(Ahmed et al., 24; and Qiang et al., 28). The preparation of PANI composites with various materials has received great attention because of their uniq

Transcription

1 Electrical Studies on the Composite of Polyaniline with Zinc Oxide Nanoparticles Shahid Pervez Ansari* and Faiz Mohammad** Inorganic/organic composites of polyaniline (PANI) with zinc oxide (ZnO) nanoparticles as inorganic filler have been prepared by solution casting method using N-methyl-2- pyrrolidone (NMP) as solvent. These composites are studied for their electrical conductivity and stability in terms of DC electrical conductivity retention using four-inline probe technique under isothermal and cyclic heating of the test samples. The composites have also been characterized by Fourier Transform Infrared (FTIR) spectroscopy. It has been found that in composites, there exist two conduction phases, as electrical conductivity first decreases with decrease in concentration of PANI. However, with the increase in concentration of ZnO nanoparticles further, the electrical conductivity of the composites increases. All the samples follow Arrhenius equation for the temperature dependence of electrical conductivity and support the semiconducting nature of the doped state. The conductivity of the as-prepared composites has been found to be in the semiconducting region. The studied samples showed good electrical conductivity stability up to the temperature of 9 C. Keywords: Polyaniline (PANI), ZnO nanoparticles, DC electrical conductivity, Stability Introduction Mutual interactions between inorganic semiconductors and conducting polymers may give rise to interesting properties which are significantly different from those of individual components (Dutta et al., 29). Nanostructures and nanocomposites of conducting polymers have emerged as a new field dedicated to the creation of smart materials for use in future technologies (Malinauskas et al., 25; and Rajesh et al., 29). Blending or encapsulation of inorganic nanoparticles in intrinsically conducting polymer matrix is believed to be an easy route to prepare and design nanocomposites where delocalized -electrons can interact with inorganic nanoparticles, resulting in materials of unique or better properties (Lei and Su, 27). Many studies on polymer nanocomposite preparation have been reported in the quest to develop new advanced materials with improved mechanical, electrical, optical and catalytic properties or to improve conduction mechanism in electronic devices. These materials have found their use in many electronic and nanoelctronic devices. Polyaniline (PANI) is a promising conducting polymer due to its easy synthesis, environmental stability and high electrical conductivity on doping with protonic acids * Research Scholar, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh 222, India. shahidzahir@rediffmail.com ** Professor, Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh MuslimUniversity, Aligarh, 222, India. faizmohammad54@rediffmail.com Electrical 21 IUP. Studies All Rights on the Reserved. Composite of Polyaniline with Zinc Oxide Nanoparticles 7

2 (Ahmed et al., 24; and Qiang et al., 28). The preparation of PANI composites with various materials has received great attention because of their unique properties and applications in various electrical and electronic devices. Several reports dealing with the preparation of conducting composites such as Fe 3 O 4 :PANI, MnO 2 :PANI, TiO 2 :PANI and ZrO 2 :PANI (Gok et al., 27; and Yavuz and Gok, 27), as well as preparation and characterization of ZnO:PANI composites have been published (Paul et al., 27; Jeng et al., 28; and Zhang, 29). However, in the present work, we have studied the electrical properties of the ZnO:PANI composites based on ZnO nanoparticles as inorganic filler material and PANI as the main matrix. We have studied the effect of ZnO nanoparticles on the electrical conductivity of PANI and its thermal stability in terms of electrical conductivity retention in two slightly different conditions. Materials and Methods The materials used include acetone (Merck, India), ammonia (Qualigen, India), aniline (Merck, India), hydrochloric acid (Rankem, India), potassium persulphate (CDH, India), N-methyl-2-pyrrolidone (MNP)(Qualigen, India) and ZnO nanoparticles (avg. size 5 nm) (mknano, Canada) (Figure 1). Aniline was doubly distilled before use and all other chemicals were used as-received. Figure 1: Transmission Electron Microscopy (TEM) Image of ZnO Nanoparticles Preparation of PANI PANI was obtained via oxidative polymerization of aniline in aqueous HCl (1 M) solution. The oxidative polymerization of aniline in HCl (1 M) was performed using potassium 8 The IUP Journal of Chemistry, Vol. III, No. 4, 21

