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Preparation and electrical properties of CDs polyaniline nanocomposites by oxidative polymerization

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  • Save International Journal of Composite M aterials 2012, 2(4): 44-47 DOI: 10.5923/j.cmaterials.20120204.01 Studies on Synthesis and Electrical Properties of CdS-Polyaniline Nanocomposite via Oxidation Polymerization Kose T D1,*, Ramteke S P2 1Department of Chemistry A C S College Tukum Chandrapur, (M S) 4424041, India 2Department of Physics, S P College, Chandrapur, (M S) 442401, India Abstract Nanocomposites of conducting polyaniline with CdS nanoparticles have been synthesized via in situ by o xi- dizing the complex of aniline with cad miu m sulfate at 3.5 p H. The effect of CdS-nanoparticles on the electrical conductivity of polyaniline was discussed. The as prepared products were characterized by FT-IR and Transmission electron Microscopy. FTIR absorption band at 3600 - 3500 c m-1 confirmed the highly attached polyaniline with CdS nanoparticles. TEM showed the CdS part icles are spherical with the average diameter of 19 n m which was evenly distributed in poly mer matrix. The uniform intercalation of CdS nanoparticles results in a cooperative phenomenon between the polyaniline and the nanoparticles, as a consequence, the CdS nanoparticles increased the electrical conductivity of polyaniline nanocomposite to 6.50x10-2 S/cm co mpared to the pure polyaniline (10-10 S/cm); Germaniu m (10-2 S/cm) and Silicon (10-4S/cm) semiconductors. Its electrica l conductivity was found to be analogous with existing semiconducting metals. The fact is supported by the ample of e xperimental results and characterizat ion evidences. Keywords Nanocomposites, Nanoparticles, Cad miu m Sulfide, Po lyaniline, Electrical Properties 1. Introduction The nanocomposites of metal and semiconductor particles are important in several optical and electronic applications[1] and their preparat ion with significant effort on the ab ility to control the size and morphology v ia innovative synthetic approach is h igh ly challeng ing part icu larly by using organometallic p recursors. Intrinsically, conducting polymers like polyaniline have potential for wide variety o f application in electronics, sensors, LED, etc owing to its easy polymerizat ion and env iron mental stability [2– 5]. Propert ies of po lyan ilin e can be tailo red by ch ang ing its o xid at ion states[6], acid dopants[7, 8] or through blending it with other organic or inorganic nano sized semiconducting particles[9]. It has been described that the large internal interface area in nanocomposites enables an efficient separation of charge, which is important for photovoltaic applications[10]. Polyan iline-Cd S n ano co mp os it e has b een already used in photovoltaic application but formation of ionic by-products (in the react ion during th e synthesis that influences the electrical properties of resulting material), ind icated some restrict ions in preparat ion of nanoco mposites. There are * Corresponding author: t.kose@redi (Kose T D) Published online at Copyright © 2012 Scientific & Academic Publishing. All Rights Reserved several reports describing nanocomposites of polyaniline with semiconducting particles such as TiO2, PbS and CdS [11]. Polyaniline can exist in various o xidation states[12] exhibit ing different properties. Transport properties of polyaniline transition metal salt co mposite have been studied[13]. Emerald ine base (EB) of polyaniline has been commonly us ed, as it is the most stable form of polyaniline. En zy matic and gas-phase plasma have been utilized in the synthesis of polyaniline[14-17]. Unfortunately, options for the processing of polyaniline are limited, since this poly mer decomposes prior to melting and it is only soluble in a few organic solvents, e.g. strong acids. This situation severely restricts the synthetic routes and desires challenging methodology for the preparation of polyaniline nanocomposites. To overcome this restriction, attempts are desired to synthesize the CdS-polyaniline nanocomposite through oxidative polymerization using hydrogen sulfide gas in solution. This study revealed a successful synthesis of incorporation of CdS-nanoparticls into polyaniline by simplest route and reported conductivities and dielectric property of CdS-polyaniline nanocomposite. 2. Experimental 2.1 Reagents and Materials All chemicals used were of AR grade, Aniline was dis- 45 International Journal of Composite M aterials 2012, 2(4): 44-47 tilled twice prior to use. Cad miu m sulfate (CdSO4.8H2O), ammon iu mpero xidisulfate[(NH4)2S2O8.2H2O], hydrochloric acid, ethanol were analytical reagents and were used as received. 