Materials Letters 175 (2016) 231–235

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Materials Letters

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Synthesis and characterization of Ag2S/PVA-fullerene (C60)nanocomposites

Narmina O. Balayeva a,b,c,n, Zamin Q. Mamiyev b,d

a Baku State University, Department of Chemistry, Z. Khalilov str. 23, AZ-1148 Baku, Azerbaijanb Institute of Physics, Azerbaijan National Academy of Sciences, H. Javid pr, 131, Baku AZ-1143, Azerbaijanc Institut fur Technische Chemie, Leibniz Universitat Hannover, Callinstrasse 5, D-30167 Hannover, Germanyd Institut für Festkörperphysik, Leibniz Universität Hannover, Appelstrasse 2, D-30167 Hannover, Germany

a r t i c l e i n f o

Article history:Received 31 December 2015Received in revised form20 March 2016Accepted 3 April 2016Available online 4 April 2016

Keywords:Ag2SNanocompositesSEMOptical propertiesPowder XRD

x.doi.org/10.1016/j.matlet.2016.04.0247X/& 2016 Elsevier B.V. All rights reserved.

esponding author at: Institut fur Technischeer, Callinstrasse 5, D-30167 Hannover, Germaail address: narmina1990@inbox.ru (N.O. Bala

a b s t r a c t

We present the chemical synthesis of silver sulfide nanocrystals (NCs) in PVA matrix and the extendedcharacteristics of the obtained nanocomposites with fullerene. The samples were prepared with thedifferent concentration of fullerene and PVA for compression of their fraction relation with the opticaland phase properties. UV–vis spectra of Ag2S show sharp excitonic features and a large blue shift fromthe bulk material. The NCs grain size was determined about 10–15 nm which is confirmed by differenttechniques such as Scanning electron microscopy (SEM), UV–visible absorption and X-ray Diffractometer(XRD). The SEM images demonstrate that the nanoparticles overlapped and stabilized with a polymermatrix. The EDAX result indicates that the prepared nanocomposites are composed of pure phase Ag, S, Cand any other irrelevant mixtures have not been detected.

& 2016 Elsevier B.V. All rights reserved.

1. Introduction

Nanoscaled inorganic–organic nanocomposites exhibit uniqueelectrical, electromagnetic, thermal, mechanical and optical char-acteristics that have attracted high interest due to their consider-able technological applications in materials science, such as cata-lysts, semiconductor sensitized solar cells (SSSCs), photo-con-ductors, magnetic materials and luminescent materials [1–4].

The semiconductor silver sulfide nanocrystals at nanoscale of-ten have outstanding photoelectric and thermoelectric propertiesand less toxicity by comparison to other metal-chalcogenides na-noparticles [5]. The silver sulfide nanoparticles in a polymer ma-trix have been applied in diverse optical and electronic devices,such as photo-conducting cells, IR detectors, solar selective coat-ings and photovoltaic cells [6].

During the last years, semiconductor quantum dots (QDs) suchas CdS, CdSe, PbS, CuS, InAs and InP have been assembled ontoporous films, nanotubes, nanowires, and nanoparticles and thenused as photocatalysts due to their narrow band gap [7]. In thisrespect, Ag2S is an important material for photocatalysis andelectronic devices, because of its potential large optical absorptioncoefficient and a direct band gap of 0.9–1.05 eV, which makes it aneffective semiconductor materials [8–11].

Chemie, Leibniz Universitatny.yeva).

Fullerene (C60) is a promising material with large-scale utili-zation in semiconductor and optoelectronic devices due to in-dividual structural, electrical and optical properties [12,13], how-ever, its coupled mechanism with metal-sulfide nanoparticles in apolymer matrix have not been elucidated properly. In the electrontransfer processes fullerene (C60) can expeditiously launch rapidphotoinduced charge separation and low charge recombinationdue to its remarkable acting as an electron acceptor [14]. C60-basedmaterials are among the most important candidates for the ex-pansion of plastic solar cells and renewable sources of electricalenergy due to semiconductor band gap energy, about 1.6–1.9 eV[15,16].

