This study focuses on the fabrication of immobilized and stable pure ZnO thin films via RF magnetron sputtering to eliminate the drawbacks of powder-based photocatalysts, such as catalyst recovery, filtration difficulties, and secondary pollution risks. While the photocatalytic potential of ZnO is well established, research investigating the structural origins of performance enhancement in undoped ZnO thin films achieved through physical vapor deposition (PVD) parameters and post-deposition annealing remains limited. In this context, the contribution of this work lies in the quantitative demonstration of the enhancement in photocatalytic performance induced by annealing at 400 °C in additive-free ZnO thin films. As-deposited and 400 °C annealed ZnO thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDX). XRD analysis confirmed a hexagonal wurtzite structure for both films, while post-deposition annealing improved crystalline quality and increased the average crystallite size from 53.3 nm to 57.2 nm. AFM measurements revealed an increase in surface roughness from 1.252 nm to 12.14 nm after annealing. Photocatalytic degradation experiments of methylene blue (MB) were conducted under UV-A irradiation, and concentration changes were monitored by UV–Vis spectroscopy. The as-deposited ZnO thin films exhibited only 11% degradation efficiency after 8 hours, whereas the films annealed at 400 °C achieved 68% degradation after 11 hours, corresponding to a sevenfold enhancement in photocatalytic performance. These results demonstrate that post-deposition annealing is an effective strategy for optimizing the photocatalytic activity of pure ZnO thin films under low-energy UV-A light.
Çetin et al. (Fri,) studied this question.