smc bulletin vol. 2 (no.1) june 2011smcindia.org/pdf/smc bulletin_vol.2( 1)2011.pdf · smc bulletin...

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SMC Bulletin Vol. 2 (No.1) June 2011

SMC Bulletin Vol. 2 (No. 1) June 2011

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Society for Materials Chemistry was mooted in 2007 with following aims and objectives:(a) tohelptheadvancement,disseminationandapplicationoftheknowledgeinthefieldofmaterialschemistry,

(b) topromoteactiveinteractionamongallmaterialscientists,bodies,institutionsandindustriesinterestedinachievingtheadvancement,disseminationandapplicationoftheknowledgeofmaterialschemistry,

(c) to disseminate information in the field ofmaterials chemistry bypublication of bulletins, reports, newsletters,journals.

(d)toprovideacommonplatformtoyoungresearchersandactivescientistsbyarrangingseminars,lectures,workshops,conferencesoncurrentresearchtopicsintheareaofmaterialschemistry,

(e) toprovidefinancial andother assistance toneedydeserving researchers forparticipation topresent theirwork insymposia,conference,etc.

(f) toprovideanincentivebywayofcashawardstoresearchersforbestthesis,bestpaperpublishedinjournal/national/internationalconferencesfortheadvancementofmaterialschemistry,

(g) toundertakeandexecuteallotheractsasmentionedintheconstitutionofSMC.

Executive CommitteePresident Dr.T.Mukherjee BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Members Dr.P.R.VasudevaRao IndiraGandhiCentreforAtomicResearch Kalpakkam,603102(TN) [email protected]

Dr.S.K.Kulshrestha AtomicEnergyEducationSociety WesternSector,AEES-6 Anushaktinagar,Mumbai,400094 [email protected]

Dr.V.K.Jain BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.C.G.S.Pillai BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.S.R.Bharadwaj BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.ManidipaBasu BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.SandeepNigam BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Co-opted Members Dr.AparnaBanerjee BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.A.K.Tripathi BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Prof.S.D.Samant InstituteofChemicalTechnology Matunga,Mumbai-400019 [email protected]

Prof.G.P.Das IndianAssociationfortheCultivationofScience(IACS) Jadavpur,Kolkata-700032, [email protected]

Prof.AshokK.Ganguli IndianInstituteofTechnology HauzKhas,NewDelhi110016 [email protected]

Vice-Presidents Dr.D.Das BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Dr.K.Nagarajan IndiraGandhiCentreforAtomicResearch Kalpakkam,603102(TN) [email protected]

Secretary Dr.A.K.Tyagi BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

Treasurer Dr.R.K.Vatsa BhabhaAtomicResearchCentre Trombay,Mumbai,400085 [email protected]

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SMC BulletinA Publication of the Society for Materials Chemistry

Volume 2 No. 1 June 2011


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SMC Bulletin Vol. 2, No.1 June 2011

Editorial BoardDr. Arvind Kumar Tripathi

ChemistryDivisionBhabhaAtomicResearchCentreTrombay,Mumbai,400085e-mail:[email protected]

Dr. Shyamala BharadwajChemistryDivision

BhabhaAtomicResearchCentreTrombay,Mumbai,400085e-mail:[email protected]

Dr. Manidipa BasuChemistryDivision


Dr. Aparna BanerjeeProductDevelopmentDivisionBhabhaAtomicResearchCentreTrombay,Mumbai,400085e-mail:[email protected]

Dr. Sandeep NigamChemistryDivision


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Editorial Note

AfterasuccessfulreleaseoftheinauguralissueofSMCbulletinduring3rdInternationalSymposiumonMaterialsChemistry(ISMC-2010)wearehappytopresentthesecondissue,athematicone,on“Nanomaterialsandtheirapplications”.Thisissuecontainstotalsixresearcharticlesonthisthemeincludingonefeaturearticleon chemistryofnanomaterials and their applications.Thesearticlespresent synthesisofdifferentoxides,mixedoxides,metallicnanoparticles,nano-compositesinvariousshapesandsizes(sphere,nanoplateetc.)viaevaporation,polyolmethodorbyemployingreactivepolymerslikepoly(vinylidenefluoride)astemplates.Applicationsof thesematerials includevarietyof areas likewhite lightgeneration,photocatalysis, tissueengineering.

Thenextissueofthebulletinwillbeathematiconeon“Chemistryoffunctionalmaterials”.ReadersareencouragedtosendtheirfeedbackswhichwillenableustoimprovetheSMCbulletin.

Editors


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From the President’s Desk

Dear Fellow members,

TheSocietyforMaterialsChemistry(SMC)isafastgrowingnationalbodywitharound540lifemembers.Inthepast,theSocietyhassuccessfullyorganizedinternationalsymposiaonMaterialsChemistry(ISMC-2006,ISMC-2008andISMC-2010)andwearenowplanningtoorganiseaNationalWorkshoponMaterialsChemistry:FunctionalMaterials,NWMC-2011(FUN-MAT)on7thand8thDecember2011inMumbai.

Iamhappytonote that the inaugural issueof theSMCbulletinbroughtoutduring the3rdDAE-BRNSInternationalSymposiumonMateialsChemistryatBARCwaswellreceivedbyourmembers.IearnestlyrequestallmemberestocontributetowardsSMCbulletinwhichispublishingarticlesonvariousthemese.g.,presentissueisonnanomaterialsanditsapplications.Ihopethatthethemebasedissuesofourbulletinwillbequiteusefulforourmembers,particularlyfortheyoungresearchersworkingintheareaofmaterialschemistry.Iexpectthatthebulletinwillcontinuetoprovideaplatformtohighlighttheadvancesmadeinthefieldofmaterialschemistryandhopethatthememberswillcontributearticlestoenrichthegoalsofthebulletin.

T. Mukherjee

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Feature Articles Page No

1. Chemistry and applications of nanomaterials A.K. Tyagi

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2. Evaporation induced self assembly of nanoparticles by spray drying D. Sen, J. Bahadur, S. Mazumder, J.S. Melo and S.F. D’ Souza

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3. Light absorption and emission in gold nanoplates assembled in small groups via poly(vinylidene fluoride) molecules B. Susrutha, A.D. Phule and S. Ram

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4. Preparation and characterization of Collagen-based Liposome Nanoparticles composite matrix Krishnamoorthy Ganesan, Praveen Kumar Sehgal, Asit Baran Mandal and Sadulla Sayeed

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5. Application of nanophosphors in solid state white light generation Dimple P. Dutta

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6. Photocatalytic Properties of mixed oxides of BaCrO4 and TiO2 Tanmay K. Ghorai, Chirantan Roy Chaudhyry, Suman Biswas, Mukut Chakraborty, Ranjan Das, Jhimli Sengupta

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News and Forthcoming Events 48

Honours and Awards 49

CONTENTS


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IntroductionNanoparticlesaresmallclustersofatomsabout1 to

100nanometerslong.‘Nano’derivesfromtheGreekword“nanos”,whichmeansdwarforextremelysmall.Essentially,thereasonisthatnanocrystalsinthe1to10nmrangemakeupanewrealmofmatterinwhichphysicalandchemicalpropertieschangeassizechanges.Contemplatingthatanynanostructuredsolidmaterialcanhavevariablepropertiesbasedonsizeessentiallymakes theperiodic tableof theelements“threedimensional”.Thepropertiesthatchangeinthenanoregimeincludebandgaps(forsemiconductors),magneticmoments (for ferro- ferrimagnetisms), specificheats,meltingpoints,surfacechemistry,andmorphology/particleshape.Forconsolidatednanoparticles,metalpiecescanbeharder,andceramicpiecescanbemoreplasticthannormalmaterialsmade frommicrocrystal-polycrystalconsolidation.Metaloxidenanoparticlesareanimportantclassofmaterialsfortheiroptical,magneticandelectronicproperties [1,2]. Thesepropertiesmakenanostructuredmetaloxidesusefulforawiderangeofapplicationssuchascatalysts,sensors,opticalmaterials,electricalmaterialsandmagneticstorages[3].Hence,overthepasthalf-decade,research in functional oxide-basednanostructures hasattractedconsiderableattentiondue to theiruniqueandinnovativeapplicationsinoptics,optoelectronics,catalysis,ferroandpiezoelectricity.

Chemistry and Applications of Nanomaterials

A. K. Tyagi Chemistry Division,

Bhabha Atomic Research Centre Mumbai- 400 085, India

E-mail: [email protected]

AbstractTheworldofsciencehaswitnessedatremendousupsurgeinthefieldofnanoscienceandnanotechnologyinthelastfewyears.Theterm‘Nano’hasnowbecomeathemeinalmostalltheestablisheddisciplinesofscience.Someofthebroadfieldslikeseparationscience,catalysis,energyconversion,nano-ceramics,biologicalformulations,coatings,bio-imagingandsemiconductorsetc.havewitnessedrevolutionarychangesaftertheadventofnanoscienceandnanotechnology.NanomaterialsarelikelytoplayanimportantroleinDepartmentofAtomicEnergy’sprogrammesalsorangingfromfrontendtobackendofthenuclearfuelcycle,Therecoveryofvaluablefromnuclearwasteanddesignofnewsorbentsforradio-isotopesforhealthapplications,justtonameafew.Thisarticleisintendedtogiveabroadoverviewofchemistryandwiderangeofapplicationsofnanomaterials.

Key-words: Soft-Chemical routes, opticalmaterials,magneticmaterials, energy conversionmaterials,sensors.

Synthesis methodsThe synthesis and characterizationofnanoparticles,

nano-tubesandothernano-unitsatalengthscaleofabout1-100nm(atleastinonedirection)isasubjectofintenseresearch.Inthisdirection,materialchemistsplayacrucialroleinthepreparation,structuralelucidationandpropertymeasurements of thematerials,which are importantingredients in thediscovery and commercialization ofnanotechnologies anddevices. Thematerials synthesismethodscanbeclassifiedintotwobroadcategoriesnamely(i)Solidstatemethodand(ii)Soft-chemicalmethods.Thelatterclassesofmethodsarebasicallylowenergysynthesismethodswhichareoftenusedunderambientorslightlyabove ambient conditions.Of late, the soft-chemicalmethodssuchascombustionsynthesis,metalnanocrystalsbyreduction,templatemethod,coprecipitation,arrestedprecipitation,radiationassistedsynthesis,polyolmethod,sono-chemical,micellermethods,impregnation,microwaveassistedsynthesis,hydro&solvothermalmethods,xero-gelmethodand solid statemetathesis etc. havegainedtremendousmomentum.Bythesemethodsitispossibletohaveanexcellentcontrolonshapeandsizeofnanomaterials.Thereisyetanothercategoryofsynthesisofnanomaterials,whichisprimarilybio-inspired.Naturemakesmostofthematerialsatambientorslightlyaboveambientconditions.


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Asfarasthinfilmsofareconcerned,inadditiontoenergyand cost intensive Physical VaporDeposition (PVD)techniques,chemicalmethodslikeink-jetprinting,screenprintingandspincoatinghavealsobecomeprominenttopreparethinfilmsoffunctionalnanomaterials.

Some of the soft-chemical synthesismethods fornanomaterialsarebrieflydescribedinthenextsection:

Sol gel synthesisThesol-gelprocess[5]isalowtemperatureapproach

forsynthesizingvariousoxidematerials.Asolisacolloidalsuspensionof solidparticles ina liquidwhereas thegelis a solidwhosepore contains liquids. It is generally atwostepprocesswhichinvolveshydrolysisofprecursorsfollowedbytheircondensationtoformoxideframeworks.Productpropertiesareaffectedbytherateofhydrolysisandcondensation.Generally,slowerandcontrolledhydrolysisleadstosmallerparticlesizes.Poresize,distribution,andinterconnectivity are also affected by other processingparameters,suchasthetypeandamountofsolventand/orcatalyst,temperature.Thislowtemperaturesoftchemicalmethod is safe, inexpensiveandcangivenanomaterialswithcomplexshapes.

Template synthesisTemplatemethodinvolvesthefabricationofthedesired

materialwithin thepores or channels of ananoporoustemplate [6]. Ingeneral,a templatemaybedefinedasacentral structurewithinwhichanetwork forms in suchawaythatremovalofthetemplatecreatesafilledcavitywithmorphological and/or stereochemical featuresrelated to those of the template. Templates can be ofseveraltypes’e.g.hardtemplates,softtemplatesandsoft-hardtemplates.Someoftheexamplesofhardtemplatesare orderedmesoporous siliceousmaterials, track-etchmembranes,porousaluminaetc.Thetypicalexamplesofsoft templatesare surfactants, colloidalparticles, shape-directingmolecules, soapbubblesandcolloids. Someofthepolycarbonatesareneither too-hardnot too-softandhencetheyformyetanotherclassoftemplatesnamelysoft-hardtemplates.Itisimportanttonotethatnearlyallthematerialscanbesynthesizedwithinnanoporoustemplates,providedasuitablechemicalpathwaycanbedeveloped.One canachieveanexcellent shape controlby templatemethod.Thereareessentiallyfiverepresentativestrategiesto carryout template synthesisofnanostructures.Theyare electrochemicaldeposition, electrodelessdeposition,chemicalpolymerization,solgeldepositionandchemicalvapordepositiontechniques.

Sonochemical synthesisUltrasound has become an important tool for the

synthesisofnanoparticles[7,8].Whenliquidsareirradiatedwithultrasonicirradiation,ultrasoniccavitationwillform.Ultrasonic cavitation is concernedwith the formation,growth,andimplosivecollapseofbubbles.Inherentlythe

Fig. 1: Two broad synthesis methods of nano materials

Gel-Combustion synthesisItisafacilesynthesistechnique[4]whichcanbeeasily

employedonalab-scaletopreparenano-crystallineceramicpowderswithreproduciblecharacteristics.Combustionisbasicallya redoxreactionbetween theoxidantand fuel,whichiscontrolledbyvariousfactorssuchasnatureandamount of fuel. First thenitrate/oxynitrate salts of themetals, in a requiredmolar ratio, aremixed together inanaqueousmediatoproduceatransparentmixedmetal-nitratesolution.Asuitablefuel(glycine,citricacid,ureaetc.)isthenaddedinanappropriateamounttothissolution.Theaqueoussolutionoffuelandoxidantsissubsequentlythermallydehydratedonahotplate(atabout80-100°C)oramufflefurnacetoobtainaviscousgel.Thegel,asformedintheabovestep,isfurtherheatedatahighertemperature(200-250°C)whichinitiatesaself-propagatingcombustion.Theexothermicdecompositionofthefuel-oxidantprecursorisvisibleintheformofflame,whichrapidlypropagatesthroughoutthegel.Therefore,thisstepisalsotermedas“auto-ignition”.The auto-ignition is a very short-livedphenomenonastheflamepersistsforonlyaboutfew(5-10)seconds.It iswithinthisshortdurationthattheproductformationtakesplace.

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cavitationbubbles arevacuumbubbles.Thevacuum iscreatedbyafastmovingsurfaceononesideandaninertliquidontheother.Theresultingpressuredifferencesservetoovercomethecohesionandadhesionforceswithintheliquid.Ultrasoniccavitationproducesavarietyofphysicalandchemicaleffects,suchashightemperature(>5000K),pressure (>20MPa), andcooling rate (>1010 Ks-1), which couldprovideauniqueenvironmentforchemicalreactionsunder extreme conditions. The sonochemical effectsobservedinchemicalreactionsandprocessescaninvolveincrease in reaction speed, increase in reactionoutput,more efficient energyusage, sonochemicalmethods forswitchingof reactionpathway, activationofmetals andsolids,improvementofparticlesynthesisandalsocoatingofnanoparticles.Thetemperatureplaysanimportantroleinsonochemicalreactions.

Nano-metals by reduction processA large number ofmetals and their alloys can be

prepared in nanoform by a facile chemical reductionmethod [9]. Theprerequisite of thismethod is awatersolublemetal salt,which can be reduced by using avarietyofreducingagents,suchasborohydride,alcoholsandhydrazineetc.,toobtainthecorrespondingmetaloralloysinnanocrystallinestate.Thecommonmetalswhichhavebeenpreparedbythismethodarenoblemetals,Cu,Co,Ni,Auetc.Itisalsopossibletomodifythesurfaceofthesenanometalsduringthecourseofreductionitself.Forexample,PVPcoatedPd,Ag,AuandCunanocrystalscanbeprepared[10]byrefluxingthecorrespondingmetalsaltsandethylalcohol(reducingagent)inthepresenceofPVP.Thebasicreactionincaseoftheborohydridereductionishydrolysisofborohydridetogeneratehydrogen,whichinturnreducesthemetalions.Inidealcases,itisalsopossibletopreparealloysandintermetallics,suchasFePt,FePdetc.,bythismethod.

Radiation-induced synthesis of semiconductor nanomaterials

The radiation-induced synthesis of nanomaterialslikemetallic and semiconductor is very effective andpowerfulmethod.Unlike in the chemicalmethods, theusageofhightemperature,inertatmosphereandseveralchemicalreagentsisavoidedinthismethodofsynthesis.Thesynthesisismainlycarriedoutbythesolvatedelectronsgenerateduponinteractionofhighenergyradiationswithsolvents.Inthecaseofwaterasthesolvent,thesearecalledashydratedelectrons.Thesehydratedelectronsarehighly

reactive species and reactwith the positively chargedmetalionsaswellasotherprecursorsionspresentintheaqueoussolutions.Synthesisofseveralmetalnanoparticlesofsilver,gold,nickeletc.andsemiconductornanoparticlesof cadmium sulfide, cadmium selenide, zinc oxide etc.through the radiation-induced route in neat aqueoussolutionsaswellas in thepresenceofdifferent cappingagentsorpolymerscanbeachieved.Inthiscase,thereactionmixturedoesnothavetoomanychemicalreagentswhichotherwiseneedtoberemovedifitisrequired.Furthermore,theshapeandsizeofthenanomaterialsarecontrolledbytheabsorbeddose,doserate,precursorconcentrationsandtheproperchoiceofamicroenvironment.Thesereactionsareperformedbybothcobalt-60gamma irradiationandelectronbeam irradiation in an electronaccelerator likelinearelectronaccelerator,LINAC.

Atypicalexampleissynthesis[11]ofcadmiumselenide,CdSe quantumdots in aqueous solutions containingequimolar ammoniated cadmium sulfate and sodiumselenosulfatebygammaandelectronbeamirradiations.Theas-grownCdSequantumdotsexistinagglomeratedformandexhibitferromagneticbehavioratroomtemperature(RTFM).TheRTFMwasabout30%higherinthecaseofCdSesynthesizedbyelectronbeamirradiationascomparedto that in thecaseofgammairradiation.CdSequantumdotssynthesizedviaelectronbeamirradiationwerefoundtobedecomposeduponexposure toairand lightwhentheyarepresent inaqueous solutions.ThedecomposedsolutionsagainproducedCdSequantumdotsuponelectronbeamirradiationsandthiscyclewasrepeatedforseveraltimes.However,thesenanomaterialsarequitestablewhendispersedinorganicsolventsandremovedfromwater.TheCdSequantumdotssynthesizedinCTABmicroemulsionsexhibitstrongphotoluminescencewithanemissionpeakat 600nmat room temperature. Itwas confirmed thatthe formationofCdSenanomaterialsproceeds throughthe reactionsofhydrated electronswithboth cadmiumandselenosulfate ions,with the formationofa transientintermediate specieshavinganabsorptionmaximumat520nm.

Thin films of nanomaterials by chemical methodsInkjetprinting technology is a simple and lowcost

methodwhichhasrecentlybecomeanattractivetechniqueofpatterningandprintingofthinfilmsofsemiconductors,conductivepolymersandorganicLEDs,electroniccircuitsand bio-nanoparticles at ambient conditions [12]. Itsversatility todeliver smallvolumesof inkswith spatial


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accuracy and direct-writing ability in a non-contactdepositionmodemakes it anovelpatterning technique.Nevertheless, reports of inkjet printing of inorganicmaterialsareinscarce.Onlyahandfulofinorganicmaterialshavebeenink-jetprinted,mainlyduetothedifficultyinsynthesizingprintableinorganicinks.Fewinkjetprintedmicrostructures of oxides, nanoparticles andpolymers,usingdispersionshavebeen recently reported [13].Theformulationofprintablesulfidebased(ZnSanddopedZnS)quantumdotsdispersionsinwater[14]havebeenreported.Dispersedparticlescanoftencauseagglomeration,whichcausecloggingof theprinthead.Thiscloggingproblemcanbeovercomebyformulatingsolventbasedprecursorinks,whichformcrystallinenanoparticlesonthesubstrateafterprintingandannealing.Recentlyfabricationofinkjetprintedfilmsandpatterns (dots, lines and junctions)ofZnOandZn0.98Mn0.02OonSiandpolyimidesubstrateswasreported [15]using theirprecursor based solvent inks,thathavebeenfinetunedtomatchthedesiredviscosity,surfacetensionandadhesivepropertybyaddingsuitableadditives.ItwasfoundbyAtomicForceMicroscopythatthesurfacemorphologyofthesethinfilmswassmootherthanthatofZnObasedfilmspreparedbyothercostintensivemethod.Typicalschemeshowingprinting,processingandpatterningofZnObasedinkisgivenbelow(Fig.2).

Bio-inspired synthesis of metal nanoparticles Nature synthesizes nanoparticles in amost energy

efficientway thatmakesuseofnohazardous chemicals

thisapproach,researchersfromallovertheworldstartedsynthesizingnanoparticlesusingextractfromplantsandmicroorganisms.Thesemethodsinvolvingawidevarietyofbiologicalprocessesprovidegreatcontroloverkineticsofthenano-particleproductionthatoftenresultsinexoticmorphologiesanduniqueopticalandelectronicproperties.Metalnanoparticlessynthesizedviabiologicalroutealsoexhibitexcellentmicrobialproperties.Organismsrangingfrombacteriatofungiandevenplantshavebeenusedtosynthesizenanoparticles.Extract fromplantpathogenicfungus FusariumOxysporum has been used for thesynthesisofAu,Ag,Au-Agalloy,SiO2,TiO2,ZrO2, Fe3O4, CdSandBaTiO3nanoparticles[16].Cell-freeextractfromT.asperellum,anon-pathogenic,commercialbio-controlagentwas used for the synthesis of variety of nano-materialsincludingsilvernanoparticles[17]LemongrassandAloeveraextracts[18]havebeenusedtosynthesizegoldnanoprismsthatexhibitanisotropicelectrontransportbehavior.Palladiumnanoparticlesweresynthesizedusingsulfatereducingbacteria[19].DNA,proteinsandviruswerealsousedtoproducenanoparticles,nanowiresetc.[20].Inbrief,bio-inspiredsynthesisofnanoparticleshasledtotheexploitationofasimplebutaltogethernewareaofresearchthatwashithertolargelyunexplored.

