Study of Optical and Charge Transport Properties of Polypyrrole-ZnO Nanocomposite

Article Advanced Science, Engineering and Medicine

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Vol. 8, 1–5, 2016 www.aspbs.com/asem

Study of Optical and Charge Transport Properties of Polypyrrole-ZnO Nanocomposite Raman Dwivedi1 , Alok Kumar Singh1 , and Anju Dhillon2
∗ 1 2

HMR Institute of Technology and Management, Hamidpur Affiliated to Guru Gobind Singh Inderprastha University, New Delhi, India Maharaja Surajmal Institute of Technology, C-4, Janakpuri, Affiliated to Guru Gobind Singh Inderprastha University, New Delhi, India Zinc oxide (ZnO) is a semiconductor with a wide band gap. In the present work zinc oxide nanoparticles (ZnO) were effectively produced by a sol–gel method by means of zinc acetate dehydrate, ethylene glycol mono methyl ether and ethanolamine being used as the precursor materials and Zinc oxide nanoparticles formed were thereby utilized to form composite with polypyrrole by in-situ chemical oxidative polymerization method in the further process. The composite obtained was characterized using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV-vis spectroscopy and dc conductivity. SEM micrograph give the average size of PPY-ZnO agglomerate is 100–700 nm and XRD results corroborate semi-crystalline nature of the nano-composites. The dc conduction mechanism has been analysed in the light of Mott, s variable range hopping model and gives the evidence of 3D hopping in the samples.

Keywords: Polypyrrole, Zinc Oxide (ZnO), Nanoparticles, Nanocomposite, Dc Conductivity. 1. INTRODUCTION Intrinsically conducting polymers (ICPs) can be used widely in synthetic metals as they can be substituted for metals and semiconductors in a great variety of electrical and electronic devices and retain the mechanical properties of conventional polymers.1 The merits of conducting polymers such as facile synthesis, electrochemical properties, bio-compatibility, significant electrical conductivity, reversibility, switching capability between conducting-oxidized and insulating reduced state is the basis of tremendous technological, bio-sensing and commercial applications.2
3 However ICPs face some demerits as they are brittle, insoluble and infusible material and suffers from poor processability because of their highly rigid conjugated back bone structure.4–7 Not so good mechanical strength of these polymers restricts their applications in various areas.8 That leads to develop polymer based organic–inorganic hybrid materials in which ICPs are required to use as organic components and various transition or non-transition metal oxides as inorganic counterpart. The metal-conducting polymer materials have led to excellent thermal stability, retention of charge and dramatic increase in the conductivity of conjugated polymers as high as approaching to exceedingly conducting metals ∗

Author to whom correspondence should be addressed.

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with attractive mechanical and physical characteristics.9–12 Conducting polymer Polypyrrole (PPY) has been prepared by chemical and electrochemical oxidation of pyrrole in organic solvents and in aqueous medium containing positive charges on the back bone. PPY through its conductivity attributed to the mobility of these charge carriers along and across the polymer chain with conjugated bonds stabilized by implanted counter-anions into the polymer chain.13 In metal–polymer composites, conductivity depends upon the several factors such as oxidant to monomer ratio, particle loading concentration, filler morphology, size, compactness and interfacial interactions between filler molecule and host matrix.14 Among the transition metal oxides, zinc oxide (ZnO) has shown considerable interest in the fabrication of PPY hybrid materials due to its variety of applications in optoelectronic devices. Zinc oxide is widely used metal oxide because of high refractive index and thermal stability, ultraviolet protection, good transparency, high electron mobility and wide band gap.15
16 These properties of zinc oxide are required to use in emerging PPY applications as thin-film transistors and light-emitting diodes. ZnO semiconductor has several favourable properties: good transparency, high electron mobility, wide band gap, strong room temperature luminescence, etc. Those properties are already used in emerging applications for

