Structural and Thermal Studies of ZnS and CdS Nanoparticles in Polymer Matrices

Hindawi Publishing Corporation Journal of Nanomaterials Volume 2016, Article ID 3296071, 14 pages http://dx.doi.org/10.1155/2016/3296071 Research Article Structural and Thermal Studies of ZnS and CdS Nanoparticles in Polymer Matrices Jejenija Osuntokun and Peter A. Ajibade Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa Correspondence should be addressed to Peter A. Ajibade; Received 17 September 2015; Revised 3 November 2015; Accepted 12 November 2015 Academic Editor: Takuya Tsuzuki Copyright © 2016 J. Osuntokun and P. A. Ajibade. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We report the synthesis and structural studies of ZnS and CdS nanoparticles in polyvinylpyrrolidone (PVP), poly(vinyl alcohol) (PVA), and poly(methyl methacrylate) (PMMA) matrices. The metal sulfides/polymer nanocomposites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, electronic spectroscopy (UV-Vis), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The particle sizes as calculated from the absorption spectra were in agreement with the results obtained from TEM and XRD data. They showed metal sulfides nanoparticles in the polymers matrices with average crystallite sizes of 1.5–6.9 nm. The TGA results indicate that incorporation of the nanoparticles significantly altered the thermal properties of the respective polymers with ZnS/PVA and CdS/PVA nanocomposites displaying higher thermal stability than the other polymer nanocomposites. 1. Introduction Nanocomposites are the fusion of two or more different materials in which at least one of the components has dimension less than 100 nm [1]. In polymer nanocomposites, the blends consist of organic polymer matrix and inorganic components (semiconductors). The lack of satisfactory mechanical, thermal, and electronic properties of the conventional polymer materials gave rise to the need to functionalize them in an attempt to improve their properties and extend their potential applications [2, 3]. PMMA, PVA, and PVP are among the most widely used polymers in the synthesis of nanocomposites because of their availability and low cost [4–7]. Among group II-VI compound semiconductors nanoparticles, ZnS and CdS are the most promising materials [8]. ZnS is a good material for detecting ultraviolet and violet radiation due to its primary band gap of 3.68 eV (345 nm) and high sensitivity. It has potential applications in optics, optoelectronics, and solar energy [9, 10]. CdS with a direct band gap of 2.42 eV (515 nm) has applications in window layers [11], light emitting diodes [12], and photodetectors. Its applications in photodetector and solar cells when used in conjunction with narrow band gap materials such as CdTe have been reported [13]. The two common routes for the synthesis of polymer nanocomposites are the ex situ and in situ methods [14–16]. The two methods are liquid based, and the end products are solid which are obtained by either coprecipitation or solvent evaporation [17]. The synthesis of MS/PMMA or PVA or PVP where M=Zn or Cd via different chemical and physical routes has been reported by many authors [18–22]. However, there is no report on comparative studies of the structural properties and thermal stability of the nanocomposites of ZnS/CdS nanoparticles in PMMA, PVA, and PVP. In this work, we investigate the structural and thermal properties of different polymer nanocomposites prepared by the incorporation of ZnS and CdS into the matrices of theses polymers: poly(methyl methacrylate) (PMMA), poly(vinyl alcohol) (PVA), and polyvinylpyrrolidone (PVP). The structural studies of the metal sulfides/polymer nanocomposites were carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy (UV-Vis), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). 2 Journal of Nanomaterials 3. Results and Discussion 2823 cm−1 that are assigned to C-H asymmetric and symmetric stretching vibrations, respectively. The bending vibrational bands of the methyl group appear around 1490 cm−1 and 1457 cm−1 [27]. Furthermore, there is a sharp and intense band at 1769 cm−1 which is attributed to the stretching vibration of the carbonyl, C=O. The ZnS/PMMA and CdS/PMMA nanocomposites showed stretching vibrations that are not really different from the pure PMMA and this is indicative of weak chemical interaction between the host polymer and the nanoparticles. Similar studies about the interaction of PMMA and nanoparticles have been reported by other researchers [28]. HDA was used as a passivating agent for the metal sulfide nanoparticle and peaks in the region of 3181– 3336 cm−1 can be ascribed to the N-H stretching of primary amine. These peaks are observable in the infrared absorption spectra of the nanocomposites and it is indicative of the presence of HDA [29, 30]. Figure 1(b) presents the overlapped FTIR spectra of pure PVA and the respective composites with ZnS and CdS nanoparticles. PVA exhibits a broadband at 3429 cm−1 which is assigned to O-H stretching frequency of the hydroxyl group. This band has been shifted to 3425 and 3424 cm−1 in ZnS/PVA and CdS/PVA, respectively. Two bands observed in the pure PVA at 2942, 1755 cm−1 which correspond to C-H and C=O stretching vibrations, respectively, are found at 2938, 1710 cm−1 and 2931, 1749 cm−1 in ZnS/PVA and CdS/PVA polymer nanocomposites. The absorption band at 1646 cm−1 due to C=C stretching in the PVA appears at 1659 and 1653 cm−1 in the ZnS/PVA and CdS/PVA nanocomposites, respectively. The observation of characteristics bands of PVA in ZnS/PVA and CdS/PVA confirms the interaction between these semiconductor inorganic nanoparticles and PVA. Similar results have also been reported for ZnS/PVA [31] and CdS/PVA [32]. The interaction between the nanoparticles and the PVP, host polymer, was also investigated. Figure 1(c) shows the overlapped spectra of PVP and their respective nanocomposites. In the FTIR spectrum of PVP, the band at 1681 cm−1 is due to the C=O stretching mode and after the formation of ZnS/PVP and CdS/PVP nanocomposites the C=O stretching band appears at 1663 and 1641 cm−1 . The red shift of 17 and 40 cm−1 , respectively, indicates a strong interaction between the nanoparticles and the PVP host. The band in the region of 1500–1300 cm−1 is fairly strong and this is because of the contribution from the in-plane C-H bending of different— CH2 and—CH moieties. Most likely the C-H bending modes are coupled with C-N stretching modes. The existence of strong interactions between ZnS and CdS with PVP has also been reported before [33, 34]. 3.1. FTIR Spectra Studies. Figure 1(a) shows the overlapped FTIR spectra of pure PMMA and the respective nanoco (...truncated)