Optical Study of ZnO nanoparticles


For the preparation of ZnO sol, the following materials was used i.e., zinc acetate dehydrate Zn(CH3COO)2 (H2O)2 and Potassium hydroxide KOH. Distilled water was used to wash substrates. All chemicals will be analytical grade, obtained from the University of Poonch Rawalakot AJK.

3.2. Preparation and processing of ZnO nanoparticles

            Zinc oxide nanoparticles were synthesized by the co-precipitation method, at 80-900 C. 2.206 g of zinc acetate dehydrate was dissolved in 100 ml deionized water to prepare zinc acetate dehydrate [Zn(CH3COO)2 (H2O)2] solution under continuous stirring. 1.131 g of (KOH) is dissolved in 10 ml deionized water. Prepared potassium hydroxide solution was added to the zinc acetate dehydrate solution dropwise under continuous stirring. Transparent colour of the solution was turned into milky white after a few minutes, the solution was then heated without stirring for 3 h at 80-900 C. The sample was centrifuged at 10000 rpm for 10 minutes, and washed with deionized water and then dried at 800 C overnight. We were fabricated ZnO nanoparticles at different temperatures 5000 C, 6000 C, 7000 C, 8000 C and 9000 C (Ghodsi et al., 2010).

Figure 3.1: Change of colour from transparent to milky

 3.3. Characterizations

Some of the following characterizations were done in order to study the morphology of ZnO nanoparticles.

3.3.1. X-ray diffraction analysis (XRD)

            Structural analysis of ZnO nanoparticles was done by the X-ray diffraction (XRD) study. X-ray diffraction spectroscopy is very effective tool for the determination of the atomic arrangement in a crystal. XRD is a very important parameter because it gives information about the phases of the nanoparticles and can make differences between crystalline and amorphous materials. X-ray diffraction (XRD) analysis of ZnO nanoparticles was carried out using powder X-ray diffractometer (Bruker D8 Advance) which was activated at a voltage of 40kV and a current of 30mA with Cu-Kα1 radiations.

                           Figure 3.2: Schematic diagram of XRD apparatus

3.3.2. UV-Vis Spectroscopy

            UV-Vis spectroscopy states to absorption spectroscopy in the ultraviolet-visible spectral region. UV-4000 spectrophotometer was used to study the optical absorption properties of zinc oxide nanoparticles.


               Figure 3.3: Schematic diagram of UV-Vis spectrophotometer

3.3.3. Electrical Properties (Four-probe technique)

            This technique is used for the current-voltage (I-V) measurements. This technique is effective when the sample is in the form of a thin film or pallet.

                     Figure 3.4: Schematic diagram of four-probe method

 3.3.4. SEM Analysis

            The morphology, size and structure of zinc oxide nanoparticles was studied by using (JSM-6510LV scanning electron microscope). Dried sample posting on the carbon coated grid and is subjected to characterization.                        

               Figure 3.5: Schematic diagram of SEM (scanning electron microscope)

Chapter 04


4.1. X-ray diffraction spectroscopy of ZnO nanoparticles

            The crystalline sizes of ZnO nanoparticles was estimated by x-ray diffraction spectroscopy (XRD). (Figure 4.1) shows the (XRD) morphology of synthesized zinc oxide nanoparticles at 5000 C, 6000 C, 7000 C, 8000 C and 9000 C for three hours. In x-ray diffraction spectroscopy various strong peaks observed at 2θ values of 31.600, 34.270, 36.280, 47.410, 56.540, 62.770, 67.900, 69.000  and 76.790corresponding to the (100), (002), (101), (102), (110), (103), (112), (201) and (202) (hkl) planes of the hexagonal wurtzite ZnO structure. X-ray diffraction spectra of all peaks of ZnO are in strong agreement with the (JCPDS No. 01-073-8765).

4.1.1. Grain size

            Debye Scherrer’s equation was used to calculate grain size of ZnO nanoparticles.

Where “λ” denote x-ray wavelength “β” is FWHM (full width half maximum) “θ” denote Bragg’s diffraction angle and “D” denote grain size (Hall et al., 2000).

            The average grain size of zinc oxide nanoparticles was around 23.1 nm at high intensity peak of (101) from Debye -Sherrer equation. XRD analysis of different peaks of zinc oxide nanoparticles are given in the Table 4.1 (He et al., 2003). As annealing temperature increase the intensity of the peaks also increases which indicate the increased in crystallinity. A line broadening of peaks at 500°C, 600°C, 700°C, 800°C and 900°C shows that the prepared NPs are in the nm range. When annealing temperature increases the average crystallite size also increase (Abdullah et al., 2017).

4.2. SEM Analysis

            The morphology of the ZnO NPs was studied by using SEM (Scanning Electron Microscope, JSM-6510LV) with an activated voltage of 25 kV at a resolution of (1) 200 nm, (2) 1 μm. ZnO NPs were a crack-free structure but when annealing temperature increases the morphologies of the zinc oxide nanoparticles were changed (Fan et al., 2005). ZnO NPs calcined at 500°C, 600°C and 700°C are rod-shaped and when annealed at 800°C, and 900°C turned into spherical shaped NPs with a size of around 400 nm. The SEM images of zinc oxide nanoparticles manifest that in the sol-gel method the agglomerations of particles are less. SEM images (Figure 4.3) of zinc oxide nanoparticles annealed at different temperatures show the existence of NPs (Kumar et al., 2013).

Figure 4.3: SEM images of zinc oxide nanoparticles annealed at 500°C, 600°C, 700°C, 800°C and 900°C.

4.3. Optical Study of ZnO nanoparticles

            Optical properties of zinc oxide nanoparticles synthesized by the sol-gel method was analyse by using UV-vis spectroscopy. The wavelength range was recorded from 300 to 800 nm. The Absorption spectra of the synthesized zinc oxide NPs are shown in (Figures 4.4 & 4.5). When transparent colour of the solution turn into milky it was the first indication of the formation of zinc oxide nanoparticles (Baruwati et al., 2006). Zinc oxide NPs prepared by sol-gel method were hexagonal wurtzite structure. From (Figures 4.4 & 4.5) it was observed that samples annealed at different temperatures have strong absorption peaks below 400 nm (Cimitan et al., 2009).

Figure 4.4: UV-Vis spectroscopy of zinc oxide nanoparticles annealed at (a) 5000 C and (b) 6000 C

Figure 4.4 (a): Extrapolation curve for band gap determination of synthesized ZnO nanoparticles annealed at 5000 C

Figure 4.4 (b): Extrapolation curve for band gap determination of synthesized ZnO nanoparticles annealed at 6000 C

Figure 4.5: UV- Vis spectroscopy of ZnO nanoparticles annealed at (a) 7000, (b) 8000 C and 9000 C

Figure 4.6 (a): Extrapolation curve for band gap determination of synthesized ZnO nanoparticles annealed at 7000 C

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