The circles indicate small particles enriched in Pd and the square points to

an intermediate layer of monolithic support due to γ-alumina.

Figure 2. Temperature dependence of conversion during complete oxidation of methane on the

investigated perovskite-based catalysts.

References

1. S. G. Stanchovska, D. N. Guergova, G. M. Ivanov, R. K. Stoyanova, E. N. Zhecheva and

A. I. Naydenov, Bulg. Chem. Commun. 50 Special issue H (2018) 61.

Acknowledgements: Project Д01-272/02.10.2020 - "European Network on Materials for Clean


"European Scientific Networks".

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Topic A

АP-26

Solid state tautomerism of 2-carbamido-1,3-indandione

N. Stoyanova1*, M. Rogojerov2, Ts. Zahariev1 and V. Enchev1


1113 Sofia, Bulgaria 2 Institute of Organic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: 2-carbamido-1,3-indandione, tautomerism, DFT, IR spectroscopy

2-Carbamido-1,3-indandione (CAID) exists in solid state as yellow-orange needles

which sinter from 180 to 2200C [1]. We have shown that two enol tautomeric forms (Fig. 1),

2-(hydroxyl-aminomethylidene)-indan-1,3-dione (a) and 2-carboamide-1-hydroxy-3-oxo-

indan (b), coexist in solution [2].

Figure 1. Tautomeric forms of 2-carbamido-1,3-indandione.

The first tautomer converts into the second and vice versa through very fast

intramolecular proton transfer, i.e., the energy barrier of the reaction is very low. Tautomers

are UV-vis distinguishable: the predicted longest wavelength absorption band of the more

stable tautomer, 2-(hydroxyl-aminomethylidene)-indan-1,3-dione is at 373 nm and the band

of 2-carboamide-1-hydroxy-3-oxo-indan is hypsochromically shifted by 44 nm [3]. Because of

strong absorption in the UVA and UVB spectral region and its relatively high photostability,

CAID is suitable for sunscreen and as a fluorescent molecular probe for the investigation of

different biomolecules [3]. In addition, we have shown that CAID possesses high binding

affinity to DNA and RNA molecules [4] which appears to change the tautomeric equilibrium.

The solid state structure of CAID is shown in Fig. 2, left. The fact that the substance

sinters from 1800C to 2200C is a prerequisite to think that in solid state there is also a

mixture of two tautomeric forms. The hypothesis has been tested by means of qunatum-

chemical calculations and spectroscopic techniques. IR solid state spectrum of 2-carbamido-

1,3-indandione has been recorded (Figure 2, right). It has a complex structure and it is not

straightforward to propose interpretation of it, solely on the basis of one tautomeric

structure. DFT calculations (PBE functional) for the isolated molecules of tautomers a and b,

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as well as solid-state periodic DFT calculations (PAW/PBE). Calculated vibrational frequencies

are compared with the vibrational modes from the solid state spectrum. An interpretation of

the latter, based on comparative analysis, is proposed.

Figure 2. X-ray structure (left) according Ref. [2] and IR solid state spectrum of 2-carbamido-1,3-

indandione.

References

1. R. L. Horton and K. C. Murdock, J. Org. Chem. 25 (1960) 938.

2. V. Enchev, I. Abrahams, S. Angelova and G. Ivanova, J. Mol. Struct. THEOCHEM 719 (2005) 169.

3. V. Enchev, I. Angelov, V. Mantareva and N. Markova, J. Fluorescence 25 (2015) 1601.

4. N. Stoyanova, N. Markova, I. Angelov, I. Philipova and V. Enchev, Photochem. Photobiol. 97 (2021),

DOI: 10.1111/php.13378.

Acknowledgements: N. Stoyanova is thankful to the financial support of Project Д01-272/02.10.2020

- "European Network on Materials for Clean Technologies", funded by the Ministry of Education and


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Topic A

АP-27

Catalytic combustion of methane over Ni modified Pd/Al2O3 catalysts

S. Todorova1*, A. Naydenov2, R. Velinova2, Y. Karakirova1, H. Kolev1 and A. Larin3

1 Institute of Catalysis, Bulgarian Acad. of Sciences, Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 3 Department of Chemistry, Moscow State University, 119992,Moscow, Russia


Keywords: methane, catalytic combustion, Pd–Ni/alumina

Methane is a major Greenhouse Gas (GHG) that accounts for 14% of the world’s total

amount of GHG emissions, originating mainly from agriculture, coal mines, land fields,

wastewater and oil and gas facilities [1]. The European Commission presented the so-called

Green Deal in December 2019, also known as the Green Pact, which is a set of policies aimed

at making Europe climate neutral by 2050. The plan is to reduce greenhouse gas production

at least by 50% compared to 1990 levels, as well as zero pollution by 2050, whether soil, air,

or water pollution. Neutralization of the methane emissions can be done by different

methods, one of them being the complete catalytic oxidation. Methane combustion is

achieved by using of noble metal loaded oxide catalysts, palladium being known to offer a

high catalytic activity. However, its deactivation at high temperatures requires the

development of new catalysts or improvement of Pd (PdO) dispersion on catalytically active

supports such as pre-modified alumina, hexaaluminates etc. An alternative for stabilization

of support and catalytic active phase could be found in the introduction of oxides to the

existing catalytic systems [2,3]. According the authors in [4] the hydrothermal stability of Pd-

based catalysts in methane combustion has been significantly improved by addition of the

Ni. Such excellent catalytic performance has been related to the stabilizing effect of the

support due to the least lattice mismatch between NiAl2O4 and Pd, which contributes to the

high Pd dispersion.

The Pd-based catalysts modified by nickel were prepared by sequential impregnation

of Al2O3 with aqueous solutions of Ni(NO3)2.6H2O and Pd(NO3)22H2O. The Pd was introduced

on Al2O3 after impregnation with Ni and next calcination. The palladium content on the

surface of all prepared samples was approximately 0.2 wt%. Characterization techniques as

X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), BET, TPR, TEM and

EPR have been used to investigate the surface structure and bulk composition of mono and

bimetallic nickel and palladium catalysts. Catalytic activity tests were performed using 750

ppm methane.

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The specific surface area decreases with increasing nickel content, which is probably

due to the partial pore blockage of the Al2O3. XRD pattern of the synthesized catalysts show

the presence of two phases namely γ-Al2O3 and Al2NiO4. The last one has also been

confirmed by HRTEM and SAED analyses. SAED patterns demonstrate the presence of Pd and

PdO as well. Diffraction lines for Pd and PdO are not observed in the XRD patterns of studied

samples revealing finely divided phases. The reduction behaviour of the synthesized

catalysts was investigated by means of TPR. Several reduction maxima were observed: at

70°C, 330°C, 420°C and above 500°C. The hydrogen consumption at 70°C is attributed to the

reduction of PdO. Two high-temperature peaks (at 330°C and 420°C) are observed in the TPR

profiles of all samples. They are less intense in the catalysts with low nickel content. The

peak with a maximum at 330 °C in the TPR spectrum is most likely due to the reduction of

finely divided NiO particles and this at 420°C, for the reduction of bulk of NiO. H2

consumption above 500 °C is due to mixed Ni-Al oxide phases. An intensive negative peak at

77°C in the TPR profile of all catalysts is ascribed to the decomposition of β-palladium

hydride. The reduction of highly dispersed PdO to metal Pd can take place even below room

temperature and this metal absorbs hydrogen, leading to the formation of the hydride

phase, which decomposes at about 70°C. The chemical state of Pd and Ni and the

percentage of the different oxidation states of these elements on the catalytic surfaces were

studied by X-ray photoelectron spectroscopy. All three oxidation states Pd0, Pd2+ and Pd4+

are established for palladium. The presence also of paramagnetic palladium species (Pd+ or

Pd3+) are suggested from EPR investigation. The doublet Ni2p XPS spectra and peak binding

energy values propose that nickel is mainly present as Ni2+ on the sample surface. According

to the EPR data part of Ni2+ ions are located in partly dehydrated Al(OH)3. The formation of

orthorhombic Ni+ species and Ni+ species in axial symmetry has been also suggested.

The catalytic activity of the nickel modified samples is higher than that of the

monometallic palladium one. The most active sample is that containing 10% Ni and the least

active is that with 0.5% Ni loading. The difference in T50 between them is only 5 °C, which

indicates that the high nickel content is not appropriate because it does not lead to a

significant increase in catalytic activity.

References

1. Federal Register/ Vol. 78, No. 63 / Tuesday, April 2, 2013 / Proposed Rules, Environmental

Protection Agency, 40 CFR Part 98, 2013 Revisions to the Greenhouse Gas Reporting Rule and

Proposed Confidentiality Determinations for New or Substantially Revised Data Elements.

2. S. Todorova, P. Stefanov, A. Naydenov and H. Kolev, Rev. Roum. Chim. 59 (2014) 251.

3. P. Stefanov, S. Todorova, A. Naydenov, B. Tzaneva, H. Kolev, G. Atanasova, D. Stoyanova, Y.

Karakirova and K. Alexieva, Chem. Eng. J. 266 (2015) 329.

4. Y. Liua, S. Wanga, T. Suna, D. Gaoa, C. Zhanga and S. Wang; Appl.Catal. B 119–120 (2012) 321.

Acknowledgements: The authors thank to the National Science Fund of Bulgaria for the financial

support under the Contract KП-06-RUSSIA-22.

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Topic A

АP-28

Comparative studies of noble metal catalysts loaded on mordenite

and ZSM-5 in CO and benzene oxidation reactions

T. Todorova1*, Yu. Kalvachev1, P. Petrova1, T. Petrova1, B. Barbov2, G. Karcheva1 and

S. Todorova1

1 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria 2 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences,



Keywords: ZSM-5 and MOR zeolites, noble metals, hierarchical materials, catalysts, CO oxidation,

benzene oxidation

The noble metals loaded over Mordenite and ZSM-5 zeolites were used to form high

active catalysts for complete CO and benzene oxidation. The zeolite supports were subjected

to post synthetic treatment with solution of HF acid and buffer NH4F. By adding of buffer

was achieved the chemical equilibrium shifts to the preferential formation of highly active

HF2- anions which showed no selectivity to one of the both zeolite skeletal elements (Si and

Al). The formed hierarchical supports on the one hand will possess the properties of the

parent samples (crystal structure, Si/Al ratio, etc.) in combination with increased active

surface area, improved diffusion properties and the presence of additional porosity

preventing the extraction of the metal phase during of the catalytic process. The metals

(platinum, palladium or copper) were loaded by the wet impregnation method over the

parent and hierarchical zeolite samples. The metal phases were fine dispersed as

nanoparticles on the functional porous materials. The selected catalytic reactions are

informative for the catalysts activity and for the structural specifications of the selected

zeolite supports (Mordenite, ZSM-5).

All samples are characterized by X-ray diffraction analysis, nitrogen adsorption,

transmission electron microscopy and temperature programmed reduction. The catalytic

activity of the samples obtained is investigated in the reaction of complete oxidation of CO

and benzene.

Acknowledgements: This work was supported by the Bulgarian National Science Fund (Contract No.

KP-06-M39/2).

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Topic A

АP-29

Effect of pre- and post-treatment operations of aluminum on the corrosion

resistance of chemically deposited on it conversion ceria coatings

R. Andreeva1, A. Tsanev2* and D. Stoychev1

1 Institute of Physical Chemistry “Acad. R. Kaischew“ – BAS, 1113 Sofia 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,



Keywords: conversion coatings, alumina, ceria, XPS, corrosion resistance

The aim of this study was to elucidate the role of "pre-treatment" operations (in

alkaline and acidic solutions) of Al substrate before deposition on it a conversion ceria

coatings (ССОСs) and phosphate "post-treatment" operation of CCOCs, leading to the

formation of additional immersion phosphate layer(s) (PhLs) on the surface of Al/ССОС, on

the corrosion-protective behavior of the so obtained mixed Al/ССОС/PhLs systems.

Layers of CCOC were deposited on substrates of "technically pure" Al 1050 (pre-

treated in 1.5М NaOH and 5M HNO3 solutions) in solution containing 0.5M CeCl3 x 7H2O +

1.10-5M CuCl2 x 2H2O. The post-treatment of as deposited on Al substrate ceria layers was

realized in two types of phosphate-containing solutions: 0.08M Na3PO4 or 0.22M NH4H2PO4.

The XPS characterization of the obtained samples were carried out on AXIS Supra electron-

spectrometer (Kratos Analitycal Ltd.) using аchromatic AlKα radiation. The electrochemical

and corrosion investigations and determination of the basic corrosion parameters (Ecor, icor,

Epit, EOCP, Rp, CR, etc.) of the studied samples (as deposited and after definite time of

exposure in model 0.1M NaCl corrosion medium) were carried out on Gamry Interface 1000,

Corrosion Technique Software (Electrochemical Impedance Spectroscopy Software and

Frequency Response Analyzer EIS300).

Based on the XPS investigations carried out with the prepared samples it has been

ascertained that there is substantial influence of the "pretreatment" and "post-treatment"

operations on the chemical composition and chemical state of the elements on their surface.

It is expressed in strong decrease in the concentration of Аl2O3 and Ce2O3 + CeO2

components in СCOС at the expense of the formation of AlPO4 and AlOOH, CePO4 as well as

PO3-, P2O5 and P4O10 compounds with Al and Се.

The highest values of corrosion resistance following the 168 hours (~700 кΩ.cm2), as

well as the 336 hours (~190 кΩ.cm2) exposure in the corrosion medium were registered for

the samples coated with CCOC and post-treated in a NH4H2PO4 solution –

Al(NaOH)/CCOC(Ce+Cu)/PhL(NH4H2PO4) system. The comparison of the results of Rp values and

concentrations of Ce3+/Се4+, Al и P (their respective oxides and phosphates) before and after

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exposure of the samples in corrosion medium (determined by XPS analysis) show that the

change of Rp and concentrations of the Се4+ and P on the surface of studied samples are

directly related. The supposed and proved formation of low soluble corrosion products on

the surface of studied systems and the accomplished synergic effects of the protective

action of formed cerium and aluminum oxides/phosphates layers determine the increase of

the Rp value (with the time of exposure in corrosion medium). It was concluded that the

mixed conversion layers, containing stable cerium oxides and phosphates, are more effective

barrier of the chloride ions diffusion to the metal surface and increase the corrosion

resistance of Al-1050 to the general and pitting corrosion.

Acknowledgements: The authors want to thank to Project Д01-272/02.10.2020 - "European Network

on Materials for Clean Technologies", funded by the Ministry of Education and Science under the


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Topic A

АP-30

Surface properties and structure of glassy carbon coatings after

prolonged stay on the international space station (ISS)

D. Teodosiev1, P. Tzvetkov2*, A. Bouzekova-Penkova1, B. Tsyntsarski3 and A. Tsanev2

1 Space Research and Technology Institute, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,

1113 Sofia, Bulgaria 3 Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of

Sciences, 1113 Sofia, Bulgaria


Keywords: glassy carbon, properties, structure, space

The main method for measuring constant and alternating electric fields in the near-

Earth plasma is the double probe method, which takes into account the differential potential

difference between two points in space (double probe method). One of the factors most

influencing the accuracy of measurement is the choice of material for the manufacture of

the probes and the quality of the work surface. These parameters are essential for reducing

the variations of the work function on the surface during irradiation with cosmic radiation

and sunlight. In practice, glassy carbon has emerged as the most suitable material with value

of the work function about 5.05 eV. Despite its long-term use for the construction of

measuring instruments in orbit, no research has been done so far on the stability and

changes in the glassy carbon layer after a longer stay in space.

The present study aims to trace a possible change in the surface properties and

structure of samples with deposited microns thick glassy carbon layer on a dense graphite

substrate after a 28-month stay on the International Space Station (ISS). The effect of open

space was studied by the methods of powder X-ray diffraction (XRD), Raman spectroscopy,

X-ray photoelectron spectroscopy (XPS), atomic force spectroscopy (AFM) and

nanoindentation. The studies did not show changes in the structure of the glassy carbon

layer, but a slight thinning of the coating was observed, probably as a result of contact of

small dust particles with the surface of the samples in Earth orbit.


Project KP-06-H27/2, 08.12.2018.

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Topic A

АP-31

A quantitative analysis of the basic and micro-nutrient elements

in three agricultural wastes

I. Uzunov1*, G. Gentscheva1,2 and Ch. Tzvetkova1


1113 Sofia, Bulgaria 2 Medical University-Pleven, 5800 Pleven, Bulgaria


Keywords: agricultural waste, biochar, biofertilizer, ICP-OES

The investigation deals with a strategy, targeted to support the idea From Large Scale

Agriculture Waste to Value-added and Ecologically Friendly Products. Taking into account

the importance of the problem of waste, the European Commission has proposed a strategy

for the so-called circular economy that adhered to the European Green Deal, adopted at the

end of 2019 [1,2]. The Green Pact is a set of policies directly related to environmental

protection. In addition to the idea of a Circular Economy, the Green Deal also includes a

strategy called From Farm to Fork. It aims to significantly reduce the use of pesticides,

fertilizers and antibiotics in agriculture. Chemical fertilizers have played an important role in

increasing agricultural productivity over the past half-century. However, it has been known

that the excessive use of inorganic fertilizers deteriorated the soil environment, lead to the

mineralization of the organic matter and also contaminated groundwater. So it is important

to overcome these drawbacks by using alternative, eco-friendly fertilizers. Among them, the

use of biochar is a novel approach having potential benefits to both environment and

agriculture. Biochar, produced by pyrolysis of agricultural wastes has been found to improve

plant growth by improving the physicochemical characteristics of the soil as well as

enhancing carbon sequestration [3-7]. Our investigation is aimed at determining the content

of essential elements for soil nutrition, such as N, P and K available in a mixture of three

agricultural wastes. The mixture comprises pyrolyzed rice husks, ash from sunflower husks

and husks of the most ancient wheat, einkorn (Triticum monoccocum L.) in a weight ratio of

1:1:1. The content of micronutrients necessary for plant development, such as Co; Cu; Fe;

Mn; Mg and Zn was determined. Analyses were performed by proximate analysis, ICP-OES

and AAS. The test also includes determining the predominant form of solubility, aqueous or

citrate, of the nutrients present in the mixture. The characteristic is related to their degree

of assimilation by plants and their durability in the soil biota. Some specific physicochemical

properties of the mixture, such as cation exchange capacity, total acidity, pH-level and

exchange acidity were determined by the method of Ganev and Arsova [8]. The nutrition

stock of the mixture is presented in Table 1.

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Table 1 Amount, % N P K C Humus

0.29 2.0 5.1 12.7 21.9

The mixture was characterized by pH/H2O 10.5; electrical conductivity 3.85 ms/cm;

cation exchange adsorption capacity (Т8.2) 43.8 mequ /100 g and 100% base saturation. The

content of water-soluble trace elements in the pyrolyzed rice husks (PRH), as well as in the

sunflower husk ash (Ash SFH) is presented in Table 2.

Table 2 Sample Co, ppm Cu, ppm Fe, ppm Mn, ppm

PRH 0.06 0.033 0.05 0.05

Ash SFH 0.06 0.033 0.05 0.02

The amount of macro-and microelements in einkorn husks, as well as their solubility,

are presented in Table 3.