2164-6627/2016/8/001/005

doi:10.1166/asem.2016.1885

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Study of Optical and Charge Transport Properties of PPY-ZnO Nanocomposite

transparent electrodes in liquid crystal displays and in energy-saving or heat-protecting windows, and electronic applications of ZnO as thin-film transistor and lightemitting diode.17
18 PPY has been used in a number of applications, such as batteries, supercapacitors, sensors, microwave shielding and corrosion protection.19–22 In preparation of electrically conducting composite, ZnO can be used as conducting filler in insulating polymer matrices. These composites provide potentials in EMI shields, electronic packaging, display devices and electrodes.23–25 The present work is required to explore the potential applications of PPY as high-performance materials by the addition of inorganic particles. PPY-ZnO are synthesized by polymerization of pyrrole moieties in the presence of zinc oxide particles in which metal salts and monomer are used as oxidizer and reducer respectively. The progress of technology and quality of life of mankind has always been closely knit with the progress in material science and material processing technology. Recent developments in nanotechnology and the demonstration of various quantum size effects in nanoscale particles, implies that most of the novel devices of the future will be based on properties of nanomaterials.26 Each nanoparticle comprise of 3 × 107 atoms/molecules. One such technology is nanocomposite materials which encompass variety of systems such as one-dimensional, twodimensional, three dimensional and amorphous materials. These materials made up of distinctly dissimilar components and mixed at a nanoscale. Nanocomposites are widely classified but the fast growing area of research is the organic/inorganic material.27 The nanocomposite materials property does not depends upon the properties of their individual parents but also on their morphology and interfacial characteristics. Nanocomposites differ from conventional composite due to high surface to volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio.

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stirred well using magnetic stirrer for an about 15–17 hrs. Remember that no precipitation should occur during this process. 2.2. Preparation of PPY-ZnO Composite Took three 100 ml conical flask with 10 ml of distilled water in each, added 0.9510 g of p-toluene sulphonic acid in monohydrate form in first flask (named as A), 1.141 g of ammonia persulphate in other flask (and named B) and 0.1006 g of pyrrole in flask (named as C) and stirred well. Then contents in the flask A and C were mixed together and again stirred well. Add ZnO solution prepared as above and again stirred well for an about 10 minutes and solution in the flask B was added drop wise to the above solution and ultrasonicated for about 15 minutes. The obtained solution was centrifuged and supernatant liquid was decanted to obtain the composite particle which was then washed with water and ethanol and dried in an oven overnight at 50  C. Samples so formed were characterized by IR spectra recorded using the PerkinElmer SPECTRUM BX FT-IR spectrophotometric system. The UV–Vis spectra were recorded using Shimadzu UV2200 spectrometer. Surface morphology was analyzed by field emission surface electron microscopy SEM using an AMETEK field emission microscope. The dc conductivity studies in the temperature range 77–300 K were carried out by a two probe method using Keithley’s 610C electrometer and 236 source meter unit (SMU).

3. RESULTS AND DISCUSSION 3.1. Fourier Transform Infrared Spectroscopy (FTIR) Figure 1 represents the FT-IR spectra of pure PPY and PPY loaded with ZnO. The spectrum of bulk PPY confirmed the formation of PPY.28 The band at 1540 cm−1 and a weak band at 1462 cm−1 are assigned to stretching vibration of C C and C–C in the pyrrole ring. PPY shows

2. EXPERIMENTAL DEATILS

2

573 3860 Transmission (arb. unit)

2.1. Preparation of ZnO Nanoparticle (Sol–Gel Method) In the present work a cost effective technique (Sol–gel method) has been used to synthesize the zinc oxide nanoparticles (ZnO) using zinc acetate dehydrate, ethylene glycol mono methyl ether and ethanolamine as a primary materials. To form the composite of Zinc oxide nanoparticles were prepared using in-situ chemical oxidative polymerization method. In this sol–gel method ethylene glycol mono methyl ether used as a solvent and ethanolamine used as a stabilizer. Accurately, weighed zinc acetate dianhydrate about 0.46–0.47 g was added into a clean and dry empty flask and then added 4.8 ml of ethylene glycol mono methyl ether. About 0.20–0.25 ml of ethanolamine was added into the same flask to prepare 5 ml ZnO solution which was

1462 1540 1040

3090

3730

1640

669

1300

PPY PPY+ZnO

3440 3500

3000

2500

2000

1500

1000

500

–1

Wavenumber (cm )

Figure 1. Fourier transform infrared spectroscopy of pure PPY and PPY-ZnO nano-composite.

