Composites: Part B 68 (2015) 431–435

Contents lists available at ScienceDirect

Composites: Part B

journal homepage: www.elsevier .com/locate /composi tesb

Synthesis and characterization of CdS nanocrystals and maleic anhydrideoctene-1 copolymer nanocomposite materials by the chemical in-situtechnique

http://dx.doi.org/10.1016/j.compositesb.2014.09.0131359-8368/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Tel.: +994 504656605.E-mail address: z_amin@bk.ru (Z.Q. Mamiyev).

Zamin Q. Mamiyev a,⇑, Narmina O. Balayeva a,b

a Institute of Physics, Azerbaijan National Academy of Sciences, Javid.pr, 131, Baku AZ 1143, Azerbaijanb Baku State University, Department of Chemistry, Z. Khalilov str., 23, AZ-1148 Baku, Azerbaijan

a r t i c l e i n f o

Article history:Received 7 March 2014Received in revised form 14 May 2014Accepted 17 September 2014Available online 28 September 2014

Keywords:A. Polymer–matrix composites (PMCs)A. Nano-structuresA. Thin filmsB. Optical propertiesAtomic Force Microscopy (AFM)

a b s t r a c t

In the present work, in-situ chemical co-precipitation method was employed for the preparation of CdSnanocrystals in the copolymer matrix. The process has been carried out successfully and the nanocom-posites have been obtained with excellent optical and structural properties. During the process it wasdetermined that the grain size of nanoparticles depend on regulation of the reaction conditions and onthe proportions of the precursors in this method. Also the results have shown that the sizes of the nano-particles increase with the increase of temperature and this shifts revealed in measurements. Surfacemorphology and crystallinity have been studied by AFM and XRD techniques, respectively. The averagesize of nanocrystals was calculated 2–6 nm by AFM and XRD measurements. Consequently, it have beendetected that elaborated CdS nanocrystals demonstrate new interesting structural and optical properties.A detailed optical property of the obtained CdS/MA-octene-1 nanocomposite material is done by charac-terizing UV–Vis, FT-IR and PL spectrophotometric methods.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Polymer–matrix composites (PMCs) represent a new alternativeto conventionally filled polymers. So the polymer nanocomposites(N/C) are materials in which nanoscopic inorganic particles, typi-cally 1–100 nm in at least one dimension, are dispersed in anorganic polymer matrix in order to dramatically improve theperformance properties of the polymer. Because of their nanometersizes, filler dispersion nanocomposites exhibit markedly improvedproperties when compared to the pure polymers or their traditionalcomposites. In semiconductor nanocrystals quantum dots, the con-finement of charge carriers to length scales less than the excitonBohr radius allows investigation and exploitation of materialbehavior in the size regime between the atomic and bulk [1–3]. Itis well known that nanocrystalline semiconductor exhibits quan-tum confinement effect and possesses properties that are differentfrom the bulk molecules [4]. In particular CdS and other chalcoge-nides have received much attention for potential applications infuture optoelectronic nanodevices and biological labelling due tothe tunable electronic band-gaps depending on the size and shapeof nanocrystals (NCs) [5]. The study of chalcogenides quantum

structures may also help to understand the formation mechanismand structures of biogenic metal chalcogenides NCs produced byvarious organisms to sequester toxic transition metals [6].

These nanoparticles exhibit size dependent properties such as ablue shift of absorption onset, a change of electrochemical poten-tial of band edge, and an enhancement of photo catalytic activities,with decreasing crystallite size. CdS nanoparticles show a directnarrow gap as semiconductor materials. This material has alsobeen used in many fields such as photography Cd2+ ions are indi-cate selective sensors and solar absorption properties [7,8]. Espe-cially CdS nano-structures have been extensively studied due totheir potential applications such as field effect transistors, lightemitting diodes (LED), photo catalysis biological sensors, solarcells, photoconductors and thin film transistors [9]. Otherexamples these metal sulfides include their nonlinear optical prop-erties, their unusual fluorescence behavior, their catalytic proper-ties, their structure and phase-transitions, their transportproperties, their surface chemistry, and their use as precursorsfor nanostructured materials processing [10,11]. Semiconductornanoparticles can be prepared with variety methods such as non-aqueous solvents, reversed micelles, vesicle, zeolites and othermethods. However some of the above methods use salt of Cd2+ ionsand H2S, Na2S, (CH4N2 S) which are in separate phase and mixedunevenly, the formation and the aggregation of CdS particles are

432 Z.Q. Mamiyev, N.O. Balayeva / Compo

uneven. The precipitation of Cd2+ with S2� is faster than theirhomogeneous mixing, the in homogeneity at early stages resultsin a broadening size distribution. Nanoparticles have a greatactivity and the important section in all of the synthesis methodsis stabilization of the nanoparticles. Recently for this purpose,copolymers especially which carrying functional groups have beenused as specific stabilizers for the solution synthesis of metalsulfide nanoparticles with varied properties.