Table 3

Element Water-soluble, mg/kg Soluble in Morgan's

solution, mg/kg Citrate-soluble, mg/kg

K 1580 2190 610

Na 1320 1859 539

Ca 136 1050 914

Zn 1.2 15 13.8

Mn 15 115 100

Cu 20 35 15

Mg 87 450 363

The high content of digestible and important for plants and soil macro-and

microelements, as well as the good physicochemical indicators, show that this mixture of

agricultural waste can be one of the cost-effective ecological biofertilizers for use in different

farming systems.

References

1. https://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1551871195772&uri=CELEX:52019DC0190

2. https://ec.europa.eu/info/sites/info/files/european-green-deal-communication_en.pdf

3. D. Kern, M. Ruivo and F. Frazão, (2009) Terra Preta Nova: The Dream of Wim Sombroek. In: Woods

W.I., Teixeira W.G., Lehmann J., Steiner C., WinklerPrins A., Rebellato L. (eds) Amazonian Dark Earths:

Wim Sombroek's Vision. Springer, Dordrecht.

4. D. Mohan, K. Abhishek, A. Sarswat, M. Patel, P. Singh and C. U. Pittman, Jr., RSC Adv. 8 (2018) 508.

5. M. Hussain, M. Farooq, A. Nawaz, A. M. Al-Sadi, Z. M. Solaiman, S. S. Alghamdi, U. Ammara, Y. S.

Ok and K. H. M. Siddique, J. Soils Sediments 17 (2017) 685.

6. Z. Fang, Y. Gao, N. Bolan, S. Shaheen, S. Xu, X. Wu, X. Xu,H. Hu, J. Lin, F. Zhang, J. Li, J. Rinklebe and

H. Wang, Chem.Eng.J. 390 (2020) 124611.

7. M.Guo, Soil Syst. 4 (2020) 1.

8. S. Ganev and A.Arsova, Bulg. J. Siol. Sci. Agrochem. Ecol. 3 (1980) 22.

Acknowledgements: The authors thank for the support of the Bulgarian Ministry of Education and

Science through the National Research Programme "Healthy Foods for a Strong Bio-Economy and

Quality of Life" approved by DCM # 577 / 17.08.2018.

https://pubs.rsc.org/en/results?searchtext=Author%3AManvendra%20Patel

https://pubs.rsc.org/en/results?searchtext=Author%3APrachi%20Singh

https://pubs.rsc.org/en/results?searchtext=Author%3ACharles%20U.%20Pittman

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Abdullah_M_-Al_Sadi

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Zakaria_M_-Solaiman

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Salem_S_-Alghamdi

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Ume-Ammara

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Yong_Sik-Ok

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Yong_Sik-Ok

https://link.springer.com/article/10.1007/s11368-016-1360-2#auth-Kadambot_H__M_-Siddique

https://www.sciencedirect.com/science/article/pii/S1385894720306021#!








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Topic A

АP-32

Transition metal chalcogenides as catalysts for carbon dioxide

reduction – a density functional study

E. Uzunova




Keywords: sulphides, selenides, CO2 reduction, DFT

The key challenge in theoretical studies of catalysts for carbon dioxide reduction is to

explain how these materials work, which of them have better performance and in this way

to provide promising synthetic targets. The present study is focused on the comparison

between transition metal oxides and chalcogenides (sulphides and selenides) of Fe, Co, Ni,

Cu, in their performance as catalysts or photocatalysts for carbon dioxide reduction in the

presence of water [1]. Water splitting in acidic media proceeds according to the reactions: 2

H2O → O2 + 4 H+ + 4e− (oxidation step) and 2 H+ + 2e− → H2 (reduction step). On some

transition metal oxides, e.g. Cu2O clusters and thin films [2], water adsorption is dissociative,

H2O → OH− + H+. The catalyst provides protons, which can be attached to CO2 in the first

step of the reduction reaction, thus lowering the activation barrier.

The materials under investigation of the present study are disulphides and

persulphides of the 3d elements from iron to copper, and respectively, diselenides. The

clusters are stabilized by the attachment of carbonyl ligands. The calculations were

performed by the B3LYP density functional, and for comparing the stability of smaller

clusters, the CCSD(T) method was applied. In terms of stability, oxides are more stable than

sulphides and selenides are the least stable. Regarding catalyst activity, oxides are more

active and provide lower energy barriers, but sulphides and selenides are capable of

photoactivation, thus compensating the higher energy barriers and improving selectivity.

References

1. E. L. Uzunova, Catal. Sci. Technol. 9 (2019) 1039.

2. E. L. Uzunova, N. Seriani and H. Mikosch, Phys. Chem. Chem. Phys. 17 (2015) 11088.

Acknowledgements: The authors acknowledge the provided access to the e-infrastructure of the

NCHDC – part of the Bulgarian National Roadmap on RIs with the financial support by the grant No

D01-387/18.12.2020 and also thank Project Д01-272/02.10.2020 - "European Network on Materials

for Clean Technologies", funded by the Ministry of Education and Science under the National

Program "European Scientific Networks".

http://dx.doi.org/10.1039/c8cy02203h

http://dx.doi.org/10.1039/c8cy02203h

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Topic A

АP-33

Congo red adsorption on cationized rice husk cellulose

P. Vassileva*, I. Uzunov and D. Voykova




Keywords: rice husks cellulose, Congo red dye, adorption kinetics and isotherms

Many industries like textiles, food, leather, paper, printing, pharmaceutical,

cosmetics and etc., generate considerable amounts of dye-bearing effluents during their

production processes. Most of the dyes represent serious problems to the ecological system

as they are considered toxic and have carcinogenic properties. Therefore, dye removal is an

important and challenging area in wastewater treatment. Congo red dye (CR) is a benzidine-

based anionic diazo dye, which is known to metabolize the benzidine, a known human

carcinogen [1,2].

The present study investigates the potential of amino-functionalized rice husk

cellulose as an adsorbent for the removal of Congo red dye from aqueous solutions.

The novel material was synthesized by modification of rice husks cellulose with N,N-

dimethyl-1-octadecylamine. Instrumental methods such as XRD, FTIR, SEM and BET were

used for its characterization. The results showed the quaternary ammonium group was

successfully grafted onto cellulose structure. The research is focused mainly on the effect of

process parameters, such as initial CR concentrations, solution pH and temperature on the

adsorption capacity of the material. Adsorption isotherms, kinetics and adsorption

mechanism were also evaluated. Equilibrium data were fitted to pseudo-first order, pseudo-

second order and intraparticle diffusion kinetic models and linear Langmuir, Freundlich and

Dubinin-Radushkevich isotherm models. The calculated kinetic parameters and isotherm

constants are presented in Table 1.

Table 1. Kinetic parameters and isotherm constants for CR adsorption onto the investigated

biosorbent

Pseudo-first order constants Pseudo-second order constants Intra-particle diffusion constants

Qe

(mg g-1)

k1 (h-

1) r2

Qe

(mg g-1)

k2

(g mg-1h-1) r2

Kid

(mg g-1 h-1/2)

C

(mg g-1) r2

22.36 0.022 0.8855 85.91 2.627 0.9999 3.805

1.118

30.14

77.43

0.9517

0.8148

Langmuir parameters Freundlich parameters Dubinin-Radushkevich parameters

Qo

(mg g-1)

K1

(L mg-1) r2

kF

(mg1-nLn g-1)

n

(L mg-1) r2

Qm

(mg g-1)

E

(kJ mol-1) r2

102.35 0.042 0.9980 28.96 5.06 0.9719 93.41 0.089 0.9082

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The adsorption process is well described by pseudo-second-order and Langmuir

models. The possible adsorption mechanism might be due to the combination electrostatic

attraction, hydrogen bonding and the competition of OH– ions. The Langmuir maximum

adsorption capacity of CR was found to be 102.35 mg g−1. The cationized rice husk cellulose

can be used as potential adsorbent for the effective removal of CR from contaminated

wastewater. The values of standard Gibbs free energy change (ΔG0), standard enthalpy

change (ΔH0) and standard entropy change (ΔS0) were calculated. The thermodynamic

parameters showed the spontaneous and exothermic nature of the process. Desorption of

CR is enhanced when the environment is alkaline and strong bases are good desorbing

agents.

References

1. Z. Jiang and D. Hu, J. Mol Liq. 14 (2019) 105.

2. A. Malik, A. Khan, N. Anwar and M. Naeem, Bull. Chem. Soc. Ethiop. 34 (2020) 41.

Acknowledgements: The authors thank to the Bulgarian Ministry of Education and Science under the

National Research Programme "Healthy Foods for a Strong Bio-Economy and Quality of Life"

approved by DCM # 577 / 17.08.2018.

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Topic A

АP-34

Hybrid CO2 adsorbents. Control on the materials properties via

new sequence of addition of the silanols

N. Velikova* and I. Spassova




Keywords: sol-gel, hybrid materials, bifunctional sorbents, mesoporous materials, CO2 sorption

As result of burning of fossil fuels, oil and natural gas CO2 concentration is

continuously increasing and this is considered one of the major anthropogenic contributions

to the global climate change. Therefore, it is highly necessary to develop technologies for

capture and removal of CO2. The most efficient method is CO2 absorption in liquid amines,

but it requires high energy consumption for the regeneration [1]. Therefore, the

development of alternative low cost methods for CO2 capture is on the agenda in recent

years. Some of the most promising solid materials for CO2 capture developed recently are

MOFs, hybrid materials, nanosponges and crystals. Research and development of novel

hybrid materials with extraordinary properties has become one of the most expanding fields

in materials chemistry nowadays. The most promising method for preparation of hybrids,

which attracts the attention of the scientists, is sol-gel. Recently, N-containing silsesquioxane

precursor, Tris[3-(trimethoxysilyl)propyl]isocyanurate (ISC), attracts the attention of the

scientists in the preparation of hybrid solid adsorbents. The reported results reveal a

promising potential of the multifunctional porous hybrid materials with incorporated

isocyanuarte group as CO2 adsorbents and carriers [2].

To the present time, the CO2 sorption properties of the multifunctional silicas

synthesized with ISC are not deeply investigated. The current work represents a

comprehensive study of three groups of bifunctional mesoporous hybrid silicas in which two

different types of organofunctional groups were introduced during co-condensation

between the respective silsesquioxanes and tetraethyl orthosilicate (TEOS) in acidic media

and their adsorption properties for CO2. The materials IN were prepared by co-condensation

of ISC and Bis[3-(trimethoxysilyl)propyl]amine (BTPA), the IS materials were prepared with

ISC and (Mercaptopropyl)trimethoxysilane (MPTMS), the NS group of materials was

prepared with BTPA and MPTMS. Soft template approach was applied with a structural

directing agent Pluronic P123. Mesitylene and KCl were used for improving of the materials`

texture. New sequences of addition of the silanol precursors into the reaction mixture was

applied in order to achieve better distribution of the functional groups on the materials

surface and for prevention of entrapment of the functional groups in the pore walls. The

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synthesized bifunctional hybrid mesoporous silicas were investigated by FTIR, N2-

physisorption, PSD, DTA/TG-MS, SEM, XPS and XRD techniques. CO2 adsorption properties of

the synthesized bifunctionalized hybrid materials were investigated. The results show that

the silanol precursors sequence of addition, type of the silsesquioxane precursors and the

presence of isocyanurate groups have significant influence on the materials texture,

morphology, pore shape and CO2 sorption properties.

Original scheme for preparation of

bifunctional mesoporous silica

Dependences of the Qst on the amount

of the adsorbed CO2

Texture characteristics of the materials and CO2 adsorption capacities

Sample SBET

m2g-1

DDFT

nm

Vt

cm3g−1

Vmi

cm³g-1

Smi

cm2g-1

CO2

mmol g-1

IN-1 453 4.1 0.54 0.02 41 1.15

IN-2 261 4.3 0.41 0.01 18 1.10

IS-1 375 3.8 0.35 0.04 81 1.22

IS-2 103 4.3 0.13 0.01 12 0.99

NS-1 257 3.9 0.33 0.001 6 0.86

NS-2 111 4.4 0.14 0.01 15 0.70

The materials analysis results show that the presence of isocyanurate groups in the

hybrid silica framework significantly improves the textural characteristics values and CO2

sorption capacity. The determined heats of CO2 adsorption evidenced physisorption process

between CO2 and the active sites of the hybrid materials.

References

1. Energy Transitions. Move over, coal: Gas now emits more CO2 in U.S. Benjamin Storrow, E&E News

reporter (2019) https://www.eenews.net/stories/1061760587. Accessed 20 Jan 2021.

2. C. Gunathilake, R. S. Dassanayake, C. S. Kalpage and M. Jaroniec, Materials 11 (2018) 2301.

Acknowledgements: This work was supported by KAKENHI (18F18768), Grant-in-Aid for JSPS Fellows.

Research equipment of distributed research infrastructure INFRAMAT (part of Bulgarian National

roadmap for research infrastructures) supported by Bulgarian Ministry of Education and Science

under contract D01-155/28.08.2018 was used in this investigation. Project Д01-272/02.10.2020 -



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Topic A

АP-35

Catalytic combustion of volatile organic compounds over

Cо-ZSM-5 zeolites

R. Velinova1*, B. Grahovski2, H. Kolev2, G. Ivanov1, S. Todorova2, A. Naydenov1




Keywords: Cо-ZSM-5 zeolites, catalytic combustion, ethane, butane, hexane

Nowadays, the major air pollutants are the volatile organic compounds (VOCs).

Usually, their origin is connected with the industrial processes. One of the most promising

technologies of the VOCs removal at low concentration in industrial gaseous effluent is the

catalytic combustion.

Several types of catalysts, such as supported noble metals or transition metal oxides

are used in practice. Within the transition metal oxide catalysts, cobalt containing catalysts

are reported to exhibit efficient catalytic performance during the oxidation of VOCs.

Regarding the dispersion of the active component on the surface, the supporting material

plays an important role. It is well know that zeolites possess an appropriate pore structures,

acidic properties, good thermal stability and ion exchange properties. Among them, metal

modified ZSM-5 was intensively investigated for catalytic combustion of different VOCs [1-3].

In the present study the Co-ZSM-5 catalysts with different Si/Al ratio were studied.

The obtained materials were characterized by N2- physisorption, XRD, XPS, TPO and TPR

methods. The N2 adsorption-desorption isotherms show that all studied samples contain

both micropores and mesopores. No cobalt oxide lines were observed for some studied

catalysts, thus indicating for the fine dispersion of Co3O4. XPS data show that Co2+

predominate on the surface. According to the TPR investigations the formation of different

cobalt oxide species wеre observed. The existence of surface adsorbed peroxy O2- (ad)

species, surface adsorbed O-(ad) species and surface lattice oxygen O2- (ad/lattice) were

suggested based of data from TPO.

The catalysts performance has been evaluated by tests on combustion of ethane,

butane and hexane. It was observed that the Co-ZSM-5 catalysts with ratio Si/Al=23 and

Si/Al=40 present the best catalytic performance. More detailed attention has been paid to

the reaction kinetics and mechanism of hexane complete oxidation. Based on the observed

reaction orders established by power – law kinetics, the following mechanistic models were

selected for consideration: Mars−van Krevelen, Langmuir−Hinshelwood and Eley−Rideal.

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It was concluded that the high catalytic activity of cobalt modified zeolites can be

explained by the high reducibility, result of lower interaction of the cobalt oxide with the

supports. The observed insignificant changes in the zeolite structure, morphology, oxide

particle size and oxide phases after reaction reveal that the zeolite structure can prevents

the agglomeration of the oxide particles, thus giving new opportunities for development of

stable catalyst for decreasing of VOCs gas emissions.

References

1. Y. Yan, L. Wang and H. Zhang, Chem. Eng. J. 255 (2014) 195.

2. A. Z.Abdullah, M. Z. Abu Bakar and S. Bhatia, J. Chem. Technol. Biotechnol 79 (2004)761.

3. E. Diaz, S. Ordonez, A. Vega and J. Coca, Micropor. Mesopor. Mat 83 (2005) 292.

Acknowledgements: The authors thank to the National Science Fund of Bulgaria for the financial

support under the contract КП-06-Н49/4. The authors are also grateful to the project Д01-

272/02.10.2020 - "European Network on Materials for Clean Technologies", funded by the Ministry

of Education and Science under the National Program "European Scientific Networks".

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Topic A

АP-36

Laccase immobilized onto hybrid carriers as an effective

biocatalytic system for phenol degradation

S. Yaneva*, N. Rangelova and N. Savov

University of Chemical Technology and Metallurgy, Department of Industrial Safety, 1756

Sofia, Bulgaria


Keywords: enzymes, laccase, hybrid carriers, biocatalytic degradation

Here in we described the phenol degradation by immobilized system based on hybrid

carriers and ligninolytic enzyme (laccase). The sol-gel method was applied for hybrids

preparation and as precursors methyltriethoxysilane (MTES), ethyltrimethoxysilane (ETMS)

and cellulose acetate propionate with high molecule weight (CAPH) were used. The carriers

were examined by X-ray diffraction (XRD) analysis, Infrared (IR), Ultraviolet and visible (UV-

Vis) spectroscopies and Scanning electron microscopy (SEM). For enzyme immobilization

glutaric aldehyde was used. The enzyme activity, catalytic properties and amount of bonded

protein of immobilized systems were determined. The results were compared to free

laccase. The immobilized systems were tested at different concentrations of phenol, the

degree of degradation and the reusability were determined.

Acknowledgements: The authors thank to Project BG05M2OP001-1.001-0008 – “Center of

Excellence in Mechatronics and Clean Technologies”, to Laboratory L2 “Bio-mechatronics and

Micro/Nano Engineering for Mechatronic Technologies, Elements and Systems”, Section S4

“Biomimetic Mechatronic System”.

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Topic B

BO-1

Porous electrodes prepared by magnetron sputtering:

from electrochemical sensing to energy applications

A. R. González-Elipe

Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ. Sevilla), 41092 Sevilla, Spain


Keywords: magnetron sputtering, thin film, electrode

This presentation deals with the control of porosity, microstructure and chemical

state of thin films prepared by magnetron sputtering (MS) for their use as electrodes in a

large variety of electrochemical applications, including sensing, water electrolysis,

electrochromic glasses or fuel cells. In these areas, a high porosity is a requirement that in

principle seems contradictory with the basic principles of MS.

Based on results from our laboratory, in a first part of this review, they will be

described the basic features of MS that can be engineered to adjust porosity and how they

can define suitable experimental strategies to achieve an effective control over porosity and

microstructure of thin films. In a second part, a series of experimental results and examples

will exemplify the possibility of various porous thin films to be used as electrodes for

different applications. A critical assessment of the performance of these systems in

comparison with conventional electrodes prepared by wet chemical routes will provide key

information about the possibilities offered and the limitations encountered by the employ of

MS for the manufacturing of electrodes in these fields of emerging interest.