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Study of Optical and Charge Transport Properties of PPY-ZnO Nanocomposite

characteristic C–N and C–H stretching vibration of pyrrole at 1300 cm−1 and 3090 cm−1 respectively in the infrared spectrum. The band observed at 936 cm−1 and 685 cm−1 may be attributed to the out-of-plane ring deformation and 3440 cm−1 to the N–H vibrations in polymer. The stretching mode of ZnO appears at around 573 cm−1 . IR spectrum of PPY/ZnO nano-composite, with strong attenuation of peaks suggests that each ZnO particle is completely coated by PPY. Significant changes in peaks positions and broadening reveal that it is not a simple mixture of PPY and ZnO and can be attributed to some chemical interactions between active sites in PPY and ZnO to change the polymer conformation. The significant band positions are explained in Table I.

PPY+ZnO PPY

(αhν)1/2

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3.50eV

3.38eV 1.5

2.0

2.5

3.0

3.5

4.0

Energy (eV)

3.2. UV-Vis Spectroscopy UV vis spectra of ZnO doped PPY and pure PPY is shown in Figure 2. The optical band gap is determined from the absorption spectrum. According to Tauc’s relation29
30 hh − Eg n

where n = 1 2 3

(1)

The present system obeys the rule of indirect transition with n = 2.  is calculated using the relation,  = d /t where d is the optical density measured at a given film thickness (t), and the extinction coefficient (k) is given by k = /4 where  is wavelength of incident photon. The value of (h1/2 with incident photon energy h is plotted in Figure 2, and the calculated band gap of pure PPY and ZnO doped PPY is 3.38 eV and 3.50 eV respectively.

Figure 2. UV-vis spectroscopy of pure PPY and PPY-ZnO nanocomposite.

3.4. Scanning Electron Microscopy (SEM) The scanning electron microscopy (SEM) imaging was done to study the morphology of the chemically polymerized PPY and PPY-ZnO composite, shown in Figures 4(a and b) respectively. Normal cauliflower morphology was observed in the SEM images of the pure PPY.

3.3. X-ray Diffraction (XRD) Figure 3 represents the diffractogram of PPY and PPYZnO. XRD pattern of pure PPY has broad peaks at diffraction angles 2 = 25 indicates the amorphous nature of the polymer. This broadening of peaks can be ascribed to the scattering of the bare PPY chains at the interplanar spacing while diffractogram of ZnO shows sharp peaks at various angles for the confirmation of crystalline nature of oxide. While PPY-ZnO nano-composite shows the mixed phase of pure PPY and ZnO angle of 32, 34, 37, 47, 56, 63 and 67. XRD results corroborate semi-crystalline nature of the nano-composite. Table I. FTIR band positions of PPY and PPY-ZnO nanocomposite. Band assignment N–H C–H C C C–C C–N C–H (def.) Zn–O–Zn Zn-PY ring

Polypyrrole

Polypyrrole/ZnO nanocomposite

3440 3090 1540 1462 1300 1040 – –

3440 3090 1540 1462 1300 1040 573 3860, 3730 cm−1

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Figure 3.

X-ray of (a) PPY and (b) PPY-ZnO nanocomposite.

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Study of Optical and Charge Transport Properties of PPY-ZnO Nanocomposite

Figure 4.

SEM images of pure (a and b) PPY and (c and d) PPY-ZnO nanocomposites.

The micrograph of the composite reveals complete encapsulation of ZnO particles in PPY matrix and agglomeration of grains having spherical morphology. SEM micrographs confirm the agglomeration of particles of non-uniform size in 100-700 nm range. 3.5. Dc Conductivity The room temperature conductivity of PPY-ZnO nanocomposite and PPY are 6.65 × 10−4 and 6.62 × 10−7 S/cm respectively. In order to study the effect of doping on the basic mechanism of charge transport, the dc conductivity has been measured in the temperature 77–300 K. Mott’s

law for variable range hopping31
32 has been widely used for PPY32–37 but here we are using the same for ZnO-PPY nanocomposite for the analysis of temperature dependence of dc conductivity. Figure 5(a) shows variation of dc conductivity as inverse temperature. As thermal energy kB T decreases with temperature, there are fewer nearby states with accessible energies, so the mean range of hopping increases, which leads to the following expression for conductivity (2)

H = 0 exp−T0 /T n where n = 1/d +1, where n is the dimensionality, thus n = 1/2, 1/3 and 1/4, respectively for 1D, 2D and 3D hopping (b)

(a) –4

PPY-ZnO PPY

–2 PPY+ZnO PPY

–4

Log σm (Ohm–1cm–1)

Log σm (Ohm–1cm–1)

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–6

–8

–10

–6

–8

–10

–12

–12 2

4

6

8

10

12

14

0.24

0.26

1000/T (K–1) Figure 5.