Applications of Nanomaterials The broad areas in which nanomaterials have

potentialtoanimpactare(a).Energy(b).Environment(c)Biomedicaland(d)Engineering.Someoftheapplicationsaresummarizedbriefly.

Nanomaterials for energy conversion applicationsNanomaterialshaveimmenseapplicationsinenergy

conversiondevices such as FuelCells (SOFC), oxygenstoragecapacitors,Li ionbatteries,hydrogengenerationandstorage,andwavelengthshifters (opticalmaterials).There isagrowingneed todevelopbetter soft chemicalsynthesis routes as the conventional solid statemethodhas several limitations.Among the available chemicalroutes,thecombustiontechniqueiscapableofproducingthe nanocrystalline powders of the oxide ceramics atlowercalcinationtemperature.Awiderangeofmaterialsfor SOFCapplicationshavebeen synthesized. In SOFCtechnology,theelectrolyteandinterconnectmaterialsneedtobehavenear theoreticaldensitieswhereasanodeandcathodematerialsneedahighdegreeofporosity.Theseopposite requirementsposea challenge to the syntheticandprocessingscientists.Sof-chemicalrouteshaveplayed

Fig. 2: Scheme representing the Ink-jet printing of functional materials

and/or any high-boiling solvents, typically employedin large-scale industrial production of the same. Forexample,magnetotatic bacteria synthesizewell-alignedmagnetic nanoparticleswithin their cells. Inspired by

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inimportantroleincircumventingsomeofthematerialsproblemsofSOFCtechnology.SeveralSOFCmaterialssuchasGdandSmdopedceria,Zr0.8Ce0.2O2,YSZ,CeO2-Y2O3 solid solution,La1-xMxCrO3(M=Ca,Sr),Sr-dopedLaCoO3 and dopedLaGaO3havebeenpreparedbycombustionmethod[21-23]. Thepowderpropertiesweretailoredtoachieveneartheoreticaldensitysinteredpellets.Amajoremphasiswasontheoptimizationoftheprocessingparameterssoas togetahighlysinteractivephasepurematerials.Thesizeandnatureofagglomerationwasfoundtobeacrucialparameteraffectingthesinterability.Thedesiredextentofporosityincathodeandanodematerialswasintroducedbyusingpore-formerslikegraphiteorstarch.Theshapeofporeswasfoundtocruciallydependonpowderpropertiesoftheporeformers.

Anotherkey issueofSOFCtechnologyis thedesignof better ionic conductors. It iswell known that ionicconductivityisahighlystructure-drivenproperty.Severalnew ionic conductors, suchNd2-xGd2Zr2O7 and Ba2In2-

xTixO5+x/2wereprepared[24]basedonthestructure-propertycorrelation.DetailedXRDandRamanspectroscopystudiesrevealed that anoptimumdegreeofdisorder enhancesthe ionic conductivity.Recently, a two steps synthesiswasdevelopedinvolvingacombustionreactionfollowedbya reduction step,whichwasused toprepare [25-28]of anumberpotential oxygen storagematerials suchasCe2Zr2O7+x,Gd2-xCexZr2O7 (x = 0.0 to 2.0), Ce0.5Sc0.5O1.75 and interestingmagneticmaterials likeLa1-xCexCrO3 in nanocrystalline form.All compounds in La1-xCexCrO3

serieswerefoundtobepredominantlyantiferromagneticin naturewith a remarkable linear increasing trend inNeeltemperature(TN)from257Kto281.5Kasafunctionof decreasingCe3+content. Interestingly, the band-gapalsoshowsalineardecreasefrom3.21eVto3.02eVasafunctionofincreasingCe3+concentrationintheLa1-xCexCrO3 series.ItwasfoundthatonoxidationCe2Zr2O7transformstoCe2Zr2O8viaan intermediate latticeatCe2Zr2O7.5.Theretentionofcubicpyrochloretypearrangementsisobservedevenup to the fully oxidizedCe2Zr2O8 composition.AcompleteoxidationofCe3+toCe4+isobservedincontrasttokinetically/stericallyhinderedoxidationproposedbyotherresearchers.Thedeepcrystallographicinsights[29]associatedwiththeoxygenintercalationanddeintercalationprocessinCe2O3/CeO2-ZrO2willhaveimmenseimportancein thedevelopment andunderstandingofnewoxygenstorage capacitors (OSC).Likewise, the ease of oxygenintercalationanddeintercalationprocessinGd2-xCexZr2O7+x

without any collapse of the structure empowers thesematerialswithvariouspropertieslikeOSC.

Biomedical applications Nanostructuredmaterialswithwelldefinedparticle

size,morphology,microstructureandsurfacecharacteristicsarecurrentlyofferinggreatpromiseassupportsinalargenumberofbiotechnological,pharmaceuticalandmedicalapplications suchasdiagnostics (assays), bioseparation,NMR imaging, cosmetics and drug delivery systems[30]. Inviewof this, a large amount ofworkhas beendone inChemistryDivision, BARC to the design andpreparationofnanomaterialswithappropriatepropertiesfor interactingwithbiologically activemacromolecules.Stable immobilization of one of the assay reagents(biomolecules) on a suitable substratewith completeretention of their biological recognitionproperties is acrucial step indeveloping efficient biosensors.Amine/iminefunctionalgroupsofpolyanilinemodifiedsurfaceshave shown improvedbindingof triiodothyronine (T3) antibodiesonpolystyrene surface that canbeusedas asubstrateforthedetectionofhumanthyroidhormoneinnanograms/mllevelusingradioimmunoassay(RIA)[31].Metalnanoparticlessuchasgoldandsilverexhibitanintense colorinthevisibleregionduetothewell-knownsurfaceplasmonabsorption.Ithasbeenshowninliterature[32]thattriangularsilvernanoprismscanbeusedtodetectproteinsbymonitoring shifts in their surfaceplasmon resonanceafterbindingof targetproteins. Silvernanoparticles aregeneratedonsurfacesusingnanospherelithography,andthenbiotinisimmobilizedonthesurfacesoftheparticles.The shift in the surfaceplasmon resonanceof the silvertrianglesbytheadditionofstreptavidinallowsdetectionofstreptavidinatconcentrationsaslowas~0.1-1pM.Theformation of particulate systemswithdefinedparticlesize and shape is of eminent interest indrugdeliveryapplications,aswell.ThepHsensitivehydrogelscanbedesignedtorespondtospecificchemicaltriggers,suchasglucoseforcontrolledreleaseofinsulinindiabeticpatients.Selfassembledstimuli responsivehydrogels canalsobepreparedfromworm-likemicellesusingsurfactantsandotherpH-sensitivemoieties.Amongthedifferentpolymer-baseddrugdeliverysystems,polymericmicellesrepresentapromisingdeliveryvehicleespeciallyintendedforpoorlywater-solublepharmaceuticalactiveingredientsinordertoimprovetheiroralbioavailability.Polymericmicelleshavebeenstudiedextensivelyasdeliveryvehiclesforinjectabledrugformulationsofpoorlywater-solubledrugssuchas


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paclitaxel,indomethacin,amphotericinB,adriamycin,anddihydrotestosterone.Overall, theyproved to behighlyeffectivedrugdeliveryvehicles.Thedoxorubcin loadedmixedmicelleswere evaluated for invitro cytotoxicityagainstvariouscancercelllinestoestablishtheirpotentialinimprovingdeliveryofthedrug.Attemptshavealsobeenmadetousedendrimersinthetargeteddeliveryofdrugsandothertherapeuticagents.Dendrimershavebeenusedascoatingagentstoprotectordeliverdrugstospecificsitesinthebodyorastime-releasevehicles.

Research on rare-earthnano-fluorides has been anintenseareaof investigations in last fewyears from thepoint of viewoftheirapplicationsasphosphorsforsolidstate lighting.Theyhavedistinct advantages comparedtoothermaterialsbecauseoftheiroutstandingpropertiessuchasverylowphononfrequencies,highthermalstabilityandsometimestunablecrystalphasesandrelatedphotophysicalproperties.Rareearthfluoridecompoundscanbesynthesizedbywetchemicalrouteslikethehydrothermalmethod,microwave irradiation, sonication and alsobyemploying ionic liquids.Polyolmediated synthesis is asimpleonepot synthesis forobtainingnano-fluoridesatlowtemperature.Inthismethod,theprecursors(generallynitrates)arerefluxedinapolyol(ethyleneglycol,glyceroletc.) in thepresenceofafluorinatingagent (NaF,NH4F, KBF4 etc.) for 2-3hours.Theproduct thusobtainedhasuniformsizedistributionandtheresultingnonopowdersarereadilydispersibleinpolarsolventslikemethanolandwater.Rareearthnanofluorides(YF3,CeF3andGdF3)wereexploredaspotentialphosphorsforultra-violetbasedlightemittingdiodesforsolidstatelighting.Preliminarystudiesonhumanbreastcancercellshaveshowngooduptakeofthesenanoparticlesbycarcinomacells(MCF-7),whichgivebrightcolorscorrespondingtothatofnanoparticlesafterbeingilluminatedwithUVlight.

Magnetic nanoparticles (MN) are used inmanyapplications such as data storage/recordingmedium,catalysis,magnetic resonance imaging as a contrastagent and targeted drug delivery in cancer therapy.Biocompatibility,sizeandmagneticpropertiesmakeFe3O4nanoparticlesprimarycandidatesofchoicefornumerousbiomedical applications such as drug delivery, cellseparation, immunoassay,magnetic resonance imaging,contrast enhancement, tissue repair andhyperthermia.Followingadministration, thesenanoparticles couldgettransferred through blood stream to desired areas oftreatment. WaterdispersibleFe3O4nanoparticles (coated

withPolyVinylPyrolidone(PVP)andPolyoxyethylene25-propyleneglycolstearate(POES)andcomplexedwithDoxorubicinhasbeenprepared[33]andcharacterizedusingX-raydiffraction(XRD),transmissionelectronmicroscopy(TEM)andvibrating samplemagnetometer (VSM).Theantitumoractivityof theseparticleshasbeenstudiedbytargetingthecomplextothetumorsite,usinganexternallyappliedmagneticfield, after oral administrationof themagneticnanoparticle-drugcomplexes.Ourresultsrevealthat the chemotherapy effect ofDoxorubicin could beconsiderablyenhancedbycombinationoftheapplicationofthedrugconjugated-magneticFe3O4nanoparticles,whicharebiocompatibleandstable,andtargeteddrugdeliverywithamagnet.

Magnetic nanoparticles (MN) smaller than 20 nmsize aremoreuseful in cancer therapybecauseof theirhigheffectivesurfaceareaforeasyattachmentofligandsandbetter tissuediffusion.MNcanproduceheatunderACmagneticfield,which is required forhyperthermiatemperature(42-44°C).Sourcesofheat-generationofMNarefromhysteresisloss,eddycurrent,Brownianrotationallossandspinrelaxation.WhenMNhavehighresistance,contributionfromeddycurrentisnegligible.Sometimes,particlesbecomesnon-ferromagnetic (i. e. coercivity,Hc iszero)astheparticlesizebecomeslessthancriticalsize(singledomain),butindividualparticleshavelargemoment(103-105 µB). In such situation, particles are consideredassuperparamagnetic.Iftheparticlesizeissmallerthansingledomain, heat generation fromhysteresis loop isalmostnegligible, and thus,main contribution toheat-generationwillbefromBrownianrotationallossandspinrelaxationunderACinductionmagneticfield.Inordertogetthefastorhighheatgenerationandalsoimportantincancertherapy,theparticlesizeofmagneticnanoparticlesshouldnotbetoosmall.Otherwise,moreparticles,moredurationofheat-treatment andhighAC frequencywillbenecessarytoachievehyperthermiatemperature(42-45°C).Particularly,Fe3O4anditsderivativecompoundsareimportant in hyperthermia application. The increasingattention to these Fe3O4nanoparticlesforvariousbiomedicalapplicationsareduetotheirbiocompatibility,injectibility,chemical stability over physiological circumferenceand substantial accumulationat thediseased site.Thus,monodispersedFe3O4nanoparticleswithsizeof8-11nmaredesirable.Everysamplewithdifferentparticlesizecanhavespecificabsorptionrate(SAR)inACmagneticfieldandthisinformationwillhelpinamountofheatgenerationfrom1

7


mgofsample.RecentlyatChemistryDivision,BARCFe3O4 andCo,NidopedFe3-xO4nanoparticleswerepreparedbyco-precipitationmethod.Inordertofunctionalizesurfaceofparticle,particlesare cappedwithPEG (polyethyleneglycol)andOA(oleicacid)soastominimizeagglomerationamongsmallermagneticparticles.About2-5mgofFe3O4 (pure)canreachhyperthermiatemperaturewithin5-10minat256kHzand400-600A.HeatingabilityofMNcappedwithOAorPEGupto42°Cwasobservedatreasonablylowconcentration(10mg)suggestingtheirsuitabilityforhyperthermiaapplications.TheefficacyofcappedMNwasfurthervalidated[34]inhumanbreastcancercellswiththeirenhancedkillingabilityunderinductionheatingconditionssuggestingtoextendthesestudiesforhyperthermiccancertherapyinsuitableinvivoexperimentalmodels.Controlreleaseofanticancerdrugattumorsiteisimportantinordertoreduceside-effecttoothernormalcellswhiledelivery/injectingtobloodvessels.

Nanomaterials in catalysisThe structure sensitive catalyticpropertiesof small-

sizeparticles are relevant forbothmetal andnon-metalcatalyst surfaces. In addition,due to the changes in theelectrondensity as a functionofparticle size, there is adisparityinchemicalpropertiesalso,therebyresultingindifferentbindingmodesoftheadsorbatemoleculesthanthatobservedinthecaseofcorrespondingbulkmaterials.Effectively,forthesupportedcatalysts,thechemisorptionpropertiesaregenerallyguidedbytheelectronicinteractionbetween the nano-dispersedmetal crystallites and thesupportmatrix.Theseaspectsareimmenselyimportantforthesemiconductor-assistedphotocatalyticprocesses.ThealterationintheparticlesizeinthecaseofnanocrystallineTiO2photocatalysts leads to changes in the transfer andthe recombination rate of surface charge carriers (e− orh+)are,therebyresultinginimprovedquantumyields.AconsiderableworkisgoingoninChemistryDivision,BARConapplicationofdesignednanomaterials in thefieldofcatalysisforvariousapplicationssuchaswatersplittingforhydrogengeneration,volatileorganiccompounds(VOC)degradation,oxidationofCOandNH3etc.Photocatalyticoxidationof thevolatileorganic compounds,under theambientconditionsbythephotocatalystssuchasTiO2 and TiO2-dispersedinthehostmatrixofMCM-41dopedTiO2, andTiO2dispersedonclothhavebeeninvestigated[35-38].Thestructure-activitycorrelationiselucidated,withfactorslikeparticlesizeeffect,effectinthechangeofthebandgap,effectoftheoxidationstatefortheeffectivechangeinthe

photo-oxidationpropertyofthecatalysts.ThehostmatrixofMCM-41wassynthesizedandtheTiO2wasimpregnatedinitbytheincipientwetimpregnationtechnique,whichleadtoformationofdifferentparticlesizeoftheguestmoleculesasafunctionofloadinginthehostmatrix.TheoxidationofmethanolwasstudiedasafunctionofdifferentparticlesizeoftheTiO2nanoparticlesinMCM-41matrix,itwasfoundthatasafunctionofsizetheactivitydecreasedfortheTiO2 nanoparticles.ThereactionmechanismfortheoxidationofthemethanolundertheseconditionswasillustratedbytheinsituFT-IRtechnique,whichshowedthatthereweredifferentspeciesproducedinthebulkTiO2andpristinehostMCM-41.IncaseofTiO2dispersedintheMCM-41therewasacombinedeffectofthesetwosystems(host-guest).Therewasanincreaseinthebandgapasafunctionofthevanadiumdoping in theTiO2 system.Theoxidationofethyleneunderambientconditionswasstudied,whichleadtotheconclusionthatnotonlythechangeinthebandgapisrequiredbutalsotheoxidationstateofthevanadiumalsoplaysaveryimportantrole.HighertheamountoftheV5+ loweristhephotocatalyticactivityofthesecatalysts.

Nanomaterials in separation science Separation processes oftenmake use of one or

combinationof processes likeprecipitation,membranefiltration, ion exchange, and adsorption. However,adsorptionusingsimpleandcheapadsorbentsisgaininglotofimportanceduetoitseconomicbenefitsaswellaseasyavailabilityofdifferentkindsofadsorbents.Hencetheresearchindevelopingnewadsorbentscanbefocusedonthedevelopmentofsimpleandeconomicproceduresforthesynthesisofthesorbentsoronthedevelopmentofmethodsforthereusabilityofthesesorbents.Activatedhighsurfaceareacarbonisthe“goldstandard”insorbenttechnology.Thereare,manyothersolidsthatserveashighsurfacearea(highcapacity)sorbents.Thishasbecomeespeciallythecaseinrecentyearswhennewsyntheticmethodshaveallowednanoscalemetal oxides likemagnesiumoxide (MgO),calciumoxide (CaO), titaniumoxide (TiO2), aluminumoxide(Al2O3),ironoxide(Fe2O3),andzincoxide(ZnO)tobeprepared.Theseoxidesinhighsurfaceareaform,andtheirphysicalmixturesand intimate (molecularornanoscale)mixtureshaveproven tobeexcellent sorbents formanyapplications.Toxicspeciessuchasheavymetalionsandfluorideionsetchasreceivedmuchattention.TheWorldHealthOrganization(WHO)hasspecifiedthetolerancelimitforfluoridecontentindrinkingwateras1.5mgL-1.Thepresenceofheavymetalsintheenvironmentisaserious


8

global, social, and environmental problem and everypossiblecareshouldbetakentokeepthemisolatedfromgettingmixedintoair,water,andsoil.BasedonitstoxicitytheUSEnvironmentalProtectionAgency(EPA)hassetthemaximumpermissiblelimitforleadionsindrinkingwateras0.05mgL−1andtheBureauofIndianStandardsas0.1mgL−1.Theselimitssuggestmorestringentrequirementfortheremovalofleadfromaqueousenvironment,whichnecessitated the development of innovative and cost-effectivetreatmentmethodsfortheeffluentscontainingtheionsbeforedischargingintonaturalwaterbodies.Theuseofnanocrystallinecompoundsassimpleadsorbentsappearedasagoodalternative.Likewise,defluoridationofwater is another important societal need.An oxideMg0.8Al0.2O1.1was prepared by combustionmethod anaveragecrystallitesizeof8nm.Itwasfound[39]tobeanexcellentadsorbentforuptakeoffluorideanionofupto120mgL-1concentrationwithauptakecapcityof10mg F- /g. Nanosizepure andmixedmetal oxides likenanocrystalline cobalt ferrite andMnO2 showed good uptake capacity for lead ion. Titania-silica (TiO2/SiO2) binarymixedoxidewasalsofoundtobeagoodsorbentfor lead ions.AnovelhybridadsorbentHMO-001wasfabricatedbyimpregnatingnanosizedhydrousmanganesedioxide(HMO)ontoaporouspolystyrenecationexchangerresinforenhancedremovalofCd(II)andZn(II)ionsfromwaters.Thenano-hydroxyapatiteparticles(nHAp)hadasorptioncapacityof1.17mmol/gofPb

Nanomaterials in DAENanomaterialsarebeingcontemplatedtoplayarole

inDepartmentofAtomicEnergy (DAE) also.Themostimportantapplicationofthesematerialsisinseparationandrecoveryofvaluableradio-isotopesfromthenuclearwastestream.Thepreparationofsinter-activethoriabasedfuelsisanotherprospectiveapplicationofnanomaterialsinDAE.EventargetsmaterialsforincorporatingminoractinidesfortheirtransmutationusingAcceleratorDrivensub-criticalSystems(ADSS)needtobehighlysintered.Someof theproposedhost lattices, likepyrochlores andzircon etc.,aredifficult to sinter tonear theoreticaldensities.Herealso,softchemicalroutes,leadingtosinter-activepowders,areexpectedtoplayanimportantrole.Likewise,carbonbasedmaterialsinthinfilmsformsaregoingtobeusedinCompactHighTemperatureReactors(CHTR).SynthesisofLi2TiO3isyetanotherexamplewheresoft-chemicalmethodsarecrucialasthereisaLi-lossifthiscompoundispreparedbyahightemperatureceramicroute.

However,inthisarticleIwillmainlydiscussaboutthenanomaterials towards radio-nuclides applications.Themostimportantcomponentofthecolumnchromatographicradionuclide generator system is the sorbentmatrix.OwingtothedifferenceintheirKdvalues,theparentanddaughter radionuclideshavedifferent retentionaffinitytowards the sorbent and can thus be easily separated.Aparticular sorbent for its application in radionuclidegeneratorsshouldhavecertaindesiredpropertiessuchas;a)Granularity and freeflowcharacteristics, b) Sorptioncapacity for the parent radioisotope, c) Selectivity ofsorptionandelution,d)Radiationandchemicalstabilityof the sorbent.Nanomaterials are expected toprovideunprecedentedopportunities indevelopinganewclassof sorbents for chromatographic applications due totheiruniquemorphological features.Due to their smalldimensions,nanomaterialshaveextremely large surfaceareatovolumeratio,whichmakesalargefractionofatomsof thematerials to be the surface or interfacial atoms,resultinginmore‘surface-dependent’materialproperties.These surface atoms are unsaturated, exhibit intrinsicsurfacereactivityandhaveatendencytochemisorbchargedspecies in aqueous solution inorder to achieve surfacestabilization.

