The preparation of tungsten oxide (WO₃) thin film by direct current (DC) reactive sputtering magnetron method and its photoelectrocatalytic properties for water oxidation reaction are investigated using ultraviolet-visible radiation. The structural, morphological, and compositional properties of WO₃ are fine-tuned by controlling thin film deposition time, and post-annealing temperature and environment. The findings suggest that the band gap of WO₃ can be controlled by adjusting the post-annealing temperature; the band gap decreased from 3.2 to 2.7 eV by increasing the annealing temperature from 100 to 600 °C. The theoretical calculations of the WO₃ bandgap and the density of state are performed by density functional theory (DFT). Following the band gap modification, the photoelectrocatalytic activity increased and the maximum photocurrent (0.9 mA/cm² at 0.6 V_SCE) is recorded with WO₃ film heated at 500 °C. The WO₃ film heated under air exhibits much better performance in photoelectrochemical water oxidation process than that of annealed under inert atmosphere, due to its structural variation. The change in sputtering time leads to the formation of WO₃ with varying film thickness, and the maximum photocurrent is observed when the film thickness is approximately 150 nm. The electrical conductivity and charge transfer resistance are measured and correlated to the properties and the performance of the WO₃ photoelectrodes. In addition, the WO₃ photoelectrode exhibits excellent photoelectrochemical stability.

Zinc oxide (ZnO) nanoflowers have huge potential for various applications. However, the growth mechanism of ZnO nanoflowers is still under debate despite various growth mechanisms having been proposed. The aim of this study is to investigate the growth mechanism of different morphologies in a single sample; hopefully, this might help to understand the exact growth mechanism of ZnO nanoflowers. Herein, two models are proposed: (I) the growth mechanism of different morphologies (shapes) in a single sample; and (II) the growth mechanism of different sized ZnO flowers in a single sample. The present work also investigates the mechanism for how morphology assists in tuning the properties of nanomaterials, which is still unclear to date. New insight into the relationship between morphology and native defects has been introduced in this work. XPS, photoluminescence, and FT-IR analyses reveal the presence of oxygen vacancy defects in the structures of the materials prepared, with respect to their morphology. These defects act as self-dopants. Therefore, a change in their concentration results in tuning the band gap and thereby the photocatalytic activity.