3 persulphate (K 2 S 2 O 8 ) as oxidant in HCl (1M) (Khatoon et al., 28). The optimum ratio of aniline:oxidant (2:1) (Luzny et al., 22) was kept constant during the reaction. Equal volume of.2 M aniline in HCl (1M) and.1m K 2 S 2 O 8 in HCl (1M) were separately cooled to -5 C in refrigerator. The two solutions were mixed and kept undisturbed overnight in refrigerator to complete polymerization. Next day, PANI (emeraldine salt) obtained was filtered and washed with double distilled water till the filtrate was neutral to ph paper followed by its dedoping using 1 M ammonia solution. It was again washed with double distilled water to get the emeraldine base form of PANI, which, after drying at 6 C in air oven for two days, was kept in a desiccator for further studies (Ahmed, 23; and Khatoon, 26). Preparation of Composites First, ZnO nanoparticles (ZnO) (1, 2, 3 mg) were dispersed in 5 ml of NMP in round-bottomed flasks for 12 h with continuous vigorous stirring at room temperature (Patil and Radhakrishnana, 26; and Zhang et al., 29). In other flasks, PANI base form (EB) (99, 98, 97 mg) were dissolved slowly with continuous stirring. Dispersion of ZnO nanoparticles were then added to PANI solution at a rate of 1 ml/min. The films of the prepared composites were obtained by solvent evaporation method at 1 C in an air oven. Thus, prepared films were cut into small pieces of rectangular shape and subjected to a pressure of 1 tons using electrically operated hydraulic press machine at 15 C to get smooth films. Finally, we prepared films of pure PANI, PANI:ZnO (1%), PANI:ZnO (2%) and PANI:ZnO (3%). These films were then treated with 1 M HCl for 24 h, washed with double distilled water repeatedly to remove traces of acid, dried at 6 C for 12 h and were used for electrical studies. Characterization The pure PANI and composites of different compositions of PANI were characterized by FTIR, DC electrical conductivity of HCl doped PANI and composite films were measured with increasing temperature (4 C-15 C) by using four-in-line probe DC electrical conductivity measuring instrument (Scientific Equipment, Roorkee, India). DC electrical conductivity ( ) was calculated using the following equations: o / 7 G W/ S W / S 2S/ ln 2 7 W...(1) G...(2) o V / I S 2 1/...(3)...(4) where G 7 (W/S) is a correction divisor (which is a function of thickness of the sample as well as probe spacing) while I, V, W and S are current (A), voltage (V), thickness of the film (cm) and probe spacing (cm), respectively. Electrical Studies on the Composite of Polyaniline with Zinc Oxide Nanoparticles 9

4 Results and Discussion FTIR spectrum of ZnO nanoparticles is presented in Figure 2a. The size of ZnO nanoparticles may be observed in Figure 1, which supports the claim of its average particles size. The broad peak ranging between 44 cm 1 to 55 cm 1 (Figure 2a) can be assigned to ZnO group (Lü et al., 27; and An lovar et al., 28). FTIR spectrum of prepared PA NI (EB) is presented in Figure 2b. The bands corresponding to out-of-plane bending vibration of C-H bond of p-disubstituted benzene rings appear at 824 cm 1 (Ahmed, 23; Blinova et al., 27; Song et al., 28; and Kalasad et al., 29). The bands corresponding to vibration mode of N=Q=N (quinoid) ring and stretching mode of C-N bond appear at 1,15 cm 1 (Yan et al., 27) and 1,37 cm 1 respectively (Zhou et al., 29). Bands at 1,582 cm 1 and 1,496 cm 1 (Olad and Rashidzadeh, 28) are assigned to C=C stretching of quinoid and benzenoid rings respectively. In case of composite prepared using PANI:ZnO (3%) in NMP (Figure 2c) peaks at 1,298, 1,678, 2,879 and 2,951 cm 1 due to characteristic peaks of NMP (Lee et al., 2). In the IR spectra of PANI:ZnO, the peaks of pure PANI shifted to lower wavenumber, indicating that all of these chemical bonds were weakened, whereas Zn-O peak broadened. According to the results of FTIR, hybridization between ZnO and PANI molecules is expected, which resulted in an intense interaction, and the chemical-adsorbed monolayer PANI structure caused an interface hybrid effect between PANI and ZnO (Zhang et al., 29). Figure 2: FTIR Spectra of (a) ZnO Nanoparticle, (b) Pure PANI (EB), and (c) PANI:ZnO (3%) c Transmittance (arb.) b a 4, 3, 2, 1, 4 Wave Number (l/cm) 1 The IUP Journal of Chemistry, Vol. III, No. 4, 21

5 The electrical conductivity of the composite films was measured from 4 C to 15 C and all were found in the upper semiconducting region. All the samples of PANI and PANI:ZnO composites of different compositions followed Arrhenius plot for temperature dependence of electrical conductivity, as shown in Figure 3, and suggest the semiconducting nature of HCl doped composites. In case of pure PANI, highest electrical conductivity was observed, as compared to the various composites. This supports the fact that PANI is mainly responsible for electrical conduction, and as its concentration decreased, a sharp decease in conductivity was observed. However, with the increase in concentration of ZnO nanoparticles, electrical conductivity increased. From the above observation, it can be said that PANI is mainly responsible for the electrical conduction, and the presence of ZnO also contributes to conduction, which is very clear from Figure 3. In the other two experiments designed to study stability of electrical conductivity in atmospheric condition, results were found to support the above claims. Cyclic electrical conductivity study on these composites suggests that the electrical conductivity of the composites is more stable than that of simple PANI, and with the increase in ZnO content, increase in electrical conductivity stability is obtained (Figures 4, 5, 6 and 7). The isothermal electrical conductivity stability study reveals that the electrical conductivity is quite stable up to the temperature of 9 C, and with the increase in concentration of ZnO, the stability increased and a much better result was observed in case of the composite containing PANI:ZnO (3%), as can be observed in Figures 8, 9, 1 and 11. Loss in electrical conductivity is because of the loss of dopants, chemical reaction of dopant with solvent and change in physical properties due to heat treatment (Zhang et al., 29). Figure 3: Arrhenius Plots of Various Composites and Pure PANI log PANI PANI (99%) ZnO (1%) PANI (98%) ZnO (2%) PANI (97%) ZnO (3%) Electrical Studies on the Composite of Polyaniline with Zinc Oxide Nanoparticles 11