99mTcisthework-horseofdiagnosticnuclearmedicine.The column chromatographic generatorusing a bedofacidicaluminahasemerged themostpopulargeneratorsystemworldover.Thecapacityofaluminafortakingupmolybdateionsislimited(2-20mgMopergofalumina).Thus,anadvancedsorbentmaterialisdesiredthathasgothighsorptioncapacityfor99Moandbetterelutionprofilefor the 99mTc.RadiopharmaceuticalsDivision,BARC, incollaborationwithChemistryDivision, has embarkedupondevelopment[40-43]ofnano-sorbentsforgeneratorapplication.Anewsorbentmaterial,polymerembeddednanocrystallinetitania(TitaniumPolymer-TiP)hasbeendeveloped, from titanium (IV) chloride and isopropylalcohol, for theadsorptionof 99Mo,whichisaprecursorto 99mTc, aworkhorse in radio-pharmaceuticals. Thesurfaceareaofthispolymerwas30m2/gwithanaveragepore sizeof 40nm.Theaverage crystallite sizeofTiO2, embeddedinpolymer,wasfoundtobe5nm.Potentialofthisadsorbentforthepreparationof99Mo-99mTcgeneratorhas been explored extensively. The feasibility of usingnano-zirconiaasaneffectivesorbentfordevelopinga99Mo/99mTcchromatographicgeneratorwasalsodemonstrated.The structural characteristicsof the sorbentmatrixwere

9


investigatedbydifferentanalyticaltechniquessuchasXRD,BETsurfaceareaanalysis,FT-IRandTEMetc.Thematerialsynthesizedwasnanocrystalline,intetragonalphasewithaverageparticlesizeof~7nmandalargesurfaceareaof340m2/g.Thesorptioncapacityofnano-zirconiais>250mgMo/g.Results of the studies indicate that 99Mo is bothstronglyandselectivelyretainedbynano-zirconiaatacidic pH and 99mTccouldbereadilyelutedfromit,using0.9%NaCl.99mTccouldbeelutedwith>85%yieldhavingacceptable radionuclidic, radiochemical and chemicalpurityforclinicalapplications. Nanostructured oxidesof Ti andZr have also been synthesized to evaluatetheir efficacyas sorbentmatrices for thepreparationof188W/188Regenerator.Theperformanceofthesematerials,inthecontextofpreparationof188W/188Regeneratorwascomparedwithrespecttotheadsorptioncapacityfor188W, flowcharacteristics in thecolumn,purityandqualityof188Reforradiopharmaceuticalsapplications.TheadsorptioncapacitiesofthenanocrystallineoxidesofTiandZrwere>300mgW/gof the sorbent,which ismuchmore thanthatofalumina.188Recouldbeelutedwithnormal(0.9%)saline solutionwithanelutionyieldof~80%withhighradionuclidic, radiochemical and chemicalpurity in anappreciablyhighradioactiveconcentration.Nanocrystallineγ-Al2O3wassynthesizedbyamechanochemicalmethod.Itisapromisingsorbentforthepreparationof188W/188Re generator.Itshowedsignificantlyhigherdynamicsorptioncapacity compared to theother reportedmaterials.Thegenerator performed consistentlywellwith respect tothepurityandelutionyieldof 188Reovertheperiodof6months.

Nanomaterials in sensor applications Nanomaterialshave shown tremendouspotential in

sensorapplicationsalso.ChemistryDivisionandTechnicalPhysicsDivision, BARC are involved in developmentof sensor for various applications. Someof the specificexamplesarenanomaterialsforsensingH2S,NH3,Lindaneandvarioustoxicmetalions.Thesensingactionisusuallyperformedbypickingthechangesinresistivityorphoto-luminescenceetc.Recently,anewinorganic-organichybridassayofAgnanorod (AgNR)-Rhodamine6G(R6G)wasdevelopedforthesensitiveandselectivedeterminationofPb2+ionsinaqueoussolutions.Thesensorcouldbeusedinconditionsandthefluorescenceintensityofthetestsolutionreachedmaximumwithin1minandthesystemshowedexcellentstabilityattestedconcentrationofmetalions.Thisopticalsensorshowed[44]thelowestdetectionlimitof50

µg/LofPb2+.Silvernanoparticlebasedopticalassayshavebeen developed that take advantage of the changes in the surfaceplasmonresonanceofnanocrystalsduetoproteinadsorption.UltrathinfilmsofSnO2developedbyLangmuir-Blodgettdepositiontechniquehasshownabilitytosenseammoniagasatroomtemperature[45,46].Localisedsurfaceplasmon resonance baseddetection ofmodel protein,bovineserumalbumin(BSA)havebeendemonstratedusingsilvernanoparticlethinfilmspreparedbyLBtechnique.AsignificantchangeinpeakpositionaswellastheabsorbancecouldbeobservedwhenthesesilvernanoparticlesthinfilmsweretreatedwithBSA[47].Forquick,onsitemonitoringof biomoleculesor environmentalpollutantshandheldbiosensors basedon electricalmeasurementswouldbepreferred. Binding of specific targetmolecules to theimmobilizedprobemoleculesinsidetheporescancauseameasurablechangeincapacitanceduetothechangeinthedielectricconstantandthickness.Thestandardizedprotocolsrequiredforthefabricationandcharacterizationofporoussiliconbasedcapacitive immunosensor thatgiveshighersensitivitycomparedtosensorsfabricatedonpolishedsiliconforthesamedieareawerereportedrecently[48].SeveralsemiconductingoxidessuchasSnO2,CuO,WO3,ZnO,In2O3 innanocrystallineformarebeingused[49-51]aspotentialgassensorsbasedontheprincipleoftheirreversiblechangeinelectricalconductance(resistance)onexposuretoredoxgases.ZnOnanoparticlesandnanowiresshowedselectiveandsensitiveresponsetoppmlevelofH2Sgas,whileCuOshowedresponsetoevensub-ppmlevelof thegas. In2O3 singlecrystalwhiskerspreparedbycarbo-thermalmethodcouldsense200ppbofH2Sgasatroomtemperature.Tethinfilmsaresensitive tobothNH3 and H2Sgasesbecauseofthenativeoxidelayerontop.1-DnanostructuresofTearesensitivetochlorinegases.

Conclusions Anattemptwasmade in this article to touchupon

chemistryaspectsandapplicationsofvariousnanomaterials.However,thissubjectistoovasttobecoveredinarathershort article, which is not exhaustive due to spaceconstraints. There arededicated books [52, 53] for thechemistryaspectsofnanomaterials.However, Iamsurethatfromtheforegoingonecaneasilygetaflavorofthisrapidlygrowingfieldofnanomaterials.

Acknowledgements I acknowledge all the colleagues, students and

collaborators(withinandoutsideChemistryDivision,BARC)


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whohave contributed to the researchonnanomaterialsreportedinthisarticle.InparticularIwouldliketoplaceonrecordsourcollaborationwithDr.A.DashofRPhD,BARC.IalsowishtothankDr.D.Das,Head,ChemistryDivision,BARCandDr.T.Mukherjee,Director,ChemistryGroup,BARCfortheirkeeninterestinandsupporttothiswork.

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Dr. A. K. Tyagi is presently Head, Solid State Chemistry Section, Chemistry Division, Bhabha Atomic Research Centre (BARC), Mumbai and also a Professor (Chemistry) at Homi Bhabha National Institute (HBNI). He joined BARC, Mumbai in 1986 through BARC-Training School. Since then he has been working in the field of Chemistry of nanomaterials, functional materials and nuclear materials. He was a Max-Planck Fellow at MPI, Stuttgart, Germany during 1995-96. In recognition of his work, Dr. Tyagi has been conferred with several prestigious awards such as Homi Bhabha Science & Technology Award, Gold Medal of Indian Nuclear Society, MRSI Medal, CRSI Medal, Dr. Laxmi Award by ISCAS, Rheometric Scientific-ITAS Award, and IANCAS-Dr.Tarun Datta Memorial Award, Rajib Goyal Prize and DAE-SRC Outstanding Researcher Award. He is a Fellow of Royal Society of Chemistry, UK (FRSC), National Academy of Sciences, India (FNASc) and Maharashtra Academy of Sciences (FMASc).

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Evaporation Induced Self Assembly of Nanoparticles by Spray Drying

D. Sen1*, J. Bahadur1, S. Mazumder1, J.S. Melo2, S.F. D’ Souza2 1Solid State Physics Division, 2Nuclear Agriculture and Bio-technology Division

Bhabha Atomic Research Centre, Mumbai-400085, India *Corresponding author; e-mail: [email protected]

AbstractNanoparticlesconfinedindryingdropletsoflessthanapicoliterareforcedtoorganizeinsub-micrometricgrainsbycapillaryforcesthatariseduetosolventevaporation.Torealizesuchevaporationinducedselfassembly,spraydryingmethodhasbeenutilized.Morphologyoftheassembledgrainsandinter-particlecorrelationoftheassemblednanoparticlesaresignificantlyinfluencedbyvariousphysico-chemicalconditionsandinterparticleinteraction.Small-anglescatteringincombinationwithelectronmicroscopycanprovidedetail informationaboutthemesoscopicstructureofthegrainsandthehierarchicalarrangementofthejammednanoparticlesinthegrains.Suchassembledgrainscanalsobeconsideredforvarioustechnologicalapplications.Herewehavedescribedsomeofourrecentresultsonsynthesisandcharacterizationofsuchassembledgrainsgivingspecialemphasisontheeffectsofslowerandfasterdryingonstructureofthegrains.

Keywords:selfassembly,aluminaandsilicananoparticles,spraydrying,SANSstudy

IntroductionSpraydryingisregardedasanindispensableindustrial

process [1] since long timebecause it has beenwidelyusedinvariousindustriessuchas,food,pharmaceutical,ceramic,polymer, chemical and severalother industriesto obtain dry particles from solution phase. Recently,thismethodhas embellished [2-9] itself innano-scienceandnano-technologywithanaimtorealizeevaporationinducedself-assembly(EISA)ofnanoparticlesatvariousphysicochemicalandthermo-dynamicalconditionsapartfromsynthesizingvariousnovelnano-composites,colloidalcrystals,mesoporousmaterials,microcapsulesetc..

Inthespraydryingprocess,liquiddropletsarepassedthroughahotchamberwheretheygetdried.Duringsuchdryingprocessofmicrometriccolloidaldroplets,shrinkageindropletsizeandarrangementofnanoparticlesinsideadropletisprimarilydrivenbyevaporation.Theconstituentparticlesgetassembledbycapillaryforcesthatcomeintoplaybecauseof thepresenceofwetting liquidbetweensolidparticles.Attheendoftheprocess,driedassembledgrainsareobtained.

At this juncture, it isworthy tomention that themorphology of the assembled grains and the internalarrangement of thenanoparticles in thegrainsdependstronglyon: (i) thephysico-chemicalparameters of the

initialnanoparticledispersionsuchas,concentration,sizeof nanopartlces and their interaction, viscosity, surfacetensionetc. and (ii) on theparameters related todryingsuchas,dryingtemperatureandtime,dropletsizeetc.Ithasbeenshown[5,8,9]thatwhentherateofdryingisslowenough,adropletcontainingstabledispersionofcolloidalnanoparticles,shrinksinanisotropicfashionandthefinalassembledgrainsarespherical.Further,forsuchasituation,the final arrangements of the nanoparticles inside anassembledgrain,correspondstoapackingduetorandomjammingof the constituentparticles. If the constituentnanoparticlesarespherical,inanidealrandomjammingsituation,thevolumefractionoftheparticlesinthegrainscorrespondsto~0.64andthecorrelationmaybeconsideredasofhard sphere type.However, if thedryingprocessis fastenough,dependingonotherphysicalparameters,variousnon-sphericalmorphologiesof thedriedgrains,suchas,doughnut,mushroometc.,areobserved[6,7].Inafewcases,evencrumpledandfracturedgrainshavealsobeenobserved.ItistobementionedthattheoriginofsuchcomplexmorphologicaltransitionduringEISAisnotfullyunderstoodyet.

The fastness of a drying process is expressedquantitatively by Peclet number (Pe), a dimensionless number,which is representedby the ratioof mix to dry wheremixisthetimeofmixing,i.e.,theaveragetimetaken

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bythecolloidalparticlestoreachtothedropletcentrefromtheboundarywhileperformingBrownianmotionanddry is thedryingtimeofthedroplets.Infact,mix can be estimated fromtheequationmix=R2

drop/D,whereRdroprepresentstheradiusofadropletandDisthediffusioncoefficientofthenanoparticlesinthedroplet.IfPe>>1,thedryingprocessisregardedasafastoneandtheformationofhollowgrainsor evenmorphological transformationofdropletsmayhappeninsuchacase.AslowdryingregimecorrespondstoasituationwherePe<<1andinthiscasethedryingprocessisisotropicasmentionedabove.

Inthisarticle,wewilldescribehowspraydryingcanbeutilizedtotailorthemorphologyofselfassembledgrainsinmicrometriclengthscaleandtheinter-particlecorrelationbetweenthenanoparticlesintheassembledgrains.

Experimental

Spray dryingFor spraydrying experimentswith slower drying

rate,i.e.,forPe<<1,asimplespraydryer(SPD-1)hasbeendeveloped [10] atBARC,Mumbai. It consists (Fig. 1)ofthreemainsstages:(i)dropletgenerator(eitherbymulti-jetcompressedairnebulizerorultrasonicnebulizer), (ii)dropletdryer and (iii)driedparticle collector (eitherby

wiremeshcollectororcycloneseparator).ForfasterdryingcasewherePe>>1,wehaveemployedcommercial spraydryerLU220andLU228 fromLABULTIMA,Mumbai.Theresidencetimeofthedropletinthedryingchambercanbefoundfromthegeometryofthedryingchamberandtheflowrateofthecarriergas.Thetypicalresidencetimeofthedropletinthechamberincaseofslowdryinghasbeen7-10sec.whilethatforthefastdryingcaseremainsasfractionofasecond.

SANS and SEMTo characterize themesoscopic structure of the

assembledgrains,small-angleneutronscattering(SANS)andscanningelectronmicroscopy(SEM)havebeenused.Forscatteringmeasurements,SANSfacilities[11,12]atGTlaboratory,Dhruvaareused.

Results and discussion

On slow dryingWhen the rate ofdrying is slowenough, adroplet

containing stabledispersion of colloidal nanoparticles,shrinksinanisotropicmannerandinsuchasituationthefinalarrangementsofthenanoparticlesinsideanassembledgrain,correspondstoapackingduetorandomjammingof the constituent particles.However, suchpacking of

Fig. 1: (a) The spray dryer for slow drying rate developed at BARC. (b) Schematic diagram of the spray dryer.

Atomizing system.

Cyclone

Heating furnace


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the constituentparticles insideassembledgrains canbemodifiedbyaltering thephysicochemicalparametersoftheself-assemblyprocess.Bydoingso,onecanalsoaltertheavailableinterfacialareainsidetheassembledgrains,whichmaybe an importantparameter in any catalyticapplications.Thepresentstudyaimedatmodificationofinternalstructure[8]insuchassembledgrainsbyadditionofelectrolyteintheinitialcolloidaldispersionandthusbyalteringthejammingmechanism.Colloidalsilicadispersionof5%inweightwaspreparedfrominitial40%colloidalsilicadispersion(~10nm)(VisaChemical,Mumbai,India)bydilutionwithpurewater(Milli-Q,Millipore).SodiumChloride(NaCl)wasaddedtothedilutedsilicadispersion.ItwasfoundthatforNaClconcentrationbeyond1.5%,thedispersionbecameunstableandgotphaseseparated.Thus,inourcasetheconcentrationofNaClinthesilicadispersionwaskeptbelow1.5wt%wheretherehasbeennophaseseparation. Silica dispersions (5%)with varyingNaClconcentrationhavebeenpreparedforfurtherspraydryingpurpose.Thefeedwaskeptat~50ml/hr.Thetemperatureoftheovenwaskeptat160oC.Theaspirationvaluewaskeptat 40 literperminute.Thedriedmicrometric/sub-micrometricpowders(P0.0,P0.1,P0.2,P0.5,andP1.0for0.0,0.1,0.2,0.5and1.0wt%NaCl,respectively)werecollectedattheendofthedryingchamberusingawiremesh(400mesh)filter.Thecollectionefficiencywasfoundtobenearly50%.SEMmicrographofthegrainsforthesamplesP0.0,P0.5 and P1.0areshownintheFig.2.Itisseenfromthefigurethatthegrainsare spherical in shape.Forhighestelectrolyteconcentrationfewbuckledparticlesarealsoseen.

SEMgives the externalmorphology of the grainsandSANS can throw light about the correlationof thenanoparticles inside thegrains. SANSdata areplotted,indoublelogarithmicscaleinFig.3(a).Itisevidentfromthefigurethattheprofilesgetmodifiedsignificantlywithadditionof electrolyte.Particularly, the functionalityoftheprofilesintheintermediateqregion(~0.05to0.5nm-1) thatprimarilybearsthesignatureofthecorrelationofthesilicaparticlesinthegraingetsalteredinasignificantway.Scatteringdatahavebeenanalyzedintermsoftwolevelstructuralmodel[8].Thedifferentialscatteringcrosssectionperunitofsolidvolumemaybegivenby

pure water (Milli-Q, Millipore). Sodium Chloride (NaCl) was added to the diluted silica dispersion. It was found that for NaCl concentration beyond 1.5 %, the dispersion became unstable and got phase separated. Thus, in our case the concentration of NaCl in the silica dispersion was kept below 1.5 wt % where there has been no phase separation. Silica dispersions (5%) with varying NaCl concentration have been prepared for further spray drying purpose. The feed was kept at ~ 50 ml/hr. The temperature of the oven was kept at 160 oC. The aspiration value was kept at 40 liter per minute. The dried micrometric/sub-micrometric powders (P0.0, P0.1, P0.2, P0.5, and P1.0 for0.0, 0.1, 0.2, 0.5 and 1.0 wt % NaCl, respectively) were collected at the end of the drying chamber using a wire mesh (400 mesh) filter. The collection efficiency was found to be nearly 50%. SEM micrograph of the grains for the samples P0.0, P0.5 and P1.0 are shown in the Fig. 2. It is seen from the figure that the grains are spherical in shape. For highest electrolyte concentration few buckled particles are also seen.SEM gives the external morphology of the grains and SANS can throw light about the correlation of thenanoparticles inside the grains. SANS data are plotted, in double logarithmic scale in Fig. 3 (a). It is evident from the figure that the profiles get modified significantly with addition of electrolyte. Particularly, thefunctionality of the profiles in the intermediate q region (~0.05 to 0.5 nm-1) that primarily bears the signature of the correlation of the silica particles in the grain gets altered in a significant way. Scattering data have beenanalyzed in terms of two level structural model [8]. The differential scattering cross section per unit of solid volume may be given by

2 2S S S g g g

S

( I (q) v P (q))I(q) (1)

φ ∆ρ ∆ρ

φ

+=

where φS is the volume fraction of silica nanoparticles in a grain of volume vg. If ρS is the scattering lengthdensity of silica, then ∆ρS=ρS-ρint (ρint being the scattering length density of interstices between silicananoparticles). As interstices between silica nanoparticles is void (when electrolyte is removed), ρint= 0 andhence ∆ρS can be taken equal to ρS. ∆ρg

2 represents the average scattering contrast of the grains hence ∆ρg=φS∆ρS + ∆ρint. As the medium in which the grains are embedded and the medium of the interstices are bothvoid/air in this case, ∆ρint=0 and thus ∆ρg= φS∆ρS. Here, Pg(q) is the normalized form factor of the grains.

2 2g g g g g

0 0

P (q) f (q,r)v (r)D (r)dr / D (r)dr (2)∞ ∞

= ∫ ∫

where fg2(q,Rgrain) represents the form factor of the grains of radius Rgrain and is represented by

grain graing grain 3

grain

[sin(qR ) qr cos(qR )]f (q, R ) 3 (3)

(qR )−

=

Dg(r) represents the size distribution of the assembled grains and is assumed as a lognormal distribution.

grain 20

g 22 2gg

[ln(R / R ) ]1D (R) exp (4)

22 R σπσ

= −

The first term in the numerator of the equation -1 corresponds to the scattering from the colloidal particles in the grains. When the colloidal particles have a distribution in their size, then Is(q) may be represented as following under local monodisperse approximation.

2S nano S nano nano nano nano

0S

nano S nano nano0

P (q, r )D (r )v (r )S(q, r )drI (q) (5)

v(r )D (r )dr

∞

∞=∫

∫

S(q,rnano) is the inter-particle structure factor. DS(rnano) represents the size distribution of the nanoparticles.PS(q,rnano) represents the normalized form factor of nanoparticles with radius rnano.

whereφSisthevolumefractionofsilicananoparticlesinagrainofvolumevg.IfρSisthescatteringlengthdensity

of silica, then∆ρS=ρS-ρint (ρint being the scattering lengthdensity of interstices between silica nanoparticles).Asinterstices between silica nanoparticles is void (whenelectrolyteisremoved),ρint=0andhence∆ρScan be taken equaltoρS.∆ρg

2representstheaveragescatteringcontrastofthegrainshence∆ρg=φS∆ρS+∆ρint.Asthemediuminwhichthegrainsareembeddedandthemediumoftheintersticesarebothvoid/airinthiscase,∆ρint=0andthus∆ρg=φS∆ρS.Here,Pg(q)isthenormalizedformfactorofthegrains.


2 2S S S g g g

S

( I (q) v P (q))I(q) (1)

φ ∆ρ ∆ρ

φ

+=



2 2g g g g g

0 0


= ∫ ∫



grain


(qR )−

=


grain 20

g 22 2gg

[ln(R / R ) ]1D (R) exp (4)

22 R σπσ

= −



0S

nano S nano nano0

P (q, r )D (r )v (r )S(q, r )drI (q) (5)

v(r )D (r )dr

∞

∞=∫

∫


wherefg2(q,Rgrain)representstheformfactorofthegrainsofradiusRgrainandisrepresentedby


2 2S S S g g g

S

( I (q) v P (q))I(q) (1)

φ ∆ρ ∆ρ

φ

+=



2 2g g g g g

0 0


= ∫ ∫



grain


(qR )−

=


grain 20

g 22 2gg

[ln(R / R ) ]1D (R) exp (4)

22 R σπσ

= −



0S

nano S nano nano0

P (q, r )D (r )v (r )S(q, r )drI (q) (5)

v(r )D (r )dr

∞

∞=∫

∫


Dg(r)representsthesizedistributionoftheassembledgrainsandisassumedasalognormaldistribution.