2.2 Synthesis of CdS-Polyaniline Nano Composite Polyaniline emeraldine base (EB) and its hydrochloric salt (Polyaniline-HCl) were prepared accord ing to the procedure reported in literature[18]. CdS-polyaniline nanocomposite was synthesized as follows: Quantitative amount of 0.1 M CdSO4.8H2O was added into the 100 ml 0.5 M aniline solution. The solution was stirred continuously for t wo hours to get complete d issolution under inert atmosphere of nitrogen gas. 0.5 M (NH4)2S2O8.2H2O solution was added drop wise with bubbling of H2S gas at 3.5 pH . The reaction was carried out with constant stirring for 24 h at roo m temperature. The products were washed thoroughly plenty of times with 95 % ethanol and acetone. The resulting product was dried in oven at 60 oC for 24 hrs. The product was named as Cd S-polyaniline nano co mp o s ite. 2.3. Characterization of Samples The nanoparticles formed were characterized by JEOL 2010F t ransmission electron microscopy (TEM).The FT-IR spectroscopy (Perkin-Elmer 100 FT-IR spectrophotometer) was used to record spectra using KBr pellets. The electrical conductivity of the samples was measured at temperature range fro m 30 0C – 100 0C with dry pressed pallets using DFP-02 four probe set up. The capacitance and D-factor of thin pallet of a poly mer sample were measured as a function of temperature using Direct Reading, LCR bridge, 8 C (Pacific), at frequency 1 KHz. are attributed to C=C stretching of the benzenoid and quinoid rings, respectively. The peak at 1298 cm-1 corresponds to C–N stretching of secondary amine in poly mer main chain and can be clearly seen in the sample. The existence of absorption band at 1120 cm-1 has been interpreted as originating fro m p lane bending vibration of C–H, which was formed in the structure of B–N+-M, Q-N+- M and N=Q=N during protonation of CdS to polyaniline. The broad absorption band ranges fro m 3600 to 3500 cm -1 was attributed to the protonation of amines functional group at polymer bac kbone and was observed for the highly attached polyaniline with CdS. Absorption band near 2900 cm-1 is assigned to aliphatic C–H stretching of the polymer. A weak vibration absorption peak at 405 cm-1 for Cd–S bond was observed, shows the concentrations of CdS in the composites was low. 3.2. TEM of CdS-pol yaniline Nano Composite For the TEM characterizat ion, a drop o f the sample was placed on a carbon film supported by a copper grid in order to obtain electron micrographs in a JEOL 2010F Electron Micro s co p e. Fig. 2 shows a micrograph of CdS nanoparticles. The shape of the particles is spherical and the average diameter is 19 n m wh ich was evenly d istributed in poly mer matrix. The high resolution micrographs of these nanoparticles display a crystal array as shown in Fig. 3 3. Result and Discussion 3.1. FT-IR of CdS-Pol yaniline Nano Composite 10.91 10.5 10.0 9.5 9.0 8.5 8.0 %R 7.5 7.0 6.5 6.0 5.5 4.98 4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 cm-1 600 450.0 Figure 1. FT IR Spectra of CdS-polyaniline nanocomposite Fig. 1 shows the FT-IR spectra of CdS-polyanile nano- composite was prepared under the optimal synthetic conditions. The presence of sharp peaks near 1510 and 1605 cm-1 Fi gure 2. TEM image of CdS nanopart icles Figure 3. TEM image of CdS-Polyaniline nanocomposite Kose T D et al.: Studies on Synthesis and Electrical Properties of CdS-Polyaniline 46 Nanocomposite via Oxidation Polymerization 3.3. Electrical Conducti vi ty The temperature dependence of the electrical conductivity data (in the middle range of temperature) fit the Arrhenius type of equation (1) in the temperature range investigated, σ( T) = σ0exp (- E0/2kT) (1) It was observed that CdS-Po lyaniline nanocomposite ex- hibited high conductivity than pure polyaniline reported in table 1. Table 1. Observed conduct ivit ies of CdS-polyaniline nanocomposit e Nano compo sit e CdS - Polyaniline Conduct ivit y ( S cm -1 ) 6.50x10-2 The activation energy σ0 (T) was calculated fro m Arrhenius equation presented in table 2. Table 2. Conductivity, Activation energy, and Dielectric constant of CdS-polyaniline nanocomposite Name of composite CdS-P o lyan ilin e σ (T) cm-1ohm -1 6.50x10-2 Act ivat ion energy (eV) 0.30 Dielectric constant (ε’) 1.15 x 102 The temperature dependence of electrical conductivity of CdS-polyaniline nanocomposite shown in figure 4. methane[20] was formed as a by-product in this reaction. 4. Conclusions Polyaniline-CdS nanocomposites have been successfully synthesized via in situ by o xidation poly merizat ion. FT-IR spectra demonstrated that the transition metal salt had been incorporated into poly mer chain. Electrical conductivity of polyaniline– CdS nanocomposites was found to be increased when co mpared to pure aniline due to its increase in crystallinity. Electrical conductivity of CdS-polyaniline nanocomposite was found to be analogous with existing semiconducting metals. Cad miu m sulfate in aqueous mediu m has been used for the first time with polyaniline and also it is the first attempt to produce nanocomposite of polyaniline -CdS via in-situ with o xidation poly merization by simplest route. ACKNOWLEDGEMENTS The author acknowledges authorities of Sophisticated Analytical Instrumentation Facility (SAIF) Chandigarh (INDIA), for FTIR and Nanotechnology Centre, University of Hyderabad for TEM facility. -1.0 -1.2 -1.4 REFERENCES Log (S/cm) -1.6 [1] Y Wang , Herron N., “Photoconductivity of CdS nanoclus- ter-doped polymers”, Chemistry and Physics Letters, vol. 200, -1.8 no. 1-2, pp. 71–75, 1992. -2.0 [2] R Rosseti , J L Ellison, J M Gibsson , L E Brus , “Size effects in the excited electronic states of small colloidal CdS crys- -2.2 Log tallites” Journal of Chemistry and Physics, vol .80, no. 9, pp., 4464-4469, 1984. -2.4 0.051 0.052 0.053 0.054 0.055 0.056 0.057 0.058 [3] Y G M Coa , P Smith, A J Heeger , “Counter-ion induced Temp (K -1/2) processibility of conducting polyaniline and of conducting polyblends of polyaniline in bulk polymers”, Synthetic M et- Figure 4. T emperature dependence of electrical conductivity of als. 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