4

0.28

0.30

0.32

0.34

T–1/4(K–1/4)

Dc conductivity of pure PPY and PPY-ZnO nanocomposite versus (a) 1000/T and (b) T −1/4 .

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Study of Optical and Charge Transport Properties of PPY-ZnO Nanocomposite

transport. T0 and 0 are constants and are expressed functionally as 3 (3) T0 = kB N EF  and (4)

0 = e2 R2 0 N EF  where T0 is the characteristic temperature,  is the dimensionless constant37–39 and is assumed to be 18.1,  is the coefficient of exponential decay of the localized states involved in hopping process, kB is the Boltzmann’s constant, N EF  is the density of states at Fermi level, e is the electronic charge, 0 is the conductivity at infinite temperatures, 0 is the phonon frequency (∼1013 Hz) and can be obtained from Debye’s temperature D30 and R is the hopping distance between the two sites. It has been observed that our conductivity data for both the samples PPY and ZnO-PPY nanocomposite fits best into linear curve for n = 1/4 and the variation of dc conductivity as a function of T −1/4 has been shown in Figure 4(b). Therefore, 3D VRH seems to be the mechanism of charge transport in both the samples.

4. CONCLUSIONS We have successfully prepared PPY-ZnO nanocomposite by adopting a cost effective method. ZnO employed in synthesis of the composite was prepared by Sol–Gel method. Conductivities obtained for the PPY-ZnO nanocomposite is in the range 6.65 × 10−4 S/cm which is higher than the conventional PPY (6.62 × 10−7 S/cm) prepared by chemical oxidative method. FTIR results corroborate significant chemical interaction between PPY and ZnO as significant changes in peak positions and broadening reveal the composite to be not a simple mixture of PPY and ZnO but persistent chemical interactions between active sites in PPY and ZnO there by changing the polymer conformation. Such enhancement in the property of the prepared composite can make it a promising candidate for future device applications such as active layer in solar cells and for electromagnetic interference shielding. Acknowledgments: Authors are highly thankful to USIC, University of Delhi and Delhi Technical University for their help in synthesis and characterization of the material.

References and Notes 1. V. K. Gade, D. J. Shirale, P. D. Gaikwad, K. P. Kakde, P. A. Savale, H. J. Kharat, B. H. Pawar, and M. D. Shirsat, Int. J. Electrochem. Sci. 2, 270 (2007). 2. A. Kassim, H. N. M. E. Mahmud, L. M. Yee, and N. Hanipah, Pac. J. Sci. Technol. 7, 105 (2008). 3. H. Zengin and B. Erkan, Polym. Adv. Technol. 21, 216 (2010).