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Topic B

BO-2

Ion conducting glasses in thin film forms by infrared techniques

E. I. Kamitsos

Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation,

48 Vass. Constantinou Ave., 116 35 Athens, Greece


Keywords: ionic glasses, thin films, IR spectroscopy

Infrared spectroscopy is a powerful tool for studies of glass structure, especially when

it is combined with proper analysis of good quality experimental spectra. This work presents

advances in infrared studies of glassy electrolytes in thin film forms, demonstrates

advantages and limitations when infrared techniques are applied to thin films, and

highlights precautions to be taken when measured infrared spectra are to be interpreted in

terms of the structure of glass films. Examples of glass films presented and discussed in this

talk show that a comparative study of measured and carefully modelled infrared spectra of

thin films allows for the identification of pure optical effects on the measured spectra.

When such an approach is applied, it becomes possible to attribute safely variations in the

infrared profiles of thin films to true structural changes effected by the mode of film

formation and other experimental conditions.

Acknowledgements: The author acknowledges the project “National Infrastructure in

Nanotechnology, Advanced Materials and Micro-/Nanoelectronics” (MIS 5002772), funded by the

Operational Program “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020) and co-

financed by Greece and the EU (European Regional Development Fund).

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Topic B

BO-3

What can photoelectron spectroscopy tell us about the transition

from Li to Post-Li batteries?

J. Maibach*, S. Dsoke and F. Jeschull

Institute for Applied Materials - Energy Storage Systems. Karlsruhe Institute of Technology,

Germany


Keywords: electrochemical energy storage, photoelectron spectroscopy

The performance of rechargeable ion batteries such as lithium- and sodium-ion

batteries largely depends on the chemistry developed at the electrode/electrolyte interface.

At the negative electrode, the solid-electrolyte interphase (SEI) forms from electrolyte

decomposition products. This interphase is crucial for safe and stable battery operation. To

analyze such surface and interface layers in Li-ion batteries, photoelectron spectroscopy is a

widely used and established technique. But can we use the same methodology to investigate

solid-state and Post-Li battery systems?

In this talk, we will present photoelectron spectroscopy approaches for battery

interface characterizations showcasing key challenges when analyzing electrodes and

electrolytes. Starting from so called post-mortem SEI studies for Li-ion batteries, we will

show how we have to rethink our experimental approach for Na-ion and K-ion batteries

[1,2]. For Na-ion batteries, photoelectron spectroscopy revealed cross-talk between the

studied working electrode and a metallic sodium counter electrode. Finally, we will discuss

our findings on using photoelectron spectroscopy to study interface phenomena in all solid-

state batteries [3].

References

1. K. Pfeifer, S. Arnold, J. Becherer, C. Das, J. Maibach, H. Ehrenberg, S. Dsoke, ChemSusChem 12

(2019) 3312.

2. F. Jeschull, J. Maibach, Electrochem. Comm. 121 (2020) 106874.

3. F. Strauss, J. H. Teo, J. Maibach, A-Y. Kim, A. Mazilkin, J. Janek, Torsten Brezesinski, ACS Appl.

Mater. Interfaces 12 (2020) 57146.

Acknowledgements: J.M. thanks the German Ministry of Education and Research for funding within

the InSEIde project (FKZ 03XP0131). This work contributes to the research performed at CELEST

(Center for Electrochemical Energy Storage Ulm-Karlsruhe) and was funded by the German Research

Foundation (DFG) under Project ID 390874152 (POLiS Cluster of Excellence).

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Topic B

BO-4

Capture and conversion of CO2 using MOF-based composite materials

D. Panayotov*, M. Mihaylov, and K. Hadjiivanov




Keywords: MOF-based composites, CO2 capture, CO2 conversion, overview

Carbon dioxide (CO2) emitted into the atmosphere from anthropogenic sources, like

power plants, steel mills and transport, leads to critical climate change, creating real threats

to the people, economies and ecosystems of our planet. CO2 concentrations in the

environment are steadily increasing, albeit with seasonal variations, despite the efforts of

different countries over the globe to reduce emissions. Therefore, decreasing anthropogenic

emissions and mitigating atmospheric CO2 concentrations are imperative tasks that require

drastic, immediate globally coordinated efforts. Currently, two technological approaches

exist regarding the post-capture application of CO2. These consist of carbon capture and

storage (CCS) and carbon capture and utilization (CCU). The difference between CCS and CCU

approaches is at the final destination of the captured CO2. In the CCS approach, captured

CO2 is transported to an appropriate location, geological formations, for long-term storage,

whereas in the CCU approach, the CO2 captured is utilized by conversion into valuable

commercial products. In the past decades, several classes of materials, including ionic liquids

(ILs), zeolites, porous carbons, porous organic polymers, covalent organic frameworks (COFs)

and metal–organic frameworks (MOFs), have been developed for CO2 capture and

conversion applications. In particular, metal-organic frameworks (MOFs) are a subclass of

coordination polymers consisting of inorganic nodes (single ions or oxide clusters, called

secondary building units - SBUs) coordinated to polytopic organic linkers thus forming 1D,

2D, or 3D structures. By designing and functionalizing SBUs, linkers and pore environments,

the physical and chemical properties of MOFs can be finely tuned, making them promising

materials for a wide range of applications, such as gas storage and separation,

heterogeneous catalysis, sensing, drug delivery, etc. With respect to CO2 capture and

conversion, MOFs serve as promising adsorbents and catalysts, respectively, because of their

unique advantages: (i) predicable, functionalizable structures that allow for incorporation of

different types of accessible capture and catalytically active sites.; (ii) formation of hybrid

structures, due to the high compatibility with other materials, which can serve as precursors

and/or templates to prepare MOF composites or MOF derivatives with extraordinary

physical and chemical properties; (iii) particular strengths for catalysis offering high catalytic

efficiency and selectivity, facile separation and reusability, and stability. All of these

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attributes make MOFs and MOF-based materials ideally suited for CO2 capture and

conversion.

Herein we present a brief summary and assessment of the development of MOF-based

composite materials for CO2 capture and conversion aimed at mitigation of climate change.

We first focus on the on interaction of CO2 with the frameworks and other components of

the composites. Some challenges and targets specific for the development of MOF-based

composites for CO2 capture are marked and briefly discussed. Next, recent advances in the

field of MOF-based composites for CO2 conversion, including heterogeneous transformation

into organic products, hydrogenation, photocatalytic reduction, and electrocatalytic

reduction, are briefly discussed. It is shown that various metal catalysts can be combined

with MOFs, yielding hybrid materials designed to catalyse CO2 hydrogenation reactions.

Figure 1 shows an example of such material, Cu nanocrystals (~18 nm) were encapsulated

within UiO-66 to yield a composite catalyst (Cu/UiO-66) for highly selective CO2

hydrogenation to methanol.

Figure 1. (a) CO2 hydrogenation using Cu/UiO-66 to give CH3OH. (b) Preparation of Cu/ZnOx@UiO-

bpy by in situ reduction of post-synthetically metalated UiO-bpy (left) for selective MeOH synthesis as

the product of catalytic CO2 hydrogenation. From Ref. 1.

Finally, some challenges and future directions in this research field are highlighted.

References

1. M. Ding, R. W. Flaig, H.-L. Jiang and O. M. Yaghi, Chem. Soc. Rev. 48 (2019) 2783-2828.

Acknowledgements: This work was supported by the Bulgarian Ministry of Education and Science

(Contract No. DO1-214/28.11.2018) under the National Research Programme “Low-carbon Energy

for the Transport and Domestic Use - EPLUS” approved by DCM #577/17.08.2018 and by the National

Scientific Fund (project DN19/2).

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Topic B

BO-5

Cation desolvation on a model electrode surface: a story of

commitment and breakup

H. Rasheev1,2*, R. Stoyanova1 and A. Tadjer1,2


1113 Sofia, Bulgaria 2 Faculty of Chemistry and Pharmacy, University of Sofia, 1164 Sofia, Bulgaria


Keywords: metal-ion batteries, DFT, dual-cation electrolyte, lithium titanate electrode

The ever-growing usage of rechargeable batteries in the endless assortment of

portable devices demands better and safer batteries. At the moment, the broadest

application in smart electronics and transport vehicles find Li-ion batteries, but their cost

and environmental impact encourage fervent on-going development of new electrode and

electrolyte materials [1]. One attractive approach is the partial substitution of Li+ as charge

carrier with ions of more abundant elements like Na and Mg, resulting in the so-called hybrid

cells. The efficiency of such hybrid batteries depends, among others, on the processes taking

place at the electrode-electrolyte interface. Such process is the desolvation of the metal

ions, occurring simultaneously with adsorption on the electrode surface. Molecular

modelling is a suitable tool for investigating these processes at atomic-level resolution. In

our study, we employ periodic Density Functional Theory calculations to assess the

interactions of a model (111) surface of lithium titanate (Li4Ti5O12) with single-ion or dual-ion

clusters of Li+, Na+ and Mg2+ with ethylene carbonate using PF6¯ as counterion. The PBE

approximation for the exchange and correlation functional and the PAW method for the

initial electronic wave functions were applied as implemented in VASP. Preferred adsorption

sites on the surface were identified. The desolvation energies of the cations were evaluated

and comparison with free-standing ion-solvent clusters was made and discussed [2]. The on-

surface behaviour of the counterion and the effect of its presence on the desolvation of

scantily solvated single/dual-cation complexes were also modelled and the proceeding

decomposition reactions were described.

References

1. M. Li, Ch. Wang, Zh. Chen, K. Xu and J. Lu, Chem. Rev. 120 (2020) 6783.

2. H. Rasheev, R. Stoyanova and A. Tadjer, ChemPhysChem 22 (2021) 1110.

Acknowledgements: The study is supported by the National Research Program E+, grant D-01-

214/2018, and Project CARiM/Vihren, grant КП-06-DВ-6/2019. The authors thank for the provided

access to the e-infrastructure of the NCDSC – part of the Bulgarian National Roadmap on RIs, with

the financial support by Grant No D01-221/03.12.2018.

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Topic B

BO-6

Machine-learning-aided discovery of efficient

organic photovoltaic materials

L. Borislavov, M. Nedyalkova, J. Stoycheva, A. Tadjer and J. Romanova*

Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria


Keywords: singlet fission, excited states, diradical

Recently, Michl et al. demonstrated that singlet fission chromophores can overcome

the Shockley–Queisser limit [1] and thus represents low-cost materials for new generation

highly efficient solar cells. In singlet fission based photovoltaic devices, photon absorption

leads to creation of twice as many charge carriers compared to the case when conventional

chromophores are used. However, singlet fission chromophores are a rare kind of

compounds and this hampers the progress in the area of organic photovoltaics.

Here, we present results of our in silico screening approach for the discovery of new

singlet fission molecules. Our strategy combines quantum-chemical calculations,

chemometrics and machine learning algorithms. It allows the exploration of the relationship

between structure and singlet fission propensity, as well as the formulation of new

guidelines for the molecular design in the field of organic photovoltaics.

References

1. J. Michl and M. B. Smith, Chem. Rev. 110 (2010) 6891.


H39/2 from 09.12.2019 and the National Research Program E+: Low Carbon Energy for the Transport

and Households, DMC 577/17.08.2018, grant agreement D01-214/28.11.2018.

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Topic B

BO-7

Three-dimensional porous metallic structures by selective dissolution of

amorphous and nanocrystalline alloys

T. Spassov*, E. Vassileva and L. Mihaylov

Faculty of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria


Keywords: nanocrystalline alloys, porous metallic structures, surface-controlled dissolution process,

batteries

Nano- and microporous metal structures are subjects of increasing research interest.

Their highly developed surface, high electrical and thermal conductivity and mechanical

stability determine various applications in catalysis, sensor devices, filtration, biotechnology,

orthopedics and drug delivery. De-alloying by selective dissolution of the less noble metal(s)

is one way to obtain porous structures. An interesting and relatively new approach to the

preparation of such functional materials involves the use of amorphous and nanocrystalline

metal alloys as precursors. In recent years, we have studied a number of amorphous alloys

based on precious metals as well as transition metals. In order to achieve the desired micro-

and nanoporous structures key conditions of electrochemical or chemical dissolution (type

and concentrations of electrolyte, temperature, time, electrochemical potential) were

optimized. For some of the metallic glasses (e.g. those based on Zr or Pd), the pores

formation was found to take place at a constant rate in three dimensions, which was

explained by a surface-controlled dissolution process. The rate of formation of the porous

structure was very high, as the whole process took only few minutes. As a result, three-

dimensional homogeneous micro (nano) porous structures were obtained. The evolution of

the morphology and microstructure of nanoporous materials in the different stages of

dissolution was also observed. Changes in the composition of the ligaments and the

microstructure at different dissolution times were associated with the composition of the

alloy and the de-alloying mechanism. The porous structures thus obtained have been shown

to exhibit high electrocatalytic activity with respect to the evolution of hydrogen and oxygen,

and were also suitable as carriers of the active phase in batteries.

Acknowledgements: The project Д01-272/02.10.2020 - "European Network on Materials for Clean


"European Scientific Networks" and the Project CoE “National Center of Mechatronics and Clean

Technologies” (BG05M2OP001-1.001-0008) are acknowledged.

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Topic B

BO-8

Molecular modelling of components for rechargeable metal-ion batteries

A. Tadjer1,2*, H. Rasheev1,2, Y. Danchovsky1,2, L. Borislavov1,2, N. Ilieva1,2 and R. Stoyanova1


1113 Sofia, Bulgaria 2 Faculty of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria


Keywords: molecular design, quantum chemistry, machine learning, battery electrodes and

electrolytes

As the steady increase in complexity of human society leads to ever growing energy

demands, research for better and cheaper materials for energy storage and conversion is at

its highest. In recent years, the global climate change effects are more and more prominent

and this places significant emphasis on low(no)-carbon energy and its clean storage. So far,

the best technology for small to medium energy storage is the Li-ion battery but concerns

like high cost and limited resources, as well as safety issues, are perpetuating new

developments in the quest for better materials for all battery components. Computational

chemistry can be a valuable ally in the search for new materials for clean energy storage.

Molecular modelling can help elucidating the intimate details of the processes occurring in

the batteries at the atomistic level and aid the design of novel compounds and architectures

offering new perspectives for the next generation batteries production. Machine learning

and statistical analysis can be harnessed to speed up the research. The endeavours of our

group in modelling components and processes in metal-ion batteries will be overviewed.

Acknowledgements: The support of Project CARiM/Vihren, grant КП-06-DВ-6/2019 and the National

Research Program E+, grant D-01-214/2018, is acknowledged.

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Topic B

BO-9

Simple synthesis and effect of the particle size and

surface area modification on electrochemical properties of Li4Ti5O12 anodes

M. Fabián1*, M. Žukalová2, L. Kavan2 and M. Senna3

1 Institute of Geotechnics, Slovak Academy of Sciences, 040 01 Košice, Slovakia 2 J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic,

CZ-18223 Prague 8, Czech Republic 3 Faculty of Science and Technology, Keio University, 223-8522, Yokohama, Japan


Keywords: Li4Ti5O12, anode, Li-ion batteries, surface area, charge capacity

In this work, we refer on simple synthesis of spinel based Li4Ti5O12 (LTO) by combination of

mechanical pre-activation of precursors followed by low-temperature calcination at 600°C.

The phase evaluation and its purity is examined by analyses of data provided X-ray powder

diffraction and 6Li MAS NMR. The charge capacity of the LTO with average crystallite size 150

nm was found to be 142 mAh/g, i.e. ~ 81 % of theoretical capacity. The capacity of our

optimised material is superior to that of commercially available spinel, although the as-

synthesized LTO is characterized by small BET-specific surface area. The superior properties

of our material were also demonstrated by galvanostatic charging/discharging. In order to

modify crystallite size and BET-specific surface area, as-prepared samples were further

treated by ball milling. X-ray diffraction analysis proves the presence of majority of

Li4Ti5O12 phase with small amount of rutile and WC impurities with negligible effect on

electrochemical properties. Transmission electron microscopy analysis revealed presence of

Li4Ti5O12 in different morphologies. Cyclic voltammetry of Li insertion and

galvanostatic chronopotentiometry at 1C rate confirm the highest charge capacity for

Li4Ti5O12 spinel with surface area of 21 m2 g−1. Due to optimized ratio of two particular

morphologies this material possesses excellent long time cycling stability during

galvanostatic chronopotentiometry at 1, 2 and 5C. Its discharge capacities reach 170 mAh

g−1 at 1C (~ 97% of theoretical value), 167 mAh g−1 at 2C and 160 mAh g−1 at 5C rates with

100% coulombic efficiency. The capacity drop was less than 1% for charging rates of 1 and 2C

and about 5% at 5C. Accordingly, the effect of crystallite size and BET-surface area on the

electrochemical properties of synthesized LTO are discussed within this work.

https://www.sciencedirect.com/topics/chemistry/rutile

https://www.sciencedirect.com/topics/chemistry/electron-microscopy

https://www.sciencedirect.com/topics/chemistry/chronopotentiometry

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Figure 1. Effect of BET surface area on capacity in as-prepared LTO powders.

Acknowledgements: This work was supported by the Slovak Research and Development Agency

APVV (No. 19-0526), Scientific Grant Agency VEGA (No. 2/0055/19) and bilateral cooperation project

between Slovak Academy of Sciences and Bulgarian Academy of Sciences (BAS-SAS-21-07).

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Topic B

BO-10

Computational modelling of metal complexes with

redox-active ligands for Li-ion batteries

Y. Danchovski1,2*, H. Rasheev1,2, R. Stoyanova1 and A. Tadjer1,2


Sofia 1113, Bulgaria 2 Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria


Keywords: electrode materials, Li-storage, DFT, coordination compounds, quinone ligands

Inorganic materials used for fabrication of electrodes in Li-ion energy storage devices

are known for decades. The utilization of organic compounds for the same purpose is an

innovative approach which is deemed to result in the production of batteries with superior

quality. Organic materials are both easily modelled and manufactured, their structure is

synthetically tuneable, they are light-weight and recyclable. Combining a transition metal

with redox-active organic ligands leads to a complex compound with multiple redox stages,

involving both the ligands and the metal ion. Indeed, these compounds, offer a unique

opportunity to design a new material with higher electrochemical activity and better

characteristics.

The current study addresses complexes of nickel and vanadium with a benzoquinone-

derived ligand and evaluates their electrochemical potential in the reduction with Li.

Complexes of two ligands with each metal ion in two oxidation states are constructed. DFT

calculations are performed to optimize the structure of the complexes at several consecutive

degrees of reduction with Li and the electrochemical potential of each stage was quantified.

Besides energetics, the changes in spatial structure and electron density distribution were

monitored. The modelled complexes of both metals exhibited potential for substantial Li

intercalation retaining structural stability. The computed electrode potentials and capacities

bear promise for possible exploitation of these complexes as efficient electrode materials.

The combination of two types of redox-active components proves to be a successful strategy

for design of prospective materials for enhanced energy storage and conversion.


214/2018, and Project CARiM/Vihren, grant KP-06-DV-6/2019.

