Effect of substrate temperature on the photocatalytic degradation efficiency of methylene blue using TiO₂ thin films

Abstract

This study aims to investigate the effect of substrate temperature on the structural, optical, and photocatalytic properties of titanium dioxide (TiO₂) thin films deposited using the Radio Frequency (RF) magnetron sputtering technique. The optical properties were analyzed using Ultraviolet–Visible-Near Infrared (UV–VIS-NIR) spectrophotometry, and the energy band gap values were determined using the first derivative method. The energy band gap values were found to be 3.70 eV, 3.69 eV, and 3.69 eV for substrate temperatures of room temperature, 100 °C, and 200 °C, indicating a minimal effect of temperature on the band gap. Structural characterization using X-ray diffraction (XRD) revealed that substrate temperature significantly affects phase formation. Notably, a diffraction peak at 25.3°, corresponding to the (101) plane of the anatase phase, was observed only in the film grown at 200 °C. This observation is supported by Scanning Electron Microscopy (SEM) images, which confirm an improved crystal structure at this temperature. The photocatalytic efficiency of the films was assessed through the degradation of organic pollutants under UVA and UVC illumination. The film grown at 200 °C exhibited the highest photocatalytic performance, with a degradation efficiency of 96.15% after 4 h of UVC irradiation. This enhanced performance is attributed to the formation of the anatase phase and improved crystal structure. In light of these findings, this study provides important insights into the optimization of TiO₂ thin films for photocatalytic applications, particularly in environmental remediation and sustainable water treatment technologies. Future work could further enhance photocatalytic efficiency by employing doping strategies or heterojunction designs.