2 2S S S g g g

S

( I (q) v P (q))I(q) (1)

φ ∆ρ ∆ρ

φ

+=



2 2g g g g g

0 0


= ∫ ∫



grain


(qR )−

=


grain 20

g 22 2gg

[ln(R / R ) ]1D (R) exp (4)

22 R σπσ

= −



0S

nano S nano nano0

P (q, r )D (r )v (r )S(q, r )drI (q) (5)

v(r )D (r )dr

∞

∞=∫

∫


Thefirst term in the numerator of the equation -1correspondstothescatteringfromthecolloidalparticlesin the grains.When the colloidal particles have adistribution in their size, then Is(q)maybe representedas followingunder localmonodisperse approximation.


2 2S S S g g g

S

( I (q) v P (q))I(q) (1)

φ ∆ρ ∆ρ

φ

+=



2 2g g g g g

0 0


= ∫ ∫



grain


(qR )−

=


grain 20

g 22 2gg

[ln(R / R ) ]1D (R) exp (4)

22 R σπσ

= −



0S

nano S nano nano0

P (q, r )D (r )v (r )S(q, r )drI (q) (5)

v(r )D (r )dr

∞

∞=∫

∫


S(q,rnano)istheinter-particlestructurefactor.DS(rnano) represents the size distribution of the nanoparticles.PS(q,rnano) represents the normalized form factor ofnanoparticleswithradiusrnano.

Analysisofscatteringdata[8] indicatesthatastickyhardsphere typecorrelation, incaseofsilicaalone,getsmodified toa fractal like correlationwhenelectrolyte isaddedpriortodrying.ThefitofthemodeltothedataareshowninFig.3(b).

Experimentswerealsocarriedout[9]byvaryingtheinitial concentration (20%, 10%, 5%and 2.5%) of silica

(2)

(3)

(4)

(5)

(1)

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Fig. 2: The spherical spray dried grains of assembled silica nanoparticles are shown. For highest electrolyte concentration few buckled particles are also seen.

Fig. 3: (a) SANS profiles of the self-assembled samples are shown in double logarithmic scale. The presence of two length scales (individual nanoparticles) in this system is evident from the profiles. The profiles get modified, mainly in intermediate and high q regimes, with addition of electrolytes. (b). Solid line shows the fit of the model to the scattering data. The profiles are shifted vertically for clarity.

nanoparticlesinthevirgindispersionpriortospraydrying.Forall thecases thegrainsremainedspherical inshape.However, SANS (Fig. 4a) andDynamicLightScattering(Fig.4b)(DLS)indicatethatvariationingrainsizeandthearrangementof thenanoparticles inside thegrainswithvaryingsilicaconcentrationininitialdispersion.

It has been found that averagepacking fraction ofthenanoparticles in thegrains reduceswith increasing

concentration.Twodistinct zones (Zone-1 andZone-2)arevisible from theSANSdata.Zone-1 corresponds tothe scattering signaldue to overall grainwhileZone-2correspondstothescatteringfromindividualnanoparticlesinthegrains.DetailanalysisofSANSdatasuggeststhatthepackingofthenanoparticles,insidetheassembledgrains,isnotuniformathighercolloidalconcentration.Forthiscase,agradientinparticlepackingathigherconcentration


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Fig. 4: (a) SANS profiles (in Porod representation) for the spray dried grains synthesized from dispersions with different silica volume fraction. (b) Dynamic light scattering data from the grains

Fig.5: (a) SEM micrograph of spray dried grains for silica 2.5 % dispersion. (b)Size distribution of the grains as obtained from the dynamic light scattering data.

ofsilicaisapossibility.in.Typicalgrainmorphologyfor2.5%dispersionisshowninFig.5(a).Thevariationingrainsizeswith silica concentration, asobtained fromDLS, isdepictedinFig5(b).

On fast dryingAsitisalreadymentionedearlierthatwheneffective

drying rate is fast enough i.e., Pe >> 1, there exists a

possibilityofmorphologicaltransformationduringEISA.Insuchasituation,asphericalcolloidaldropletwhiledryingbecomes initially viscous and a shell of nanoparticlesformsdue to capillary forceat theairwater interface.Eventually, such shell becomes elastic in nature andacts as a porousmembrane throughwhichwater istransportedout. If thestabilizationforcesbetweenthenanoparticles overcome the attractive capillary force,

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(a)

(b)

Fig.6: (a) SEM micrograph of doughnut like spray dried alumina colloids (2%). (b) SEM micrograph of spherical spray dried alumina colloids (5%).

thenthenanoparticlescanrearrangethemselvesinsuchawaythatanoverallshrinkageinthedropletvolumeoccurs.However,ifthestabilizationforceisnotstrongenough compared to the attractive capillary force, therearrangementbetweentheparticlescannotoccurandtheoverallsizeofthedropletcannotdecreaseafteracertaintime.Insuchasituationbecauseofpressuredifferenceacross the shell, the droplet buckles.Of course, suchbucklingdependsontheshellthicknessandtheeffectiveelasticmodulusoftheshell.

UsingspraydryersLU220andLU228,LABULTIMA,we have performed several investigations related tothe effect of various physico-chemical conditions onbuckling. Ithasbeen found [6] that sphere todoughnutlikemorphological transformation occurswhen theconcentrationofnanoparticlesinthevirgindispersionislessbutsuchtransformationishinderedathighernanoparticleconcentration.

Itisworthytomentionthatspraydryingtechniquecanbeusedveryefficientlyinfastsynthesisofporousgrainsbyuseofpropertemplatematerialsandremovalofsuch


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templatematerials afterEISA.Wehaveused [7]E. colibacteriaastemplatefortworeasons,firstlytoseetheeffectofsoftmaterialparticlesonthemorphologicaltransformationandbucklingphenomenonduringEISAandsecondlytosynthesizeporousgrainsofnanoparticle assemblywithcylindricalpores.Itisworthytomentionthatcolumnofsuchporousgrainshasfound[13]potentialapplicationsinwater purification fromE. coli contaminatedwater.SuchE. coli templatedporousgrains consistingof silicananoparticlesareshowninFig.7.Inthevirginsuspensionbeforedryingtheamountofsilicananoparticleswas2wt%andtheamountwetE.coliwasvariedas2,4and6wt%.FromtheSEMmicrographs,individualnanoparticlesare

notvisiblebecauseofresolutionconstraint.However,theirpresenceisevidentfromtheZone-IIIoftheSANSprofilesasshowninFig.8.Zone-IcorrespondstothescatteringfromoverallgrainsandZone-IIprimarilybearsthesignatureofthescatteringfromtheporesastemplatedbyE.coli.ThespecificsurfaceareaofthegrainswereestimatedfromthePorodlevelofSANSdataandwerefoundtobe40,20and18m2/gmforE2,E4andE6samples.Ithasrecentlybeenfoundthatsuchmorphologicaldeformation[7]andbuckling[14]canbearrested[15]bypropertuningofsurfacechargeandotherphysico-chemicalconditions.

It is observed from the SEMmicrographs that thebuckling becomesmore vigorous as E. coli fraction isincreased.From theobservations it seems that the size,shapeandelasticmodulusoftheassemblingparticlesinthedropletsareimportantfactorsasfarasthesebucklingdeformations are concerned. As the Peclet numberismore for bigger particles, the deformation, duringbuckling, ismorewhenE. coli ispresent. Further, it ismuchsofter(LongitudinalYoung’smodulus~25MpaandcircumferentialYoung’smodulus~75MPadensity~1.1gm/cm3)thansilica(~75000MPa,density~2.5gm/cm3).Thustheincorporationofthebacterialcomponentresultsindecreaseintheelasticconstantsvis-à-vistheenhancementof the buckling probability of the formed shell of thejammedparticlesattheboundaryofthedryingdroplets.Thisfacilitatesinrelativelyeasierbuckling.Further,thenonsphericalshapeoftheparticles(asinthepresentcaseforE.coli),causessomewhatanisotropicvariationofthecapillaryforcesatdifferentzonesofthegrains,whichgivesrisetomultiinvaginationzoneonthesurfaceofthedroplet.Thisenhancesthedeformationduringbucklingandthegrains

Fig. 7: E. coli templated porous grains of assembled silica nanoparticles for three different ratios of silica to E. coli. The ratio increases from left to right. Individual nanoparticles are not seen from SEM micrographs due to resolution constraints. However, their presence is evident from SANS profile.

Fig. 8: SANS profiles from the E. coli templated porous grains of assembled silica grains.

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Figure 9: (a) SEM micrographs of the spray dried ceria grains (15 min. sonication). (b) 60 min. sonication Pores are evident from the micrograph. Individual nanoparticles are not visible due to resolution constraint. (c) SANS profiles for the grains. No significant change with sonication time is observed as far as small-angle scattering data are concerned.

withdimpledmulti-faceddeformeddoughnutshapearerealized (Fig. 7). From the SEMmicrographs it is quiteevidentthatthedeformationgetsamplifiedwithincreaseinthevolumefractionoftheE.coliinthedroplets.

Ceriaisoneofthemostimportantcatalyticmaterialsthatcanplaymultiplerolesowingtoitsabilitytoreleaseanduptake oxygenunder catalytic reaction conditionsandthushaspotentialforthetreatmentofemissionsfrom


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automobiles.Inthisconnection,synthesisofmeso/macroporousceriagrainsattractsagreatdealofattention.Aqueousdispersionofceriananoparticles(M/S.Cottorindustries,Mumbai)wassonicatedfor15min.and60min.priortothespraydrying.TheporousnatureofthepowdergrainsisevidentfromtheSEMimages(Fig.9).Themesoscopicstructureoftheassembledgrainsandtheinteractionoftheceriananoparticleswithinthegrainswereprobedbysmall-anglescattering.Normally,templatematerialsareusedtotemplateporesinsuchgrains.However,thesynthesizedgrains, in thepresent, case arehighlyporous innaturewithoutanyadditionoftemplates.Thisisattributedtothefactthatagglomeratesofnanoparticlesgetlockedsuddenlyduringthefastdryingprocess.Itisneedlesstomentionthatsuchporeseffectivelyincreasetheavailablesurfaceareaforanycatalyticreaction.Unlike,thespraydryingofastabledispersionasmentionedearlier,thecolloidaldropletsinthepresentsituationdonotshrinkinanisotropicfashionandtheinterlockingofvariousagglomerateswithinadropletgivesrisetosuchpores.Aslopeof-3.2of thescatteringprofilesinlog-logscalesupportstheagglomeratenaturewithin thegrains.Multi level structureof thegrains isevidentfromtheprofiles.

ConclusionsIt hasbeendemonstrated that evaporation induced

self assemblyofnanoparticles canbe realizedby spraydrying. Spherical grainsof assemblednanoparticles arerealizedbecause of isotropic compressionof the spraydroplets during drying. By varying physico-chemicalconditions, it ispossible to synthesizeassembledgrainswithnon-sphericalshapeslikedoughnutormultifaceteddoughnut etc. Suchmicrometricgrainswith interestingporemorphologycanalsobesynthesizedbyadditionoftemplateorbytuningtheagglomerationbehavior.Whiletheoverallmorphologyof the assembledgrains canbeobtainedby electronmicroscopy, small-angle scatteringcanprovidethehierarchicalstructuralinformationinthegrains.Suchmicrometricassembledgrainswithdefiniteporestructuremaybeconsideredaspotentialcandidatesforvariousapplicationssuchasfiltrationapplication,drugdelivery,catalysis,nuclearwastemanagementetc.

AcknowledgementDSwouldliketothankDr.ShovitBhattacharya,TPD,

BARCforSEMmeasurementsandalsotoMr.ArshadKhan,RPAD,BARCforhisactivehelptowardsthedevelopmentofthespraydryerwithslowerdryingrate.

References1. K.Masters,SprayDryingHandbook,5thEdition,Longman

Scientific&Technical,England,1991.2. F.Iskandar,L.Gradon,K.Okuyama, J. Colloid and Interface

Sci., 265,296-303(2003).3. N. Tsapis, E.R. Dufresne, S.S. Sinha, C.S. Riera, J.W.

Hutchinson,L.Mahadevan,L.D.A.Weitz,D.A.Phys. Rev. Lett. 94,018302(2005).

4. D.Sen,O.Spalla,L.Belloni,T.Charpentier,A.Thill,Langmuir, 22,3798-3806(2006).

5. D.Sen,O.Spalla,O.Taché,P.Haltebourg,A.Thill,Langmuir, 23,4296-4302(2007).

6. D.Sen,S.Mazumder,J.S.Melo,A.Khan,S.Bhattyacharya,S.F.D’Souza,Langmuir, 25(12)6690–6695(2009).

7. D.Sen,J.S.Melo,J.Bahadur,S.Mazumder,S.Bhattacharya,G.Ghosh,D.DuttaandS.F.D’Souza,European Physical Journal-E, 31,(2010),393-402

8. D.Sen,ArshadKhan;J.Bahadur;S.Mazumder;B.K.Sapra,J. Colloid & Interface Science, 347,(2010)25-30

9. J. Bahadur,D. Sen, S.Mazumder, Bhaskar Pal,ArshadKhan,G.Ghosh J. Colloid and Interface Sci. 351 357-364(2010)

10. ArshadKhan,D.Sen,B.K.SapraandS.Mazumder;Proceedings of the 54th DAE SSPS(2009),pp-445-446.

11. S.Mazumder,D.Sen,T.Saravanan,P.R.Vijayaraghavan,J. Neutron Research, 9,39(2001).

12. V.K.AswalandP.S.Goyal,Curr. Sci.2001,79,947.13. J.S.Melo,D.Sen,S.MazumderandS.F.D’Souza.In proceedings

of the Indian Desalination Association and Asia Pacific Desalination Association Conference on desalination and water purification held atChennai,Indiapp411-417,2010.

14. J. Bahadur, D. Sen, S.Mazumder, S. Bhattacharya,H.Frielinghaus,G.GoerigkLangmuir 2011,27(13),pp8404–8414

15. DebaisSen, JoseSavioMelo, JitendraBahadur, SubhasishMazumder,ShovitBhattacharya,StanislausFrancisD’Souza,HenrichFrielinghaus,GünterGoerigk,RudolfLoidlSoft Matter 75423-5429(2011)

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D. Sen has joined the Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai, India in 1996 after completion of 39th batch of BARC training school from Physics discipline. He obtained his Ph.D. degree in Physics from Mumbai University in 2004. He has worked extensively on mesoscopic structural properties in several technologically important materials using small-angle neutron and x-ray scattering. His current field of interest is evaporation induced self-assembly of nanoparticles and porous media. He has to his credit more than seventy publications in international journals.

J. Bahadur obtained his M.Sc. in Physics in 2005 from the University of Allahabad. He joined the 49th batch of BARC Training School and was awarded the Homi Bhabha prize for standing first in his discipline. On completion of training, he joined Solid State Physics Division of BARC, Mumbai, India. He is currently working in the field of small angle neutron and x-ray scattering on nano-ceramic and nano-composite materials. His research interests include sintering behaviour of nano-ceramics and evaporation driven self-assembly of colloids.

S. Mazumder is a senior scientific officer at the Solid State Physics Division, BARC, Mumbai, India. He is from 27th batch of BARC training school and has interest in scattering techniques for material investigation. His current field of interests includes evolution of structure during cement hydration.

J. S. Melo obtained a M.Sc. in Biochemistry in 1984 and Ph.D. degree in Biochemistry in 1990 from Mumbai University. Currently he is a senior scientific officer of the Nuclear Agriculture & Biotechnology Division at Bhabha Atomic Research Centre, Mumbai, India, and is also an Associate Professor at the Homi Bhabha National Institute. In the field of bioprocessing, he has developed a number of novel techniques for immobilization of enzymes, cells and preparation of coimmobilizates. His current field of interest is bioremediation, nanoscience and sensors. He has to his credit several publications in International Journals, Symposia and Workshops.

S. F. D’Souza is currently the Associate Director of the Biomedical Group and also Head, Nuclear Agriculture and Biotechnology Division, at Bhabha Atomic Research Centre. Mumbai, India, wherein he coordinates institutional programs on food agriculture and biotechnology. He is also Senior Professor at the Homi Bhabha National Institute. He has a Ph.D in Biochemistry and his major research interest has been in the field of enzyme and microbial technology with special reference to immobilized cells for use in bioprocessing, biosensors, bioremediation and nanotechnology. He has to his credit over 200 scientific papers and invited reviews in reputed International Journals.


22

Light absorption and emission in gold nanoplates assembled in small groups via poly(vinylidene fluoride) molecules

B. Susrutha, A.D. Phule and S. Ram* Materials Science Centre, Indian Institute of Technology, Kharagpur- 721302, India

*Corresponding author: E-mail: [email protected]

AbstractAsimplein-situchemicalreductionofagoldsaltbyusingpoly(vinylidenefluoride)(PVF2)moleculesinDMFwithultrasonicsinhotconditionsisexploredtoprepareAu-nanoparticles(Au-NPs)informofananofluid.ItisshownthatPVF2moleculesbondprimaryAu-NPs(usuallyplateswith120-180 nmwidthand10-15nmthickness)oneanotherinsmallassembliesinasphericalshape(~920nmdiameter).AnanofluidcontainingAu-NPsassmallas0.5wt%exhibitsanintenseopticalabsorption,intherange330-760nm,inthreewell-separatedband-groupsat385nm,540nm,and675nm.The540nmbandhasthemaximumpeakintensity,showingamolarextinctioncoefficient1.105×104L/mol-cm.Adifferentspectrumoccursintheemissionwithaprominentbandat476nm.Here,PVF2moleculesimmobilizeAu-NPssothatthesurfacestabilizedAu-NPsassembleinaspecificsphericalshapeinminimizingthetotalsurfaceenergy.ThisismodeledassumingapreferablylinearPVF2structureofabondedlayeronthenascentAu-NPs.Thebondedlayerconfinesalocalizeddistributionofthesurfaceplasmonsintheinterfaceregimeandinturncontrolsthelightabsorptionandemissioninacomplexfunctionofthesurfacebridgingandthelocaldielectricfield.

Keywords: Au-PVF2nanoassembles,opticalabsorption,photoluminescence,nanofluids

IntroductionNoblemetalnanostructureshavedrawnconsiderable

interestinrecentyearsbecauseoftheirwideapplicationsin catalysis, biosensing, optics, andmedicaldiagnostics[1-4].Inparticular, itisknownsincefarlongthatopticalproperties of gold-nanoparticles (Au-NPs) are stronglyinfluencedbytheshape,sizeandsurfacetopologyaswellas the local environments [5, 6]. Severalmethodshavebeendeveloped to fabricate shape controlledAu-NPswith functionalproperties [7-9]. Two-dimensional (2D)shapessuchasnanodisks,nanoplates,andnanobeltsarehighlysensitiveintailoringsuchproperties[10,11].Thesegeometrical attributes are especially useful in cancerhyperthermia and othermedical applications becausethesurfaceplasmonresonance(SPR)bandcanbetunedeasily from thevisible tonear infrared region [12, 13].Limitedstudieshavebeencarriedoutonsubmicrometerormicrometer-sized plates that are not so stable in asolutionphase,andthuslosecolloidalproperties[14-16].Withinthelastonedecade[17-20],ourgroupsynthesizeddifferentnanofluidscontainingsilverorgoldofdifferentsizes and shapes using reactive polymermolecules ofpoly(vinylalcohol)(PVA),poly(vinylpyrrolidone)(PVP),orpoly(vinylidenefluoride)(PVF2)inasinglestepofin-

situreactionatmoderatetemperature.Inadditionto(i)amodelreductantand(ii)amodelsurfacestabilizer,thesepolymermoleculesserveasatemplatewhengrowinga2D-metallicstructureinasolution.Au-nanoplatelets(0.5-1.0wt%)embeddedinPVAmoleculesandcastasfilmsexhibittwoSPRbandsnear570-595 nm and820-830nm [18].Au-nanoplates(30-140nmwidthand6-10nmthickness)obtainedusing cetyltrimethyl ammoniumbromidehastwobandsof760nmand1055nmusefulforbiomedicalapplications[21].

In this article,we report on light absorption andemissioninAu-nanoplateswhichareassembledinsmallgroupsviaPVF2molecules.Peculiarly,asharpabsorptionbandofsymmetricshapeariseswithaveragepeakpositionat 540 nm at a specificAu-content of 0.5wt%. PVF2 moleculesbondAu-NPsinthisspecificshapeofasphereinminimizingthetotalsurfaceenergy.Aratherdifferentbandoccursintheemissionwithaverageposition~476nmfromasurfaceinterface.

ExperimentalAnanofluidAu-PVF2waspreparedinasinglestepofa

reactionAu3+→Authatwascarriedoutusing(i)agoldsaltHAuCl4·3H2O(99.99%purefromMerckchemicals),(ii)PVF2

23


ofweightaveragemolecularweight~40,000(spectroscopicgradefromAlfaAesar),and(iii) triethonolamine(TEA)inadilutesolutioninN,N-dimethylformamide(DMF)inhotconditions.TheTEAwasusedtoservenotonlyasasurfacestabilizertoproduceAu-NPsinsmallassembliesbutalsoamodestreductanttomonitoracontrolledAu3+ →AureactioninarheologicalfluidinpresenceofthePVF2 molecules.Ithasbeenobservedthatwhenaddingdropwise(1-2%volumewise),TEApromotestheAu3+→Aureaction,showingadistinctvisiblecolorfromsurfacestabilizedAu-NPsanddispersedthroughthePVF2molecules.Atypicalreactionbatchcarriedoutused0.1mlofaHAuCl4solution(0.075Mconcentration),5mlofa0.3g/LPVF2and0.01mlTEAinatotal5.11mlvolume.Tobeginthereaction,theHAuCl4solutionwasaddedtothePVF2solutiondrop-wisebyultrasonicatingat50-60°C.10minheatingatthistemperature inpresenceofultrasonication followedby20-30minnormalheatingontoamagneticstirrerresultsinanintensebluishvioletcolorednanofluidmostlyfreefrombyproductvolatileimpurities.