For example, polyester chains with a thiol end group, maleicanhydride and olefin were used as a covalently attached stabilizerfor the preparation of stable CdS nanoclusters in dimethylformam-ide and tetrahydrofuran, which were further used for the prepara-tion of homogeneous dispersions of CdS nanoparticles in acopolymer matrix [12–14]. Also immobilization of metal sulfidesusing ionomers, such as block copolymers [15]. In this paper westudy a chemically prepared MA-octene-1 copolymer/CdS nano-composite by a chemical in-situ method. The superiorities of ourobtained CdS nanoparticles are well-distributed in polymer matrixwhich is clearly seems from its AFM morphology results.

2. Experimental

2.1. Materials and instrumentation

The azobisisobutylonitrile (AIBN), maleic Anhydride C2H2(CO)2-

O, octene-1, dioxane C4H8O2, thiourea [NH]2CS, N,N-dimethylform-amide (DMFA), cadmium acetate [C4H6O4Cd�2H2O], Potassiumhydroxide (KOH) were all commercial products of the highest pur-ity and have been used as initial materials.

The obtained N/C material was characterized by several meth-ods including X-ray diffraction using a Bruker D2 Phaser powderdiffractometer, A_IST-NT’s SMART SPM™ Atomic Force Microscope,SPECORD 250 PLUS-223G1020 UV–Vis, Cary Eclipse Spectrofluo-rometer (PL) and Varian 3600 FT-IR spectrophotometer.

2.2. Preparation of the copolymer and the nanocomposite

Here in, we report the synthesis of the metal sulfide and copoly-mer nanocomposite materials via in-situ including technique. Inthis present work maleic anhydride/octene-1 copolymer matrixhas been used for stabilizing the generated nanoparticles in thesolution. CdS nanocrystals were synthesized in DMFA solutionwhere cadmium acetate (CH3COO)2Cd�2H2O and thiourea (CH4N2

S) have been used as a Cd and S precursors, respectively and addedinto copolymer powder for stabilization. In the first part of theresearch work we have synthesized the copolymer in laboratorycondition. For conducting the process maleic anhydride have beenadded in a 50 ml ampule and dissolved into 4 g ether (dioxane).After that for further polymerization 0.2 g azobisisobutylonitrile(AIBN) as initiator and 7 ml octene-1 were slowly added into thesolution. The total volume of this mixture solution brought up to20 ml with performing of dioxane solvent and copolymerizationprocess was carried out at 80 �C by heating in glycerin bath andmaintained at this temperature for five hours. The increasing ofviscosity and the color changes indicate the formation of copoly-mer. After then the copolymer was precipitated from the solutionby the presence of isopropanol and rinsed with heptene. Thereaction occurs on radical copolymerization reaction presence ofinitiator and the course of the reaction is shown below.

OO O

+ t=80 oCdioxane(AIBN)

CH CH

CO

C

O O

CH2 CH )n(

(CH2)5CH3

Precipitates of were filtered and dried at room temperature for10 h in vacuum by PH-070A Drying incubator. In the next stage we

have synthesized CdS/MA-Octene-1 PMCs from appropriatecompounds. For this purpose a mixture of 0.0021 mol or 0.65 g(CH3COO)2Cd�2H2O and N,N-dimethylformamide and 51.6 mMKOH solution (to get PH = 9.5) was sequentially loaded in a threeneck reaction flask as the Cd precursor and prepared 1% solution.Then the solution was heated to 90 �C in water bath for 4 hours withstirring and after that 0.0021 mol thiourea (CH4N2 S) was added rap-idly into the three neck reaction flask with a syringe. The reactionwas continued for another 1 hour maintained at this temperatureand the color change is observed at the end of the reaction, so goldenyellow solution was gotten, which indicated the formation of CdSnano-structures. During the heating of metal salt solution Cd2+ ionsdeposited in the copolymer matrix and then thiourea added into thesolution when metal ions paired with S�2 ions.

