Effect of capping agent on Cu doped ZnO nanoparticles by solvothermal method

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1 ISSN Number (online): Effect of capping agent on Cu doped ZnO nanoparticles by solvothermal method S.DaphneRebekal ab, S.MeenakshiSundar b*, R. Venkataraman c, K.Upendar Reddy d, C. Prema b a Rani Anna Govt.College for women, Department of Chemistry, Tirunelveli Tamil Nadu, India. b Post Graduate and Research Department of Physics, Sri Paramakalyani College, Alwarkurichi , Tirunelveli, Tamil Nadu, India. c Post Graduate and Research Department of Chemistry, Sri Paramakalyani College, Alwarkurichi , Tamil Nadu, India. d Department of Physics, Birla Institute of Technology and Science-Pilani, Hyderabad Campus, Hyderabad , Telangana State, India. *Corresponding Author: S.MeenakshiSundar Tel: ; Fax: smsun_1964@yahoo.co.in Received: 29/2/2016, Revised: 26/04/2016 and Accepted: 7/06/2016 Abstract Copper doped Zinc oxide nano particles were synthesised using poly vinyl pyrrolidone (PVP) as a capping agent by solvothermal method. The influence of the capping agent was studied. The prepared samples were characterised by XRD, IR, UV VIS, TEM, SEM with EDAX and PL. TEM study shows spherical-like particle structure with average size of 25 nm. This is in good agreement with that estimated by Debye sscherrer s formula from the XRD pattern.the band edge emission peaks at 415 nm and 629 nm. The higher concentration of PVP, which enhances illuminenscence of Cu doped ZnO nano particles. ZnO hexagonal structure are detected by X-ray diffraction pattern with preferred orientation along (200) direction. The atomic % of Cu and ZnO are almost equal to their nominal stoichiometry within the experimental error. EDAX spectrum shows that the well agreement with experimental concentration elemental composition of Cu doped Zin Oxide nanoparticles. The band gap energy of the bulk ZnO nano material was 3.2 ev (388 nm) at room temperature. The band gap energy decreases with increasing concentration of PVP. SEM image reveals that the ZnO nano particles have spherical-like particle structure and it 1

2 is homogeneous and uniformly distributed throughout the structure. Key words: Cu doped ZnO nanoparticles, Capping agent PVP, SEM with EDAX, TEM, XRD, FTIR. 1. Introduction ZnO is well known as a direct band gap between 3.37ev room temperature and has distinguished performance in electronics, optics and photonics [3 5]. ZnO has been one of the most promising materials for electrical devices, including transparent conductive films, light emitting diodes and photo catalyst [6 11]. The prevention of the aggregation of nanoparticles is serious concern. Capping nanoparticles has been one of the most important methods used to solve these problems. Nanoparticles of various morphologies were formed, and the photoluminescence intensity was increased because of the passivation of surface defects in the nanoparticles [12]. ZnO nanoparticles have been synthesized in conjunction with different polymer capping agents such as polyethylene glycol (PEG) and poly(n-vinylpyrrolidone) (PVP). The fluorescence of ZnO has been observed in the UV region due to the exciton luminescence of the band gap and in the visible region due to oxygen defects and/or interstitial zinc caused by UV excitation [13,14,15].Guo et.al has studied the capping of ZnO nano particles using poly vinyl pyrrolidone and poly vinyl butryal (PVB) previously [16 17]. In this present work, Cu doped ZnO has been prepared with various concentration of Poly vinyl pyrrolidone(pvp) by solvothermal method. Influence of capping agent on optical, morphological, elemental composition, structural and functional groups were investigated. 2. Experimental 2.1.Materials All chemicals were used analytic reagent grade. Zinc acetate dihydrate, Copper acetate monohydrate, Urea, Ethylene glycol, Poly vinyl pyrrolidone and acetone were purchased from HPLC, India. 2