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Topic B

BP-1

Investigation of low temperature modified carbon black by XPS

I. Avramova1*, D. Dimov2, G. Avdeev3 and T. Milenov2


1113 Sofia, Bulgaria 2 Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria 3 “R. Kaishev” Institute of Physical Chemistry, Bulgarian Academy of Sciences,



Keywords: carbon black, X-ray photoelectron spectroscopy

Carbon black (CB) has industrial applications in the production of electronics, electrical

batteries, epoxies, rubbers, radar absorbing materials, and etc. Cabot Corporation SPHERON

5000 carbon black which possess low surface active area was modified by acetone and

further by thermal treatment. The thermal treatment was done at temperatures range from

270oC till 850oC for 3h at air atmosphere. The pristine and the modified CB were

characterized by X-ray photoelectron spectroscopy (XPS). We used the C1s photoelectron

line for each of the samples for evaluation of sp2- and sp3- type of carbon bonds, as well as

other existing over the surface carbon to oxygen types of bonds. The oxygen to carbon

ration (O/C) was calculated, also. The results showed that by increasing the temperature for

the thermal treatment till 720oC the O/C ration reach its minimal value. Further by increasing

the temperatures of treatment this ration slowly increase.

The results from XPS were supported from scanning electron microscopy (SEM) as well

as X-ray powder diffraction (XRD).

The modification results were compared also with those from the modification of

carbon black with a large surface active area ENSACO 350 GRANULAR.

The obtained results will be presented and discussed in details.

Acknowledgements: The author gratefully acknowledges financial support from the National Science

Fund of Bulgaria under grant DN18/9-11.12.2017 and Cabot Corp. for providing Spheron 5000 Carbon

black. The author gratefully acknowledges financial support from the Project Д01-272/02.10.2020 -



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Topic B

BP-2

Machine learning aided design of organic redox materials for

metal-ion batteries

L. Borislavov1,2*, I. Kichev2, N. Ilieva1,2, R. Stoyanova1 and A. Tadjer1,2


1113 Sofia, Bulgaria 2 Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria


Keywords: electrode materials, machine learning, statistics, small organic molecules

The less familiar and exploited organic materials for battery electrodes possess

numerous advantages over the inorganic ones: they are cheaper, lighter and more

environmentally friendly. Furthermore, the organic battery electrode materials are more

versatile in terms of design since their structure, and hence their properties, could be

synthetically tuned to attain maximum performance.

Machine learning and statistics, on the other hand, have proven to be very powerful

approaches for efficient in silico design of novel materials. For the needs of the present

study, a database of small organic molecules that potentially can serve as organic battery

electrode components was created. A large number of quantum chemical and chemometrics

descriptors was generated for each molecule and subsequently different statistical

approaches were applied to select the descriptors that most prominently characterize the

relationship between structure and redox- potential.

Various machine-learning methods were employed to build models for screening of

prospective organic battery electrode materials. Models that rely both on classification of

the organic compounds with respect to their redox-potential and on direct prediction of the

redox-potential value were tested and compared to select the most trustworthy strategy for

machine learning aided design of organic redox materials.


214/2018, and Project European Twinning on Materials Chemistry Enabling Clean Technologies

(TwinTeam), grant D01-272/02.10.2020

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Topic B

BP-3

Characterization of Mg2NiH4 type hydrides by TEM

E. Grigorova1*, P. Markov1 and D. Nihtianova1,2


1113 Sofia, Bulgaria 2 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences,



Keywords: hydrogen storage, Mg2NiH4 hydride, TEM

The intermetallics Mg2Ni is very attractive hydrogen storage material, because of its

fast hydrogen sorption kinetics and relatively high theoretical absorption capacity. In our

study we synthesized hydrides based on Mg2NiH4 in a simplified way. A mixture of Mg, Ni

and V with compositions Mg2.05Ni0.7V0.3 and Mg2.1Ni0.7V0.3 with addition of 5 wt% of activated

carbon derived from apricot stones are prepared by ball milling under argon in a planetary

mill for 180 min. Magnesium powders with purity 99% and 325 mesh or 50 mesh purchased

from Strem Chemicals were used. The mixture with composition Mg2.05Ni0.7V0.3 with 325

mesh Mg and the other one with increased excess of magnesium- Mg2.1Ni0.7V0.3 with 50

mesh Mg were prepared and 5 wt. % activated carbon derived from apricot stones was

added. The received mixtures after ball milling were put in the volumetric Sievert’s type

apparatus reactor for investigation of their hydrogen absorption-desorption characteristics

at different temperatures. Structure, phase and surface composition of the starting

compounds and of the materials before and after hydriding are determined by XRD and TEM

for the samples after hydriding. The detailed results about absorption- desorption

characteristics, X-ray diffraction analyses and electrochemical tests as negative electrodes in

a Ni/MH battery of these samples can be found in [1]. TEM characterization of these

materials poses some challenges because of their sensitivity to oxidation and the high

energy of the electron beam exposure, which could cause negative impact. After hydriding

for 60 min. at 573 K and P= 1 MPa TEM (SAED, HRTEM) results showed the following phase

composition: monoclinic Mg2NiH4, orthorhombic Mg2NiH4, MgO, VHx and graphite for both

samples. A particle size distribution using ImageJ programme was made. The average

particles size diameter is 6 nm for Mg2.05Ni0.7V0.3- 5 wt% of activated carbon derived from

apricot stones and 13 nm for Mg2.1Ni0.7V0.3- 5 wt% of activated carbon derived from apricot

stones [Fig. 1].

The formation at such low temperature of monoclinic phase, but also some

orthorhombic Mg2NiH4 during cycling has great effect on hydrogen sorption properties of

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magnesium. The most of the methods of Mg2NiH4 synthesis published in the literature are

done at higher temperatures and more complicated procedures.

Figure.1 Bright field micrograph and histogram from TEM analysis of the Mg2.1Ni0.7V0.3- 5 wt. % of

activated carbon derived from apricot stones after hydriding.

References

1. Grigorova E., Tzvetkov P., Todorova S., Markov P., Spassov T., Materials 14 (2021) Article Number:

1936.

Acknowledgements: The authors would like to thank to the European regional development fund

within the Operational Programme “Science and Education for Smart Growth” under the project CoC

Hitmobil BG05M2OP001-0014-C01 and Project Д01-272/02.10.2020 - "European Network on


National Program "European Scientific Networks". Part of the experiments were performed with

equipment included in the National Infrastructure ESHER (NI SEVE) supported by the Ministry of

Education and Science under grant agreement DО1-385/18.12.20.

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Topic B

BP-4

Thermoelelctrical properties of composites between perovskites and

misfit layered oxides

S. Harizanova*, E. Zhecheva and R. Stoyanova




Keywords: thermoelectric oxide materials, composite materials, Co-based materials

Nowadays, the most perspective alternatives to the conventional thermoelectric

semiconductors are cobalt-based oxides. Among them, two groups of cobaltates can be

highlighted: LaCoO3 with a perovskite structure and layered misfit Ca3Co4O9. LaCoO3 displays

a high Seebeck coefficient and low thermal conductivity, which is of importance for its

thermoelectric properties. Recently, we have demonstrated that multiple metal substitution

for Co ions in LaCoO3 leads to a dramatic improvement of its thermoelectric efficiency [1].

This is a result from the reduction of the thermal conductivity through introducing specific

structural disorder with multicomponent substitution for cobalt while maintaining the

electric conductivity high by preserving the perovskite-type structure as a whole [1, 2]. As in

the case of perovskite oxides, the charge and spin-state of the Co ions in the misfit oxides,

Ca3Co4О9, contribute mainly to the transport properties. It has been recognized that the

layer Ca2CoO3 is an insulating subsystem which maintains the charge supply for the

conducting CoO2 layer, where both Co3+ and Co4+ ions coexist. The doping in CoO2-layer

layers will influence the physical properties of the Ca3Co4O9 system more significantly [3].

Herein, we report a new approach for improving the thermoelectric properties of Co-

based perovskites and misfit oxides. This approach consists in formation of multiphase

composites between two well defined thermoelectric materials: multiple substituted

perovskite, LaCo0.8Ni0.1Fe0.1O3, and misfit layered oxide, Ca3Co4O9. Structural and

morphological characterizations are carried out by powder XRD and SEM analyses. The

thermoelectric efficiency of samples is determined by the dimensionless figure of merit (ZT),

calculated from the independently measured Seebeck coefficient (S), electrical resistivity (ρ),

and thermal conductivity (λ).

Co-based perovskite and layered oxides are prepared by a Pechini-type method. The

homogeneous mixture between LaCo0.8Ni0.1Fe0.1O3 and Ca3Co4O9 is pelletized and sintered at

900oC for 40 hours. The ratio of LaCo0.8Ni0.1Fe0.1O3 to Ca3Co4O9 is 20 and 80 wt. %. The

composites are denoted as LCO20Ca80 and LCO80Ca20, respectively.

The morphology of Ca3Co4O9 consists of big particles with dimensions between 3 and 5

µm, while small particles at around 0.5 µm are observed for LaCo0.8Ni0.1Fe0.1O3. Inside the

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composite, there is a close particles contact: the bigger particles of Ca3Co4O9 are packed in a

way so that the holes between them are filled with smaller perovskite particles. This type of

packing allows to modify the interface between Ca3Co4O9 and LaCo0.8Ni0.1Fe0.1O3, which

results in the improvement of the thermoelectric properties of composites. Table 1

compares the electrical resistivity, Seebeck coefficient and thermal conductivity of

LCO20Ca80 and LCO80Ca20 with that of individual constituents. The same Table displays the

calculated power factor and figure of merit. The data reveals that the thermal conductivity

of the composites undergoes severe change in comparison with the individual components.

This reflects the specific interface formed in composites. In comparison with thermal

conductivity, the electrical resistivity and Seebeck coefficient are slightly changed in

composites.

In conclusion, we demonstrate that interfacial effects contribute mainly to the thermal

conductivity, as a result of which the thermoelectric activity of the LCO20Ca80 composite

becomes higher than that of the individual Ca3Co4O9.

Table 3. Electrical resistivity, Seebeck coefficient, Power factor PF=S2/ρ, Thermal conductivity, Figure

of merit S2T/(ρ.λ)

Samples ρ, (Ω.cm) at 300K

Seebeck coefficient,

mV/K

Power Factor, PF=S2/ρ,

μW/(K2.cm)

Thermal Conductivity, λ, W/(m.K)

± 0.04

Figure of merit,

S2T/(ρ.λ) T=300K

LaCo0.8Ni0.1Fe0.1O3 0.065 234 0.84 0.157 0.161

LCO80Ca20 0.052 208 0.83 0.179 0.139

LCO20Ca80 0.013 137 1.44 0.467 0.093

Ca3Co4O9 0.010 130 1.69 0.620 0.082

References

1. V. Vulchev, L. Vassilev, S. Harizanova, M. Khristov, E. Zhecheva and R. Stoyanova, J. Phys. Chem. C

116 (2012) 13507.

2. S. Harizanova, E. Zhecheva, V. Valchev, M. Khristov and R. Stoyanova, Mater. Today – Proceeding 2

(2015) 4256.

3. Y. Huang, B. Zhao, S. Lin and Y. Sun, J. Phys. Chem. C 119 (15) (2015) 7979.

Acknowledgements: The structural and morphological properties are determined on equipment

included in the scientific infrastructure INFRAMAT (D01-155/28.08.2018 and D01-284/18.12.2019),

while the electrical properties are measured on equipment included in NSI "Energy Storage and

Hydrogen Energy “NSI ESHER, ( DО1-385/18.12.20) ; Project Д01-272/02.10.2020 - "European


under the National Program "European Scientific Networks").

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Topic B

BP-5

Synthesis of nanostructured copper oxide supported on mesoporous

manganese-titanium oxides: Characterization and application as catalysts

for hydrogen production

R. Ivanova1*, G. Issa1, M. Kormunda2, M. Dimitrov1, J. Henych3, M. Šťastný 3 and

T. Tsoncheva1

1Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of

Sciences, 1113 Sofia, Bulgaria 2Faculty of Sciences, University of Jan Evangelista Purkyne, Ceske Mladeze 8, 400 96 Usti nad

Labem, Czechia 3Materials Chemistry Department, Institute of Inorganic Chemistry AS CR v.v.i., 25068 Ŕeź,

Czechia


Keywords: copper oxide, hydrogen production, Ti-Mn mixed oxides, catalysts

The development and improvement of new catalytic processes, as well as the creation

of new types of catalysts, are major ways to improve the efficiency of the chemical,

petrochemical, and refining industries, which can be used to achieve sustainable

environmental protection. The synthesis of an effective catalyst, however, is a complex

process that requires optimization of the composition and conditions for its production, as

well as a good knowledge of the nature of the active sites and the mechanism of the

processes on them. Mesoporous manganese-titanium mono- and bi-component oxides with

different compositions (1:2, 1:1, or 2:1 mol ratio) were obtained by co-precipitation of the

initial metal chlorides with ammonia in the presence of surfactant. These materials were

used as support for the preparation of copper oxide nanoparticles by incipient wetness

impregnation. A complex of different physicochemical techniques, such as nitrogen

physisorption, XRD, TPR, UV-Vis, FTIR, Raman, and XPS spectroscopies, was applied for

samples characterization. Their catalytic behavior was studied in methanol decomposition to

CO and hydrogen as a potential alternative fuel. The binary oxides demonstrated improved

textural characteristics in comparison with the single oxides, and they were most

pronounced for 1Mn1Ti. The copper oxide addition decreases the surface area and pore

volume of supports probably due to the incorporation of small CuO particles within the

support pores. The XRD analysis showed the co-existence of anatase, Mn2O3, Mn5O8, and

Mn3O4 for both 1Mn2Ti and 2Mn1Ti, while only well-crystallized anatase and rutile TiO2

phases were found for 1Mn1Ti. After the modification with copper more homogeneous and

finely dispersed copper oxide species were registered for 8Cu/1Mn2Ti, 8Cu/1Mn1Ti

modifications. XRD and Raman analyses demonstrate that the close contact between

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different metal oxide particles creates an interface layer or mixed oxide structure, where

copper ions are penetrated the support lattice with simultaneous formation of oxygen

defects. The formation of this mixed oxide structure seems to facilitate the stabilization of

finely dispersed, easily reducible, and highly active CuO nanoparticles. The catalytic behavior

of the modifications was considered as a complex dependence on the support composition,

morphology, and location of the copper oxide nanoparticles in the porous matrix. The role of

each component on the catalytic activity in the methanol decomposition to CO and

hydrogen was discussed in detail.

Acknowledgements: The authors thank the project КП-06-ПМ39/1, to the European Regional

Development Fund within the Operational Programme “Science and Education for Smart Growth

2014 - 2020” under the Project CoE “National center of mechatronics and clean technologies“

BG05M2OP001-1.001-0008 for the financial support and bilateral project BAS-AS CR for the help with

the physicochemical characterization of the samples.

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Topic B

BP-6

Improved electrochemical performance of Na2/3Ni1/2Mn1/2O2 through

stabilizing the oxygen redox activity

M. Kalapsazova*, P.Markov, R. Kukeva, E. Zhecheva and R. Stoyanova



E-mail: [email protected], [email protected]

Keywords: post lithium-ion batteries, electrochemistry, oxygen-storage

The ever-growing renewable energy storage industry imposes great demands that the

current most efficient storage devices, lithium-ion batteries (LIBs), are unable to meet.

Among all post lithium-ion battery approaches, the sodium-ion technology (SIBs) apparently

is the most interesting. Unlike lithium, sodium is an abundant and cheaper element.

Although SIBs provide similar performance, the current drawbacks of sodium-ion batteries

are the limited number of cycles and energy storage densities. The shortest route to increase

the energy density of sodium-ion batteries is through the simultaneous activation of

transition metal and oxygen redox reactions (i.e. TMm+/TMn+ and O2−/O2n−) at intercalation-

type electrode materials.

Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-

storage materials as efficient buffer supplying and receiving an oxygen during alkali-ion

intercalation. The concept consists in treatment of intercalation oxides, P3-

Na2/3Ni1/2Mn1/2O2, with “oxygen-storage” material, namely CeO2.

In the mixture between P3-Na2/3Ni1/2Mn1/2O2 and CeO2 phases, there is a close

particles contact, which is developed on a nano-scale range. The CeO2 suppresses the

particle aggregation of the layered oxide and particles with dimensions between 10 and 40

nm become dominant (Fig.1). This type of modification with CeO2 does not affect the bulk

structure of layered oxide.

Figure 1. TEM images of CeO2-modified P3-Na2/3Ni1/2Mn1/2O2 and particle distribution curves.

mailto:[email protected]


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The modified oxides display drastic increase in the reversible capacity when used as

cathodes in Na-, Li- and hybrid Li,Na-ion cells. The highest capacity of about 285 mAh/g is

reached for the modified oxide cycled in hybrid Li,Na-ion cell. The reversible capacity

increases following the order Na+ intercalation < Li+ intercalation < Li+,Na+ co-intercalation

(Fig.2). On the one hand, this indicates a synergistic effect of the dual Li+,Na+ intercalation in

order to reach a higher capacity. On the other, irrespective of the type of alkali ion

intercalation the higher intercalation capacities of the modified oxide are in agreement with

the concept of the beneficial effect of CeO2 on oxygen-redox reaction. It is worth mentioning

that CeO2 is not participating in the electrochemical reaction, according to the ex-situ HR-

TEM.

Figure 2. Cycling stability for the pristine (black lines) and CeO2-modified (red lines) P3-

Na2/3Ni1/2Mn1/2O2 oxide in Na- (left), Li- (midle) and Li,Na-ion cells (right).

In addition, CeO2 affects also the inter-phase interaction between electrode and

Li/NaPF6 salt electrolyte. These data could serve as guidelines to achieve colossal reversible

capacity at layered lithium and sodium transition metal oxides – research dream from the

beginning until now in the development of lithium-ion batteries.

Acknowledgements: The authors thank for the financial support of the project CARiM (NSP Vihren,

КП-06-Д B-6) and Project Д01-272/02.10.2020 - "European Network on Materials for Clean



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Topic B

BP-7

Theoretical investigation on nitrogen containing singlet fission organics

I. Kichev, J. Stoycheva, A. Tadjer and J. Romanova*



Keywords: heterocyclic hydrocarbons, photovoltaics, singlet, triplet

Nowadays, singlet fission organics are regarded as photo-active boosters of the solar

cell efficiency. Recently, it was demonstrated that the nitrogen doping of acenes is a

constructive approach for development of singlet fission materials for solar cells

applications. Here we present a quantum-chemical investigation on the singlet fission

potential of a series of underexplored in this respect nitrogen containing polycyclic

hydrocarbons. Several fruitful organic materials for photovoltaics implementation are

highlighted.


H39/2 from 09.12.2019.

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Topic B

BP-8

Mechanochemically induced transformation of NaFePO4 maricite:

anion redox activity and high specific capacity

T. Boyadzhieva, V. Koleva* and R. Stoyanova




Keywords: NaFePO4, mechanochemical treatment, structural transformation, Na-ion battery

The rapid depletion of lithium as a key chemical element in the lithium-ion technology

and the continuous increase in its cost have posed the urgent task of researchers to develop

alternative batteries such as Na-ion batteries based on more abundant, readily available,

inexpensive and environmentally-friendly electrode materials. The commercialization of the

Na-ion battery, however, is still a great challenge and one of the important issues is

attributed to the choice of the most suitable electrode materials. Among sodium–host

compounds of interest, the incorporation of a cheap and widely available redox element

such as iron in the stable phosphate framework could largely meet the economic, safety and

environmental requirements.