½NH�2CS$ H2S " þH2NCN

½C4H6O4Cd � 2H2O� þH2S! CdSþ 2CH3COOH

According to the weak and degradable bonds between polymersmolecules they were dividing into if the reaction would continuefor a long time or the temperature is increasing more than 90 �Cthe grey color sediment would be observed, because of, the smallerpolymer chain cannot be stabilized the nanoparticles. So, by thedecreasing the copolymer chains the nanoparticles aggregationprocess is accelerating. As the nanoparticles exceed the size limit,they undergo sedimentation. Therefore, it is necessary to deter-mine the concentration ranges the primary substances in the solu-tion. Also it is fact that nanoparticle sizes increase with an increaseof Cd2+ and S�2 ions concentration.

Synthesized nanocomposite materials were dried at room tem-perature for 72 hours in vacuum by PH-070A Drying incubator. Onthe other stage, for AFM characterization the CdS/MA-Octene-1nanocomposite thin films were obtained by the precipitationmethod on the glass substrate from the formed polymer nanocom-posite solution which was taken reaction condition.

3. Result and discussion

3.1. FT-IR characterization

Fourier transform infrared spectroscopy (FT-IR) is a powerfultechnique for the elucidating the molecular structure of polymersand blends. All spectra exhibited characteristic bands of stretchingand bending modes of OAH, CAH, HACAH, C@O and CAO groups.IR spectra (KBr pellets) were recorded on a Varian 640 FT-IR Spec-trometer at room temperature. Fig. 1 shows the FTIR spectrum ofthe pure copolymer and CdS/copolymer nanocomposite in theregion 400–3000 cm�1. As shown in the obvious changes wereobserved in the spectrum of the copolymer. The band at723 cm�1 were assigned to the vibrations of Cd@S. The mediumsome bands at 650 cm�l and 850 cm�l has been assigned as CdASband. The characteristic signals of valence oscillations of SACbonds in the range of 610–725 cm–1 were recorded in the FT-IRspectra of the powder prepared under reprocessing of the copoly-mer with thiourea. However, a new weak band at 659 cm�1 couldbe noticed, which was assigned to the stretching vibration of theC@S group. The presence of this band indicated the existence ofchemical bonding between CAC (polymer chains) bonds andsurface of CdS nanoparticles. One can propose that since thecopolymer macromolecules contain the saturated CAH and CACbonds, single CAO bonds and double C@O bonds, interaction ofhydrocarbon with elementary sulfur is possible by known reac-tions. The characteristics of both nanoparticles and copolymer sur-rounding them vary for this interaction. The band corresponding to

sites: Part B 68 (2015) 431–435

Fig. 1. FT-IR spectra of the copolymer and CdS NCs.

Z.Q. Mamiyev, N.O. Balayeva / Composites: Part B 68 (2015) 431–435 433

CH2 asymmetric stretching vibration occurs at about 2870–2950 cm�1. The intensity of this band was increased for withincrease the filler. The band at about 1030 cm�1 corresponds toCAO stretching of acetyl groups present on the copolymer back-bone. The band around 1593 cm�1 corresponds to C@O stretchingvibration which confirms the intermolecular interaction betweenOAH groups and carbonyl groups. Appearing of C@O stretching isdue to the semi-crystalline nature of the blend.

The sharp band at 1454 cm�1 is assigned to CH2 scissoringvibrations and the increase of its intensity. The result indicatesthat the hydroxyl groups are the active cites during synthesisand a strong interaction between this group and CdS nanoparti-cles [16].

3.2. Description of the structures by X-ray diffraction

The structural properties and phase characterization of thesamples were determined by X-ray powder diffractometer underCu Ka radiation (k = 1.54060 Å) with Ni filter and the 0.5 h rangeused was from 20 to 60 at a scanning rate of 0.02 c/s.).