There are different approaches for the synthesis of nanodi-mensional systems, such as the solvothermal method [17], hy-drothermal route [18], sonochemical route, single-source pre-cursor routes [19], sol–gel method [20], in-situ [21], and ion-ex-change technique [22], etc. In the presented work, we report thesynthesis of Ag2S nanoparticles on PVA polymer matrix andmoreover coupled semiconductor Ag2S/fullerene nanocompositein PVA with different concentration. Herein, a facile chemical one-pot synthesis method has been applied for the preparation ofAg2S/PVA–fullerene nanocomposites.

These nanocomposites have unique photoelectric, thermo-electric and photocatalytic properties which are promising mate-rials for diverse applications on photocatalyst, photovoltaic field inthe future. One of the advantages of our work: that we have notused the oxidation agent, thus C60 takes part in oxidation process

Fig. 1. The FT-IR spectra (a), proposed stabilization process (b) and powder XRD patterns (c) of the obtained nanocomposites.

N.O. Balayeva, Z.Q. Mamiyev / Materials Letters 175 (2016) 231–235232

and PVA stabilizes the nanoparticles due to its functional activegroups as a capping agent.

2. Experimental

2.1. 1. Materials and methods

The polyvinyl alcohol (PVA), fullerene (C60), toluene (C6H5CH3),thiourea CS(NH2)2, silver nitrate AgNO3 and hydrazine were allcommercial products with the highest purity (99,9%) purchasedfrom Sigma-Aldrich. All initial substances were used without fur-ther purification for the preparation of fullerene/metal-sulfidenanocomposites. The obtained nanocomposite material wascharacterized by several methods. The powder X-ray diffractionspectra of the films and powder specimens were recorded on aBruker D2 Phaser X-ray diffractometer under Ni filtered CuKαradiation (λ¼1.5406 Å). The surface morphology and elementalcontent analysis were investigated on a Field Emission ScanningElectron Microscope with Energy dispersive spectrometer andElectron Backscattered Diffraction System, respectively. The opticalproperties of synthesized nanocomposites were measured by UV–vis absorption spectrometer and Fourier transmission infraredspectroscopy (FT-IR).

2.2. Synthesis of Ag2S/PVA-fullerene (C60) nanocomposites

Chemical synthesis of polymer nanocomposites was carried outin a jacketed four neck round-bottom 250 ml reaction flaskequipped with a mechanical stirrer, thermometer and reflux con-denser for adjusting the temperature. The reaction went out in the

hot water bath and the temperature has been increased graduallyup to 373 K.

In the first stage, for the synthesis of polymer capped Ag2Snanocrystalline, 3 g polyvinyl alcohol was dissolved in 30 mldeionized (DI) water. While the water bath slightly heated up, thepolymer mixture was vigorously stirred about 30 min for solvingthe polymer properly. On the other hand, 0.1 M AgNO3 stock so-lution was prepared by dissolving in 100 ml distilled water. Simi-larly, 0,76 g thiourea CS(NH2)2 was dissolved in 100 ml distilledwater. From each these solutions, we have used 20 ml in the firstreaction step. Initially, 20 ml AgNO3 salt solution was added intothe reaction flask and vigorously stirred with polymer mixture halfan hour and a film was prepared on a glass substrate by takingfrom the reaction conditions. Afterward, 20 ml thiourea waspoured into a solution by dropwise with strongly stirring. Whilethe color of the solution changed from transparent to the darkestbrown some drops of solution have been taken for preparing a filmon a glass substrate. In 5 min, we have added 2 ml hydrazine in thereaction condition for precipitation of Ag2S/PVA nanocompositematerial. The last stage of the reaction was carried out one an halfhour. The powder was completely separated from the solution andwashed up 5 times with excess DI water for purification. The ob-tained nanocomposite powder firstly dried at ambient conditionand then in a vacuum furnace at 60 °C for the complete removal ofwater.