In present contribution our attention is concentrated on maricite-type NaFePO4 (M-

NFP). More recently, it has been found that the design of maricite nanostructures integrated

with conductive carbonaceous material allows to achieve high electrochemical performance.

Moreover, first principle calculations have shown that anionic (O2-) redox processes in

NaFePO4 are also visible, which is apparently different from LiFePO4.

The maricite phase NaFePO4 is synthesized by thermal decomposition of freeze-dried

formate-phosphate precursor and further annealing at 400 °C. In order to enhance the

electrical conductivity and to reduce the particle sizes to nanoscale region, M-NFP is ball-

milled with conductive carbon black Super C/65 in air media. The electrochemical properties

of the as-formed composite M-NFP/C are studied in half sodium and lithium ion cells using

NaTFSI and LiPF6 electrolytes in galvanostatic and potensiostatic mode at different

charge/discharge and scan rates.

The mechanochemical treatment is found to cause a complete structural

reorganization and the initial maricite structure (space group Pnma) is fully transformed into

NASICON-type structure (space group C2/c) with change in the composition into NaFe0.67PO4

(Na3Fe2(PO4)3) and preservation of the crystallinity (Fig. 1A-D). The cyclic voltammograms

(CV) of the as-formed NASICON phase evidence that Na+ and Li+ intercalation proceeds with

participation of the Fe2+/Fe3+ ionic pair, but in a different way: Na+ intercalation is one step

process in contrast to the consecutive Li+ intercalation (Fig. 1E).

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(C) (D)

(E) (F)

Figure 1. Rietveld refinements of M-NFP (A) and composite M-NFP/C (B); maricite-and NASICON-type

structures (C and D, respectively); CV curves of M-NFP/C in NATFSI and LiPF6 electrolytes (E) and

charge-discharge curves (5th cycle) at different rates in NaTFSI electrolyte (F).

The as-generated nanosized NASICON phase Na3Fe2(PO4)3 exhibits good storage

performance in both Na- and Li-ion cells. The specific discharge capacity in LiPF6 at C/50 is

112 mAh/g (97 % of the theoretical one) and 59 mAh/g at C/1 rate (Fig. 1F). Ex-situ XRD

measurements reveal that the NASICON structure is preserved during the prolonged Na+ and

Li+ electrochemical cycling. However, due to the smaller ionic size Li+ is localized on

tetrahedral crystallographic sites in the NASICON structure which causes a change in the

crystal symmetry: from monoclinic C2/c to rhombohedral R-3 symmetry. The obtained

results clearly manifest that the mechanochemically generated NASICON Na3Fe2(PO4)3 phase

has a great potential as a positive electrode for Na-ion batteries.

Acknowledgements: The authors thank for the financial support of the project CARiM (NSP Vihren,

КП-06-ДB-6) and the National Research Programme “Young scientists and postdoctoral students”

approved by DCM # 577/ 17.08.2018.

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Topic B

BP-9

The role of conformation in the design of singlet fission chromophores for

photovoltaic applications

G. Kostadinova1, R. Lyapchev1, J. Stoycheva1, A.Tadjer1, M. de Wergifosse2 and J.Romanova1*

1Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria 2Mulliken Center for Theoretical Chemistry, Institut für Physikalische und Theoretische

Chemie, Bonn, Germany


Keywords: NHC-carbene dimers, excited states, cis-trans

The utilization of singlet fission compounds as photoactive materials in solar cells

allows the surpass of the Shockley–Queisser limit and thus the fabrication of highly efficient

photovoltaic devices. Here, we demonstrate that conformation is a key factor in tailoring the

singlet fission propensity of molecules. The idea is proven in a family of NHC-carbene dimers

recently designed in our lab by means of quantum-chemical calculations. In addition to

conformational variety, the molecules differ also in topology and donor/acceptor strength of

substituents. All investigated compounds are synthetically feasible and therefore potent for

real photovoltaic applications.



agreement D01-214/28.11.2018.

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Topic B

BP-10

Fast method of synthesis of Li2Mn(SO4)2 cathode material and

electrochemical performance

D. Marinova*, K. Veselinov, M. Kalapsazova, P. Markov and E. Zhecheva




Keywords: lithium-ion batteries, intercalation cathode materials, transition metal sulfates

Nowadays, lithium-ion batteries have become an indispensable part of our daily lives,

as evidenced by the Nobel Prize in Chemistry for 2019. The mechanism of action of the

battery consists in the reversible intercalation of Li+ between the cathode and anode. The

most studied electrode materials so far are mixed oxides of lithium and transition metals

(cobalt, nickel and manganese). In recent years, double salts of lithium and transition metals

have been considered as an alternative to oxide electrodes. The advantage of these

compounds over oxides is that the intercalation potential of Li+ ions can be controlled not

only by the type of transition metal ions, but also by the nature of the polyanionic group

(phosphate, sulfate, borate or silicate). Of all the known compounds, the sulphate salts have

the highest potential.

The present research is aimed at developing a new, easy and reproducible method for

the synthesis of lithium manganese sulfate as a cathode material for lithium-ion batteries

and further electrochemical investigations. The method of synthesis consists in a

dehydration of crystal hydrate precursors, which are prepared by lyophilization of sulfate

solutions of lithium and manganese. Electrochemical characterization of sulfates was

performed in model lithium-ion cells with different non-aqueous electrolytes in

galvanostatic and potentiostatic regimes. The TEM experiments were undertaken to

establish the morphology of the precursors and to observe structural changes after cell

cycling.

The data show that lithium manganese sulfate displays a good electrochemical

performance in terms of potential of Li+ intercalation and capacity stability. These findings

could initiate further investigations on sulfate-based electrode materials as safe and low-

cost alternatives.

Acknowledgements: The authors are grateful for the financial support of project KП-06-КИТАЙ/8,

bilateral projects-BULGARIA-CHINA competition of the Bulgarian National Science Fund and project

Д01-272/02.10.2020, funded by the Ministry of Education and Science under the National Program


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Topic B

BP-11

Compromise between stability and singlet fission propensity of

organic molecules: a theoretical study

V. Petakova, L. Borislavov, J. Stoycheva, A.Tadjer and J. Romanova*



Keywords: diradical character, excited states, solar cells, photovoltaics

Molecules with low to intermediate diradical character are potential singlet fission

compounds and are therefore suitable for photoactive molecules in solar cells. However, the

diradical character is also associated with high reactivity and instability, which represent

disadvantages for real application. Therefore, we have performed theoretical investigation in

order to quantify the intimate relation diradical character-stability-singlet fission propensity.

The study gives insight on the inherent properties of chromophores able to undergo singlet

fission and allows to precise the desired diradical character range for photovoltaic

applications.



agreement D01-214/28.11.2018.

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Topic B

BP-12

Influence of the initial compounds on the synthesis and morphology of

Ba7Nb4MoO20 ceramic used as electrolyte in solid oxide fuel cells

M. Tsvetanova, D. Kovacheva*, P. Tzvetkov and V. Tumbalev




Keywords: SOF, synthesis, XRD, DTA, fuel cell

The need for highly efficient production of electricity from environmentally friendly

sources defines high-temperature fuel cells as a very important alternative for various

applications. In addition to hydrogen, high-conversion carbon-based natural hydrocarbons

can also be used as energy sources. Due to the high operating temperature of these devices

(> 700oC) processes of degradation of the used materials are observed, such as diffusion of

the contact between the different surfaces and oxidation of the wiring contacts. This

necessitates the development of new electrolytes that have high proton or oxygen

conductivity at more moderate temperatures (300 – 700oC) [1]. Recently, results were

published for excellent oxygen and proton conductivity of Ba7Nb4MoO20 (P-3m1, a = 5.870 Å,

c = 16.538 Å) at temperatures of 500 – 800oC [2]. In addition to suitable conductivity for solid

electrolyte at moderate temperatures, Ba7Nb4MoO20 also has excellent chemical resistance

in oxidation and reduction atmosphere. These features provoked us to study the possibilities

for obtaining Ba7Nb4MoO20 by solid-state synthesis from various precursors. The aim of the

study was to determine the influence of the starting precursors (BaCO3 vs. Ba(NO3)2 and two

polymorph modifications of Nb2O5) on the synthesis temperature and purity of the obtained

products.

As starting reagents BaCO3, Ba(NO3)2, MoO3 and two polymorph modifications of

Nb2O5 (monoclinic P2 and orthorhombic Pbam) were used. All four samples were obtained

by annealing at 1050oC for 12 hours with intermediate regrinding after the first 6 hours. The

resulting compounds (named after the caption on Figure 1) were characterized by powder X-

ray diffraction (XRD) for qualitative and quantitative phase composition, thermal analysis

(DTA/TG) and scanning electron microscopy (SEM).

Thermal studies performed on samples obtained from BaCO3 showed a decrease in the

reaction temperature by about 170oC using orthorhombic Nb2O5 in comparison with

monoclinic one (Figure 1a). The impurity phases also decrease sharply from a total of four

for sample M-CO3 to only one for O-CO3. When Ba(NO3)2 is used instead of BaCO3, the

reaction proceeds in different stages and process ends at about 700oC for both Nb2O5

polymorph modifications (Figure 1b). X-ray diffraction analysis shows the presence of two

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impurity phases in small quantities for sample M-NO3 and only traces of them in sample O-

NO3 (Figure 1c).

Figure 1. X-ray and thermal analysis of Ba7Nb4MoO20 from different precursors: M-CO3 (monoclinic

Nb2O5 and BaCO3); O-CO3 (orthorhombic Nb2O5 and BaCO3); M-NO3 (monoclinic Nb2O5 and Ba(NO3)2);

O-NO3 (orthorhombic Nb2O5 and Ba(NO3)2).

The study performed demonstrates that with suitable starting compounds, the

synthesis temperature and purity of the resulting Ba7Nb4MoO20 can be significantly

improved. In this sense, the combination of orthorhombic Nb2O5 with Ba(NO3)2 shows the

best results as precursors for solid-state reaction.

References

1. W. Kan, A. Samson, V. Thangadurai, J. Mater. Chem. A 4 (2016) 17913.

2. S. Fop, K. McCombie, E. Wildman, J. Skakle, J. Irvine, P. Connor, C. Savaniu, C. Ritter, A. Mclaughlin,

Nat. Mater. 19 (2020) 752.

Acknowledgements: The authors wish to thank Project D01-272/02.10.2020 - "European Network on



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Topic B

BP-13

Capture of CO2 by CeO2 materials of different origin and

CeO2(75%)ZrO2(25%)

V. Zdravkova*, O. lagunov, S. Andonova, I. Spassova, E. Ivanova, M. Mihaylov,

D. Panayotov and K. Hadjiivanov




Keywords: ceria materials, CO2 capture, static and dynamic adsorption, FTIR spectroscopy, water

Capturing carbon dioxide from large CO2 emission sources, like power plants and steel

mills, is technologically the first important stage of the storage and utilization approaches

aimed at mitigating the global warming. Nowadays, separation of CO2 using liquid sorbents

such as amine liquids is a mainstream CO2 capture technology. This separation technique

utilizes the temperature dependence of CO2 sorption. Namely, the separation involves

cycling between CO2 absorption from exhaust gas at low temperature and CO2 desorption at

high temperature. Alternatively, CO2 can be separated by solid materials such as adsorbents

and membranes. One of the advantages of solid sorbents as compared to liquid solvents is

their smaller specific heat capacity. This allows decreasing the required heat for CO2

recovering and thus lowering the energy consumption for CO2 separation. In this regard,

solid-based CO2 adsorbents have attracted a great deal of research efforts. There are many

reports on adsorbents using zeolites, metal organic frameworks, amine-grafted silica,

carbon-based materials and metal oxides. The investigated metal oxides include cerium

oxide, iron oxide, lithium oxide, magnesium oxide, aluminium oxide, titanium oxide, and

zirconium oxide. CeO2 is shown to exhibit one of the highest numbers of surface basic sites

among a number of selected metal oxides, which is advantageous in terms of CO2 capture.

Mesoporous CeO2 is shown to exhibit a significant CO2 adsorption capacity. In addition, the

presence of metal dopants was found to further tune the surface functionalities, such as the

surface acid–base properties and defect sites, which impact the adsorption behaviour of CO2

on the CeO2 surface.

This work studies CeO2 and CeO2-ZrO2 adsorbent materials with different origin. Two of

them were commercial nanoparticulate CeO2 powders obtained from two different

suppliers, Alfa Aesar and US Research Nanomaterials. Both samples have comparable

nanoparticle size and specific surface area. The third CeO2 nanoparticulate sample was

prepared in our lab by precipitation with ammonia from of a Ce(NO3)3.6H2O aqueous

solution. The fourth nanoparticulate material was CeO2(75%)ZrO2(25%) obtained via co-

precipitation with ammonia from of a mixed aqueous solution of Ce(NO3)3.6H2O and

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ZrO(NO3)2.xH2O. The physicochemical characteristics of the studied samples are reported

elsewhere. The CO2 adsorption capacity was measured for both the static and dynamic CO2

adsorption regimes. The chemisorption of CO2 forming different surface species was studied

by FTIR spectroscopy. As shown in Figure 1, the CeO2(75%)ZrO2(25%) material has the

highest dynamic capacity for CO2 capture.

Figure 1.Dynamic CO2 adsorption/desorption measurements in a flow of Ar.

The thermal stability of surface CO2-related species was also studied for the oxygen-

activated, H2-reduced and water-covered adsorbents. The FTIR spectroscopy data showed

the presence of bridge, hydrogen, mono and bidentate carbonate, as well as polydentate

carbonate CO2 surface species. The relative population of these species is almost identical

for the commercial CeO2 samples, while for the precipitation prepared samples the coverage

of more strongly bonded bi- and polydentate carbonate species is prevailing. Moreover, the

CeO2(75%)ZrO2(25%) sample showed almost no indication to loose its CO2 capacity when the

surface is pre-covered with water, as was the case with the commercial samples. The results

of this study showed that the synthesized CeO2(75%)ZrO2(25%) is a material with promising

potential for CO2 capture applications.

Acknowledgements: The authors thank to the Ministry of Education and Science for the support

provided by the Project Д01-272/02.10.2020 - "European Network on Materials for Clean

Technologies" and by the National ResearchProgramme “Low Carbon Energy for the Transport and

Domestic Use (E+)” approved by DCM No. 577/17.08.2018 (contract DO1-214/28.11.2018).

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Topic B

BP-14

A new class of high entropy AB2O4 spinel oxides prepared by

mechanochemical synthesis

O. Porodko1*, M. Fabián1, H. Kolev2, M. Lischnichuk3, M. Žukalová4, V. Girman3

1Institute of Geotechnics, Slovak Academy of Sciences, Košice, Slovakia. 2Institute of Catalysis, Bulgarian Acdemy of Sciences, Sofia, Bulgaria.

3Institute of Physics, P.J. Šafárik University, Košice, Slovakia. 4J. Heyrovský Institute of Physical Chemistry, Czech Academy of Sciences, v.v.i., Prague 8,

Czech Republic.


Keywords: spinel structure, high entropy oxide, nanomaterials, mechanosynthesis

Nanocrystalline oxides of formula AB2O4 were prepared by mechanochemical

synthesis. The phase evolution as well as the structure of the prepared oxides, i.e.

(Zn0.25Cu0.25Mg0.25Co0.25)Al2O4 (HEOAl), were studied by XRD. The microstructure and

morphology of the prepared materials were investigated by HR-TEM, EDX and XPS

spectroscopy. Selected high entropy oxides were doped with lithium and fluorine / chlorine

in order to test them as potential components for Li-ion batteries with the final composition

Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5F0.5 (LiHEOAlF) and

Li0.5(Zn0.25Cu0.25Mg0.25Co0.25)0.5Al2O3.5Cl0.5 (LiHEOAlCl). As a result of the synthesis, the X-ray

diffraction peaks of mechanosynthesized compounds containing lithium and

fluorine/chlorine are shifted towards higher 2 Theta angels. Obtained theoretical and

observed data were compared with each other. It is identified that the mechanochemically

synthesized Li containing high-entropy spinels have modified value of lattice parameter, i.e.

observed lattice contraction as a consequence of lithium incorporation into the spinel

structure with different Shannon radii of ions [1] and formation of oxygen defects for

electroneutrality compensation. Table 1 summarizes the structural data: lattice parameter a,

interplanar distances d for individual Miller indices and crystallinity size D. The high-

resolution XPS spectra of individual samples were performed to study the effect of the

preparation method and subsequent co-doping on the oxidation state of the respective

elements. Oxidation-reduction processes took place during the mechanochemical reaction,

and different degrees of oxidation of several elements were detected compared to their

oxidation state before ball milling. The electrochemical performance of the HEOAl, LiHEOAlF

and LiHEOAlCl samples was investigated by cyclic voltammetry of Li insertion in the potential

window of 0.0–3.0 V vs Li+/Li at scan rate of 0.1 mV s-1. The charge capacity of HEOAl

determined from the cyclic voltammogram was found to be 54 mAh g-1. This value is slightly

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increased for LiHEOAlF (71 mAh g-1) while there is no signifficant effect of lithiation and

anionic exchange in LiHEOAlCl with charge capacity of 52 mAh g-1.

Table 1. The lattice parameters, interplanar distances and average crystallite size for HEOAl, LiHEOAlF and LiHEOAlCl.

Sample Lattice parameter, a (Å)

Interplanar distance, d

observed (Å)

Interplanar distance, d

calculated (Å)

Crystallite size, XRD (nm)

Crystallite size, TEM (nm)

HEOAl 8.1024(3) 2.7 for (hkl=300) 2.7 for (hkl=300) 15 16

LiHEOAlF 8.0443(6) 5.6 for (hkl=110) 5.7 for (hkl=110) 15 17

LiHEOAlCl 8.0331(1) 2.4 for (hkl=311) 2.4 for (hkl=311) 11 6

References

1. R. D. Shannon, Acta Crystallogr. A 32 (1976) 751.

Acknowledgements: This work was supported by the Slovak Research and Development Agency

APVV (No. 19-0526), Scientific Grant Agency VEGA (No. 2/0055/19) and bilateral project (BAS-

SAS/21-07).

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Topic C

CO-1

Mesoporous ceramics: applications in biomedical research

A. Diaz-Cuenca

Materials Science Institute of Seville (ICMS), joint CSIC-University of Seville Center,

Seville 41092, Spain


Keywords: SBA-15, mesoporous bioactive glass (MBG), drug delivery, bone therapy

Mesoporous ceramics are a class of nanoporous materials with organised pore sizes

between 2 and 50 nm. Their unique properties of high surface area, large pore volume and

morphological control represent key characteristics for its use in a number of industrial

processes for environmental protection and remediation. Besides, biocompatible

compositions based on silica are being highly considered for advanced biomedical

applications, including drug delivery, tissue engineering and gene therapy [1]. The lecture

will review main aspects in the synthesis of mesoporous silica-based materials as well as

related phosphate composites and formulations, both in the form of microparticles and

nanoparticles. Presented biomaterials physicochemical parameters will be analysed in

relation to their biological response and functionality. Examples of their processing and

implementation in hard tissue engineering and cell therapy will be discussed [2-3].