Fig. 2 shows the X-ray diffraction (XRD) patterns of the cad-mium sulfide (CdS) nanocrystals confirmed the formation of cubicphase of CdS nanocrystals by comparing with the standard database from ICSD (File No. 01-079-3166). The corresponding peaksare indicating that the size of the particles are in nanorange withaverage grain size 7–10 nm. The XRD pattern of CdS have fivestrong peaks at the angles (2h) of 24.3, 28.3, 31.6, 40.3 and 47.7which could be indexed to diffracting from the [111], [200],[210], [220] and [311] planes, respectively, which correspondsto the typical CdS cubic nanocrystalline lattice constant parametersof a = b = c = 6.3032 and a = b = c = 90�.

The Debye–Scherrer diffraction formula has been applied tocalculate the average size of nanoparticles by using Full Width atHalf Maximum (FWHM) on the basis of 111 diffraction.

Fig. 2. XRD pattern of CdS NCs.

D ¼ akb cos h

Here D is the mean size of the ordered (crystalline) domains, ais a dimensionless shape factor, k-is the X-ray wavelength, b-is theline broadening at half the maximum intensity (FWHM), h-is theBragg angle [17]. In order to verify the results of DIFFRAC.EVA.V2.1and achieve more informative information the parameters fornanocrystals calculated by TOPAS 4.2 program for polycrystallineand noted in following. During the refinement process of the crys-talline parameters the Bragg constant (R) equal to 0.361 and thecrystalline size 4–7 nm they appropriate to Pa-3 (205) space groupwith cubic structure.

3.3. UV–Vis studied

Well known that the most dramatic property of semiconductornanoparticles is the size evolution of optical absorption spectra, so,it has been used to focus the optical properties of nanoparticles.The UV–Vis absorption spectra of the colloidal solutions of NCmaterial in DMFA solution were measured at room temperatureby using of SPECORD 250 PLUS-223G1020 device in the range of300–800 nm and illustrated in Fig. 3. The UV–Visible spectrumshows that the onset of absorption for the sample is 464 nm.

It is well known that the principal absorption energy, whichappropriate to the transmission from valance zone to conductionband, is employed to determine the band gap of the sample.

The direct band gap energy can be estimated from a plot of(ahm)2 versus photon energy (hm). It is clear that the diameter ofthe particles is associated with the absorption edge. Hence UV–Vis-ible absorption spectroscopy method is one of the most commonlyused methods for determining nanoparticle size. In our work opti-cal band gap is calculated using the Tauc relation. Tauc relation isdescribed below.

ðahmÞ1=n ¼ Aðhm� EgÞ

where A is a constant, hm is photon energy, a is the absorption coef-ficient and Eg is the band gap of the materials and exponent ndepends on the type of transition [18]. So a plot of (ahm)2, energy(hm) is shown in Fig. 4. The direct band gap values of the samplehave been obtained from (ahm)2 and plot as shown in Fig. 4 andthe linear portion of the curve is extrapolated to hm axis to deter-mine the band gap energy. The direct band gap value of sample isfound to be 3.08 eV, this value is shifted compared with the bulkvalue (band gap = 2.54 eV for bulk CdS) and this could be a conse-quence of a size quantization effect in the sample.

Fig. 3. UV–Vis optical absorption spectra of CdS/MA-octene-1N/C materials.

Fig. 4. Determination of band gap of from absorption onset for CdS/MA-octene-1N/C.

Fig. 5. AFM images of the CdS NCs on the MA-octene-1 copolymer matrix. (a) 2dand (b) 3d.

Fig. 6. Absorbance and PL spectra of the CdS NCs embedded in MA/octene-1copolymer matrix.

434 Z.Q. Mamiyev, N.O. Balayeva / Composites: Part B 68 (2015) 431–435

3.4. AFM characterization

The morphological characterization and surface analysis of thenanocomposite (N/C) have been studied via AFM. For this purposethe thin film has been prepared by deposition on the glass sub-strate from solution. The AFM images were captured in the SemiContact Mode using an e-scanner with a maximum scan dimension

of 1.2g*1.2g in the laboratory atmosphere and showed in Fig. 5.Morphological analysis showed that the grain sizes of CdS nano-crystals were in agreement with the result observed in the XRDtechnique.

From AFM images, we obtain the average particle size ofapproximately 2–6 nm, which is almost the same with averagevalues calculated from the absorption spectrum of UV–Vis andXRD powder pattern. As seen from the picture CdS nanoparticlesare relatively evenly distributed in the copolymer matrix and thisshould be considered ordinary case for the method that we use.

