Tin-Doped Titanium Dioxide Photocatalysts Prepared via Hydrothermal Method: Effect of Calcination Temperature on Dye Degradation Efficiency

Abstract

The widespread discharge of persistent and toxic synthetic dyes from the textile industry into aquatic ecosystems has critically compromised global access to clean water. Conventional treatment techniques are often inefficient in removing these pollutants. Among advanced oxidation processes (AOPs), photocatalysis has emerged as a promising solution for degrading dye-contaminated wastewater. While titanium dioxide (TiO₂) is a prominent photocatalyst for wastewater treatment, its practical application is limited by a wide band gap (3.2 eV) and rapid electron-hole recombination. This study reports the preparation of tin-doped titanium dioxide (Sn-doped TiO₂) as a photocatalyst via a hydrothermal method, with a systematic focus on optimizing calcination temperature. The as-prepared photocatalysts were characterized by X-ray diffraction (XRD), which confirmed a pure anatase phase with the crystallite size increased at higher calcination temperature. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) analysis verified the presence of tin within particle clusters, while diffuse reflectance ultraviolet-visible (DR UV-Vis) and Fourier transform infrared (FTIR) spectroscopies confirmed extended visible-light absorption and successful lattice incorporation. Furthermore, photoluminescence (PL) results indicated that Sn-TiO₂ (400 °C) exhibited a more ordered crystal structure, reducing non-radiative recombination. Photocatalytic evaluation via methylene blue (MB) degradation under visible light revealed that Sn-doped TiO₂ calcined at 400 °C achieved the highest efficiency of 65.2% after 7 hours. This enhanced performance was attributed to the synergistic effects of a narrowed band gap (3.14 eV), high crystallinity, and optimized crystallite size. These findings demonstrate that controlling calcination temperature is crucial for developing efficient, visible-light-active photocatalysts for sustainable industrial wastewater remediation.