References

1. M. L. Ramiro-Gutiérrez, L. Santos-Ruiz, S. Borrego-González, J. Becerra and A. Díaz-Cuenca,

Micropor. Mesopor. Mat. 229 (2016) 31-43.

2. S. Borrego-González, L.B Romero-Sánchez, J. Blázquez and A. Díaz-Cuenca, Micropor. Mesopor.

Mat. 256 (2018) 165-176.

3. L. B Romero-Sánchez, M. Marí-Beffa, P. Carrillo, M.A. Medina and A. Díaz-Cuenca, Acta Biomat. 68

(2018) 272-285.

Acknowledgements: The author gratefully thanks the support provided by the Project “European

Twinning on Materials Chemistry Enabling Clean Technologies - TwinTeam” of the National Bulgarian

Programme “European research network”.

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Topic C

CO-2

Effect of amino acids on the chemical, phase and morphological

characteristics of wet-synthesized calcium phosphates

D. Rabadjieva*, R. Gergulova, K. Sezanova, D. Kovacheva




Keywords: calcium phosphates, biomimetic synthesis, amino acids

Ion-modified calcium phosphates, that mimic the inorganic part of blood plasma,

have been obtained in simulated body fluids with a view to simulate the composition of the

mineral component of hard tissues and to strengthen some of their specific biologically

important characteristics. The natural biomineralization process, however, takes place under

the control of organic molecules (proteins and polysaccharides) that affect nucleation and

growth of the inorganic crystals. Therefore, research on the synthesis of calcium phosphates

in the presence of organic molecules is a promising trend in the biomimetic synthesis of

materials applicable in dental and orthopedic medicine.

In this study, the effect of three low-weight amino acids (glycine, alanine and valine)

present during the wet biomimetic synthesis of double-doped (with Mg2+ and Zn2+ ions)

calcium phosphates, on their chemical, phase, morphological and structural characteristics

was considered. Amino acids under study participate in the acidic domains of non-collagen

proteins (NCPs) and are also present in small amounts as free acids in the blood plasma.

Modification with Mg2+ and Zn2+ ions is associated with their importance for bone formation

and growth. The studies were performed at two different concentrations of amino acids: (i)

dilute solutions (7.5 g.L-1); and (ii) saturated solutions - 220, 142 and 60 g.L-1, for glycine

(Gly), alanine (Ala) and valine (Val), respectively. The differences are due to the different

solubility of the amino acids.

It was found that both the type and concentration of amino acids affect the amount

of doped elements in the amorphous precipitate, and hence, the structural parameters of

the Mg- and Zn-modified β-tri calcium phosphate (β-TCP) obtained after precursors

calcination. Upon precipitation in a dilute solution of an amino acid almost all Zn2+ ions (2.8-

3 mol %) and about a half of Mg2+ ions (7-8 mol %) present in the initial solution are included

in the amorphous precipitate. Upon precipitation in a concentrated solution of an amino

acid the amounts of included Mg2+ and Zn2+ ions increase in the order: Gly (5.9 mol % Мg

and 0.74 mol % Zn) – Ala (6.4 mol % Мg and 1.4 mol % Zn) – Val (11 mol % Мg and 3 mol %

Zn). The observed processes were explained by the formation of complexes of different

types and different stability in the initial solutions. In the case of dilute solutions of amino

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acids, the concentration of the latter is commensurable with that of Cl- ions in the simulated

body fluid. Thus, OH-, Cl- ions, H2O molecules and Gly/Ala/Val zwitterions compete for being

involved in the coordination shell of the metal ions. In the case of concentrated solutions,

the amount of amino acids exceeds several times that of the sum of other ions. MeL (Me =

Mg, Zn, L=Gly, Ala, Val) complexes become dominant and inclusion of Mg2+ and Zn2+ ions in

the composition of the precipitates will be determined by the stability of these complexes,

which decreases in the order: MeGly>MeAla>MeVal and ZnL>MgL>CaL

The Rietveldt refinement of XRD data of samples calcinated at 1000oC confirmed that

both Mg2+ and Zn2+ ions preferentially substituted the Ca2+ ions in the octahedral Ca(5) sites

of (Mg,Zn)-β-TCP, in some cases fully repelling Ca ions from it. This results in a drastic

decrease of the Me-O distances in this position and, respectively, of the unit cell parameters

in comparison with the unsubstituted β-TCP. These changes in structural parameters are

more pronounced for samples obtained in dilute amino acids due to the higher total

percentage of substitution.

A difference was found in the shape of the primary precipitated particles and the

specific surface of the precursors in the case of precipitation in concentrated solutions of

glycine and alanine. Spherical particles with a specific surface area in the range of 37 -

48 m2/g were obtained by precipitation in dilute solutions of the studied amino acids, as

well as in a saturated solution of valine (60 g/l). The higher concentrations of glycine and

alanine in their saturated solutions, which exceed 2-3 times that of valine, lead to a strong

elongation of the particles along one of the axes and to a 2- to 5-fold increase in specific

surface area (222-242 m2/g) and pore volume.

During the annealing process, the particles aggregate and the specific surface is unified

and drastically drops to 4 m2/g.

Acknowledgement: The authors thank the Bulgarian Ministry of Education and Science for the

financial support under the projects: КP-06-Н49-6/2020 “Investigation on novel hybrid modified

calcium phosphates systems with enhanced biomineralization activity” (Program “Competition for

financial support of basic research projects – 2020”) and D01-272/02.10.2020 "European Network

on Materials for Clean Technologies" (National Program "European Scientific Networks").

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Topic C

CO-3

Energy transfer and photophysical propertires of luminescent

[Eu(Phen)2]3+/SiO2 - based composites: theoretical study

Ts. Zahariev*, N. Trendafilova and I. Georgieva




Keywords: luminescence, europium complexes, silica matrices, quantum-chemical calculations,

simplified TDDFT

Optical complexes of Eu(III) with chromophore ligands are an object of continuous

interest from a wide group of researchers, because of their high luminescent efficiency. The

red emission of europium is highly monochromatic and is characterized by a sharp, well-

defined spectral interval. Such properties are extremely valuable for the development of

LEDs, displays and lasers [1]. One major disadvantage of the luminescent lanthanide

complexes is their relatively low mechanical and thermal stability. In order to make them

applicable for technological uses, the complexes can be incorporated into a stable rigid

matrix.

An alternative strategy is to embed the luminescent species into solid or amorphous

oxide-based matrices. It has been demonstrated, that the functionalization of SiO2-based

matrices with luminescent complexes, containing a Eu(phen)2+ -fragments leads to increased

lifetimes and in some cases – higher luminescent quantum yields [2,3] of the resulting

materials. However, the complicated structure of the resulting composites does not allow a

straightforward design of novel composites with pre-determined optical and photophysical

properties. A fundamental understanding of the interactions between the luminescent

structure and the oxide substrate, and the effect of the incorporation of the complex into

the host, is needed. This could be achieved by means of theoretical modelling, in particular

with the help of quantum-chemical calculations.

The effect of SiO2-based substrates on the red luminescence of EuX3(phen)2 (where X ≡

Cl-, NO3-) complexes is studied by means of semiempirical methods (Sparkle/AM1; INDO/S-

CIS) and the simplified TDDFT method of Grimme and coworkers [4]. Structure,

spectroscopic properties and energy diagrams are reproduced, and the most concurrent

energy transitions are determined. Ligand-to-metal energy transfer mechanisms and the

emission properties of the lanthanide ions were assessed with the help of Judd-Ofelt theory,

the QDC model of Freire and co-workers, and the theory of Malta. All theoretical estimates

are validated by comparison with available experimental results. The factors that stimulate

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the high emission intensities and contribute to the efficiency of light conversion are

discussed.

References

1. J. G. Bünzli, Eur. J. Inorg. Chem. (2017) 5058.

2. N. Danchova, S. Gutzov, K, Matras-Postolek, M. Bredol, N. Lesev, S. Kaloyanova, T. Deligeorgiev, J.

Incl. Phenom. Macrocycl. Chem., 78 (2014) 381.

3. T. Jin, S. Inoue, K.-I. Machida, G.-Y. Adachi, J. Alloys Compd., 265 (1998) 234.

4. C. Bannwarth and S. Grimme, Comput. Theor. Chem., 1040 (2014) 45.


NCHDC – part of the Bulgarian National Roadmap on RIs, with the financial support by the Grant No

D01-387/18.12.2020. The financial support of the project Д01-272/02.10.2020 - "European Network

on Materials for Clean Technologies", funded by the Ministry of Education and Science under the

National Program "European Scientific Networks", is also acknowledged.

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Topic C

CP-1

Crystallization and luminescence properties of

50ZnO:40B2O3:10WO3:xEu3+ glass-crystalline materials

L. Aleksandrov*, M. Milanova, R. Iordanova and I. Koseva




Keywords: glass, glass-crystal, DTA, luminescence

Homogenous and transparent glasses with nominal compositions

50ZnO:40B2O3:10WO3:xЕu3+ (x = 1 and 5), mol% were obtained by melt quenching method.

The obtained glasses were characterized by X-ray diffraction (XRD), differential thermal

analysis (DTA) and photoluminescence spectroscopy (PL). Based on DTA analysis the

synthesized glasses were aneled at 600oC for 3 and 6 hours in electrical furnace in order to

exam their crystallization behavior. It was found that the main crystallization mechanism in

ZnO-B2O3-WO3 glasses is surface crystallization and ZnWO4 is the main crystalline phase in

crystallized glasses. After thermal treatment of the glass containing 1 mol% Eu2O3 formation

only of ZnWO4 with average particle size ~ 75 nm was detected. The presence of several

crystalline phases: ZnWO4, ZnB4O7 and H3BO3 was established after crystallization of the

glass containing 5 mol% Eu2O3.

The crystallized glass consisting of Eu3+ doped ZnWO4 crystals is characterized with

enhanced photoluminescence emission properties as compared to the base glass (containing

1 mol% Eu2O3) due to the lower site symmetry of Eu3+ ions in the crystallized samples.

Figure 1. Photoluminescence spectra at room temperature of Eu3+ ions in

50ZnO:40B2O3:10WO3:1Eu2O3 glass and glass crystallized samples at 600°C for 3 and 6 hours.

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Acknowledgements: This work is supported by Bulgarian National Science Fund under project КП-06-

Н29/7. The authors are also grateful to the National Science Programme “European research

network” under project TwinTeam Д01-272/02.10.2020.

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Topic C

CP-2

Synthesis, crystallization and properties of TeO2/TiO2/B2O3 glasses

A. Bachvarova-Nedelcheva*, R. Iordanova, K. L. Kostov and M. Peneva




Keywords: glasses, crystallization, IR spectroscopy, UV-Vis spectroscopy

Boron oxide (B2O3) is a classical glass former considered as the best one. Borate glasses

have a random network consisting of tetrahedral (BO4) and trigonal boron (BO3) units and

their combinations form diborate, triborate, tetraborate and pentaborate groups [1].

Incorporated in different glass compositions B2O3 improves their chemical and thermal

stability. Another well-known family of glasses is the tellurite ones where the TeO2 is a

conditional network former, and it does not form glass alone. The multicomponent tellurite

glasses are attractive because of their excellent optical properties (high refractive index, high

third order nonlinear properties, wide optical window from the ultraviolet to the infrared

region, etc.). When two glass formers such as B2O3 and TeO2 are mixed, their structural units

connect and form mixed structural units that usually enhance some glass properties [2].

Dimitriev et al. [3,4] have investigated the binary TeO2-B2O3 system as a part of the

TeO2-B203-V205 three component one and they established that below 75 mol % of TeO2 a

wide region of liquid-liquid phase separation in the binary system exists. On the basis of this

survey we decided to expand this study by verifying the glass formation ability in the ternary

TiO2-TeO2-B2O3 system as well as to investigate the peculiarity of the amorphous network

formation combining one classical network former (B2O3), one conditional network former

(TeO2) and one intermediate oxide (TiO2).

Ternary TiO2/B2O3/TeO2 glasses have been obtained applying melt quenching method

(up-down) from compositions containing high TeO2 content (> 80 mol %). It was established

that stable, homogeneous glasses were obtained near the TeO2 corner (Fig. 1). No liquid

phase separation was observed in the investigated system. The glasses obtained were

transparent and brownish colored. Some physical parameters (density, molar volume,

oxygen molar volume and oxygen packing density) were estimated and they gave additional,

useful information for the network connectivity. The analysis of IR spectra showed that the

glass network consists mainly of TeO4 (tbp) units. The XPS spectroscopy reveals the existence

of bridging oxygen bonds (M-O-M) and mixed bridging bonds (M-O-M′). The UV-Vis

spectroscopy established a red shifting of the cut-off depending on composition.

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Figure 1. Obtained glasses in the TiO2-TeO2-B2O3 system.

References

1. B. N. Meera, J. Ramakrishna, Raman spectral studies of borate glasses, J. Non-Cryst. Sol. 159

(1993), 1-21.

2. K. Maheshvaran, P. Veeran, K. Marimuthu, Structural and optical studies on Eu3+ doped boro-

tellurite glasses, Solid State Sci. 17 (2013) 54-62.

3. Y. Dimitriev, E. Kaschieva, Immiscibility in the TeO2-B2O3 system, J. Mater. Sci. 10 (1975) 1419-

1424.

4. E. Kashchieva, PhD Thesis, 1981, Sofia.

Acknowledgements: The authors are thankful to the project Д01-272/02.10.2020 - "European

Network on Materials for Clean Technologies", under the National Program "European Scientific

Networks".

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Topic C

CP-3

Luminescent complexes of Eu(III) and Sm(III) with

pyrolidinedithiocarbamate ligands: Synthesis and theoretical description

of the energy transfer mechanism

B. Borrisov1*, M. Tzvetkov2, Ts. Zahariev1, I. Georgieva1


1113 Sofia, Bulgaria 2 Faculty of Chemistry and Pharmacy, Sofia University “St. Kliment Ohridski”, 1,



Keywords: lanthanide luminescence, dithiocarbamates, quantum calculations, excited states, charge

transfer

Lanthanide-based compounds are widely employed in the development of materials

with unique magnetic and optical properties [1]. Luminophores containing lanthanide

species are usually characterized by better stability, compared to the organic structures

reported in the literature. In particular, the Ln(III)-containing compounds are characterized

by the narrow bands of their emission spectra, as well as by longer emission lifetimes. The

main disadvantage, which hinders their application, is the low molar absorption in the UV-

Vis range of the spectrum, resulting in relatively low quantum yields. This problem can be

overcome through the antenna effect, in which a ligand, absorbing intensively in the UV-Vis

region, can do a resonance transfer of energy towards the Ln(III)-ion [2,3]. The search for

new organic antenna-chromophores is a key challenge in the design of novel, highly efficient,

luminescent materials. One prospective strategy is the inclusion of dithiocarbamate anions

in the structure of Ln(III) complexes. The resulting structures form a class of compounds,

which has attracted significant attention in the last decades [4,5]. In particular, neutral

structures, containing 1,10-phenanthroline (phen) as an additional antenna have been

studied by means of spectroscopic techniques. It has also been demonstrated [6,7] that the

combination of phen and dithiocarbamate leads to better sensitization for Sm(III) and Pr(III)-

ions than for Eu(III), Tb(III) and Dy(III). However, a systematic study of the mechanism and

the exact role of the charge-transfer states not been performed.

A combined theoretical and experimental study, focused on the spectroscopic and

photophysical properties of Ln(PDTC)3phen (where PDTC ≡ pyrolidinedithiocarbamate, Ln ≡

Sm, Eu) complexes, is performed. The solid state structure of the complexes is characterized

by X-Ray powder diffraction and IR-spectroscopy. The experimental absorption, excitation

and emission spectra of the complexes, lifetimes and luminescence quantum yields are

obtained. The detailed mechanism of the antenna-effect in the two compounds is predicted

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with the help of DFT/TDDFT/ωB97xD – method. The molecular geometry at ground, first

singlet and first triplet excited state is optimized. The vertical and adiabatic electronic

transitions between the ground and the excited states are described. Spin-orbit coupling

between singlet and triplet states is assessed on the basis of quasi-degenerate perturbation

theory (QDPT) formalism. The estimates are further used to calculate the intersystem

crossing rates, as well as rates of phosphorescence. In the case of Eu(PDTC)3phen, the theory

of Malta, as implemented by Freire and coworkers, was employed to obtain ligand-to-metal

energy transfer rates. A comparative analysis of all experimental and theoretical results is

performed, in order to elucidate the role of charge-transfer states in the process of

sensitization. Finally, a quantitative assessment of the efficiency of the Ln(PDTC)3phen as

light/energy converters is obtained.

References

1. J. G. Bünzli, Eur. J. Inorg. Chem. (2017) 5058.

2. К. Binnemans, Chem. Rev. 109 (9) (2009) 4283.

3. J. G. Bünzli, C. Piguet, Chem. Soc. Rev. 34 (2005) 1048.

4. W. M Faustino, O. L. Malta, E. E. S.Teotonio, H. F. Brito, A. M.Simas, G. F. de Sá, J. Phys. Chem. A

110(7) (2006) 2510.

5. Yu. A.Bryleva, L. A. Glinskaya, I. V. Korol’kov, A. S. Bogomyakov, M. I. Rakhmanova, D. Yu. Naumov,

T. E. Kokina, S. V. Larionov, J. Struct. Chem. 55(2) (2014) 319.

6. M. D. Regulacio, M. H. Pablico, J. A. Vasquez, P. N. Myers, S. Gentry, M. Prushan, S.-W. Tam-Chang,

S. L. Stoll, Inorg. Chem. 47(5) (2008) 1512.

7. A. S. Kupryakov, V. F. Plyusnin, V. P. Grivin, J. A. Bryleva, S. V. Larionov, J. Lumin. 176 (2016) 130.


NCHDC – part of the Bulgarian National Roadmap on RIs, with the financial support by the Grant No

D01-387/18.12.2020. B. Borrisov, Ts. Zahariev and I. Georgieva thank for the financinal support of the

project Д01-272/02.10.2020 - "European Network on Materials for Clean Technologies", funded by

the Ministry of Education and Science under the National Program "European Scientific Networks".

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Topic C

CP-4

Rare earth concentration dependence on the glass optical properties

in the system CaO-GeO2-Li2O-B2O3 (RE=Dy3+)

I. Koseva1, V. Nikolov1, 3, M. Gancheva1*, L. Aleksandrov1, P. Ivanov2, P. Petrova2,

R. Iordanova1, R. Tomova2


1113 Sofia, Bulgaria 2 Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences,




Keywords: germanate glasses, Dy doped glasses, luminescence properties

Glasses doped by rare earth ions are of great importance in science and modern solid

state optical technology. They are widely used as sensors, solid state lasers, optical fibers in

telecommunication, phosphors for displays, monitors and lightning applications [1]. The

germanate glasses possess good luminescent characteristics, appropriate conductivity and

low thermal quenching [2-4]. Dy3+ has a strong excitation band around 350 nm and emits

two intensive lines – blue in the region 470-550 nm (4F9/2→6H15/2 transition) and yellow in

the region 570-600 nm (4F9/2→6H13/2 transition). Therefore Dy3+ ion is of special interest due

to the possibility for achieving of white light in one host with single doping [5].