3.5. Photoluminescence analysis (PL)

Fig. 6 demonstrated the Photoluminescence (PL) spectrum ofCdS/Copolymer N/C with excitation wavelength 404.6 nm andthe PL peak is about 492.3 nm. The photoluminescence originatesfrom the recombination of the surface states of integral parts.

PL measurements were carried out in DMFA solution of thePMCs material and were used Cary Eclipse Spectrofluorometerwith Xenon lamp as a source of illumination during a practice. Sofar, comparison of the macro size and nanoscale metal sulfidecompounds photoluminescence properties shows that, in the aftermath from bulk to nanoscale the excitation spectra shifting toright. It can be explained by the influence of quantum size effectsto formation of electrons orientation in atoms in very small nano-sized as in the ultraviolet. PL spectrum of the capped CdS nanopar-ticles N/C was observed the emission peak an additionalinteresting feature, namely a strong and narrow emission bandcentered about 492 nm might be assigned to the surface trapinduced emission, which involved the recombination of electronstrapped inside a sulfur vacancy with a hole in the valence bandof the CdS nanoparticles. In our case, the enhancement and blueshift of the emission could be understood as a consequence of cur-ing of surface defects due to the formation of chemical bondsbetween thiourea and surface of CdS nanoparticles, whichenhanced the possibility of electron–hole recombination.

4. Conclusions

In summary, the in-situ method for preparation of CdS nanopar-ticles by using a chemical reaction has been described. Accordingto XRD results the corresponding peaks are indicating that the sizeof the particles is in nanorange with average grain size 4–7 nm. Thesurface morphology was studied by AFM, and set the average par-ticle size 2–6 nm. The CdS nanoparticles showed blue shift in theirUV–Vis absorption (k = 418 nm) spectrum. The band gap of

Z.Q. Mamiyev, N.O. Balayeva / Composites: Part B 68 (2015) 431–435 435

obtained CdS nanoparticles is calculated 3.08 eV which is higherthan the bulk due to quantum confinement. The PL spectrum ofCdS nanoparticles showed a fluorescence band with a maximumat about 492 nm.

References

[1] William Gacitua E, Aldo Ballerini A, Jinwen Zhang. Maderas Ciencia ytecnología 2005;7(3):159–78.

[2] McDonald SA, Cyr PW, Levina L, Sargent EH. J Appl Phys Lett2004;85(11):2089–91.

[3] Lagashetty A, Venkatarama A. General article. Resonance 2005;10(7):49–57.[4] Khiew PS, Huang NM, et al. J Mater Lett 2004;58:516–21.[5] Bansal P, Jaggi N, Rohilla SK. Res J Chem Sci 2012;2(8):69–71.[6] Nanfeng Zheng, Xianhui Bu, Haiwei Lu, Qichun Zhang, Pingyun Feng. J Am

Chem Soc 2005;127. 11963–11965 9 11963.

[7] Cosuwa J, Oriaku CI, Mgbaja EC. J Chalcogenide Lett 2010;7(12):679–84.[8] Rebecca Somers C, Bawendi⁄ Moungi G, Nocera Daniel G. J Chem Soc Rev

2007;36:579–91.[9] Wu Chunyan, Wang Li, Zhang Zihan, Zhang Xiwei, Peng Qiang, Cai Jiajun, et al. J

Front Optoelectron China 2011;4(2):161–5.[10] Vossmeyer T, Katsikas L, Gienig M, Popovic IG, Diesner K, Chemseddine ⁄A,

et al. J Phys Chem 1994;98:7665–73.[11] Annie Freeda M, Rode Madhav N, Mahadevan CK, Ramalingom S. J

Nanotechnol Nanosci 2010;1(1).[12] Dwivedi DK, Dayashankar, Dubey Maheshwar. J Ovonic Res 2010;6(1):57–62.[13] Esmaili M, Habibi-Yangjeh. Chinese J Catal 2011;32(6):933–8.[14] Qi Limin, Co1lfen Helmut, Antonietti Markus. J Nano Lett 2001;1:261–5.[15] Balogh Lajos, Tomalia Donald A, et al. J Nanopart Res 1999;1:353–68.[16] Khan Ziaul Raza, Zulfequar M, Shahid Khan Mohd. J Mater Sci 2011;46:5412–6.[17] Al-Aani Muhammad A. Iraqi J Phys 2010;8(11):1–7.[18] Balayeva Narmina O et al. Compos Part B 2013;53:391–4.