The formation reaction of silver sulfide nanoparticles in thepolymer matrix can be written as following:

AgNO3þCS(NH2)2-Ag2S↓þ….AgNO32AgþþNO3

� .(NH2)2CSþOH�2CH2N2þH2OþHS� .HS�þOH�2H2OþS2� .

Fig. 2. The SEM images (a,b,c) and EDAX result (d) of the obtained Ag2S/PVAþC60 (20 ml) powder nanocomposites.

N.O. Balayeva, Z.Q. Mamiyev / Materials Letters 175 (2016) 231–235 233

AgþþS2�-Ag2S↓.The second reaction was carried out as the same procedure, but

amount of the precursors were changed. For diminishing grain sizeof nanocomposites, we have used 7 g PVA in 70 ml DI water and30 ml AgNO3 salt solution. Subsequently, 30 ml thiourea addedinto the reaction flask drop by drop as described in the first re-action. Before precipitation of nanocomposites, 10 ml (2�10�2 M)fullerene in toluene solution was poured into reaction condition bystirring. From this stage, the reaction was continued in dark am-bient to minimize potential light exposure. After 20 min 10 mlfullerene solution was added to the solution, and consequently, thenanocomposite film deposited on a glass substrate for character-ization. Then, 2 ml hydrazine has been used for precipitation ofpowder during the continued process at 373 K about 2 h. Thepowder Ag2S/PVA-fullerene (C60) nanocomposites were obtainedas described in the first reaction and supposed stabilization pro-cess has been described in Fig. 1b.

3. Results and discussion

3.1. FT-IR measurements

Infrared energy is emitted or absorbed when molecular struc-ture of polymers and blends change their rotational vibrationmovements which could accurately interpret by intense FT-IRtechnique.

FT-IR spectra of the obtained Ag2S/PVA, Ag2S/PVAþC60

nanocomposites films were recorded in the 4000–400 cm�1 fre-quency region, for comparatively studying of the functionalgroups. As shown in Fig. 1a the presence of fullerene in the na-nocomposites manifest itself in the IR spectra with differencestrong detects. The humps at 2949 cm�1 and 1334 cm�1 whichascribed to C–H the stretching vibration was strengthened andslowly shifted while adding fullerene and extinguished by in-creasing the amount from 10 ml to 20 ml. The band at 1633 cm�1

attribute to C¼O and show significant shifting by variation of C60fraction in nanocomposites. The intensity of this band is a measureof the degree of crystallinity of PVA, presumably a C–Omode in thecrystalline region.

Furthermore, the C¼O band vibration was observed at1716 cm�1 for less amount of fullerene which supported by theweak interaction between the double bond of C60 and polymerfunctional active groups. In addition, the remarkable change wasobserved in the intensity of the sharp band at 1145 cm�1 in thePVA/Ag2S and shifted while treated with a small amount of full-erene, consequently disappeared with the more addition offullerene.

From the IR spectra, it can be seen that the peak intensities ofthe functional groups on fullerene treated nanocomposites(Fig. 1a) decreased compared to initial nanocomposite due to theinteraction of functional groups with C60.

3.2. XRD Studies

The indexed powder XRD patterns of the as-prepared

Fig. 3. UV–vis absorption spectra (a) and band-gap determination (b) of the as-synthesized nanocomposites.

N.O. Balayeva, Z.Q. Mamiyev / Materials Letters 175 (2016) 231–235234

nanocomposites are given in Fig. 1c. The broadening effect wasobserved in this diffraction peaks due to nano crystalliteformation.

X-ray diffraction patterns were recorded from 2θ¼20° to2θ¼80° and observed that both of the powder nanocompositespossess monoclinic structure having lattice constant a¼4.231,b¼6.930 and c¼9.526 Å (α¼γ, β¼129.40°) and with the spacegroup of P21/n (PDF 00-014-0072). From the XRD pattern, nocharacteristic peaks of impurity phases have been observed. Theaverage particle size of the Ag2S nanoparticles was estimated fromthe half-width of diffraction peaks using Debye–Scherrer's formula[23] and was found to be 30 nm, which drastically decreased while

increasing PVA ratio. Therefore, from the second reaction theaverage nanocrystallite size was calculated 13 nm. The particlessize estimated from XRD results were well consistent with theSEM images. It is supposed that fullerene prevents further growsof nanocrystals due to its double bonds help to increase the sta-bilization capability of the polymer chain.