Morphology and size distribution of theAu-NPsin a nanofluidwere studied byusing a field emissionscanningelectronmicroscope(FESEM)ofSUPRA-40withan acceleratedvoltage 2-30 kV.The optical absorptionspectrum (200-800nm)of thenanofluidwasmeasured(against theparentPVF2 solution)with aPerkinElmerabsorption spectrophotometerofLambda750.APerkinElmer(Model-LS55)luminescencespectrometerwasusedwitha redsensitivePMTdetector (RS928)andapulsedxenonlamp(20kWpowerfor8μs)tostudyemissionofthesamesample.

Results and DiscussionTypical FESEM imagesmeasured fromanAu-PVF2

nanofluid at three selectivemagnifications in order toillustratethemicrostructuralfeaturesthatincuratdifferentlength scales are shown inFig. 1 (a-c).All these imagesweretakenfromthesamesamplewhichcontained0.5wt%Auinformofabasicstructureofnanoplates(Fig.1c).Asmentionedabove,thisspecificsamplehasbeenstudiedindetailbecauseitpresentsaprominentabsorptionbandofasymmetricshapeinthegreenregion540nmalongwithaweakbandintheredregion675nmandaweakbandinthevioletregion385nm.Thesethreeseparatedabsorptionbandscanbeexploredtotailorlightemissionoverawiderange300-800nmfordifferentapplications.InFig.1a,theFESEMimageswhentakenataratherlowmagnificationpresent distinct assemblies of near spherical shapes,

Fig. 1: FESEM images (a-c) of Au-NPs (0.5 wt%) embedded in PVF2

from a nanofluid in an organic medium of DMF, showing that PVF2

molecules bond Au-NPs in clusters.


24

showingafairlysharpsizedistributionwithanaverage920nmdiameter.AscanbeseenfrommagnifiedFESEMimages in Fig.1b, thePVF2molecules are interbridgingsmallAu-NPs in stableassemblies.Withinanassembly,thePVF2molecules bondprimaryAu-NPs,mostly thinplateswith120-180nmwidthand10-15nmthickness.ThisisdemonstratedwellwithhighresolutionFESEMimagesinFig.1c.

Fig. 2presents absorption spectrumof anAu-PVF2 nanofluid,containing0.5wt%Au-NPs,measured in therange330-760nm.Asexpected,theAu-nanoplatesrevealtwodistincttransverse(T)andlongitudinal(L)modesoftheabsorptioninthelocalizedSPsonthemetallicsurfaceuponatightlybondedpolymersurfacelayer.TheT-modereflectsinaprominentbandat540nmwhiletheL-modeassumesaratherpoorintensitybyanorderofmagnitudewith average position lying at 675 nm. Both of thesebandshaveadoubletstructureascanbeseenwiththeirdeconvolutions.Asaresult,twobandsof534nmand553nm comprisetheT-modewhilethoseof658nmand682nmcomprisetheL-mode{seetheinset(a)inFig.2}.Thered-shiftedbandcomponentsarisefromtheAu-SPswhichbondthesurfacepolymerlayerwhilethemainbandcomponentsarise from the regularAu-SPs in the surfacemodifiedAu-nanoplates and coalesced in spherical assemblies asshownintheFESEMimages.AsgiveninTable-1,amolarextinctioncoefficientεmax=1.105×104L/mol-cmisobtainedforthe540nmbandgroup.Thisspecificvalueisanorderoflargermagnitudewhencomparingtoavalueεmax=1×103 L/mol-cmobserved inanabsorptionbandat562nmin0.5wt%Au-NPsembeddedinPVPmoleculesinformofananofluidinwater[17].

Furthermore,anorderoflowerεmax-valueisobservedinthe675nmband,orinanothersimilarlyweakbandshownatshorterwavelengthover340-440nminFig.2.Table-1alsoincludesthevaluesfortheoscillatorstrength(fosc) in thethreemajorbandgroupsobservedat385nm,540nm,and675nminFig.2.

Thefosc-valuehasbeencalculatedfromtheintegratedareainabandgroupbyusingthestandardrelation[22],

heating onto a magnetic stirrer results in an intense bluish violet colored nanofluid mostly free from byproduct

volatile impurities.

Morphology and size distribution of the Au-NPs in a nanofluid were studied by using a field emission

scanning electron microscope (FESEM) of SUPRA-40 with an accelerated voltage 2-30 kV. The optical

absorption spectrum (200-800 nm) of the nanofluid was measured (against the parent PVF2 solution) with a

Perkin Elmer absorption spectrophotometer of Lambda 750. A Perkin Elmer (Model-LS 55) luminescence

spectrometer was used with a red sensitive PMT detector (RS928) and a pulsed xenon lamp (20 kW power for 8

s) to study emission of the same sample.

Results and Discussion

Typical FESEM images measured from an Au-PVF2 nanofluid at three selective magnifications in order

to illustrate the microstructural features that incur at different length scales are shown in Fig. 1 (a-c). All these

images were taken from the same sample which contained 0.5 wt% Au in form of a basic structure of nanoplates

(Fig.1c). As mentioned above, this specific sample has been studied in detail because it presents a prominent

absorption band of a symmetric shape in the green region 540 nm along with a weak band in the red region 675

nm and a weak band in the violet region 385 nm. These three separated absorption bands can be explored to

tailor light emission over a wide range 300-800 nm for different applications. In Fig. 1a, the FESEM images

when taken at a rather low magnification present distinct assemblies of near spherical shapes, showing a fairly sharp size distribution with an average 920 nm diameter. As can be seen from magnified FESEM images in

Fig.1b, the PVF2 molecules are interbridging small Au-NPs in stable assemblies. Within an assembly, the PVF2

molecules bond primary Au-NPs, mostly thin plates with 120-180 nm width and 10-15 nm thickness. This is

demonstrated well with high resolution FESEM images in Fig. 1c.

Fig. 2 presents absorption spectrum of an Au-PVF2 nanofluid, containing 0.5 wt% Au-NPs, measured in

the range 330-760 nm. As expected, the Au-nanoplates reveal two distinct transverse (T) and longitudinal (L)

modes of the absorption in the localized SPs on the metallic surface upon a tightly bonded polymer surface

layer. The T-mode reflects in a prominent band at 540 nm while the L-mode assumes a rather poor intensity by

an order of magnitude with average position lying at 675 nm. Both of these bands have a doublet structure as

can be seen with their deconvolutions. As a result, two bands of 534 nm and 553 nm comprise the T-mode while

those of 658 nm and 682 nm comprise the L-mode {see the inset (a) in Fig. 2}. The red-shifted band components arise from the Au-SPs which bond the surface polymer layer while the main band components arise

from the regular Au-SPs in the surface modified Au-nanoplates and coalesced in spherical assemblies as shown

in the FESEM images. As given in Table-1, a molar extinction coefficient εmax = 1.105×104 L/mol-cm is

obtained for the 540 nm bandgroup. This specific value is an order of larger magnitude when comparing to a

value εmax = 1×103 L/mol-cm observed in an absorption band at 562 nm in 0.5 wt % Au-NPs embedded in PVP

molecules in form of a nanofluid in water [17].

Furthermore, an order of lower εmax-value is observed in the 675 nm band, or in another similarly weak band shown at shorter wavelength over 340-440 nm in Fig. 2. Table-1 also includes the values for the oscillator

strength (fosc) in the three major bandgroups observed at 385 nm, 540 nm, and 675 nm in Fig. 2.

The fosc-value has been calculated from the integrated area in a bandgroup by using the standard relation

[22],

94.314 10 ,oscf dε ν

∞−

−∞

= × (1)

where the ε-value (the molar extinction coefficient) is taken per unit concentration of Au-NPs in mol/L

and ν = λ-1 expresses the band in an energy scale.

wheretheε-value(themolarextinctioncoefficient)istakenperunitconcentrationofAu-NPsinmol/Landν=λ-1expressesthebandinanenergyscale.

Table 1: SPR bands observed in absorption spec-trum in a 0.5 wt % Au-PVF2 nanofluid

Band position λmax (nm)

εmax -value(L/mol-cm) fosc-value

385 0.13×104 0.26540 1.11×104 0.33675 0.11×104 0.12

Thereactionwascarriedoutwith0.594mMHAucl4in 0.3g/LPVF2inDMF.

In Au-PVF2 assemblies in a nanofluid, a shortwavelength absorption observed over 340-440 nm is anewbandgroupforAu-NPs.Inallpossibleexperimentalshapes,Au-NPsareknowntoabsorbonlyabove450nminausualSPsstructure[1-5].Alsothisbandgroup(Fig.2b)consistsoftwobandcomponentsof373nmand399nminasimilarsequenceofbandintensitiesasthoseshowninthe675nmbandgroupassignedtotheL-modeoftheAu-SPsinAu-nanoplatesmodifiedbyabondedsurfacePVF2layer.ConsideringaclosesimilaritywiththeL-modeoftheAu-SPsintheabsorptionprofile,thisspecificbandgrouparisespossiblywhentheL-modeiscoupledtotheT-modeinthelocalizedAu-SPsontheAu-nanopalatesmediated

Fig. 2: Optical absorption spectrum in a nanofluid containing 0.5 wt% Au-NPs embedded in PVF2 in DMF, with deconvolution of the weak bands (a) 680 nm and (b) 385 nm in the inset.

25


throughthebondedsurfacePVF2molecules.Forexample,acombinationofaT-bandobservedat534nmandanL-bandat658nmcangenerateanewbandof339nm,whichisnotveryfaroffadeconvolutedbandat373nmifaddingasmallenergylossof0.033eV.Consideringasimilarenergy-lossininteractionwiththesurroundingsduringtheabsorptionofthephotonsdescribestheotherabsorptionbandcomponentshown at 399nm in a combination of the twodistinctbandsobservedat 553nm (T)and682nm (L) inFig. 2.This result confers that abondedpolymerPVF2surfacelayerontheAu-NPscausesdesirablynotonlyalocalizedstructureoftheAu-SPsontheAu-NPsbutalsomediatesanexchangecouplingbetweenthetwomodesoftheAu-SPs.

Asexpected,itmodifiesthelocaldielectricfieldaroundasurfacemodifiedAu-nanoplateintheassembliessothatthefieldmodulateselectronictransitionsinthelocalizedSPsinanexchangecoupledcompositesystem.

ConsideringtheFESEMimages(Fig.1)incorrelationtotheabsorptionbands(Fig.2)impliesthatthePVF2moleculesvery efficiently immobilizingAu-NPs in the shape ofnanoplatessothatasurfacestabilizedsamplecoalescesinaspecificsphericalshapeinminimizingthetotalsurfaceenergy.FormationofamolecularPVF2bondingthroughAu-atoms from the surfaceof amodelAu-nanoplate isdemonstratedinFig.3.(a-e).AmodelstructureinFig.3adescribesalinearmolecularPVF2bridgingwhichadjoinsa

Fig. 3: A model chemical bonding of PVF2 molecules on a gold surface; (a) a linear molecular bridging and (b) a molecule adjoining two Au-atoms, and (c-e) polymer molecules interbridging two Au-particles in three different local bonding from the two basic structures. Model displacements of the bonded surface layer (f) perpendicular and (g) along the sample surface.


26

singleAu-atomfromthesamplewhereasaPVF2moleculeinamodelstructureinFig.3badjoinstwodifferentAu-atoms.Other three configurationsproposed in Fig. 3 (c-e) arederivedjustbybridgingtheabovetwobasicconfigurationsside-toside.Allthesethreeconfigurationsbondafluorinerich interface layerwith the surfaceAu-atoms from ananoplate.Althoughaveragenumberdensityoffluorineatomsdoesnotchangeintheseconfigurations,theydifferonefromanotherintermsofthelocalsitesymmetryinthefluorineatoms.Fromgeometricalstabilitypointofview,the configuration (d)made-upof a binary combinationof twobasic structures (b)wouldbe rathermore rigidandstable in interbonding twoAu-NPs.Obviously, thisrepresents themostpreferred interface configuration inastableassemblyofAu-NPs. Theconfiguration(e), i.e.,abinarycombinationoftwodifferentbasicstructures(a,b)maybemoreusefulinorderinganon-centrosymmetricconfigurationoftheelectricdipolesofthefluorineatoms,usefultomodulatethe localelectricfieldinananofluid.Evidently,modeldisplacementsofabondedPVF2surfacelayerperpendiculartotheinterface(Fig.3f)andalongthe interface (Fig.3g)wouldaffect theT-modeandL-mode

oscillationsoftheAu-SPsboundedbyasurfacelayer.Thelocalelectricfieldfromabondedsurfacechargelayer,whichconfinesAu-SPsintheinterface,inducesmixingbetweentheT-andL-modesintheconfinedAu-SPs.

We also studied light-emission in the Au-PVF2 nanofluidhaving0.5wt%Au-NPsbyexcitingthespecimenatdifferentwavelengths(λex)byapulsexenonsource.Fig.4ashowsatypicalemissionspectrumwhenmeasuredover420-600nmbyexcitingataspecificvalueoftheexcitationmaximum.λex~390nm.Itconsistsoftwobandsofpeakpositions466nmand473nmwhicharenotshownintheabsorption spectrum inFig.2. It arises from the surface-interfaceintheAu-NPsonabondedPVF2layer.Theλex-valuehasbeenchosentomeasurethelightemissioninFig.4aaspertheexcitationspectrumasgiveninFig.4b.Asexpected, thisexcitationspectrumcontainseveralbandsover 320-420 nmwhenPVF2surfacemodifiedAu-NPscoalesceinassemblesinfromofahybridcomposite.

ConclusionsTheAu-nanoplates(120-180nmwidthand10-15nm

thickness)whenembeddedinPVF2moleculesfollowingan

Fig. 4: (a) Emission (λex = 390 nm) and (b) excitation (λem = 440 nm) spectra in a nanofluid containing 0.5 wt% Au-NPs embedded in PVF2 in DMF.

27


in-situchemicalreductionreactionAu3+→AuinpresenceofPVF2moleculesinaliquidsuchasDMFcoalesceinsmallassembles.TheproductisastablerheologicalnanofluidatAu-NPscontentsbelow5.0Wt%.Aspecificcomposition,whichcontained0.5wt%Au-NPs,presentsuniquelyanintenseabsorptionbandofsymmetricshapewithaveragepeakpositionlyingat540nm.AsymmetricabsorptionischaracteristicofasharpsizedistributionofAu-NPsandthatisfeasibleonlyonimmobilizedAu-NPswithastablesurfacelayer.Twoweakbandgroups340-440nmand600-740nmshare thespectrum.Adifferentspectrumincursin the emission,with averageposition lyingat 476nm,fromthesurface-interface,whichismodeledassumingapreferablylinearPVF2bondedlayeronthenascentAu-NPs.AbondedlayerconfinesalocalizeddistributionoftheAu-SPsintheinterfacesothatitcontrolsthelightabsorptionandemissioninacompositestructure.

AcknowledgementThisworkissupportedbyaresearchgrantDAE-BRNS,

GovernmentsofIndia.

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B. Susrutha studied M. Sc. (Analytical Chemistry) at Osmania University during 2004-06. She is currently doing Ph. D. at Materials Science Centre, IIT Kharagpur, under the supervision of Prof. S. Ram (IIT Kaharagpur) and Prof. A. K. Taygi (BARC, Mumbai). Her research area includes synthesis of nanofluids and ceramic composites with a dielectric or ferroelectric host for efficient light emission, energy transfer, and other functional properties for biological and other applications.

A. D. Phule received his M. Sc. (Organic Chemistry) from Pune University during 2005-07. At present he is a Ph. D. scholar at Materials Science Centre, IIT Kharagpur, jointly under the supervision of Prof. S. Ram (IIT Kaharagpur) and Prof. A. K. Taygi (BARC, Mumbai). His area of research interest includes development of nanofluids and hybrid nanocomposites with polymeric hosts for optical sensor, barcodes, light emitters, and different biological and drug applications.

Dr. S. Ram received his M. Sc. (Physics) and Ph. D. (Physics) degrees From Banaras Hindu University in 1978 and 1982 successively. He has received several awards including the Alexander Humboldt Fellowship-1994-96, 2004 (Germany), CNRS Fellow-1989 (France), and MRSI (India) medal-2003. He was visiting Scientist/Professor at McMaster University-1988-89 (Canada), Domain University-1989-92 (France), and Ulm University-2005, 06, 07, 08 (Germany). He joined Materials Science Centre, Indian Institute of Technology at Kharagpur, as an assistant professor in 1996, and presently Professor in this Centre. Till date, he has published over 210 peer-reviewed papers, 11 patents, 07 Book chapters, supervised 12 Ph.D., 33 M. Tech., and 21 B. Tech. theses, and carried out about 10 sponsored projects on nanomaterials, biomaterials and applications. His research interest includes glasses, magnetoceramics, intermetallics, nanofluids, magneto-optic materials of garnets, cermets, high-energy-density magnets, ferroics, superconductors, magnetic sensors, GMR, GMS and GMC materials, hydrogen energy storage materials, solid fuels, nanostructured solids, fibres and composites, photonics

29


Preparation and Characterization of Collagen-based Liposome Nanoparticles Composite Matrix

Krishnamoorthy Ganesan*, Praveen Kumar Sehgal, Asit Baran Mandal and Sadulla Sayeed Bioproducts Laboratory-Biomaterial Development Division,

Central Leather Research Institute (Council of Scientific & Industrial Research), Adyar, Chennai-600 020, Tamil Nadu, India

*Corresponding author: email: [email protected]

AbstractThemineralized collagen-cholesterol (CH)-free liposomenanoparticle (LNP) compositematrixhas beenpreparedandcharacterized foruseas tissueengineeringapplications.TheCH-freeLNPwaspreparedbyheatingmethodundertheN2atmosphereandthisabovecompositematrixwaspreparedbyincubationofbovineAchillestendoncollagenwithpreformedCa2+andPiloadedLNP.TheparticlesizeanalysisshowedthatthisLNPwasinthevarioussizerangesbetween20-300nm.TheresultsfromThermomechanical(TMA),DifferentialScanningcalorimetric(DSC)andThermogravimetric(TGA)analysisofthecollagenmatrixalsoindicatesanincreaseinthetensilestrength(TS),denaturationtemperature(TD)andsignificantlydecreasestheweightloss.Thecellviabilityassayshowedmorethan90%fibroblastviability(NIH3T3)96h.Thiscompositematrixdemonstratesahigherresistancetocollagenolyticactivity.Thismatrixcouldbeusefultobone,dentalimplantandduramatter.

Keywords:Biomaterial;Collagen;Liposomenanoparticles;Mineralizedcollagenmatrix

IntroductionThe combinationofpolymeric biomaterials such as

chitosan, alginate, dextran, fibrin, gelatin and collagenwith liposomes could revolutionize the current state ofdrugdeliveryandtissueengineeringtechnology[1,2].Thecombination of collagen and liposomes based technologies fordrugdeliverysystemhasbeenlongachieved[3,4].Inthis case,drugs andotherbioactive agentswerefirstly,encapsulatedintheliposomesandthenembeddedinsideadepot composedof collagen-based systems, includingscaffoldsandinjectablegels[5].Thecombinationofthistwobiomaterial(i.e.,collagenandliposomes-basedsystem)hasimprovedstoragestability,prolongedthedrugreleaserate,and increased the therapeutic efficacy [6,7].ThoughCHincreasingthestabilityofliposomes,itunfortunately,createscertainproblemswhenusedinhumanpharmaceuticals,verydifficulttoatherosclerosisconditionsinthecardiovascularsystem,readilyoxidizedandcreatingstabilityproblems.Asanalternativemethodology,anumberofresearcheshavebeenperformedtodesignandcharacterizetheCH-freeLNPtopharmaceuticsapplication.Todate,littleisknownabouttheapplicationofCH-freeLNPsforretentionofentrappedsolutesandthesereasons,alone,weresufficienttoproposethatCH-freeLNPsmayberelevantcarriersforagentsthat

arenot currently retained in conventional formulations.Whileinmostcasesnaturalandsyntheticphospholipidsarethemajorcomponent,differenttypesofbiocompatibleplantextractcanbeemployedforimprovingthestabilityanddrugdeliveryefficiencyofconventionalLNP[8]. Inaddition,astudywasconductedthattemperaturesensitiveliposomesandcollagenmaythermallytriggerthereleaseofCa2+andPi[9].Thecollagen-basedbiomaterialcompositematrixwithliposomefortissueengineeringapplicationssuchashardtissuereplacementiscurrentlynotavailable.

Recentstudiesalsodemonstratemineralizedcollagencomposite for tissue engineering application [9]. Thenucleation of newmineral phase in embryonic boneand rapidlymineralizing skeletal tissues takes placethrough thepresenceofmatrixvesicles rich in calciumbindingphospholipids.Thepossibility that short chainsofhydrophobicgroupscanserveasanchorsforcollagenonto liposomes,wasdemonstrated [10]. Inviewof this,collagencanattachtotheLNPsurfaceinastableway,andformthemineralizedcollagenmatrixprotectingstructuredshells, thus improving their stability.Among themanybiomoleculesinvolvedinthebonemineralizationprocesses,phospholipidsplay an important role because of theirability tobindCa2+/Pi.ThisCa2+-bindingphospholipids


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as a coatingmaterial for implant osteo integrationhasstudied [11]. The collagenmolecules interactwith thealkyl chains of phospholipidswith the hydrophobicresiduesonthecollagenmoleculesurface[12,13].Recentevidence suggesting that non-collagenousmaterialassociatedwithcollagenserveas themineralnucleationsite [14]. Role of phospholipids in bone repair and itstechnologicalexploitationwasstudied[15,16].Blendingofthebiomaterialwithlecithinstoimprovehydrophobicityandbiocompatibilityhasstudied[17-19].

In this study, we used phenolic glycosides forpreparationofCH-freeLNP.TheobtainedCH-freeLNPcombinewithcollagenforcompositematrixformationinanattempttodevelopanovelbiomaterial.

