Synthesis of Nickel doped ZnO nanoparticles

MATERIAL AND METHODS

3.1. Materials

            For the preparation of Nickel doped Zinc oxide Nanoparticles the following materials was used i.e., zinc acetate dehydrate [Zn(CH3COO)2(H2O)2], nickel nitrate[Ni(NO3)3-6H2O] and Sodium hydroxide (NaOH). Distilled water was used to wash substrates. All chemicals were analytical grade, obtained from the University of Poonch Rawalakot AJK.

3.2. Synthesis of Nickel doped ZnO nanoparticles

                        The method used for the synthesis of effect of nickel doping on Zinc oxide was Co-precipitation method. The formula used to study the effect of nickel doping on structural, optical and electrical properties is Zn1-xNixO where x = 0.0, 0.02, 0.04, 0.06 and 0.08. By varying the composition in this formula effect on physical properties were studied. The zinc acetate dehydrate and nickel nitrite were completely dissolved in 100 ml of distilled water separately. In case of doping two solutions were mixed and stirring the solution for 30 minutes at 500 rmp by using hot plate with magnetic stirrer. Simultaneously 10 ml NaOH solution (10M) was added drop by drop in solution and stirring the solution for 2 hours at 500 rmp at room temperature. After 2 hours greenish white precipitate were produce, filter the precipitates and washed with ethanol and distilled water many times. Put the precipitates in oven for 3 hours at 900C. Dried precipitates were ground in mortar to produce fine powder. Finally the powder was annealed at 5500C in furnace for 2 hours (Raja et al., 2014).

3.3. Characterizations

            Some of the following characterizations were done in order to study the properties of Nickel doped ZnO nanoparticles.

3.3.1. X-ray diffraction analysis (XRD)


            Structural analysis of nickel doped 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 nickel doped 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 3.1: 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 Nickel doped zinc oxide nanoparticles.


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               Figure 3.2: 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 3.3: Schematic diagram of four-probe method

Chapter 04

RESULTS AND DISCUSSION

4.1. X-ray diffraction spectroscopy of Nickel doped ZnO nanoparticles

            The crystalline sizes of Nickel doped ZnO nanoparticles was estimated by x-ray diffraction spectroscopy (XRD). (Figure 4.1) shows the X-ray diffraction (XRD) patterns of Zn1-xNixO (x = 0.0, 0.02, 0.04, 0.06 and 0.08.) NPs.  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 structure. X-ray diffraction spectra of all peaks of Ni-doped ZnO are in strong agreement with the (JCPDS No. 01-078-3346). The XRD patterns of Ni-doped ZnO are same as that of pure ZnO, showing that small amount of Ni-doping did not change the ZnO structure.

4.1.1. Grain size

            Debye Scherrer’s equation was used to calculate grain size of Ni-doped 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.

            The average grain size of Nickle-doped zinc oxide nanoparticles was around 37.1 nm at high intensity peak of (101) from Debye -Sherrer equation. From the X-ray line broading the crystalline size of ZnO and Ni-doped ZnO are estimated clearly shows the average particle size is reduced by the addition of Ni in different concentrations. XRD analysis of different peaks of Nickle-doped zinc oxide nanoparticles are given in the Table 4.1(Raja et al., 2014).

4.2. Optical Study of Nickle-doped ZnO nanoparticles

              The effect of Ni substitution on wurtzite structure of ZnO was further confirmed using UV-visible otical spectroscopy measured in the range 300-800 nm.The optical absorption spectra of undoped and nickel doped ZnO nano-particles are shown in (Figures 4.2). When transparent colour of the solution turn into greenish white it was the first indication of the formation of Nickle-doped zinc oxide NPs. The absorption band edge of undoped ZnO is observed at 379 nm and it gets shifted towards longer wavelength region for the 2%, 4%, 6% and 8% Ni-doped ZnO samples and different peaks were observed at 407, 417, 590 and 597 nm. The emission band around 379 nm is a spontaneous emission peak of ZnO in UV region, which originates from a near-band-edge (NBE) transition of wide band gap of ZnO.

Therefore, the observed green emissions at 590 and 597 nm is likely related to the oxygen vacancies. The emission peak positions are slightly shifted for the Ni doped ZnO samples (Husain et al., 2013).

                       Figure 4.2: Absorbance spectra of undoped and Ni-doped ZnO

4.3. Electrical Properties (Four-probe technique)

            The physical characteristic of the material is very important because of its use in everyday life. The electrical characteristic is one of the basic physical properties. The current-voltage characteristics of the Nickle-doped ZnO NPs synthesized by a co-precipitation method are measured by using a four-probe source meter. The current-voltage characteristics of the synthesized Nickle-doped ZnO NPs are measured for the electric resistivity measurement. For all the samples of Ni-doped and pure ZnO the electric current is a function of voltage as shown in (Figure 4.3). The current-voltage graph of all the samples of Ni-doped and pure ZnO shows a straight line behaviour which means that the contacts made on Ni-doped and pure zinc oxide (sample) are of ohmic. This straight-line region of all the samples of Ni-doped and pure zinc oxide is a high resistance region. In the straight-line region, the electric current is dependent on voltage (Abdullah et al., 2017).

          Figure 4.3: (a) I-V characteristic of Ni-doped (2%, 4%) and undoped ZnO

                            Figure 4.3: (b) I-V characteristic of Ni-doped (6%, 8%)

SUMMARY

            Ni-doped ZnO (Zn1-xNixO where x = 0.0, 0.02, 0.04, 0.06 and 0.08) nanoparticles was synthesis by co-precipitation method. The effect of Ni substitution on wurtzite structure of ZnO was further confirmed using UV-visible optical spectroscopy measured in the range 300-800 nm. The absorption band edge of undoped ZnO is observed at 379 nm and it gets shifted towards longer wavelength region for the 2%, 4%, 6% and 8% Ni-doped ZnO samples and different peaks were observed at 407, 417, 590 and 597 nm. The crystalline sizes of Nickel doped ZnO nanoparticles was estimated by x-ray diffraction spectroscopy (XRD). 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 76.790 corresponding to the (100), (002), (101), (102), (110), (103), (112), (201) and (202) (hkl) planes of the hexagonal wurtzite structure. X-ray diffraction spectra of all peaks of Ni-doped ZnO are in strong agreement with the (JCPDS No. 01-078-3346). The XRD patterns of Ni-doped ZnO are same as that of pure ZnO, showing that small amount of Ni-doping did not change the ZnO structure. The current-voltage characteristics of the Nickle-doped ZnO NPs synthesized by a co-precipitation method are measured by using a four-probe source meter. The current-voltage graph of all the samples of Ni-doped and pure ZnO shows a straight line behaviour which means that the contacts made on Ni-doped and pure zinc oxide (sample) are of ohmic. This straight-line region of all the samples of Ni-doped and pure zinc oxide is a high resistance region.

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