The purpose of this study is to find out how the rare earth ion concentration influences

on the glass spectral characteristics.

Dy3+ doped glasses from the oxide system CaO-GeO2-Li2O-B2O3 with different

compositions were prepared by melt quenching technique.

The X-ray analysis reveals amorphous nature of the as-synthesized glasses. Different

thermal analysis shows that glasses with composition G8 are more thermally stable

compared with other two glasses and the influence of rare earth ion is negligible. The IR

spectroscopy exhibited that the amorphous network is built from BO3, BO4, GeO4 and LiO4

structural units. Some changes in the structure were established after doped by Dy3+ ions.

The luminescence spectra of the investigated glasses possess characteristic peaks of

the Dy3+ ion - two intense and one weak peaks in the blue, the yellow and the red regions

[5]. The CIE coordinates are placed in the yellow region and the colour slightly depends on

the glass composition. Dy3+ doped glasses from the system CaO-GeO2-Li2O-B2O3 could be

used as yellow phosphors.


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Table 1. Glass compositions from the oxide system CaO-GeO2-Li2O-B2O3 and concentrations Dy3+ ions

in the glasses.

CaO

[mass%] GeO2

[mass%] Li2O

[mass%] B2O3

[mass%] Dy3+

[at%]

Glass

G1 45 38 5 12 0.5, 1, 2

G8 40 43 5 12 2, 3, 4

L9 28 53 15 5 0.5, 1, 3, 6

Figure 1. CIE coordinates of the Dy 3+ doped glasses with composition G1, G8 and L9.

References:

1. P. Yasaka, J. Kaewkhao, Luminescence from lanthanides-doped glasses and applications: A review.

In 2015 4th International Conference on Instrumentation, Communications, Information Technology,

and Biomedical Engineering (ICICI-BME) (2015) 4.

2. P. Guo, F. Zhao, G. Li, F. Liao, S. Tian, X. Jing, Journal of luminescence, 105 (2003) 61.

G. Keiser, Optical fiber communications, Wiley Encyclopedia of Telecommunications (2003)

3. D. Di Martino, L.F. Santos, A.C. Marques, R. M. Almeida, Journal of non-crystalline solids, 293

(2001) 394.

4. R. S. Liu, (Ed.) Phosphors, up conversion nano particles, quantum dots and their applications (201)

343. Berlin: Springer. DOI https://doi.org/10.1007/978-3-662-52771-9

Acknowledgements: The authors thank of the financial supported by the National Science Fund of

Bulgaria (Contract No. KP-06-H29/10). Research equipment of Distributed Research Infrastructure

INFRAMAT, part of Bulgarian National Roadmap for Research Infrastructures, supported by Bulgarian

Ministry of Education and Science was used in this investigation.

https://doi.org/10.1007/978-3-662-52771-9

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Topic C

CP-5

Spectroscopic investigations on barium titanate containing

oxide glass-ceramics

R. Harizanova1*, I. Avramova2, Z. Cherkezova-Zheleva3, D. Paneva3, R. Kukeva2,

R. Stoyanova2, I. Mihailova1, I. Gugov1 and C. Rüssel4

1 University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,


4 Otto Schott Institute for Materials Research, Jena University 07743 Jena, Germany


Keywords: barium titanate, crystallization, glass-ceramics, XPS, EPR, Mössbauer spectroscopy

Materials simultaneously containing dielectric and magnetic phases find application in

energy storage, microelectronics and as sensor devices for environmental protection. Oxide

glass-ceramics prepared from glasses by means of controlled crystallization are materials in

which such functional properties can be realized. The synthesis of glass-ceramics with pre-

determined phase compositions and controlled crystal sizes and volume fractions requires

thorough knowledge on the structure, valence states and coordination in which the glass-

constituting elements are present, in order to achieve the envisaged application.

Thus, the synthesis of glasses with the mol% composition

20.1Na2O/23TiO2/23.1BaO/3Al2O3/7.6B2O3/17.4SiO2/5.8Fe2O3 was carried out using

traditional melt-quenching technique. During heat treatment above the glass transition

temperature in the glasses cubic BaTiO3 as a major phase and minor quantities of hexagonal

BaTi1-xFexO3-δ crystals are simultaneously precipitated. The valence states of the ions in the

parent glass and the glass ceramics are studied with X-ray photoelectron spectroscopy. The

presence of the oxidized species, including Fe ions present as Fe3+ and Ti ions – as Ti4+ in

both tetrahedral and octahedral coordinations, is concluded. Depending on the thermal

history of the samples, the Ba2+ ions occur in different coordinations and the number of

bridging and non-bridging oxygen ions varies. The valence states and the coordinations of

Fe-ions in the glass and selected glass ceramic samples were investigated by Mössbauer

spectroscopy which detected Fe3+ ions in both tetrahedral and octahedral coordinations in

the glass. Fe3+ was also found to be incorporated in distorted octahedral and pentahedral

coordinations in the Ti4+ sites of hexagonal BaTiO3 crystals. The electroneutrality is preserved

by the occurrence of oxygen vacancies. Electron paramagnetic resonance spectroscopy

revealed that four types of Fe3+ ions that are non-uniformly distributed in the samples exist:

Fe3+ ions in magnetic domains, isolated Fe3+ in a rhombic crystal field, magnetically coupled

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Fe3+ ions in BaTiO3 and Fe3+ ions located in a crystalline phase. The ratio between the

different types of Fe3+ ions depends on the crystallization time.

Acknowledgements: The authors express their gratitude to the Bulgarian National Science Fund,

contract КП-06-Н28/1 for the financial support.

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Topic C

CP-6

NMR and thermal characteristics of poorly crystalline hydroxyapatite

R. Ilieva1*, P. Shestakova2, E. Dyulgerova3, D. Rabadjieva1



Sciences, 1113 Sofia, Bulgaria 3 Dental Medicine Faculty, University of Medicine, 1431 Sofia, Bulgaria


Keywords: hydroxiapatyte, solid state NMR, Thermal analysis

Two synthetic calcium phosphate materials were synthesized by wet chemical

precipitation in order to obtain an approximate model of the mineral phase of tooth enamel.

They were characterized by solid state NMR and thermal analysis. Method of double

decomposition of 1M solution of Ca(NO3)2 and 0.6M solution of (NH4)2HP04 were applied at

Ca/P of 1.67 typical for hydroxyapatite under controlled conditions (pH=10.5-11 provided by

NH4OH). The precipitate maturated for a period of 24 h, and then it was centrifuged, washed

3 times with de-ionized water and dried at 80oC for 10 h (called further HAP80) and part of it

calcined at 500oC (called further HAP500).

Results from the chemical analysis showed Ca/P ratio of 1.6 (typical for tooth enamel.)

XRD and BET analysis revealed obtaining of poorly crystalline apatite with specific surface

area of 80 and 57 m2/g at average grain size of 19 and 27 nm respectively for HAP80 and

HAP500.

The results from thermal analysis of the both samples studied combined with mass

spectrometric analysis of water vapor (m/z 18) and carbon dioxide (m/z 44) showed strong

endo-effect in the temperature region of 50 – 170oC, accompanied by weight loss of 1.9%

and 0.66% respectively for HAP80 and HAP500 due to release of absorbed and part of

chemically bonded water. The next temperature range (170 – 720оС) is characterized by a

number of weak endo-effects (smaller number at HAP500), accompanied by the release of

water and CO2, by which weight loss continues smoothly (2.8% at HAP80 and 1% at HAP500).

These effects can be attributed to the elementary processes with participation of the HPO43-

and CO32- ions carried out in the hydration shell of the poorly crystalline samples. The as

formed P2O72- interact with the available OH- ions in the temperature range 720-820

whereby water is released and a strong endo-effect is registered in the DTA curve. The

weight loss (about 0.7% for both samples) is not only due to the release of water, but also

due to the release of CO2 from the decomposition of impurities from CaCO3.

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1H, single pulse 31P and 1H→31P cross-polarization (CP) MAS solid state NMR spectra

provided additional insight to the structural characteristics of the studied hydroxyapatite

samples and confirms the results from thermal analysis. The 31P MAS NMR spectra of both

samples show a peak at 2.3 ppm, which is typical for HAP (Figure 1a). The lineshape of the

peak composed of a relatively narrow main signal overlapped with the broad low intensity

resonance suggests the presence of crystalline and poorly crystalline (nanocrystalline) HAP

phases. The 1H NMR spectrum indicates the presence of hydrogen phosphate units (HPO42-)

in both nanocrystalline HAP samples. This suggestion was further supported by the analysis

of the CP efficiency as function of the CP pulse length (Figure 1b).

Figure 1. a) 31P spectrum of HAP80; b) CP efficiency as function of the CP pulse length for HAP (red

dots) and hydrogen phosphate phase (blue squares).

For HPO42- the CP efficiency is high at short CP times, reaching a maximum at about 1

ms, followed by a subsequent decrease due to 1H relaxation. In HAP, however, the protons

are not part of the phosphate groups, and the distance between the phosphorus nucleus

and nearest protons is larger. Therefore, the CP efficiency was much slower and increased

with increasing the CP time, which is another characteristic of HAP. The two HAP samples

showed similar NMR characteristics, however in HAP500 the formation of a small amount of

pyrophosphate is suggested by the presence of a weak signal at around -8 ppm in its 31P

spectrum.

The obtained materials are suitable artificial substrate to study re-mineralization

potential of newly synthesized calcium-phosphate systems.

Acknowledgements: The authors thank the Bulgarian Ministry of Education and Science under

projects КP-06-Н49-6/2020 –“Investigation on novel hybrid modified calcium phosphates systems

with enhanced biomineralization activity” funded under the program “Competition for financial

support of basic research projects – 2020” and D01-272/02.10.2020 - "European Network on

Materials for Clean Technologies", funded under the National Program "European Scientific

Networks". Research equipment of Distributed Research Infrastructure INFRAMAT, part of Bulgarian

National Roadmap for Research Infrastructures, supported by Bulgarian Ministry of Education and

Science was used in this investigation.

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Topic C

CP-7

Optical properties of the glasses from the system CaO-GeO2-Li2O-B2O3

doped by terbium

I. Koseva1*, V. Nikolov1,3, M. Gancheva1, L. Aleksandrov1, P. Ivanov2, P. Petrova2,

R. Iordanova1 and R. Tomova2


1113 Sofia, Bulgaria 2 Institute of Optical Materials and Technologies, Bulgarian Academy of Sciences,




Keywords: germanate phosphor, rare-earth doped glasses, photoluminescence

Glasses doped by rare earth ions are of great importance in science and modern solid

state optical technology. Such optical materials are widely used as sensors, solid state lasers,

optical fibers in telecommunication, phosphors for displays, monitors and lightning

applications.

Tb3+ has a strong excitation band in the near UV region (around 380 nm) and emits

green light (around 550 nm) because of the 5D4→7F5 transition. This line is the strongest in

almost all hosts. The intensity depends on the Tb3+ concentration. When the concentration

of the dopant is low, the emission from high excited states can be observed in the blue part

of the visible spectra. In higher dopant concentrations, cross-relaxation quenching appears

because of the small distances between terbium ions in the host lattice. As the human vision

is most sensitive to green light, Tb3+ ion becomes more and more important. Besides, Tb3+

ion can be co-doped with Eu3+ ion for obtaining of white light emitting medium.

Terbium doped glasses with three different compositions and different dopant

concentrations were prepared from the oxide system CaO-GeO2-Li2O-B2O3. Glass

compositions and dopant concentrations are presented in Table 1.

Table 1. Glass compositions from the oxide system CaO-GeO2-Li2O-B2O3 and concentrations

of Tb3+ ion in the glasses.

CaO

[mass%] GeO2

[mass%] Li2O

[mass%] B2O3

[mass%] Tb3+

[at%]

Glass

G1 45 38 5 12 1, 2, 3, 5, 6, 7

G2 40 43 5 12 3, 4, 5

G3 28 53 15 5 0.5, 1, 2, 3

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DTA analyses show weak influence of the rare earth ion and its concentration on the

glass thermal properties. The glasses with composition G2 are more thermally stable

compared to the other two groups of glasses (G1 and G3).

The FTIR spectra of the glasses G1, G2 and G3 are complicated exhibiting presence of

BO4, BO3, GeO4, CaO and LiO4 units and B-O-Ge linkages. Detailed examination of the non-

doped glass spectra shows some differences depending on the glass composition. In the

non-doped glass with composition G3 bands attributed to vibration of B-O from BO4 units,

are very weak. The absorption band of B-O-Ge linkages is not observed in the G2 glass

composition spectra. On the other hand, bands of GeO4 units and CaO units are more

pronounced. After cooling of this glass composition Ca5Ge3O11 crystalizes as a main phase.

The band connected with LiO4 units, is clear presented in the G3 glass spectra, where

Li2CaGeO4 crystallizes after thermal treatment.

The presence of the Tb3+ ion in the glasses with composition G1 leads to breaking the

B-O-Ge linkages and to partially transformation of BO4 to BO3 units. The same structural

changes are observed in the glasses with composition G3. In glasses with composition G2 the

linkages between borate structural groups is formed when the dopant concentration

reaches 5 at%.

Excitation and emission spectra of the doped glasses possess the characteristic

transitions of Tb3+ ion. Peaks in all emission spectra are wide. It is expected, as the glasses

are not with a clear structure in opposite to the crystalline spices. Peaks locations are not

dependent on the rare earth ion concentration, as well as the glass composition, but some

splitting appears. When BO4 groups transform to BO3 ones and B-O-Ge linkages are broken, 5D4 →7F6 and 5D4 →7F4 transition are split in the emission spectra. No concentration

quenching is observed in Tb3+ doped glasses with composition G1 up to 7 at%. In Tb3+ doped

glasses with compositions G2 and G3 it appears at 4 and 2 at% respectively.

Chromaticity coordinates of Tb3+ glasses are placed in a wide area including green and

green-yellowish colors. The obtained results show that terbium doped glasses from the

oxide system CaO-GeO2-Li2O-B2O3 can be used for green phosphors. The color can be tune to

some extend by changing the glass composition and dopant concentration.

Acknowledgements: The research is financial supported by the National Science Fund of Bulgaria

(Contract No. KP-06-H29/10). Research equipment of Distributed Research Infrastructure INFRAMAT,

part of Bulgarian National Roadmap for Research Infrastructures, supported by Bulgarian Ministry of

Education and Science was used in this investigation.

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Topic C

CP-8

Luminescence properties of tungsten modified zinc borate glass and glass-

crystalline materials doped with Eu3+ ions, obtained by melt quenching

M. Milanova*, L. Aleksandrov and R. Iordanova




Keywords: europium, photoluminescence, melt quenching

Glass and glass-crystalline materials of 50ZnO:(50-x)B2O3:xWO3, x = 5, 10, 15, 20 mol%

doped with 1 mol% Eu2O3 were synthesized by melt quenching method. According to the

XRD data, glass-crystalline samples comprising ZnWO4 as crystalline phase were obtained

from the compositions having, 15 and 20 mol% WO3. X-ray amorphous samples were

prepared from the compositions containing 5 mol% and 10 mol% WO3. By optical

microscope observations, phase separation in the glass with 5 mol% WO3 was established,

while glass with 10 mol% WO3 was found to be homogeneous. The PL emission spectra at

room temperature of the prepared glass and glass crystalline materials obtained in ZnO-

B2O3-WO3 system were measured. The intensity of emission increases drastically in the glass-

crystalline samples compared with the glass sample, which is due to the incorporation of the

active Eu3+ ions with low symmetry into the crystalline ZnWO4 phase.

450 500 550 600 650 700 750 800 850

ex.

=385 nm 50ZnO:40B2O

3:10WO

3:1Eu

50ZnO:35B2O

3:15WO

3:1Eu

50ZnO:30B2O

3:20WO:1Eu

3

Wavelength, nm

PL

In

ten

sity (

a. u

.)

Figure 1. PL emission spectra of Eu3+ doped glass and glass crystalline materials in ZnO-B2O3-WO3

system.

Acknowledgements: This work is supported by Bulgarian National Science Fund under project КП-06-

Н29/7 and National Science Programme “European research network” Д01-272/02.10.2020 г.

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Topic C

CP-9

Europium doped glasses from the oxide system CaO-GeO2-Li2O-B2O3 for LED

application

I. Koseva1, V. Nikolov1,3, M. Gancheva1, L. Aleksandrov1, P. Ivanov2, P. Petrova2*,

R. Iordanova1 and R. Tomova2


1113 Sofia, Bulgaria 2 Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy

of Sciences, 1113 Sofia, Bulgaria 3 Institute of Mineralogy and Crystallography, Bulgarian Academy of Sciences,



Keywords: germanate phosphor, rare-earth doped glasses, photoluminescence

Doped with rare earth ions glasses attract great interest due to the significant

application such as optical fibers, waveguides, solar cells, light-emitting diodes, optical

switches, lasers, planar waveguides optical detectors, optical amplifiers, bio-medical

applications, thermo-luminescent materials and so on.

In this study is presented how the rare earth europium ion concentration influences

spectral characteristics of doped glasses from oxide system CaO-GeO2-Li2O-B2O3.

Europium doped glasses with three different compositions (G1, G2 and G3) and

different dopant concentrations (Table 1) are prepared from the oxide system CaO-GeO2-

Li2O-B2O3. DTA analyses show that the influence of the rare earth ion and its concentration

on the glass thermal properties is very weak. The glasses with composition G8 are more

thermally stable compared to the other two groups of glasses (G1 and G3). The FTIR spectra

display some variations between glass structures depending on the glass composition and

dopant concentration. The presence of Eu3+ in the glasses leads to transformation of BO4

units into BO3 ones and to breaking the B-O-Ge bonds. The excitation and emission spectra

of all glasses consist of characteristic peaks of Eu3+ ion. In the excitation spectra monitored

at 613 nm in the range 310-500 nm the strongest intensity is located at 393 nm (caused by 7F0→5L6 transition) for all glass compositions and active ion concentrations. Other transitions

are located at 318 nm (7F0→5H3), 362 nm (7F0→5D4), 382 nm (7F0→5L7), 414 nm (7F0→5D3) and

464 nm (7F0→5D2). For glasses with composition G1 peak intensity is almost the same in all

glass spectra independent on the active ion concentration. For glasses with compositions G8

and L9 highest intensity is seen in the 5 at% Eu3+ doped glass spectra. Emission spectra of the

studied glasses in the range 410-720 nm, monitored at 393 nm excitation also consist of the

Eu3+ ion characteristic peaks, caused by 5D1→7F1, 5D1→7F2, 5D0→7F0, 5D0→7F1, 5D0→7F2,

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136

5D0→7F3, 5D0→7F4 transitions. The peaks in the range 410-530 nm caused by higher levels are

not developed. Highest emission intensity is observed when the dopant concentration is 3

at% Eu3+ in the glass with composition G1, 4 at% Eu3+ in the glass with composition G2 and 7

at% Eu3+ in the glass with composition G3. Some changes are observed in the 5D0→7F0

transition and 5D0→7F1 transition in the emission spectra when the B-O-Ge bonds are

broken. Chromaticity coordinates are placed in a relatively narrow area in the red part of the

diagram and weakly depend on the glass composition and Eu3+ concentration (Figure 1). The

obtained results show that europium doped glasses from the oxide system CaO-GeO2-Li2O-

B2O3 can be used for red phosphors.