3 2.2.Preparation of Cu doped ZnO nano particles of solvothermal method Zinc acetate and Copper acetate were taken together in the required composition and urea in 1:3 molecular ratios and PVP was mixed with 0.1 g; 0.2g, 0.3, and 0.4 g dissolved in 50 ml of EG and kept in a micro wave oven. Micro wave irradiation was carried out till the solvent was evaporated completely. The obtained precipitate was cooled and washed several times for water and then acetone to remove the organic impurities. The sample was then dried and collected. We have prepared the following ratios Zn 0.9 Cu 0.1 PVP 0.1 O, Zn 0.9 Cu 0.1 PVP 0.2 O, Zn 0.9 Cu 0.1 PVP 0.3 O, Zn 0.9 Cu 0.1 PVP 0.4 O. All the samples were annealed at C temperatures for one hour. 3. Characterization techniques X-ray diffraction patterns of Zn x Cu 1 x O nano particles were obtained using advance diffractometer (for 2θ range from 10º to 80 º) with monochromatic CuKα radiation(λ=1.54å) to identify crystalline nature of the samples.tem images were taken using Hitachi 600 transmission electron microscopy Zn x Cu 1 x O nano particles.the morphology and composition of the films was investigated by Scanning electron microscopy (SEM; XL 30 FEG Philips, Hillsboro, OR) and energy-dispersive X- ray spectroscopy (EDAX). FTIR spectrum of Zn x Cu 1 x O nano particles was done in the range 4000 to 400cm -1 using thermo Nicolet V-200 FTIR Spectrometer by KBr pellet technique. The UV-visible spectrum of Zn x Cu 1 x O nano particles was recorded employing Jasco V-530 dual beam spectrometer. The PL property of Zn x Cu 1 x O wasstudied by using FP-6500 Spectro fluro meter- 67 at room temperature. 4. Results and Discussion 4.1.X-ray diffraction pattern Fig.1 shows XRD pattern of Cu doped ZnO with various concentration of PVP(0.1,0.2,0.3 and 0.4). The samples were annealed at C for one hour. 3

4 Fig.1 X-ray diffraction pattern of Cu doped ZnO nano particles with various concentration of PVP at C The structure shows exact diffraction pattern of ZnO hexagonal structure peaks appearing at 2θ = 31 7, 34 4, 66 3 and 47 5 are due to (100), (002),(200),(102),(110) and (311) planes respectively. The XRD peaks were compared with Standard Joint Committee powder diffraction standards (JCPDS file No ). Particle sizes were calculated using Debye Scherer s formula. λ Where λ is wave length of X- ray (0.154nm), is FWHM (full width half maximum) and θ is diffraction angle [18]. From table 1 we observed that the ratio of the PVP concentration is increased the yield is increased. Table. 1. PVP concentration with various doping ratios Sample Zn 0.9 Cu 0.1 PVP 0.1 Zn 0.9 Cu 0.1 PVP 0.2 Zn 0.9 Cu 0.1 PVP 0.3 Zn 0.9 Cu 0.1 PVP 0.4 Yield (g) Colour Time taken 3 Pale green Pale green Greenish white 40 4 white 45 4

5 From table 2, we found that the concentration of the capping agent is increased with decreasing particles size. Table. 2.Structural properties of Cu doped ZnO with PVP Sample Particle size from TEM XRD Zn 0.9 Cu 0.1 PVP 0.1 A C Zn 0.9 Cu 0.1 PVP 0.2 A C Zn 0.9 Cu 0.1 PVP 0.3 A C Zn 0.9 Cu 0.1 PVP 0.4 A C The average particle size was found to be 26 nm. It was confirmed that the advantageous of PVP size controlled. 4.2.Transmission electron microscope Fig.2 shows the TEM image of Cu doped ZnO nano particles. Particle size was found to be in the range between nm. Fig.2 TEM image and SAED pattern of Cu doped ZnO nano particles with PVP 0.4 g at C. SAED pattern shows that the particles are well crystallized aswell as proves the hexagonal structure of as prepared ZnO nano particles. 4.3.SEM with EDAX Fig. 3 shows the surface morphology and compositional analysis of Cu doped ZnO with PVP 0.4 g A C. SEM image reveals that the ZnO nano particles have spherical-like particle structure. It has homogeneous and uniformly distributed throughout the structure[19] 5

6 Elemental composition of Cu doped Zin Oxide nanoparticles are shown in Fig.3. Fig.3 SEM with EDAX image of Cu doped ZnO nano particles with PVP 0.4 g at C.The EDX analysis confirms the presence of Cu in ZnO, their nominal percentage and chemical purity of the samples. The atomic % of Cu and ZnO are almost equal to their nominal stoichiometry within the experimental error. EDAX spectrum shows that the well agreement with experimental concentration elemental composition of Cu doped Zin Oxide nanoparticles are given in the table.3. Table.3. Elemental composition of Cu doped Zin Oxide with PVP as Capping agent Element Weight % Atomic % O K Cu K Zn K

7 4.4 FT-IR spectrum of the Cu doped ZnO nano particles with PVP FTIR spectrum of the Cu doped ZnO nano particle is shown in fig.4. Fig.4 FTIR spectrum of Cu doped ZnO nano particles with PVP 0.4 g at C.Band assignment and wave numbers are given in the table 4. Table.4. FTIR spectrum of Cu doped ZnO nano particles with PVP 0.4 g at C Sample Wave number (cm -1 ) Band assignment Zn 0.9 Cu 0.1 PVP 0.4 A C Zn O bond C=C, CH and C=O stretching OH group A broad band has been observed at around 460 cm -1 for the pure ZnO corresponding to the formation of Zn O bond [20]. A broad band has been observed at and cm -1 are 7