Thus, by adding fullerene the particles size slightly decreased asseems from XRD results. However, the XRD peaks show sig-nificantly increment in intensity which is expectable in the pre-sence of fullerene. The SEM pictures of the obtained PVA/Ag2S@C60 nanocomposites are given in Fig. 2a, b and c whichdepicts the crystalline grain sizes. The chemical compositions ofthe synthesized silver sulfide nanocomposites were also de-termined by EDAX technique from the selected areas of the na-nocomposites. The EDAX result indicates that the prepared na-nocomposites are composed of pure phase Ag, S and C as pre-sented in Fig. 2d.

3.3. UV–vis absorption results

The optical absorption spectra of the samples were recorded onUV–visible spectrometer at room temperature in the wavelengthrange 200–800 nm. Fig. 3a shows the absorption spectra of PVA/Ag2S, PVA/(Ag2S)@C60 (10 ml) and PVA/(Ag2S)@C60 (20 ml) nano-composites films and PVA/(Ag2S)@C60 powder with significantlyblue shift compare to the bulk Ag2S (515 nm, Eg¼0.9 eV) [24],which is explained by the characteristic quantum confinementeffect of photogenerated electron–hole pairs due to reduction insize to a few nanometers [25].

It is determined that all absorbencies of fullerene added na-nocomposites are much more extended than PVA/Ag2S in thewavelength range of 200–700 nm. Thus, visible light absorption ofPVA/Ag2S nanocomposites is observed in the range of 300–500 nm. However, absorption curves of PVA/(Ag2S)@C60(10 ml),PVA/(Ag2S)@C60 (20 ml) films and PVA/(Ag2S)@C60 powder nano-composites are detected at lower wavelength such as 323, 351 and345 nm respectively which is mainly attributed to the presence offullerene. The optical band gap (Eg) was calculated using Tauc'sformula [26]:

α = ( − )( )

A hv Eghv 2

n

Where α is the absorption coefficient, hν is the incident photonenergy, A is the constant and the exponent n depends on the typeof transition. Herein, the transitions are direct so we take n¼1/2.The value of the optical band gap is calculated by extrapolating thestraight line portion of (αhν)2 vs hν graph (Fig. 3b) to hν axis anddetermined 1.85 eV, 2.0 eV, 2.16 eV and 2.26 eV for PVA/Ag2S, PVA/(Ag2S)@C60 (10 ml), PVA/(Ag2S)@C60 (20 ml) films and PVA/(Ag2S)@C60 powder nanocomposites, respectively.

Moreover, the average particle size of the obtained materialswas calculated from the absorption onset by using the relationbetween the energy band gap of the NPs and the bulk Ag2S andwas found to be 12 nm which is in good agreement with the re-sults obtained from both of the XRD and SEM measurements [27].

4. Conclusion

In this paper, a simple chemical route has been reported for thepreparing of high-crystalline Ag2S nanoparticles with a relativelynarrow size distribution in the PVA matrix. The structural andoptical properties of Ag2S nanoparticles were found to be depen-dent on polymer and fullerene concentration as observed by FT-IR,XRD, SEM and UV–visible absorption measurements.

N.O. Balayeva, Z.Q. Mamiyev / Materials Letters 175 (2016) 231–235 235

The obtained nanoparticles show relatively sharp optical ab-sorption edges and strong blue shift indicating the size confine-ment effect with respect to bulk Ag2S. X-ray diffraction studyconfirmed the formation of monoclinic phase Ag2S nanocrystals inthe polymer matrix with the particle size in the 10–15 nm range.

The UV–vis absorption results reveal that the adding of full-erene leads to enhancement in optical properties with reducingparticle size.

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