The synthesis and characterization of the ZnO nanoparticles
Tshabalala, Modiehi Amelia
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ZnO has been by far the most interesting semiconductor because of its properties. The ZnO nanostructures were synthesized by a sol-gel method and the samples were annealed in air at various temperatures capped with polymers PVP (Polyvinyl Pyrrolidone) and PEG (Polyethylene glycol). Again the ZnO was synthesized using different solvents; ethanol, methanol or water at various temperatures. Characterizations of the powders were carried out using different techniques. The structure and the particle size of the samples were obtained using the XRD (x-ray diffraction). The morphology was determined by the SEM (scanning electron microscopy) and the chemical composition was analyzed using the EDS (energy x-ray dispersed spectroscopy). The PL (photoluminescence) data were collected using the He- Cd (Helium-Cadmium) laser and also using the Cary Eclipse fluorescence spectroscopy at room temperature. The absorption spectra were analyzed using the UV-Vis spectroscopy. The PL spectra for the ZnO nanostructures capped and prepared using polymers showed broad emissions in the visible range. The broad emission in the visible range with maximum intensity peaks at 449 nm and at 530 nm for the PVP capped ZnO nanoparticles were observed annealed at 150°C. This was influenced by the addition of various molar masses of PVP on the Zn(Ac)2. The green emission band at 560 nm and a blue emission at 450 nm were obtained for the PEG encapsulated ZnO nanostructure. The PL of the ZnO nanoparticles prepared using various solvent was shown, the different shifts from the emission peaks were observed and the fluctuation of the intensity which was attributed to an increase and a decrease on the annealing temperatures. The effect of pH values on the ZnO prepared using different solvents. The PL on these samples exhibited a strong broad blue emission, for all the ZnO prepared using ethanol, methanol or water as solvents. The intensities differed with the amount of NaOH which was added onto the Zn(Ac)2 solution. The XRD pattern for all the prepared ZnO nanostructures exhibited the peaks corresponding to that of various planes of ZnO wurtzite structure with the JCPDS (Joint Committee on Powder Diffraction Standards) file no. (13-1451). The absorption spectra of the PVP capped ZnO nanostructures did not show any shifts while the absorption spectra for the PEG encapsulated ZnO nanostructures showed a shifts with an addition of the molar masses of the PEG. The UV-Vis spectroscopy for the ZnO prepared with ethanol, methanol or water as solvents at various temperatures gave the absorption edges and also the blue shifts that occurred with and increase on the annealing temperatures 300, 400, 500 and 600°C. It was observed from the UV absorption of the ZnO using different solvents with various pH values that the band gaps for all the samples were determined to be larger than that of ZnO bulk. The NaOH solution which was slowly added on the Zn(Ac)2 solution took control over the surface of the ZnO surfaces.