8 mainly due to C=C and C=O stretching [21]. A broad peak observed at 3400 cm -1 has been attributed to OH group of water. This indicates the existence of water adsorbed on the surface of nano crystalline powder. FTIR study confirms presence of Cu doped ZnO and polymeric stabilizer. the absorption in the region of1200 cm 1 is due to overlap absorption bands of PVP with bands of the hydrated zinc oxide, as well as interaction betweenthem occurs. 4.5 UV-VIS absorption spectrum of Cu doped ZnO with PVP nano particles Fig. 5 show that the absorption spectra of Cu doped ZnO with various concentration of PVP. Fig.5 UV vis absorption spectrum of Cu doped ZnO nano particles with various concentration of PVP. The optical band gap of Cu doped ZnO with PVP nano particles were calculated by using the following relation. where α is the absorption coefficient in cm -1, hν is the photon energy, A is an energy dependent constant and Eg is the energy gap.the absorption spectra revealed a sharp absorption peak at 3.38 ev. No significant shift of the absorption edge was noted for the increase of concentration of capping agent. The band gap energy of the bulk ZnO nano material was 3.2 ev (388 nm) at room temperature [22]. In our work, PVP is a capping polymer. The concentration of PVP is 8

9 increased the band gap energy is gradually decreased. This phenomenon indicated that particle sizes of the ZnO nanoparticles were almost the same, even when polymers were added. The concentrations of some solutions were probably decreased by the precipitation of ZnO nanoparticles by aggregation. The efficiency of the ZnO nano particles was increased by capping the ZnO nanoparticles. Band gap energy was given in the table. 5. Table.5.Band gap energy the Cu doped ZnO nano particles with various concentration of PVP Sample Band gap energy (ev) Zn 0.9 Cu 0.1 PVP 0.1 A C 5.5 Zn 0.9 Cu 0.1 PVP 0.2 A C 5.4 Zn 0.9 Cu 0.1 PVP 0.3 A C 5.3 Zn 0.9 Cu 0.1 PVP 0.4 A C PL spectrum of the Cu doped ZnO nano particles with various concentration of PVP Fig.6 shows the PL spectra of ZnO nanoparticles with different concentrations PVP.The the emission bands appear at 415 nm and 630 nm. Mohan et.al reported that higher concentration of PVP-capped ZnS nanoparticles shows broad band at 440 nm[23]. Fig.6 Cu doped ZnO nano particles with various concentration of PVP. In our work we have found broad band at 415 nm.the luminescence peak shift to longer wavelength for 630nm 9

10 along with the increasing of doping concentration. From this study; we concluded that the higher 5. Conclusion content of PVP enhances the optical property of the Cu doped ZnO nanoparticles. Cu doped ZnO nano particles were synthesised successfully by solvothermal method. From SEM and TEM study, it is found that nano particles are spherical-like particle structure with average size of 20 nm. The band edge emission peaks at 415 nm and 629 nm. The band gap energy of the bulk ZnO nano material was 3.2 ev (388 nm) at room temperature. In our work, PVP is a capping polymer. The concentration of PVP is increased the band gap energy is gradually decreased.the higher concentration of PVP, which enhances illuminenscence of Cu doped ZnO nano particles. XRD shows ZnO hexagonal structure Cu doped ZnO nano particles. SEM image reveals that the ZnO nano particles have spherical-like particle structure. It has homogeneous and uniformly distributed throughout the structure. Acknowledgements The authors are thankful to ManonmaniumSundaranar University of Tirunelveli, Tamilnadu, India and Indian Institute of Technology, Mumbai for providing instrumental facilities. References: [1]Mitra S Mandal A,Banerjee S Dutta ABhattacharya S, Bose A and Chakravorty 2011 Indian J.phys, 85:649. [2] Bhattacharya S and Gosh A 2006 J.Appl.phys. Lett.88: [3] Mirkin CA Science :2095. [4] Chakraborty R Das U Mohanta D and ChouhuryA IndianJ.Phys.83:553. [5]Newton MC and Shaikhaidarov R J.Appl.Phys. Lett [6] Vanheusden K Seager CH Warren WL Tallant DR and Voigt JA 1996.Appl. Phys. Lett. 68: [7]Dayan NJ Sainkar SR Karekar RN and Aiyer RC1998. Thin Solid Films 325: [8]Chen CS Kuo CT Wu TB and Lin IN 1997.Jpn. J. Appl. Phys. Part 1 36:

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