Physical Properties of ZnO-NPs Induced by the Thermal Annealing of Hydrozincite Derived from Adansonia Digitata Leaves Extract

In this study, we investigated the effects of the annealing temperatures on the physical properties of zinc oxide nanoparticles produced by the decomposition of the hydrozincite obtained from Adansonia digitata leaves. The results of the X-ray diffraction revealed the formation of well-crystallised hexagonal zinc oxide with an average crystallite size of 11.80 nm, 11.90 nm, 11.97 nm and 15.28 nm for the samples annealed at 400 °C, 500 °C, 600 °C and 700 °C, respectively. The crystallite size of the hydrozincite constituting the unannealed sample was 22 nm. In the spectra of the Fourier transform infrared spectroscopy, the appearance of the peaks at 520 cm-1 for all synthesised materials confirms the formation of pure wurtzite zinc oxide. The band gap determined from diffuse reflectance ultraviolet-visible spectroscopy was found to be 3.19 eV, 3.21 eV, 3.23 eV and 3.24 eV for the samples annealed at 400 °C, 500 °C, 600 °C and 700 °C, respectively. These values increase with the annealing temperature and are still lower than the band gap of pure bulk zinc oxide (3.3 eV) owing to the structural defects as confirmed by the broad emission bands in the visible depicted from the photoluminescence analysis.