Effect on Annealing Temperature on Zno Nanoparticles

ZnO nanoparticles were prepared via simple chemical precipitation method at different annealing temperature. The X-ray diffraction results showed that hexagonal structure of ZnO nanoparticles with grain size in the range of 25 – 50 nm has been obtained. SEM & TEM images show the formation of ZnO nanoparticles with particle size ranging from 25-50 nm (± 0.1nm). The FTIR and Raman spectra exhibited peaks corresponding to the ZnO. Optical absorption studies reveal that the absorption edge has red shifts and increased in the absorption values with increasing annealing temperature. In this report, we were able to develop a method for synthesis of nanoparticles based on the annealing temperature. Key Word: ZnO nanoparticle, XRD, TEM, FTIR, annealing and optical property Corresponding. Introduction Zinc oxide is non-toxic, semiconductor with wide band gap (3.37eV) and natural n-type electrical conductivity [1]. ZnO have superior durability, greater selectivity and heat resistance than organic and inorganic materials [2]. Due to noble properties of ZnO it could be used in various materials and products, including medicine, cosmetics, concrete and solar cells [3]. ZnO is toxic to microorganism but non toxic to human beings and also have good biocompatibility to human cells [4, 5]. ZnO nanoparticles have been prepared by various methods such as thermal decomposition [6], solvothermal reaction [7], chemical vapor deposition [8], hydrothermal method [9] and chemical precipitation method [10]. This article gives a comprehensive overview of the progress that has been made within the context of one-dimensional (1D) ZnO nanostructures. In the present investigation, the ZnO nanoparticles were synthesized by using chemical precipitation method and then the effect of annealing temperature on the syntheses ZnO nanoparticles was examined. Experimental ZnO nanoparticles have been prepared using the required precursors by chemical precipitation method. An aqueous solution of 0.2 M Zinc acetate dihydrate {Zn(CH3(COO))2. 2H2O} dissolved in water and stirred for about 30 min at room temperature. Sodium hydroxide (NaOH) (0.3 M) was added drop wise to the above mentioned solution. The colour of the solution changed into milk white coloured, indicating the formation of ZnO nano particles in the solution. The solution was stirred for 4 hours at room temperature. After the reactions completed, the supernatants were removed and the deposited precipitate was centrifuged and washed with water and ethanol several times. The samples were then suspended in ethanol and allowed to age for 2 hours without stirring. After centrifugation, the samples then dried in oven at 60°C for 2 h. Then, the as prepared ZnO nanoparticle is placed in the middle of a muffle furnace in silica crucible. The samples have been annealed at 400°C for one hour. The prepared ZnO nanoparticles at 400 °C are annealed at different temperature of 500 oC and 600 oC in muffle furnace. Sugapriya S et al /Int.J. ChemTech Res. 2015,8(6),pp 297-302. 298 X-ray diffraction studies have been carried out using PANalytical x-ray diffractometer and surface morphology of the samples with compositional analysis has been studied using Field emission scanning electron microscope (CARLZEISS SIGMA version). Fourier Transform Infrared spectrum has been recorded using SHIMKDZU IRAffinity – 1 instrument. Optical absorption spectrum has been recorded using JASCOUV–Vis-NIR Spectrophotometer (JASCO V570). Result and Discussion Figure 1 (a-c) shows the X-ray diffraction patterns of the ZnO nanoparticles at different annealed temperature i.e., (400, 500 & 600) °C. In all the pattern, the diffraction peaks at 2θ (degrees) of 31.63°, 34.61°, 36.32°, 47.66°, 56.94°, 62.97°, 66.57°, 68.12°, 69.48°, 72.11° and 72.26° are respectively indexed as the (100), (002), (101), (102), (110), (103), (200), (112), (201), (004) and (202) planes of ZnO. All the diffraction peaks in the 2θ range measured corresponds to the hexagonal structure of ZnO with lattice constants a = 3. 253Å and c = 5. 214Å and are in good agreement with those on the standard data card (JCPDS card No. 36-1451). The sharpness of the diffraction peaks suggests that the product is well crystallized. The crystallite size of ZnO is calculated using Scherrer’s equation where, D is the grain size, K is a constant taken to be 0.94, λ is the wavelength of the x-ray radiation, β is the full width at half maximum and θ is the angle of diffraction. The crystallite size has been calculated and is found to be in the range 25-50 nm for the different annealing temperature i.e., (400, 500 & 600) °C of ZnO nanoparticles. These observations indicate that the particle size of ZnO nanoparticles increase with increasing annealing temperature and the crystallite size improvement is responsible for the sharpness in the diffraction intensity peaks from Figure 1 (a) to (c). Figure 1. X-ray Diffraction pattern of ZnO Nanoparticles (a) 4000C (b) 5000C and (c) 6000C annealed samples Figure 2 displays an SEM image of the prepared ZnO nanoparticles at different anneling temperature. SEM image of ZnO nanoparticles at 400 °C is shown in figure 2a shows the particles are small in size. As the annealing temperature increases to 500 °C & 600 °C, the particles resulting in increase of size (Figure 2(b & c)). It can be clearly seen that the size of the ZnO nanoparticles increase rapidly with increase in annealing temperature. The SEM investigations of all samples reveal that the crystallites are of nanometer size. Figure 3(a-c) shows the transmission electron microscope (TEM) image of ZnO nanoparticles (a) 4000C (b) 5000C and (c) 6000C annealed samples. Using the particle number and particle diameter of the particle in the TEM image the particle size has been calculated. The particle size of ZnO Nanoparticles (a) 4000C (b) 5000C and (c) 6000C annealed samples is found to lie in the range of 25-50 nm (± 0.1nm). q b l Cos K D = 10 20 30 40 50 60 70 80 In te ns ity (a . u .) 2q (degree) (a) (b) (c) (1 00 )