Experimental

Preparation of CH-free LNPTheLNPwaspreparedbythefollowingmethod[20].A

knownamountofliposomeingredients(phosphatidylcholine(PC):CH,PC:Phenolicglycoside)wereaddedtoapreheated(60°C,5min)glycerol(finalconcentration3%,v/v)withaqueousCaCl2(0.2M)orNa2HPO4(0.2M).Themixturewasfurtherheated (60°C)while stirring (approx. 1000rpm)on a hotplate stirrer for a period of 45–60min undernitrogenatmosphere.ForthepreparationofCH-containingformulations,CHwasfirstdissolvedintheaqueousphaseofMilliQwater(autoclaved)atelevatedtemperatures(c.120°C)whilestirring(approx.6500-24000rpm)foraperiodof 15–30minundernitrogenatmospherebefore addingtheothercomponentsmentionedabove.AfterpreparationoftheLNPsamples, theywereleftatroomtemperatureunderN2 for 30min to stabilize.TheCH-freeLNPwasproducedbypassingtheemulsionrepeatedlythroughapolycarbonatemembranehavingpores 400and200nmindiameter.Thediameterof theLNP isdeterminedbytheporesizeofthemembraneusedduringtheextrusionmethod. The LNPproduced using thesemethods areunilamellar.TheresidualsolventisremovedbysubjectingtheLNPfilmtoahighvacuumonagoodlyophilizerfor90-120min.Theparticlesize,shapeandzetapotentialwereanalyzedbyDynamiclightscattering(DLS).

Preparation of collagen-LNP composite matrixAknownamountof isolated collagen [21] in 0.05M

aceticacidwithpH7.4(1NNaOHinthepresenceof10xHEPES bufferwith a final concentration of 0.5×)wasprepared.Thegellingmixturewasplaced inside an ice

waterbathat4°Ctoslowdownthepolymerizationratefor5min.LNPwasaddedtothemixtureandthoroughlymixedwell.Amixtureofoliveoilandsiliconoilataratioof1:1waslaiddownontheaqueousgellingmixtureatavolumeratioof6:1.Anonionic surfactant,Tween20,wasaddedto theaqueousphasebeforeemulsification.Themixturewashomogenizedatamaximalspeed(6,500-24,000rpm)for30min.Theemulsions formedwere thenplaced ina 37°Cwaterbathtospeedupthepolymerization.Duringtheprocess,thesolutionbecameawhitemilkysuspension.Themixturewasincubatedfor30minuntilequilibrium.Themixturewascentrifugedbrieflyat10,000rpmfor10mintoseparatethesolidmatrixfromtheliquidphase,includinganaqueousandanoilphase.Afterdiscardingtheoilandtheliquidphases,thiscompositematrixwasrinsedtwicewithMilliporewaterandreadyforfurthercharacterizations.

Characterization of collagen-LNP composite matrixTheTMA((TMA,InstronseriesIIAutomatedMaterials

TestingSystem),DSC(DSC,TA-DSCQ200)andTGA(TGA,TA-TGAQ50)wereusedforanalysisofmechanicalandthermalstabilityofthiscompositematrix.Thewater-uptakeand swelling studies ratiowas obtainedby incubationof the samples (W0andS0respectively)inwateratroomtemperaturefor2h.Thewater-uptakeratioisdefinedas(Wt-W0)/(W0).Theswellingratioisdefinedas(St-S0)/(S0).FT-IR(PerkinElmerspectrometer)spectrawereusedforanalysisof structural elicitationof thismatrix.TheSEM(SEM, FEI-Quanta 200)were used to observe the sizeand surfacemorphologyof thismatrix.Biodegradationofcollagencompositematrixwasanalyzedbyfollowingmodifiedmethod[22].

Results & DiscussionThe analyses of the sizedistributionofCa2+ andPi

loadedLNPwererevealedbyDLS.Theparticlesizesweremorepreferablyfrom20to900nm,mostpreferably100-250nmrangesandzetapotentialobserved30to-60mV.Therefore, zetapotentialofLNPobserved30 to -60mVweresufficientlyhighforelectrostaticstabilizationprobablybecause of the charges of phenolic glycosides inLNP.Tensilestrengthofthecollagenmatrixincreasedwiththepresenceofmineraloncollagenmatrix.The%elongation,on theotherhand, showeda same trend.Furthermore,mineralization leads to a significantly improve tensilestrengthcomparedtothecollagenmatrix.

TheTD of thenative, collagen-LNPandmineralizedcollagenwere shown at 69.89, 84.04 and 108.87 °C for

31


all collagen respectively.Mineralized collagen exhibitsan increase in thedenaturation temperature (TD) when compared tonative collagen. From thisdata, it canbeobservedthataninitialthermaltransitionalchangeoccursbetween the temperature rangeof200-500 °C forall thecollagen,withmaximumpercentage glass transitional(Tg)weightlossat54.06,59.46and70.64%foralltreatedcollagenrespectively.Whencollagen/Ca2+andPi loaded LNPweightratiois2:1,thecoatingofcollagenontothisLNPcanremarkablyimprovetheirinvitrostabilitybecauseithasbasicallynoeffectonthefluidityofthisLNP.

Themineralized collagenmatrixwas resulting fromthermally triggered self-assemblyof collagenfibril andliposomemineralization.Heatingoftheprecursorfluidto37°Cinducescollagenmonomerstoself-assembleintoacollagen,intowhichmineralcrystalsaredeposited.Water-uptakeandswellingratioofthecollagen,collagen-LNPandmineralizedcollagencompositematrixwere85,40and20%and8,4and2%atpH7.4respectively.Generally,thewater-uptakeratioiscontrolledbyhydrophilicityandwatermaintenanceofthematrix.AlthoughtheformationofCa2+ andPiloadedLNPparticlesmaydecreasemoreorlesstheamountofhydrophilicgroupsofthecollagen.

Themineralized collagenmatricespresented lowerswellingratio.Thiscompositematrixexhibited42and11%degradationof collagen as against 93%degradation inthe caseof thenative collagenmatrix at 96hperiodofincubation.ThestabilityofthiscompositematrixagainstChCwouldhavebeenpreventedbytheLNPwithcollagennetwork,which linksmicrofibrils, shielding in collagenhelices. Small and largerLNP (100-200nm)on collagenmatrixwere detected in the SEM image [Fig. 1]. ThesurfacesofbothasobservedbySEMweresphericalandsmooth. In addition, collagen is ahydrophobicproteinand the compositematrixprepared from it has amore

Table 1 : TS, %E, TD , Tg, % Degradation and % cell viability mineralized collagen.

Process TS (Mpa) %E TD (oC) % Tg % Water uptake

% Swelling % Degradation % Cell viability

Nativecollagenmatrix

11.13 20.04 69.89 54.06 85 8 93 100

Collagen-LNP matrix

13.28 24.71 84.04 59.46 40 4 42 95

Mineralizedcollagenmatrix

17.78 22.34 108.87 70.64 20 2 11 98

morphologies.Moreover,comparedwiththecontrol,theirproliferationonthecollagenmatrixwassignificantlyup-regulated.

Fig.2: Cell viability analysis of A) collagen, B) collagen-LNP and C) mineralized collagen matrix

Inourexperiments, theresultssuggestthatcollagen

Fig 1: SEM analysis of A) collagen, B) collagen-LNP and C) mineralized collagen matrix

hydrophobic. Thesematrices exhibitedmore than 90%fibroblastviability(NIH3T3)at96h[Fig.2].MineralizedcollagencompositematrixwithLNP,suggestingthehighdegreeofbiocompatibilityevidencedthatcollagenmatrixmaybeofpotentialuseintissueengineering.

Incurrentstudies,theinvitrobiocompatibilityefficacyof the collagenmatrix to support cell proliferation andviabilitywas assessed by growingNIH 3T3 fibroblastandwere found to be grownuniformlywith normal


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mayhavetheabilitytonucleatemineralgrowthundertheseaboveconditions.Thepracticalsignificanceofthisfindingisthatitsuggeststhatinsituliposomalmineralizationofthecollagenmatrixmayprovidearoutefortheformationof themineral/collagen composite biomaterialswithsignificant interactionbetween themineralandcollagenphases. In addition, LNPalsopromotemineralization.Lipids arepresent in the extracellularmatrix at sitesofthemineralization and are associatedwith themineralphasesuchasregulatingthegrowthofpreformedmineralcrystal.However,forthisapproachestobepracticalwillrequireasignificantincreasethemechanicalstabilityintoa rangemore suitable for repair ofhard tissue. Furtherexperimentswillbenecessarytoinvestigatethepossibilityof significantly increasing themineralization capacityofLNP.This collagen compositematrixmay representmaterialsofchoiceforanewgenerationofbiomaterialsforhardtissuereplacement.

ConclusionsTowardanultimategoalofboneregeneration,wehave

introducedLNPasamodifyingadditive in thecollagenmatrix,basedonwhichaseriesofnovelcollagen/LNP-Ca2+ andPicompositematrixisdeveloped.Thiscompositematrixwas successfullyprepared through interactionsbetweencollagenwithCa2+andPiloadedLNP.TriggeredmineralreleasefromtemperaturesensitiveLNPwascombinedwiththermalcollagengelationtoformamineralizedcollagenmatrix,therebymimickingtheprocessesthatoccurduringnaturalmineralizedtissueformation.Thisstrategytakesadvantageofliposomalencapsulationofmineralsandtheirreleaseintoacollagenmatrixformedbythermallytriggered

self-assemblyofacid-solubletypeIcollagen.Theapproachisdesignedtoyieldaninjectablecollagen-LNPcompositeprecursorusefulforminimallyinvasivereconstructionofbone,dentaltissueandduramatter.Biomimeticcompositematrixmay representmaterials of choice for a newgenerationofrapidlyosteointegratingmaterials.

References1. K.Y.LeeandS.H.Yuk.Prog. Polym. Sci. 32 (2007)669.2. M.S.Mufamadi,V.Pillay,Y.E.Choonara,L.C.DuToit,G.

Modi,D.NaidooandV.M.K.Ndesendo.J. Drug Deliv.2011(2011)1.

3. H.Wang,P.Zhao,W.Su,S.Wang,Z.Liao,R.NiuandJ.Chang.Biomaterials 31(2010)8741.

4. P.S.Nunes,R.L. Albuquerque-Júnior, D.R.Cavalcante,M.D.Dantas,J.C.Cardoso,M.S.Bezerra,J.C.Souza,M.R.Serafini,L.J.Quitans,L.R.BonjardimandA.A.Araujo.J. Biomed. Biotechnol.9(2011).

5. L.Weiner,S.S.Carpenter-GreenandE.C.Soehngen.J. Pharm. Sci.74(1985)922.

6. X. Shi,W.Ma,C. Sun and S.Wu.Biomaterials 22 (2001) 1627.

7. R.Nair,M.Sevukarajan,T.Mohammed,BadivaddinandC.K.AshokKumar.J. Innov Trends. Pharm. Sci.1(2010)288.

8. D.B.FenskeandP.R.Cullis.Exp. Opin. Drug Deliv.5(2008) 25.

9. A.W. Pederson, J.W. Ruberti and P. B.Messersmith.Biomaterials24(2003)4881.

10. J.Pokorny,J.Davidek,V.Chocholata,J.Panek,H.Bulantova, W.Janitz,H.ValentovaandM.Vierecklova.Nahrung. 34 (1990) 159.

11. M.Santin,W.Rhys-Williams, J.O’Reilly,M.C.Davies,K.Shakesheff,W.G.Love,W.A.LloydandS.P.Denyer.J. R. Soc. Interface3(2006)277.

Fig.2: Cell viability analysis of A) collagen, B) collagen-LNP and C) mineralized collagen matrix

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12. J. Filipovic-Grcic,N. Skalko-Basnet and I. Jalsenjak. J. Microencapsul.18(2001)3.

13. M.J.Fonseca,M.A.AlsinaandF.Reig.Biochim. Biophys. Acta (BBA)-Biomembr.1279(1996)259.

14. H.P.Wiesmann,U.Meyer,U.PlateandH.J.Hohling.Int. Rev. Cytol.242(2005)121.

15. A.MerolliandM.Santin.Molecules 14(2009)5367.16. J.H.CollierandP.B.Messersmith.Annu. Rev. Mater. Res.

31(2001)237.

17. Y.Wang,F.Z.Cui,Y.P.Jiao,K.HuandD.D.Fan.Biomed. Mater.3(2008)

18. R.Nirmala,H.M.Park,R.Navamathavan,H.S.Kang,M.H.El-NewehyandH.Y.Kim.Mater. Sci. Engine.C.31(2011) 486.

19. X.Shi,Y.Wang,L.Ren,W.HuangandD.A.Wang.Int. J. Pharm.373(2009)85.

20. G. Krishnamoorthy, P. Stephen, M. Prabhu, P. K. Sehgal and S. Sadulla. AIP conf. Proc.1276(2010)163.

21. P.K.Sehgal,M.R.Ahmed,R.JayakumarandR.Sripriya.Aprocessforthepreparationoftransparentsoftcollagenfilm.Indian Patent.DEL2001,p.201.

22. G.Krishnamoorthy,B.Madhan,S.Sadulla,J.RaghavaRao andW.Mathulatha.J. Appli. Polym. Sci.108(2008) 199.

Mr. Ganesan Krishnamoorthy obtained his MSc degree in Biochemistry from Bharathidasan University, Tiruchirappalli and currently pursuing PhD in Biotechnology at Anna University, Chennai. Major objectives of his research work are Green chemistry approach to stabilization of collagen based biomaterials and coating of liposome nanoparticles on collagen matrix for biomedical applications (Drug delivery, Tissue engineering and Regenerative medicine).

Dr. Praveen Kumar Sehgal obtained his PhD degree in Chemistry from Madras University, Chennai. He is presently scientist G, CSIR-CLRI, Chennai. Major objectives of his R & D work are better utilization of slaughter by-products and biomedical application of animal tissues (Drug delivery and Tissue engineering applications).

Prof. Dr. Asit Baran Mandal obtained his PhD degree in Chemistry from Jadavpur University, Kolkata. He is a fellow of the Academy of Saint Cecilia (FASc) and Royal Society of Chemistry (FRSC), UK. He is presently Director of CSIR-CLRI, Chennai. Major objectives of his current research work are development of methodologies and physico-chemical techniques for the characterization of micellar and reverse micellar systems involving collagen, peptides, drugs, synthetic and vegetable tanning materials and polymeric surfactants.

Prof. Dr. Sayeed Sadulla obtained his M.Tech degree in Leather Technology from Madras University and PhD from Anna University, Chennai. He has more than 35 years of experience in R & D in Leather Technology, Education and Training & Science and Technology Management. He had a distinguished career as a scientist and educationist at CSIR-CLRI, Chennai from 1975 to 2007 and superannuated as Director Grade Scientist. His current research interest/activities include Green Chemistry (Leather processing) and Collagen based biomaterials for industrial and biomedical applications.


34

Application of Nanophosphors in Solid State White Light GenerationDimple P. Dutta

Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 e-mail : [email protected]

AbstractSolid-statelighting(SSL)isemergingasahighlycompetentfieldandapossiblealternativetoexistinglightingtechnologies.Phosphorconvertedlightemittingdiodes(pc-LED)formanintegralpartofthisgenreofresearch.In thismanuscript, thepotential ofdifferent rare earth/transitionmetaldopedhostmaterialshavebeendiscussed.Thehostmaterialsstudiedweregadolinia,zincaluminateandzincphosphate.Theeffectofdopantionconcentrationaswellasthatofthesynthesistechniqueemployed,ontheresultantCIEcoordinatesofthephosphorshavebeenstudied.ThenanophosphorsweresynthesizedthroughsonochemicalprocessorpolyolmethodandcharacterizedbyusingX-raydiffraction (XRD), transmissionelectronmicroscopy (TEM)andphotoluminescence(PL)spectrophotometry.TheresultsofXRDandTEMshowthatresultantnanoparticlesaresinglephaseandhavesphericalshape.Thedopedsamplesshowedmulticoloremissiononsinglewavelengthexcitation.Energytransferwasobservedfromhosttothedopantions.CharacteristicblueandyellowemissionfromDy3+ions,greenfromTb3+ionsandredfromEu3+ionswereobserved.However,theMn2+ionsinzincgallatehostyieldedredemissionwhichhasbeenassignedtocharge-transferdeexcitationassociatedwithMn2+ion.

Keywords:Gadolinia,Zincgallate,Zincaluminate,Nanoparticles,Photoluminescence

TheemphasisonresearchonSSLhasgainedtremendousmomentum in the past decade due to their inherentadvantagesofhighlightefficiency,lowenergyconsumptionandlongservicelifetimecomparedtoconventionallightsources[1-5].Therearevariousapproachestogetefficientsolid state sources forwhite light generation.We candirectlymix light from three (ormore)monochromaticsources, red,greenandblue (RGB), toproduceawhitesourcematchingwiththeRGBsensorsinthehumaneye.AnothermethodistouseablueLEDtopumponeormorevisiblelight-emittingphosphorsthathasbeenintegratedintothephosphor-convertedLED(pc-LED)package.Thepc-LEDisdesignedtoleaksomeofthebluelightbeyondthephosphortogeneratetheblueportionofthespectrum,whilephosphorconvertstheremainderofthebluelightintotheredandgreenportionsofthespectrum.WecanalsouseanultravioletLEDtopumpacombinationofred,greenandbluephosphorsinsuchawaythatnoneofthepumpLEDlightisallowedtoescape.

Eachof these approacheshaspotential advantagesandcleartechnicalchallenges.Mixingtheemissionfromred,blueandgreencoloredLEDs ismostadvantageoussincethereisnoquantumdeficitarisingfromStokesshiftandhence offers infinitely graduated color andwhitepoint control.However, this form requires independentoutputpowercontroloneachLEDs,thereisagapinthe

operatingvoltagebetween themandboth these factorsmakestheoperationquitecumbersome.In1996,thewhiteLEDs fabricated fromblue LED chips combinedwithyellowphosphorsCe3+(YAG)werecommercialized[6].Thisphosphor-conversionwhiteLEDrepresentedaninnovationinsolid-statelighting,becausetheyweresmall,lightweight,hada long lifetimeandwas easy tooperate.However,theywere inherently less efficient than anRGB sourcebecauseoftheunavoidableenergylossconcomitantwiththewavelength-conversionofaphotonfromwavelengthλ1toλ2withλ2>λ1.Theenergylossisparticularlylargeforwavelength-conversionprocesses from theUV (400nm)tothered(625nm)wherethelossis36%.ThethirdapproachistohaveUV-LEDs.InthiscasetheUVlightiscompletelyadsorbedbythephosphorsandthemixedRGBoutputappearswhite.Thequantumdeficitbetween theUVpumpandthephosphors,especially the low-energyredphosphor,dissipatessignificantenergyandmakesthisapproachinherentlylessefficientthaneithertheRGBorthepc-LEDschemesforgeneratingwhitelight.However,theUV-LEDapproachhas theadvantage that color canbecontrolledbythephosphormixatleastatonepointintimeandatonetemperatureandhencethecolorrenderingshouldbeexcellent.

Theuseofphosphorsbymanprobablystartedmorethan2000yearsagowhentheywereusedinfireworksto

35


modifythecolouroutput.However,theimportanceofLEDphosphorsforwhiteandcolouredlightgenerationmustbe consideredan importantmarketdriver in the future.Phosphorsareusuallymadefromasuitablehostmaterial,towhichanactivatorisadded.Theyarecomposedofaninert host lattice (silicate/phosphate/oxide/fluoride/sulfide)andanopticallyexcitedactivator,typicallya3dor4felectronmetalion,whichiscapableofexhibitinghighphotoluminescenceefficiency,stabilityandhighabsorptioncross-section[7].Oxidephosphorsofferpotentialadvantageoverthecommonlyusedsulfidephosphors,duetotheirsuperior chemical and photo-stability and excellentluminescent properties [8,9]. The unique luminescentproperties of rare-earth elements hosted in differentmatricesfind technologically important applications inoptoelectronicdevices suchasplasmapanels,flatpaneldisplays, luminescent lighting, IRwindows etc [7,10].Phosphorsarenowcriticaltothelong-termperformanceofLEDlighting,andtheidealphosphormaterialshouldhaveabroadexcitationspectruminthedesiredspectralregion,narrowemissionbandscenteredonsuitablewavelengths,highquantumefficiency(>90%),highlevelsofabsorptionat theexcitationwavelength, high temperaturestabilityof emission spectra andquantumefficiency alongwitha suitablemorphology.Thequalityof thewhite light isdeterminedfromitsCIEcoordinatesalongwithcorrelatedcolor temperature (CCT).CCT is the temperatureof anequivalentblackbodyradiatorthathasacolorwhichmostcloselymatchestheemissionfromanonblackbodyradiator.Forhighqualitywhitelight,sourceswithCIEcoordinatesintherangex=0.28to0.35andy=0.30to0.37withaCCTbetween2500and6500Kare required [11,12].TheCCTrangesignifieshowwarmorcool thewhite light is,viz,awarmer (i.e., lower temperature) light isoftenused inpublicareastopromoterelaxation,whileacooler,whiterlightisusedinoffices.

Conventionalphosphorsareinmicrometerscale,lightscattering at grain boundaries is strong anddecreaseslightoutput.Conventionalphosphorsobtainedby solidstatesinteringmethodhaslowerconcentrationquenchingthresholdduetonon-uniformdoping.Nanophosphorsinsizefromtenstohundredsofnanometersthataresmallerthan the lightwavelength can reduce scattering. Softchemical routes to synthesize thesenanophosphors canimproveuniformityofdopingand lift theconcentrationquenching threshold.Somesoft chemical techniquesarealso capable formassiveproductionat lowcost. In this

have been synthesizedusing soft chemical techniqueslikesonochemicalmethodorpolyolroute.Sonochemicalsynthesisisbasedonacousticcavitationresultingfromthecontinuousformation,growthandimplosivecollapseofthebubblesinaliquid[13,14].

Gadoliniumoxide(Gd2O3),arareearthsesquioxide,hasuniquepropertieswhichcanbeutilizedinawiderangeoftechnologicalapplications.Gadoliniumoxide(Gd2O3) is an attractivehostlatticeforseverallanthanideionstoproduceefficientphosphorsemittingavarietyofcolors.Recently,Gd2O3:Eu3+phosphorhasbeen consideredasoneof thebetterphosphorcandidateforflatpaneldisplays(FPDs)owing to itsgoodcolorpurity [15-17].The red-emittingEu-dopedGd2O3 phosphor is gaining importance dueto its favorable low thermal expansion,phase stability,highmeltingpoint[18].IthasbeenwidelyusedasX-rayscintillatormaterials,highdefinitionprojectiontelevisions,flatpaneldisplays, andphotoelectronic apparatus [19].Over the past decade, Eu3+ and Tb3+ activatedGd2O3 phosphorshadbeen investigatedextensively [17,20-22].Tb3+,Dy3+andEu3+ ionsdopedGd2O3particleshavegotpotentialapplicationinimmunoassays[23].