Table 1. Glass compositions from the oxide system CaO-GeO2-Li2O-B2O3 and concentrations of Eu3+

ion in the glasses.

CaO

[mass%] GeO2

[mass%] Li2O

[mass%] B2O3

[mass%] Eu3+

[at%]

Glass

G1 45 38 5 12 2, 3, 4

G2 40 43 5 12 3, 4, 5, 6

G3 28 53 15 5 3, 4, 5, 7, 10

Figure 1. CIE coordinates of Eu3+

doped glasses from the system CaO-GeO2-Li2O-B2O3.

Acknowledgements: The research is financial supported by the National Science Fund of Bulgaria

(Contract No. KP-06-H29/10). Research equipment of Distributed Research Infrastructure INFRAMAT,

part of Bulgarian National Roadmap for Research Infrastructures, supported by Bulgarian Ministry of

Education and Science was used in this investigation.

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137

Topic C

CP-10

Structure and antimicrobial ability of copper doped SiO2/HPC composites

N. Rangelova1*, L. Aleksandrov2, T. Angelova1, N. Georgieva1, S. Yaneva1

1 University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria 2 Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,



Keywords: sol-gel silica composites, cellulose ether, copper, antimicrobial effect

In this study SiO2/hydroxypropyl cellulose matrix doped with different amount of

copper ions was obtained by sol-gel route. The SiO2 was derived from tetraethyl

orthosilicate. The carbohydrate content in all samples was 5 wt.%, and the amount of

Cu(NO3)2*3H2O added as a source of Cu ions was varied from 0 to 5 wt.%. The principles of

the composites formation were developed using structural data from Fourier transform

infrared spectroscopy (FT-IR), Ultraviolet and visible (UV-Vis) spectroscopy and Differential

thermal analysis (DTA/TG). Based on the structural studies was shown that the interaction

between silica and the cellulose ether it occurs by formation of H-bonds by analogy of our

previous works [1, 2]. By optical microscopy, it was found that in all samples the copper ions

are homogenous distributed in the amorphous matrix.

The final stage of this investigation was to test the antimicrobial activity of materials

against to model strains of Gram + (Bacillus subtilis 3562) and Gram - (Escherichia coli K12)

bacteria and the model strain fungi (Candida albicans 74). The studies have shown that the

highest sensitivity to the test materials, with the formation of the greatest inhibitions zones

is observed by B. subtilis and C. albicans.

References

1. N. Rangelova, L. Aleksandrov and S. Nenkova, J. Sol-Gel Sci. Technol. 85(2) (2018) 330.

2. N. Rangelova, L. Aleksandrov, Ts. Angelova, N. Georgieva and R. Müller, Carbohydr. Polym. 101

(2014) 1166.

Acknowledgements: The authors thank to the Scientific Investigation Sector at UCTM-Sofia (contract

12148).

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Topic C

CP-11

Effect of the reaction medium modification on the chemical and phase

composition and morphological characteristics of biomimetically synthesized

calcium phosphate ceramic powders

K. Sezanova1*, S. Tepavitcharova1, P. Shestakova2, R. Gergulova1, and D. Rabadjieva1



Sciences, 1113 Sofia, Bulgaria


Keywords: calcium phosphates, biomimetic synthesis, reaction medium, ceramic powders

Essential requirement to calcium phosphate ceramic powders, as regards their use as

fillers for bone defects or as ceramics and cements for orthopedics and dentistry, is their

uniformity and nanosize.

The present study deals with the biomimetic synthesis of ion-modified calcium

phosphates with a view to mimic biomineralization processes and to obtain products with a

chemical composition close to that of natural enamel, dentin and bone. The reaction

medium was a simulated body fluid (SBFс) buffered with glycine (SBFс/GB). The effect of two

modifiers of the medium - glycerin (for the system SBFc/GB-GL) and xanthan gum (for the

system SBFc/GB-XG) - on the composition and morphology of the obtained precursors was

followed. The modifiers were chosen as to prevent the growth of primary nuclei. Glycerin

acts as a lubricant of the particles while xanthan gum forms negatively charged hydrogel

chains which could increase the nucleation.

The precursor preparation procedure includes the method of continuous precipitation

at pH 8 with a Ca/P ratio of 1.67 at a standard temperature, under vigorous stirring. Then the

suspensions were matured for 24 h and the difference in the crystallinity and habit of the

particles was determined. In the non-modified SBFc/GB system the precipitate remains

amorphous with a spherical shape of the particles, while in both cases of modification poorly

crystalline apatite with particles being extended along one axis was obtained. After few

procedures of washing, gelling and lyophilization the precursors were gradually heated at a

temperature of 200, 400, 600, 800 and 1000 °C kept constant for 3 hours on each step.

The results show that the biomimetic synthesis allows precipitation of amorphous

calcium phosphate (ACP) with a Ca/P ratio of 1.4-1.5 incorporating Mg2+, Na+, K+, CO32- and

Cl- ions at levels close to those of natural enamel, dentin and bone with spherical

nanoparticles. The precipitation of ACP instead of the thermodynamically stable

hydroxyapatite reveals that kinetic factors were decisive for the precipitation processes.

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139

Influence of medium modification on the specific surface area of the obtained

precipitates was established. For the precursors precipitated in the non-modified SBFc/GB-

system it was 28 m2/g. Three to four times higher was the specific surface area of precursors

precipitated in modified reaction media - 146 m2/g and 106 m2/g for SBFc/GB-GL and

SBFc/GB-XG systems, respectively. The distribution of the pore volume corresponds to the

measured specific surface area. The obtained results are explained in terms of the shape of

the precipitated particles and the specific properties of the modifiers.

A specific effect of the two modifiers on the particle distribution by size after high-

temperature treatment was established, bi-phase ceramic powders consisting of

hydroxyapatite and β-tricalcium phosphate being obtained. In the biomimetically

unmodified medium (SBFc/GB-system) the particle size is in the range of 0.1 – 1.8 µm, 70 %

of which is between 0.4 – 1 µm with a clearly expressed maximum at 0.6 µm. Narrower

ranges of particle size variation are found in the modified reaction media (more than 90% of

the particles are with a size between 0.1 and 1.2 µm) and the maxima are shifted toward the

lower values. Most uniform by size are the particles obtained in the system SBFc/GB-XG,

where 70% of them are in the range of 0.25 - 0.55 µm with a maximum at 0.4 µm. The

particles obtained in the system SBFc/GB-GL are characterized with two distribution ranges –

40% of them are between 0.05 – 0.2 µm with a clearly expressed maximum (30%) at 0.15 µm

while about 55% are between 0.3 – 1 µm showing no maximum but a broad plateau

between 0.5 – 0.75 µm.

Acknowledgements: The authors thank the Bulgarian Ministry of Education and Science under

projects КP-06-Н49-6/2020 –“Investigation on novel hybrid modified calcium phosphates systems

with enhanced biomineralization activity” funded under the program “ Competition for financial

support of basic research projects – 2020 ” and D01-272/02.10.2020 - "European Network on

Materials for Clean Technologies", funded under the National Program "European Scientific

Networks".

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140

Topic C

CP-12

Plant-mediated synthesis of ZnO nanoparticles using

Mentha Arvensis leaves: morphology and physicochemical characterization

D. Stoyanova1, I. Stambolova1, P. Georgieva1, E. Mitkova1*, V. Dyakova2, Y. Kostova2 and

R. Mladenova3


1113 Sofia, Bulgaria 2 Institute of Metal Science, Equipment and Technologies with Hydro- and Aerodynamics

Centre “Acad. A. Balevski”, Bulgarian Academy of Sciences, 1574 Sofia, Bulgaria

3 Institute of Catalysis, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria


Keywords: green approach, pore size distribution

Zinc oxide is multifunctional material with wide scope of applications such as gas

sensors, catalysts, photocatalysts, optical devices, drug delivery etc. The green synthesis of

nanosized particles is a low cost, еco-friendly approach in comparison to the classical

chemical methods, which are aimed to limit their harmful effects on the environment.

Various plant extacts were used as an effective reduction/oxidizing agents for preparation of

ZnO particles.

In the present study, ZnO nanoparticles were prepared by precipitation of zinc acetate,

urea, and using as stabilizing/reducing agent: extract of Mentha Arvensis leaves, followed by

hydrothermal treatment at 180°C for 12 hours, (sample code BS-Zn). The resulting powder

samples were characterized by X-ray phase analysis (XRD), infrared spectroscopy (IRS),

Scanning electron microscopy (SEM) and electron Paramagnetic Resonance (EPR). The

specific surface area and pore size distribution were measured by the Brunauer-Emmett-

Taylor (BET) method. The morphology was investigated by means of Scanning electron

microscopy (SEM/ FIB LYRAI XMU, TESCAN) equipped with an EDX detector (Quantax 200,

Brücker) at 1 to 30kV. Electronic paramagnetic resonance spectra of TiO2 were recorded at

room temperature and 123 K by JEOL JES-FA 100 EPR spectrometer, operating within the X–

band with standard TE011 cylindrical resonator.

The bio-synthesized samples have a higher degree of crystallinity, compared to the

reference powder. All IR spectra show broad bands in the region of 400-550 cm-1, which are

characteristic of the formation of the Zn-O bond. The intensity of the bands within the range

of 400-1700 cm-1 for BS-Zn powders decreases with the increasing of the Mentha Arvensis

extract content. The remaining recorded bands belong to organic groups derived from the

zinc precursor, precipitator and Mentha Arvensis extract. The hydrothermal method allows

the production of ZnO particles having developed surface (S = 168 m2/ g). The application of


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141

plant extract reduces the specific surface area by about 20%. The isotherms of the samples

do not differ significantly from each other, as they belong to the type V (according to UPAC

classification). The application of leaf extract increases the relative proportion of mesopores

in BS-Zn samples. This is a favorable prerequisite for their future use as absorbents or

catalysts.

The EPR spectra of the green synthesized samples consist not only of transition metal

ions signals, but also of two additional narrow resonance lines having different intensity. The

more intensive line (approximately 4 times) is recorded at g=1.954 is associated with so-

called shallow effective mass donor center, or briefly the shallow donor (SD) center in ZnO

single crystals.

According to the SEM analyses the initial sample particles have various sizes having

platelike shape with not distinct boundaries. The thickness of the plates decreases with the

increasing of plant extract. The particles are arranged in such a way as to form cavities

between them.

Acknowledgements: The authors thank for the support of the contract “Mono-and poly-component

catalytic systems for waste water and polluted air purification from model contaminants”- is within

the Non-currency Equivalent Exchange Bilateral Cooperation between the Bulgarian Academy of

Sciences and the Serbian Academy of Sciences and Fine Art and Project Д01-272/02.10.2020 -



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Index of participants

Akbari S. S. AP-1

Aleksandrov H. AP-19

Aleksandrov L. CP-1 CP-4 CP-7 CP-8 CP-10

Andonova S. AP-1 AP-13, BP-13

Andreeva R. AP-29

Angelova T. CP-10

Atanasova G. AP-2 AP-3 AP-8 AP-18

Avdeev G. AP-11, BP-1

Avramova I. BP-1, CP-5

Bachvarova-Nedelcheva A. CP-2

Baeva A. AP-3

Barbov B. AP-4 AP-28

Blin J. L. AP-15

Borislavov L. BO-6 BO-8 BP-2 BP-11

Borrisov B. CP-3

Boshkov N. AP-24

Boshkova N. AP-24

Bouzekova-Penkova A. AP-30

Bower R. AO-4

Boyadzhieva T. BP-8

Burdina G. AP-5

Caballero A. AO-1

Chakarova K. AP-6 AP-19

Cherkezova-Zheleva Z. CP-5

Danchovski Y. BO-8 BO-10

Detcheva A. AP-7

Diaz-Cuenca Ar. CO-1

Dikovska A. Og. AP-2 AP-3 AP-8

Dilova T. AP-2 AP-3 AP-8

Dimitrov L. AP-21

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143

Dimitrov M. AP-12 BP-5

Dimov D. BP-1

Drenchev N. AP-13

Dsoke S. BO-3

Dyakova V. CP-12

Dyulgerova E. CP-6

Enchev V. AP-26

Fabián M. BO-9 BP-14

Gancheva M. CP-4 CP-7 CP-9

Gaudin P. AP-15

Gemishev O. AP-10 AP-20

Gentscheva G. AP-31

Georgieva M. AP-5

Georgieva I. AP-9 CO-3 CP-3

Georgieva N. CP-10

Georgieva P. CP-12

Gergulova R. CO-2 CP-11

Gicheva G. AP-10 AP-20

Girman V. BP-14

González-Elipe R. BO-1

Grahovski B. AP-35

Grigorova E. BP-3

Gugov I. CP-5

Gulkova D. AP-21

Hadjiivanov K. AP-1 AP-6 AP-13 AP-18 AP-19 B-O4 BP-13

Harizanova R. CP-5

Harizanova S. BP-4

Haynes P. AO-2

Henych J. BP-5

Hristova I. AP-11 AP-15

Ilieva N. BO-8 BP-2

Ilieva R. AP-16 CP-6

Iordanova R. CP-1 CP-2 CP-4 CP-7 CP-8 CP-9

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144

Issa G. AP-12 BP-5

Ivanov P. CP-4 CP-7 CP-9

Ivanov G. AP-35

Ivanova E. AP-13 AP-19 BP-13

Ivanova L. AP-7

Ivanova R. AP-12 BP-5

Jeschull F. BO-3

Jiratova K. AP-21

Kalapsazova M. BP-6 BP-10

Kaluza L. AP-21

Kalvachev Yu. AP-4 AP-28

Kamitsos E. I. BO-2

Karadaş F. AP-1

Karakirova Y. AP-27

Karashanova D. AP-23

Karcheva G. AP-4 AP-28

Kavan L. BO-9

Kersten M. AP-9

Kichev I. BP-2 BP-7

Kichukova D. AP-14

Kolev H. AP-11 AP-15 AP-27 AP-35 BP-14

Koleva V. BP-8

Kormunda M. BP-5

Koseva I. CP-1 CP-4 CP-7 CP-9

Kostadinova G. BP-9

Kostov K. L. CP-2

Kostova Y. CP-12

Kovacheva A. AP-16

Kovacheva D. AP-5 AP-12 AP-14 AP-17 AP-22 AP-23 BP-12 CO-2

Kukeva R. BP-6 CP-5

Lagunov O. AP-18 BP-13

Larin A. V. AO-3 AP-27

Larin V. A. AO-3

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145

Lischnichuk M. BP-14

Lyapchev R. BP-9

Maibach J. BO-3

Marinkov N. AP-5

Marinova D. BP-10

Markov P. BP-3 BP-6 BP-10

Mihailova I. CP-5

Mihaylov L. BO-7

Mihaylov M. AP-6 AP-13 AP-18 AP-19 B-O4 BP-13

Milanova M. CP-1 CP-8

Milenov T. BP-1

Mintcheva N. AP-10 AP-20

Mitkova E. CP-12

Mladenova R. CP-12

Naydenov A. AP-11 AP-17 AP-25 AP-27 AP-35

Nedyalkov N. N. AP-2 AP-3 AP-8

Nedyalkova M. BO-6

Nihtianova D. AP-18 BP-3

Nikolov V. CP-4 CP-7 CP-9

Nikov Ro. G. AP-3 AP-8

Nikov Ru. G. AP-2 AP-3

Palcheva R. AP-21

Panayotov D. AP-18 B-O4 BP-13

Panayotova M. AP-10 AP-20

Paneva D. AP-1 CP-5

Peneva M. CP-2

Petakova V. BP-11

Petkov P. AP-19

Petrov P. AO-4

Petrova P. AP-28 CP-4 CP-7 CP-9

Petrova T. AP-28

Porodko О. BP-14

Rabadjieva D. AP-16 CO-2 CP-6 CP-11

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Radev D. D. AP-22

Rangelova N. AP-36 CP-10

Rasheev H. BO-5 BO-8 BO-10

Rogojerov M. AP-26

Romanova J. AO-5 BO-6 BP-7 BP-9 BP-11

Rosmini C. AP-23

Rüssel C. CP-5

Rybakov, A. A. AO-3

Savov N. AP-36

Senna M. BO-9

Sezanova K. CO-2 CP-11

Shestakova P. CP-6 CP-11

Shipochka M. AP-24

Spassov T. BO-7

Spassova I. AP-1 AP-14 AP-17 AP-18 AP-34 BP-13

Stambolova I. AP-24 CP-12

Stanchovska S. AP-25

Šťastný M. BP-5

Stoyanova D. AP-24 CP-12

Stoyanova R. AP-25 BO-5 BO-8 BO-10 BP-2 BP-4 BP-6 BP-8 CP-5

Stoyanova N. AP-26

Stoychev D. AP-29

Stoycheva J. AO-5 BO-6 BP-7 BP-9 BP-11

Tadjer A. AO-5 BO-5 BO-6 BO-8 BO-10 BP-2 BP-7 BP-9 BP-11

Teodosiev D. AP-30

Tepavitcharova S. AP-16 CP-11

Todorova S. AO-3 AP-11 AP-15 AP-27 AP-28 AP-35

Todorova T. AP-4 AP-28

Tomova R. CP-4 CP-7 CP-9

Trendafilova N. CO-3

Trubnikov D. N. AO-3

Tsanev A. AP-29 AP-30

Tsoncheva T. AP-12 AP-23 BP-5

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Tsvetanova M. BP-12

Tsyntsarski B. AP-30

Tumbalev V. AP-5 AP-17 BP-12

Tunega D. AP-9

Tyuliev G. AP-21

Tzankov D. AP-5

Tzvetkov M. CP-3

Tzvetkov P. AP-30 BP-12

Tzvetkova Ch. AP-31

Uzunov I. AP-31 AP-33

Uzunova E. AP-32

Vassileva E. BO-7

Vassileva P. AP-7 AP-33

Vayssilov G. AP-19

Velikova N. AP-34

Velinov N. AP-17 AP-23

Velinova R. AP-17 AP-27 AP-35

Veselinov K. BP-10

Voykova D. AP-33

Wergifosse M. BP-9

Yaneva S. AP-36 CP-10

Zahariev Ts. AP27 CO-3 CP-3

Zdravkova V. AP-13 AP-18 AP-19 BP-13

Zhecheva E. AP-25 BP-4 BP-6 BP-10

Žukalová M. BO-9 BP-14

third workshop on size-dependent effects in materials for

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