6 Figure 4: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI by Cyclic Technique.2 1/Temp. (K) log Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Figure 5: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI:ZnO (1%) Composite by Cyclic Technique log /Temp. (K) Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 12 The IUP Journal of Chemistry, Vol. III, No. 4, 21

7 Figure 6: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI:ZnO (2%) Composite by Cyclic Technique log /Temp. (K) Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Figure 7: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI ZnO (3%) Composite by Cyclic Technique log Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 1/Temp. (K) Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Electrical Studies on the Composite of Polyaniline with Zinc Oxide Nanoparticles 13

8 Figure 8: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for Pure PANI by Isothermal Technique / Time (min) / (5 C) / (7 C) / (9 C) / (11 C) / (13 C) Figure 9: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI:ZnO (1%) by Isothermal Technique / / (5 C) / (7 C) / (9 C) / (11 C) / (13 C) Time (min) The IUP Journal of Chemistry, Vol. III, No. 4, 21

9 Figure 1: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI:ZnO (2%) by Isothermal Technique / Time Time (min) (min) / (5 C) / (7 C) / (9 C) / (11 C) / (13 C) Figure 11: Degradation of Conductivity in Terms of DC Electrical Conductivity Retention for PANI:ZnO (3%) by Isothermal Technique / Time (min) / (5 C) / (7 C) / (9 C) / (11 C) / (13 C) Conclusion In this study, various stable composites of PANI and ZnO nanoparticles were prepared. FTIR spectra of the samples support the interaction of PANI chain with ZnO, which causes the thermal stability of the composites. Electrical conductivity study of the samples favors that PANI is mainly responsible for the electrical conduction; however, a little Electrical Studies on the Composite of Polyaniline with Zinc Oxide Nanoparticles 15

10 increase in conductivity was observed with the increase in ZnO content, and its effect is prominent in the case of the composite having 3% ZnO nanoparticles. Cyclic and isothermal study reveals that loss of dopants and electrical conductivity has decreased with increased ZnO concentration, consequently, increased stability of the composites. Acknowledgment: The authors thank Mohd. Omaish Ansari, Tariq Anwer (Research Scholars, Department of Applied Chemistry) and Dr. Shagufta Praveen (Guest Faculty, Boys Polytechnic) of AMU for the assistance provided by them in their respective capacities. The authors also thank SAIF AIIMS for providing TEM facility. References 1. Ahmed A A (23), Preparation and Characterization of Composites Based on Electrically Conducting Polymer, Ph.D. Thesis, Aligarh Muslim University, pp. 9 and Ahmed A A, Mohammad F and Rahman M Z A (24), Composites of Polyaniline and Cellulose Acetate: Preparation, Characterization, Thermo-Oxidative Degradation and Stability in Terms of DC Electrical Conductivity Retention, Synthetic Metals, Vol. 144, No. 1, p An lovar A, Orel Z C and Zigon M (28), Nanocomposites with Nano-to-Sub- Micrometer Size Zinc Oxide as an Effective UV Absorber, Polimeri., Vol. 29, No. 2, p Blinova N V, Stejkal J, Trchova M et al. (27), Polyaniline and Polypyrrole: A Comparative Study of the Preparation, Eur. Polym. J., Vol. 43, No. 6, p Dutta K, Manna S and De S K (29), Optical and Electrical Characterizations of ZnS Nanoparticles Embedded in Conducting Polymer, Synthetic Metals, Vol. 159, No. 3, p Gok A, Omatsova M and Prokes J (27), Synthesis and Characterization of Red Mud/Polyaniline Composites: Electrical Properties and Thermal Stability, European Polymer Journal, Vol. 43, No. 6, p Jeng J, Chen T, Lee C et al. (28), Growth Mechanism and ph-regulation Characteristics of Composite Latex Particles Prepared from Pickering Emulsion Polymerization of Aniline/ZnO Using Different Hydrophilicities of Oil Phases, Polymer, Vol. 49, No. 15, p Kalasad M N and Rabinal M K J (29), Tunnelling Conductivity in Conducting Polymer Composites: A Manifestation of Chemical Interaction, J. Phys. D: Appl. Phys., Vol. 42, No. 6, p Khatoon A (26), Electroanalytical Studies on Polyaniline:Polyacrylonitrile Composites, M. Phil. Dissertation, Aligarh Muslim University, p The IUP Journal of Chemistry, Vol. III, No. 4, 21

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