Recently,wehavereportedthesonochemicalsynthesisof a novel nano-crystallineGd2O3:RE (RE=Dy3+, Tb3+) phosphorwhichsimultaneouslyemitsblueandyellowlightfromitsactiveregiononexcitingthehostandconsequentlyisexpectedtohavetremendousapplicationsinwhitelight

Fig. 1: XRD patterns of Gd2O3 nano powders (a) as prepared (b) annealed (c) doped with rare-earth ions.


36

emittingdeepUV-LEDs[24].Figure1(a,b)illustratesthediffractionpatternsoftheaspreparedandannealedGd2O3 nanoparticles, respectively. It is evident from theXRDpatternsthatthestructure-lessfeaturesdetectedfortheaspreparedsamplesweredue to theamorphousnatureoftheproduct.Onannealingthepowderat500°Cfor1h,diffractionpeakswereobservedwhichmatchedwiththereporteddata forGd2O3 (PC-PDFcard#76-0155). In thecaseofEu3+andDy3+dopedGd2O3 samples, annealing at 500°Cyieldedcrystallinenanoparticles;whereasforTb3+ dopedGd2O3, the annealing temperature requiredwas800°C.TheXRDpatternsofthesingle,doubleandtripledopedGd2O3nanoparticles, obtainedafter annealingat800 °C, are similar andone such representativepatternis shown in Figure 1c. The emission spectra ofGd2O3:Dy3+(1.95%):Tb3+(0.05%) onexcitationat 230nm,247nmand277nmisillustratedinFigure2.Itshowedthepresenceofcharacteristicyellow,blueandgreenemissionsduetoDy3+andTb3+ions,respectively.Asseeninthespectrum,onexcitationat themainhost site (230nm), there is anefficient energy transfer fromhost toDy3+ dopant, and hencemaximumemissionisobservedat575nm.However,onexcitingthesampleat247nm,theintensityofemissionat575nmreducesconsiderably, though it is stillhigherthan thatobserved forexcitationat277nm.Thiscanbeattributed to the fact that as the energyassociatedwithhigherwavelengthexcitationis lower, theprobabilityofenergytransferfromhosttoallthedopantsiscomparativelyreduced.TheCIEchromaticitycoordinatescalculatedfrom

Fig. 2: Emission spectrum of Gd2O3:Tb3+:Dy3+ (Tb = 0.05% and Dy = 1.95 mol%) nano particles obtained after excitation at 230 nm, 247 nm and 277 nm.

Fig. 3: CIE chromaticity diagram for Gd2O3:Dy3+(1.95%):Tb3+(0.05%) nanoparticles at λexc = 247nm.

article,wereport theworkdoneonnanophosphors likeGd2O3:RE(RE=Eu,Dy,Tb),ZnAl2O4:MandZnGa2O4:M(whereM=Dy3+,Tb3+,Eu3+andMn2+).Thenanophosphors

Fig. 4: Photographs of Gd2O3:Dy3+(2%) film on quartz under ultraviolet light with room lights switched off. Bright white emission is observed with the ultraviolet excitation.

37


6500Kwhichrepresentsstandarddaylight.Forthisdoubledopedsample,anexcitationat247nmresultedinaCCTof6508KwhichwasextremelyclosetothatofD65.Duetothenondispersibilityof the sonochemically-synthesizedGd2O3:Tb3+:Dy3+nanoparticleinaqueous/organicsolvent,polyolmethodof synthesiswas explored [25].TheCIEchromaticity coordinates (x= 0.270, y= 0.328) and theCCTvalue(9157K)oftheGd2O3:Dy3+(1.95%):Tb3+(0.05%)phosphor synthesizedbypolyol routewasdistant fromthat of the D65 point (6500K).Thisproves thatmethodof synthesisplays amajor role in optical properties ofnanomaterials.DispersibleGd2O3:Dy3+(2%)phosphorwasthen synthesizedusingpolyol technique.Thephosphorshowedwhite luminescence in solid form, as aqueoussolutionandalsowhenspincoatedonquartzsubstrate.ForthespincoatedsampleCIEcoordinateswerex=0.313andy=0.296andthecorrelatedcolortemperaturewas6815K.ThephotographinFigure4showaspincoatedGd2O3:Dy3+(2%)phosphorfilmonaquartzslidesubstrate,andthebrightwhiteluminescenceofthisfilmobservedunderultravioletlightwithλexc=310nm.ThisdemonstratesthatGd2O3:Dy3+(2%)filmsaregoodcandidatematerialsfornewlightingdevices.

Recently,ZnAl2O4andZnGa2O4haveattractedattentionasanimportantphosphorhostmaterialforapplicationsinthinfilmelectroluminescentdisplays,mechano-opticalstress

Fig. 5: PL emission spectra monitored at λ exc = 380nm for ZnGa2O4:Dy3+(1.5%): Tb3+(0.25%):Eu3+(0.25%) nanoparticles.

Fig. 6 : Chromaticity diagram for ZnAl2O4:Dy3+(1.5%):Tb3+(0.25%):Eu3

+(0.25%) nanoparticles with λexc A = 380nm, B = 364nm, C = 396nm

theemissioncurveofGd2O3:Dy3+(1.95%):Tb3+(0.05%)for247nmexcitationwerex=0.315andy=0.316(Figure3).ThesevaluescorrespondalmostexactlytotheCIEcoordinatesofthebalancedwhitelightregionofthechromaticitydiagramwherex=0.33,y=0.33.ThecorrespondingCCTvaluewasfoundtobe6508K.CIEstandardilluminantD65hasaCCTof

Fig. 7: Emission spectra monitored at λ exc = 340nm for (a) ZnGa2O4:Dy3+(2%): Tb3+(0.5%):Mn2+(1.5%) and (b) ZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(2.5%) nanoparticles.


38

sensors,andstressimagingdevices[26-30]. TheopticalbandgapofpolycrystallineZnAl2O4 semiconductors is 3.8eV,whichindicatesthatzincaluminateinthepolycrystallineformistransparentforlightpossessingwavelengths>320nm[31].TheopticalbandgapofZnGa2O4isapproximately4.4eV.Likeotherwidebandgapsemiconductors,ZnGa2O4 exhibitsablueemissionunderexcitationbybothultravioletlightandlow-voltageelectrons[32]. ActivationwithMn2+, Eu3+,Tb3+ionsshiftstheemissiontogreenorred.

Wehave reported the synthesis of nanocrystallinesingle, double and tripledopedZnAl2O4:M (M=Dy3+, Tb3+ and Eu3+) and ZnGa2O4:M (M =Dy3+, Tb3+ and Eu3+/Mn2+),bysonochemicalmethod[33].Inourstudy,Dy3+,Tb3+ andEu3+/Mn2+ ionswere single,double andtripledoped inZnAl2O4andZnGa2O4host latticeusingsonochemical technique. By altering the individualdoping concentrations in the triple doped samples,the desired photoluminescence emission at selectedwavelengthcouldbeobtained.ThehighlightoftheworkisthesynthesisofanovelcompositionofnanocrystallineZnAl2O4:Dy3+:Tb3+:Eu3+ and ZnGa2O4:Dy3+:Tb3+:Mn2+ phosphorswhichsimultaneouslyemitsblue,green,yellowandredlightfromitsactiveregiononexcitingthehostandhaveveryimpressiveCIEandCCTvalues.

ThePLemissionspectrumofZnAl2O4:Dy3+(1.5%):Tb3+(0.25%):Eu3+(0.25%)sampleatλexcof380nmisshowninFigure5.Itispossibletodistinguishfouremissionbandscenteredat∼595,611,644and686nmwhichcorrespondto5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4transitionsofEu3+ ions,respectively.TheemissionsfromDy3+ionscenteredat480nm(4F9/2→6H15/2)andalessstrongoneintheyellowregioncenteredat571nm(4F9/2→6H13/2)arealsoclearlydiscernible.Theemissionbandsobservedat495and543nmareduetothe5D4→7F6 and 5D4→7F5transitionsofTb3+ions.Thebroadbandat∼506nmisduetotheintrinsicluminescenceofthehostlattice.ThecoloremissionoftheZnAl2O4:Dy3+(1.5%):Tb3+(0.25%):Eu3+(0.25%)nanoparticleswasevaluated.CIEcoordinateswithcorrespondingCCTfordifferentλexcisshowninTable1.ThechromaticitydiagramshowninFigure6indicatesthatalltheemissionswithλexc=364and380nmliepredominantlyinthewhiteregion.FromthediagramitisevidentthatclosesttowhitelightregionistheemissionobtainedfromtheZnAl2O4:Dy3+(1.5%):Tb3+(0.25%):Eu3+(0.25%)nanoparticleswithλexc=380nmanditsCCTvalue(6689K)isalsoclosetothatofnoondaylight(6500K,commonlyknownasD65point).

Table 1: CIE and CCT values of ZnAl2O4: Dy3+

(1.5%) :Tb3+(0.25%):Eu3+(0.25%) nanoparticles for various λexc

Excitation wavelength (nm)

X y CCT(K)

364 0.305 0.293 7475380 0.312 0.307 6689396 0.259 0.272 15329

Similarly,inanefforttogetwhitelightfromzincgallatephosphor,wecodopedtheZnGa2O4:Dy3+(2%)nanoparticleswithTb3+ andMn2+ ions.Theemission spectraobtainedfromtheZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(1.5%)andZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(2.5%)nanoparticlesonexcitationat 340nmare shown inFigure7.Apart fromemissions from the host (in the blue region) andDy3+ ions,strongbroadredemissionsfromMn2+ dopants have beenobservedbetween650to700nm.Averyweakgreenemissionwasalsoseenat519nmwhichoriginatesfromthe4T1→6A1transitionofMn2+.Theemissionat544nmisduetothetransitionbetweentheexcited5D4 state and the 7F5 groundstateofTb3+ion.TheCIEcoordinatesforZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(1.5%)andZnGa2O4:Dy3+(2%):Tb3+(0.5%):Mn2+(2.5%)nanoparticleswasfoundtobex=0.265,y=0.285andx=0.304,y=0.310,respectivelywithCCTvaluesof12298Kand7251K.

The highlight of the work is the synthesiso f n o v e l c ompo s i t i o n s o f n a n o c r y s t a l l i n eGd2O3:Dy3+(1.95%):Tb3+(0.05%),ZnAl2O4:Dy3+:Tb3+:Eu3+ and ZnGa2O4:Dy3+:Tb3+:Mn2+phosphorswhichsimultaneouslyemits blue, green, yellowand red light from its activeregiononexcitingthehostandhaveveryimpressiveCIEandCCTvalues.Suchco-dopednanocrystallinephosphorsareexpectedtohavetremendousapplicationsastunablemulticolordisplaysandinwhitelightemittingUV-LEDs.TheresultsthusprovideapracticalbasisforthedesignofwhitelightilluminationsourcesbyblendingthiskindofphosphorswithanappropriateUVemitter.

References1. S.Nakamura,Appl.Phys.Lett.,64(1994)1687.2. S.Aanegola,J.PetroskiandE.Radkov,SPIE10(2003)16.3. Y.Narukawa,Optics&PhotonicsNews,4(2004)25.4. L.S.Rohwer,A.M.Srivastava:Electrochem.Soc.Interface,

12(2003)36.

39


5. J.Y.Taso:Ed.LightEmittingDiodes (LEDs) forGeneralIllumination Update 2002; Optoelectronics IndustryDevelopmentAssociation:Washington,DC,(2002).

6. K.Bando,K.Sakano,Y.Noguchi,andY.Shimizu,J.LightVis.Environ.,22(1998)2.

7. J.McKittrick, L. E. Shea,C. F. Bacalski andE. J. Bosze,Displays,19(1999)169.

8. M. FlynnandA.H.Kitai, J. Electrochem. Soc., 148 (2001)H149.

9. M.Yu, J.Lin,Y.H.ZhouandS.B.Wang,Mater.Lett.,56(2002)1007.

10. JustelT,NikolHandRondaCAngew.Chem.Int.Ed.,37(1998)3084.

11. B.W. D’Andrade and S.R. Forrest, Adv. Mater., 16(2004)1585.

12. J.McKittrick, L. E. Shea,C. F. Bacalski andE. J. Bosze,Displays,19(1999)169.

13. S.SundarManoharanandM.RaoEncyclopediaofNanoscienceandNanotechnology edNalwaH S (U.S.A.:AmericanScientificPublishers)(2004)67.

14. K.S.Suslick,Science,247(1990)143915. J.C.Park,H.K.Moon,D.K.Kim,S.H.Byeon,B.C.Kimand

K.S..Suh,Appl.Phys.Lett.,77(2000)216216. Y.C.Kang,S.B.Park,I.W.LenggoroandK.Okuyama,J.

Phys.Chem.Solids,60(1999)379.17. B.Mercier,C.Dujardin,G.Ledoux,C.LouisandO.Tillement,

J.Appl.Phys.,96(2004)650.18. H.Guo,N.Dong,M.Yin,W.Zhang,L.LouandS.Xia,J.Phys.

Chem.B,108(2004)19205–19209.19. A.Bril andW.L.Wanmaker, JournalofElectrochemistry

Society,111,(1964)1363–1368.

20. Y.Li,G.LiuandG.Hong,JournalofRareEarths,22(2004)70–74.

21. G.-X.Liu,G.-Y.Hong, andD.-X. Sun,Chinese Journal ofInorganicChemistry,20(2004)1367–1370(Chinese).

22. G.-X.Liu,J.-X.Wang,X.-T.Dong,andG.-Y.Hong,JournalofInorganicMaterials,22(2007)803–806,(Chinese).

23. W.O.Gordon,J.A.CarterandB.M.Tissue,J.Lumin.,108(2004)339.

24. V.Bedekar,D.P.Dutta,M.Mohapatra, S.V.Godbole,R.GhildiyalandA.K.Tyagi,Nanotechnology,20(2009)125707(9pp)

25. V.Bedekar,D.P.Dutta andA.K.Tyagi, J.NanoscienceNanotech.,10(2010)8234-8238.

26. T.Minami,Y.Kuroi,T.Miyata,H.YamadaandS.Takata,J.Lumines.,72(1997)997.

27. J.S.Kim,S.G.Lee,H.L.Park,J.Y.ParkandS.D.Han,Mater.Lett.,58(2004)1354.

28. H.Matsui,C.N.XuandH.Tateyama,Appl.Phys.Lett.,78(2001)1068.

29. E.Martinez-Sanchez,M.Garcia-Hipolito, J.Guzman, F.Ramos-Brito, J. SantoyoSalazar,R.Martinez-Martinez,O.Alvarez-Fregoso,M.I.Ramos-Cortes,J.J.Mendez-DelgadoandC.Falcony,Phys.StatusSolidia,202(2005)102.

30. Z.Lou,J.Hao,Appl.Phys.A,80(2005)151.31. S.K. Sampath, J. F.Cordor, J.Am.Ceram.Soc., 81 (1998)

649.32. I.K.Jeong,H.L.Park,S.Mho,SolidStateCommun.,105(1997)

179.33. D.P.Dutta,R.GhildiyalandA.K.Tyagi,J.Phys.Chem.C,

113(2009)16954–16961.

Dr. Dimple P. Dutta joined the BARC Training School in 1996 after obtaining her M.Sc. in Chemistry from IIT Kanpur. Subsequently, she joined the Chemistry Division and has worked on design and development of Group III metal organic compounds as single source precursors for III-VI materials like gallium and indium chalcogenides. She was a postdoctoral Fellow at University of Heidelberg, Germany, during the period 2001-2002. Her major area of research includes synthesis of optical and magnetic nanoparticles using soft chemical techniques and studying their properties. She has an impressive list of publications to her credit and has presented her research work at several forums. Dr. Dutta also serves as reviewer for many journals of international repute.


40

Photocatalytic Properties of mixed oxides of BaCrO4 and TiO2 Tanmay K. Ghorai *, Chirantan Roy Chaudhyry, Suman Biswas, Mukut Chakraborty, Ranjan Das, Jhimli Sengupta

Department of Chemistry, West Bengal State University, Barasat, North 24 Pgs, Kolkata-700126, India *Corresponding author: E-mail: [email protected]

AbstractMixedoxidesofTiO2andBaCrO4(upto5mol%)havebeensynthesizedbymechanicalalloyingmethod.InitiallyBaCrO4werepreparedbyco-precipitationtechnique.BaCrO4/TiO2oxideswerecharacterizedbypowderX-raydiffraction,BET,EDAX,SEM,ESRandphotocatalyticactivitymeasurementsbyUV-VISabsorptionspectroscopy.TheresultsshowthatthesolidsolutionofTiO2with1molepercentofBaCrO4(BCT1)exhibitphotocatalyticactivity3-5timeshigherthanthatofP25TiO2foroxidationofvariousdyes(RB,TB,MOandBG)underUVlightirradiation(λ>420nm).AmongthealldyestheoxidationofRBisfaster.DuetothesmallerionicradiusofthebariumcationandthespecialelectronicstructuresofBaCrO4the1mol%ofBaCrO4inTiO2(BCT1)showshighestphotocatalyticactivity.TheaveragecrystallitesizesofBCT1werefoundtobe~12nmmeasuredfromXRDandgrainsizeabout100±5nmmeasuredfromSEMwhichalsogavethemorphologyofthecompounds.TheEPRspectrumofBCT1indicatesthattheejectionofelectronhelpstodegradethedyemoleculefaster.

Keywords:TiO2andBaCrO4,Characterization; Photocatalyst;Photooxidation.

IntroductionMostofthetextiledyesandotherindustrialdyestuffs

constitutealargegroupoforganiccompoundswhicharehazardousfortheenvironment.Duetothelargenumberofaromaticgroupspresentindyemoleculesandthestabilityofmoderndyes,traditionalandconventionaltechniquesareineffectivefordiscolorationanddegradationofdyes,andjusttransferorganiccompoundsfromwatertoanotherphase.Thisisthereasonforinvestigatingthenewmethodswhichshouldconductcompletedecompositionofdyes[1].

Titania is a very versatilematerialwith attractiveapplicationsaspigmentinpaintings,intheproductionofelectrochemistryelectrodes,capacitors,solarcells,catalysisand photocatalysis. Regarding the latter application,purification of contaminatedwaters through completemineralizationof pollutants has extensively beenused[2-7].

However, itswideband-gap energy (ca. 3.0 eV forrutileand3.2eVforanatase)meansthatonly5%ofsolarspectrumisused.Moreover,TiO2presentsarelativelyhighelectron-holerecombinationratewhichisdetrimentaltoitsphotoactivity.Inthissense,dopingwithmetalsormetaloxidescouldmakeadoubleeffect:firstly,itcouldreducethebandgapenergy,thusshiftingtheabsorptionbandtothevisibleregion.Secondly,metalscouldprovokeadecreaseinelectron-holerecombinationrate,actingaselectrontraps.

Therefore, thereare someexamples in the literatureof thedopingof titaniawithmetals such asNi (II) [8],Cu(II) [9],Nb(V) [10],Cr(III) [11-12],Fe(III) [13-16],andmetalmolybdates [17].Thesewere reported to improvethephotocatalyticpropertieswithenhancedabsorptionofvisible/ultravioletlight.

The photocatalytic property of amulticomponentsystemisstronglyinfluencedbythecompositionandthepreparationprocedure. In recent years, the applicationof heterogeneous photocatalysis on the removal ofcontaminants in air andwastewater has fetched someinterest [18-19].Due to thehighphotocatalytic activityandstabilityoftitaniumdioxide,itisgenerallyusedasaphotocatalystfortheremovaloforganicpollutantsfromwaterorair[20-22].

Therefore, binarymetal oxides such asTiO2/WO3, TiO2/MoO3, TiO2/SiO2 and TiO2/ZrO2 have been widely studied for theirunique chemical, physical andphotocatalyticproperties[23-26].JiangYinetalshowsthatMCrO4(Ba,Sr)hasphotocatalyticproperties[27]butsofarnostudieshavebeenreportedonphotocatalyticpropertiesofBaCrO4/TiO2mixedoxides.

Furthermore, photoactivity is highly dependenton surface area, crystallinity or crystal sizewhich, inturn, are influencedby themethodof synthesis.As faras suchmethodsare concerned, the catalyticproperties

41


are closely related to their structureanddependon themethod of preparation and on the thermal treatment.The BaCrO4/TiO2mixed oxides in taken in differentmoleratiosandsubjected tomechanicalmillingmethod(usingaballmill)andtheirphotocatalyticactivitieswereevaluatedby thephotooxidationsofdifferentdyes likeRhodamineB (RB),Methyl orange (MO), thymol blue(TB)andBromocresolgreen(BG)underUVlight(400-WHg lamp;λ>420nm) irradiation.ThisworkdealswithmechanochemicalactivationofBaCrO4andTiO2“inordertoobtainnanocrystallineandsingle-phaseproducts.Theadvantagesofthisapproacharethattheuseofvoluminoussolutions and complicated operations aswell as thesinteringofthefinalproductcanbeavoided.

Experimental

Synthesis of BaCrO4/TiO2 photocatalystsThe total synthesisofBaCrO4andTiO2 indifferent

mole ratio has been performed by two steps. In thefirststep,thestartingmaterialofbariumchromatewasprepared. Barium chromateswere synthesized by co-precipitationmethod.Equimolaramountofbariumnitrateand ammoniumdichromate solutionswere taken in abeaker.ThentheaqueousammoniawasaddeddropwiseviavigorousstirringtotheabovesolutiontoadjustpH

toabout9andalightorangeamorphousprecipitatewasformed.ThesynthesisprocedureispresentedinFig.1.