4. X. Feng, Z. Sun, W. Hou, and J. J. Zhu, Nanotechnology 18, 195 (2007). 5. J. Jiang, L. Ai, and L. Li, J. Phys. Chem. B 113, 1376 (2009). 6. J. Jiang and L. H. Ai, J. Mater. Sci. 21, 687 (2010). 7. H. Li, Y. Jia, S. Luan, Q. Xiang, C. C. Han, G. Mamtin, Y. Han, and L. An, Polym. Compos. 29, 649 (2008). 8. A. Bhattacharaya, D. C. Mukherjee, J. M. Gohil, Y. Kumar, and S. Kundu, Desalination 225, 366 (2008). 9. K. Majid, R. Tabassum, A. F. Shah, S. Ahmad, and M. L. Singla, J. Mater. Sci.: Electron. 20, 958 (2009). 10. X. Feng, Z. Sun, W. Hou, and J.-J. Zhu, Nanotechnology 18, 195603 (2007). 11. H. Yuvaraj, E. J. Park, Y.-S. Gal, and K. T. Lim, Colloids Surf. 313–314, 300 (2008). 12. F. Kanwal, S. A. Siddiqi, A. Batool, M. Imran, W. Mushtaq, and T. Jamil, J. Synth. Met. 161, 335 (2011). 13. A. Varesano, C. Tonin, F. Ferrero, M. Stringhetta, and J. Therm. Anal. Calorim. 94, 55 (2008). 14. H. C. Pant, M. K. Patra, S. C. Negi, A. Bhatia, S. R. Vadera, and N. Kumar, Bull. Mater. Sci. 29, 379 (2006). 15. S. R. C. Vivekchand, K. C. Kam, G. Gundiah, A. Govindaraj, A. K. Cheetham, and C. N. R. Rao, J. Mater. Chem. 15, 4922 (2005). 16. X. Q. Wei, Z. Zhang, Y. X. Yu, and B. Y. Man, Opt. Laser Technol. 41, 530 (2009). 17. C. W. Bunn, Proc. Phys. Soc. London 47, 835 (1935). 18. D. R. Lide (ed.), CRC Handbook of Chemistry and Physics, 73rd edn., CRC Press, New York (1992). 19. J. M. Pernaut and J. R. Reynolds, J. Phys. Chem. 17, 4080 (2000). 20. K. Jurewicz, S. Delpeux, V. Bertagna, F. Beguin, and E. Frackowiak, Chem. Phys. Lett. 347, 36 (2001). 21. C. W. Lin, B. J. Hwang, and C. R. Lee, Mater. Chem. Phys. 55, 139 (1998). 22. J. W. Goodwin, G. M. Markham, and B. J. Vinent, Phys. Chem. 101, 1961 (1997). 23. H. P. de Oliveira, C. A. S. Andrade, and C. P. de Melo, Synth. Met. 155, 631 (2005). 24. Y. Wang and X. Jing, Polym. Adv. Technol. 16, 344 (2005). 25. C. W. Lin, B. J. Hwang, and C. R. Lee, Mater. Chem. Phys. 58, 114 (1999). 26. D. P. Valençaa, K. G. B. Alvesa, C. P. de Melob, and N. Bouchonneaua, Materials Research 18, 273 (2015). 27. V. T. Bhugul and G. N. Choudhari Inter. Jour. of Sci. and Res. Pub. 5, 1 (2015). 28. R. Singh and A. K. Narula, J. Appl. Phys. 82, 4362 (1997). 29. J. Tauc, R. Grigirovici, and A.Vancu, Phys. Status Solid 15, 627 (1966). 30. G. B. V. S. Lakshmi, V. Ali, A. M. Siddiqui, P. K. Kulriya, and M. Zulfequar, Eur. Phys. J. Appl. Phys. 39, 251 (2008). 31. N. F. Mott and E. A. Davis, Electronic Processes in Noncrystalline Materials, 2nd edn., Oxford University Press, London (1979). 32. T. Fatima, T. Sankarappa, and R. Ramanna, Res. Jour. of Mat. Sci. 3, 1 (2015). 33. R. K. Singh, J. Kumar, R. Singh, R. Kant, R. C. Rastogi, S. Chand, and V. Kumar, New J. Phys. 8, 112 (2006). 34. R. Singh, J. Kumar, A. Kaur, K. L. Yadav, R. Bhattacharya, E. Hussain, and S. Ali, Polymer 47, 6042 (2006). 35. T. Yamamoto, M. Abla, T. Shimizu, D. Komarudin, B. L. Lee, and E. Kurokowa, Polym. Bull. 42, 321 (1999). 36. X. Jiang, R. Patil, Y. Harima, J. Oshita, and A. Unnai, J. Phys. Chem. B 109, 221 (2005). 37. S. Ukai, H. Ito, K. Marumoto, and S. I. Kuroda, J. Phs. Soc. Jpn. 4, 3314 (2005). 38. A. B. Kaiser, Rep. Prog. Phys. 64, 1 (2001). 39. D. K. Paul and S. S. Mitra, Phys Rev. Lett. 31, 1000 (1973).

Received: 10 February 2016. Revised/Accepted: 17 April 2016. Adv. Sci. Eng. Med. 8, 1–5, 2016

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