InthesecondstepthestoichiometricmixtureBaCrO4and TiO2powderswith differentmole ratios (bariumchromateinTiO2is1mol%,3mol%and5mol%)wereground andmixed thoroughly inwater and subjectedtomechanical grinding in a planetary ballmill. Thismechanicalmillingwas allowed for 4 h for completemixingoftheoxidesformingasolidsolution.ThemillingwasperformedinFritschPulverisetteNo.6planetaryballmill, using a rotational speedof 250 rpmat a constantrotationdirectionandaball topowderweight ratioof10:1.Thebothcontainerandballsweremadeofaluminiumoxide.Thepreparedsamplesweredriedat100°Cfor15hinanovenandphotocatalyticactivitywasstudied.ThetotalprocedureispresentedinFig.1.Thesamples,whenheat treated above 200C, showedpoor photocatalyticactivity.

RhodamineB(RB),Methylorange(MO),Thylmolblue(TB),Bromocresol green (BG) and4-nitrophenol (4-NP)wereA.R.reagentsprocuredfromMERCKIndia.

Photocatalytic experimentPhotocatalytic experimentswere conducted using

nanophotocatalystsinpresenceofdifferentphotocatalytically

Fig.1 : Flow-chart synthesis for the different compositions of BaCrO4/TiO2 mixed oxides


42

degradable dyes inwater solution. ThephotocatalyticreactionwascarriedoutunderUVlightirradiationwithslowstirring(usingmagneticstirrer)ofthesolutionmixtureandBaCrO4/TiO2photocatalysts.Thelightsourcewasa400-WHglamp(PHILIPS-HPL-N,G/74/2,MBF-400)andwavelengthisλ>280nm.ThecontainerconsistsofaPetridishofvolume200ml.Thereactionswereperformedbyaddingnanopowderofeachphotocatalyst(0.1g)intoeachsetofa100mlofdifferentsolutionofdyes.

Analytical methodsAsmallvolume(1ml)ofreactantliquidwassiphoned

outat regular intervalof time for analysis. Itwas thencentrifuged at 1100 rpm for 15min, filtered through a0.2µm-milliporefiltertoremovethesuspendedcatalystparticles and concentration of dyewasmeasured byabsorption spectrometry usingUV-VIS spectrometer(UV-1601,SHIMADZU)at itswavelengthofmaximumabsorption.

Characterization The crystal structure of theprepared sampleswas

determinedby theX-raydiffractometer (XRD) (Model:PhilipsPW1710)equippedwithaCuKαradiation.Theacceleratingvoltageandcurrentusedwere40kVand20mA,respectively.The2θrangedfrom15to70°.

Crystallite sizes (D) of the obtainedpowderswerecalculated by the X-ray line broadening techniqueperformed on the direction of lattice using computersoftware(APD1800,PhilipsResearchLaboratories)basedonScherer’sformula[28].

D=(1)0.89λ

βcosθ

WhereDistheCrystallitesize,λistheX-raywavelength,θistheBragg’sangleandβisfullwidthathalfmaxima.ThestoichiometryofBaCrO4/TiO2alloyshavebeenexaminedby energydispersiveX-ray spectroscopy (EDX) (GEOLJMS-5800)which is consistentwith theamount takenofBaCrO4andTiO2duringsynthesis.

BET surface areameasurementswere carried outusingaBECKMANCOULTERSA3100throughnitrogenadsorption-desorptionisothermat77K.Theaveragesizesofnanoparticlesweremeasuredinthescanningelectronmicroscopy (SEM) (JEOL JMS-5800).TheESR spectrum

was obtained by BURCKERER083CSmodel at roomtemperature (ca. 298K).TheUV–VISdiffuse reflectancespectra of the prepared powderswere obtained by aUV–VISspectrophotometer(UV-1601Shimadzu)atroomtemperature.

AfterleachingtheBaCrO4/TiO2solidsolutionthroughfiltrationwithwhatman-42, the reaction solution (afterreaction)was subjected to inductively coupledplasma(ICP)analysisinordertomeasuretheamountofleachedBaCrO4/TiO2solidsolution.

Fig. 3: EDAX of BaCrO4 (1 mol%)/TiO2 (BCT1)

Fig. 2. XRD of BaCrO4, BaCrO4/TiO2 mixed oxides (, BCT1, BCT2, BCT3) and TiO2 at 100 °C for 15 h

43


Results and discussion

XRD analysisTheXRDpattern of the different compositions of

BaCrO4/TiO2 heat treatment at 100 °C for 15 h in airatmospherewasshowninFig.2.Ithasbeenrevealedthatthephasesprepared atdifferentmolar ratios ofmixedoxidesBaCrO4andTiO2[BaCrO4(1mol%)/TiO2(BCT1),BaCrO4 (3mol%)/TiO2 (BCT2), BaCrO4 (5mol%)/TiO2 (BCT3), andTiO2)have anatasephaseup to 1mol%ofBaCrO4 (asper JCPDSNo. 72-0746).After that increasetheBaCrO4concentrationsinTiO2latticetheBaCrO4peaks are appear,which shown in theXRDofBCT3,becauseBaCrO4didnotresolvedinTiO2latticeandphotocatalyticactivity is decrease. TheXRDpattern at TiO2 sample showsdistinctpeaksof theanatasephases,withoutanyindication of rutile phases.Average crystallite sizes ofthepreparedphotocatalystswerecalculatedaccordingtoScherer’s formulaand indicated that thecrystallite sizesofthesampleswere~12nm.TheatomicleveldispersionBaCrO4inTiO2havebeenpresentedinFig.3 throughenergydispersiveX-rayspectroscopy.

Specific surface area (BET) analysisTheBETsurfaceareaofBaCrO4/TiO2(BCT1)composites

calcinedat100oCwas55.4m2/g,whilethesurfaceareaofP25 is 49.1m2/gand the surface areaof otherpreparedphotocatalysts arepresented inTable 1.Though surfaceareaofBCT2,BCT3andDegussaP25arecomparable,butphotocatalyticactivityofBCT1is5timesgreaterthanP25TiO2.Therefore,amongallthepreparedphotocatalysttheBCT1ismorephotoactiveforfasterdegradationofdifferentdyeslikeRB,MO,TBandBGunderUVlight(400-WHglamp;λ>280nm).

Sample Reaction rate Constant

k(h-1)

SBET (m2/g) Crystallite size (nm)

Photo degradation efficiency (%)

RB TB MO BG p-NP

BCT1 7.77 55.4 12.03 99.8 61.8 49.9 18.6 7.9BCT2 5.41 49.5 12.35 94.3BCT3 2.83 39.1 12.55 70.6

P25TiO2 4.98 49.1 12.42 95.7BaCrO4 0.36 1.3 18.21 7.9

Table 1 : Resultant properties of BCT1, BCT2, BCT3, P25 TiO2 and BaCrO4 composites

Reactionrateconstantmeasuredafter50%degradationofRhodamineBunderUVlightandcatalyst;BETsurfaceareameasured by dinitrogen adsorption desorptionisotherm at 100 ºC; Crystallite size in nm calculatedfromScherer equation;Photodegradationefficiency;RB:RhodamineB;TB:ThymolBlue;MO:MethylOrange;BG:BromocresolGreen;p-NP:pareNitroPhenol.

Scanning electron microscopy (SEM) analysisFig.4 showsscanningelectronmicroscopyofBCT1.

Thegrains separatedbywell-definedgrainboundariesarevisiblewhichareuniformlydistributedandshapeoftheparticleisnotdeterminedprecisely.TheaveragegrainsizeofBCT1sample isabout100±5nm.Thegrain sizescalculated from themicrographsusingUTI image toolsoftware(version2.0).

EPR spectrum studyFig. 5 illustrates theESR spectrumof theBaCrO4/

TiO2recordedat298K.Thecharacteristic featureof thisspectrumisasignalatag-tensorvalueof2.001,indicatingthepresenceofBa2+/Cr+3onirradiatedTiO2.DuetoabsenceofanyhyperfinelineinESRspectra,itcanbesuggestedthat Ba2+/Cr3+cationsarewellseparated.NoEPRsignalwasdetectedonpureTiO2orBaCrO4species.TheEPRsignalofBaCrO4/TiO2indicatesthattheejectionofanelectronisthecrucialroleforphotooxidationofRBunderUVlight.

Photocatalytic activity of the prepared samplesThephotooxidationofdifferentcoloureddyessolution

like RB,MO, TB, BG and 4-nitrophenil to colourlesssolutionusingthepreparedphotocatalystsandUVlight(400-WHglamp;λ>280nm)irradiationisshowninFig.6.UV–VIS spectra ofRB,MO,TB,BGand 4-NP takenafter the irradiationwithBaCrO4/TiO2 (BCT1)BaCrO4/


44

Fig. 4: Scanning electron microscopy (SEM) of BCT1 calcined at 100 °C for 2 h at resolution a) 5000 and b) 7500.

Fig. 5: ESR spectra of BaCrO4/TiO2 mixed oxides at room temperature Fig. 6: Effect of BCT1 on diff. dyes under UV light

TiO2(BCT2),BaCrO4/TiO2(BCT3),TiO2andBaCrO4/TiO2 (BC) compositions,weremeasured and correspondingabsorbanceofdyeswerefoundat554,464,597and616nmrespectively.Amongallthefourdyesincluding4-NPtherateofdegradationofRhodamineBisfasterinthepresence

ofBCT1andUVlight.ThetimerequiredforcompletelydecolorizationofRBis5h.Forallthecasesthecatalystsweretakenat1g/landdifferentdyeconcentrationwasabout10mM.Fig. 7 shows thephotooxidationofRB inpresenceofdifferentcatalyst(BCT1,BCT2,BCT3,P25TiO2,

Irradiation Time (h)

45


Fig.7: The changes in concentrations of RB solution at 554 nm in the presence of BCT1, BCT2, P25 TiO2, BCT3, BC and absence of catalyst, the catalyst concentration is Ccatalysts = 1 g/l. Rhodamine B concentration is CRB = 10 mM, 400-W Hg lamp (λ > 280 nm).

Fig. 8: Catalytic efficiency of BCT1 on Different dyes under UV light

Fig. 9: The effect of calcinations temperature for 15 h for 100 °C, 200 °C and other temperature is for 2 h on the photocatalytic activity of BCT1, the catalyst concentration is Ccatalysts = 1 g/l. Rhodamine B concentration is CRB = 10 mM, 400-W Hg lamp (λ > 280 nm).

BCandabsenceofcatalyst)andUVlight.UnderUVlightirradiation,thealloyBaCrO4/TiO2(BCT1)exhibitedhighestphotocatalyticactivitythanthatofothercompositionsof

BaCrO4/TiO2mixedoxides,P25TiO2,andbaricumchromate(BC). It is also observed that in absenceof catalyst thedegradationofdyesisnotpossibleunderUVlight(showninFig, 6).TheBCT1 compositeshave shownfive timeshigherphotocatalyticactivitythanthatofP25TiO2 in case ofRhodamineB.TheincrementofBaCrO4concentrationbeyond1mole%leadedlowerphotocatalyticactivity.Thedegradationrateconstant(k)forRB,MO,TBandBGusingBCT1,BCT2,BCT3,P25TiO2,BCphotocatalystshavebeenpresentedasthetimerequiredfor50%decolourizationofdyessolutionsinTable1.ThecatalyticefficiencyofBCT1onDifferentdyesunderUVlightwasshowninFig.8.ThephotooxidationefficiencyofRBishighestamongallotherdyesandp-NPinpresenceofcatalystandUVlight.

Effect of heat-treatment temperaturesThe effect of heat-treating temperature of the solid

solution or composites on the photocatalytic activitywas also investigated. Fig. 9 shows theprofiles of thephotooxidationsofRhodamineBunderUVlight(λ>280nm)irradiationusingBCT1solidsolutioncalcinedat100ºC,200ºC,300ºC,400ºCand500ºC.Thesamplescalcinedat100ºCshowedhighestphotocatalyticactivity.Itseemsthattheincreaseofthecalcinationtemperaturedecreasesthedefect-statesonthesurface.Above100ºCtheactivityofcatalystdecreaseswithriseofcrystallitesizesofsolidsolution. It is alsoobserved that adsorptionofdye (RB,


46

TB,MO,andBG)decreaseswithincreaseofheattreatmenttemperatureofthecatalyst.Thisisprobablyduetodecreaseofdefect-structureon the surfaceof solid catalyst.Thusdefectstructuresignifiesitscrucialroleforphotocatalyticactivity.

ConclusionsSynthesisofnano-sizedcompositesorsolidsolution

of BaCrO4andTiO2withhighphotocatalyticactivityforoxidativedegradationofdifferentdyeswassuccessfullyobtainedthroughmechanochemicalsynthesis.XRDdatashows the formation ofmixed oxides having anatasestructurewithnofreeBaCrO4upto1mole%ofBaCrO4/TiO2.BaCrO4/TiO2catalysthavecrystallitesizeabout12nmmeasuredfromXRDandgrainsizeabout100±5nmmeasuredfromSEM.ThemaximumsolubilityofBaCrO4

inTiO2is1molpercentandthiscompositionhashighestphotocatalyticactivitythatis5timeshigherthanP25TiO2

fortheoxidationofRB.WealsoobservedthattherateofdegradationofRhodamineBisfastestamongallthefourdyeswiththepreparedcatalystinvisiblelight.

AcknowledgementsThisworkwas supported by theDepartment of

ScientificandTechnology,India.Theauthorsaregratefulforitsfinancialsupport.

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47


Dr. Tanmay Kumar Ghorai is presently working at Department of Chemistry in the West Bengal State University as an Assistant Professor since 2009. He received the Young Scientist Award (2010) from the Department of Science & Technology (DST) in the Fast Track Scheme, Govt. of India. He also received the prestigious fellowship BOYSCAST from DST in the year 2010-11, Govt. of India. He is involved in the complete synthesis procedure, characterization and study of the photocatalytic application of BaCrO4 and TiO2 mixed oxide synthesized by mechanical alloying.

Dr. Chirantan Roy Choudhury is presently working at Department of Chemistry in the West Bengal State University as an Assistant Professor since 2009. He is involved in the synthesis of BaCrO4 and TiO2 mixed oxide in different mole ratio by mechanical alloying.

Dr. Suman Biswas is a permanent faculty at Department of Chemistry in the West Bengal State University as an Assistant Professor since 2009. He is basically an organic chemist. His contribution is mainly the synthesis and study of the catalytic application of BaCrO4 and TiO2 mixed oxide in different mole ratio by mechanical alloying.

Dr. Mukut Chakraborty is a permanent faculty at Department of Chemistry in the West Bengal State University as a Reader since 2009. He is the recipient of Convention Award for Young Scientists by Indian Chemical Society in the year 1999. His current research work is Conducting Polymer, Nanocomposites synthesis and characterization of polymeric nanomaterials. His main role is the write up of SEM and ESR characterization of BaCrO4 and TiO2 mixed oxide synthesis.

Dr. Ranjan Das is working at Department of Chemistry in the West Bengal State University as an Associate Professor since 2010. He worked as an Associate Research Scientist of CNRS in Institut Gilbert Laustriat - UMR 7175, Strasbourg in 2007-08. In 2010, he was nominated to the position of Invited Professor in the Laboratoire de Biophotonique et de Pharmacologie, University de Strasbourg, France. His current research interests are in photophysics of charge-transfer dyes, core-shell nanoparticles, dye encapsulated nanomaterials. His main function in the manuscript is correcting the grammatical error and helping to response to the reviewer comments

Dr. Jhimli Sengupta is presently working at Department of Chemistry in the West Bengal State University as an Assistant Professor since 2009. She received the Young Scientist Award (2010) from the Department of Science & Technology (DST) in the Fast Track Scheme, Govt. of India. Her main activity in this manuscript is the systematic study of the catalytic activity of oxidation of different organic dyes under UV light


48

News and Forthcoming EventsYear2011isbeingcelebratedasInternationalChemistryYearthroughouttheworld.

SomeoftheInternationalConferencesbeingorganisedinINDIA,intheyear2011are:

1. InternationalConferenceonVistasinChemistry2011(ICVC-2011), Kalpakkam,India,Oct.2011,e-mail:[email protected]

2. 14thISMASSymposiumcumWorkshoponMassSpectrometry Munnar,Kerala,Nov.7-11,2011,http://www.ismas.org

3. InternationalSymposiumonChemistryandComplexity IACS,Kolkata,Dec.6-8,2011,e-mail:[email protected]

4. ISEAC-WS-2011,InternationalSymposiumcumWorkshoponElectrochemistry. Goa,India,Dec.7-10,2011, http://www.iseac.org

5. 56thDAESolidStatePhysicsSymposium(DAE-SSPS2011) Kattankulathur,Tamilnadu,Dec.19-23,2011,e-mail:[email protected]

Some of the International Conferences being organised in the year 2011-2012 are:

1. 2011InternationalConferenceonSolidStateDevicesandMaterials(SSDM2011) Nagoya,Japan,Sept.28-30,2011,e-mail:[email protected]

2. 7thInternationalSymposiumonNovelMaterialsandtheirSynthesis. Shanghai,China,Oct.11-14,2011,e-mail:[email protected]

3. The12thPacificPolymerConference(PPC12) JejuIsland,Seoul,Korea,Nov.13-17,2011,e-mail:[email protected],

4. 4thInternationalSymposiumonStructure-PropertyRelationshipsinSolidStateMaterials June24-29,2012,Bordeaux,France,e-mail:[email protected]

4. 15thInternationalCongressonCatalysis Munich,Germany,July1-6,2012,e-mail:[email protected]

5. ICACCE2012:InternationalConferenceonAppliedChemistryandChemicalEngineering Amsterdam,Netherlands,July25-27,2012.http://www.waset.org.

6. 4thEuCheMSChemistryCongress Praha,CzechRepublic,Aug.26-302012,e-mail:info@euchems-prague2012.

7. ISCRE22,InternationalSymposiumonChemicalReactionandEngineering Maastricht,Netherlands,Sept.2-5,2012,e-mail:[email protected],

49


Achievements, Honours and Awards received by the SMC membersName of the member & affiliation Name of the award/honour Conferred by

Dr. M. K. Chattopadhyay RRCAT, Indore

Scientific & Technical ExcellenceAward

DepartmentofAtomicEnergy

Mrs. Sunaina Devi University of Allahabad

Prof.G.GopalaRaoCentenaryYoungScientistAward

AnnualConventionofChemists

Dr. Dimple P Dutta BARC, Mumbai

Member, National Academy ofSciences,India

NationalAcademyofSciences,India

Neha Gupta University of Allahabad

Prof.G.GopalaraoCentenaryYoungScientistAward

AnnualConventionofChemists

Neha Gupta University of Allahabad

Prof.A.K.DememorialAward AnnualConventionofChemists

Dr. Tanmay Kumar Ghorai West Bengal State University

BOYSCASTFellowship DepartmentofScience&Technology

Dr. Vinita Grover Gupta BARC, Mumbai

YoungScientistAward IndianSocietyforChemistsandBiologists

Atul Kumar Kushwaha University of Allahabad

Dr.U.V.RaoMemorialAward AnnualConventionofChemists

Dr. G. P. Kothiyal BARC, Mumbai

INSScienceCommunicationAward IndianNuclearSociety

Dr. Raman Kumar Mishra BARC, Mumbai

IANCASProf.H.J.ArnikarBestThesisAward–2011

IndianAssociationofNuclearChemists andAlliedScientists

Dr. T. Mukherjee BARC, Mumbai

LifetimeAchievementAward FreeRadicalSocietyofIndia

Prof. Anjali M. Rahatgaonkar Institute of Science, Nagpur

NominatedasNationalRepresentativefor India to the IUPACDivisionVIICommittee.DivisionVIICommittee.

InternationalUnion of Pure andAppliedChemistry(IUPAC)

Dr. Mainak Roy BARC, Mumbai

Young Associate ofMaharashtraAcademyofSciences

MaharashtraAcademyofSciences

Prof. Nandlal Singh The M.S.University of Baroda

Fellow-GujaratAcademyofSciences GujaratAcademyofSciences

Dr. V. Sudarsan BARC, Mumbai

YoungAchieverAwardfortheYear2010

DAE Solid State Physics symposium 2010(DAE-SSPS2010)

Dr. A. K. Tyagi BARC, Mumbai

Fellow,Royal Society ofChemistry(FRSC)

RoyalSocietyofChemistry,UK

Prof. Sandeep Varma IIT, Kanpur

Shanti Swarup Bhatnagar Prize inChemicalSciences

CSIR,NewDelhi

Prof. Sandeep Varma IIT, Kanpur

Fellow,IndianAcademyofSciences IndianAcademyofSciences,Bangalore

Dr. P. R. Vasudeva Rao IGCAR, Kalpakkam

MRSI-ICSC Superconductivity andMaterialsScienceSeniorAward

MaterialsResearchSocietyofIndia

Dr. P. R. Vasudeva Rao IGCAR, Kalpakkam

CRSISilverMedal ChemicalResearchSocietyofIndia


50

51


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Tel.: 2446 2632 / 2446 3872 Tel Fax: 2444 9765 Email : [email protected] / [email protected]


52

In this issue

Feature articles1 Chemistryandapplicationsofnanomaterials

A.K. Tyagi1

2 EvaporationinducedselfassemblyofnanoparticlesbyspraydryingD. Sen, J. Bahadur, S. Mazumder, J.S. Melo and S.F. D’ Souza

12

3 Lightabsorptionandemissioningoldnanoplatesassembledinsmallgroupsviapoly(vinylidenefluoride)moleculesB. Susrutha, A.D. Phule and S. Ram

22

4 PreparationandcharacterizationofCollagen-basedLiposomeNanoparticlescompositematrixKrishnamoorthy Ganesan, Praveen Kumar Sehgal, Asit Baran Mandal and Sadulla Sayeed

29

5 ApplicationofnanophosphorsinsolidstatewhitelightgenerationDimple P. Dutta

34

6 PhotocatalyticPropertiesofmixedoxidesofBaCrO4andTiO2

Tanmay K. Ghorai, Chirantan Roy Chaudhyry, Suman Biswas, Mukut Chakraborty, Ranjan Das, Jhimli Sengupta

40

NewsandForthcomingEvents 48

HonoursandAwards 49

Society for Materials Chemistry C/o. Chemistry Division Bhabha Atomic Research Centre, Trombay, Mumbai, 400 085 (India)

E-mail: [email protected],Tel: +91-22-25592001

smc bulletin vol. 2 (no.1) june 2011smcindia.org/pdf/smc bulletin_vol.2( 1)2011.pdf · smc bulletin...

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