Synthesis,characterization and photocatalytic performance of W,N, S-tri-doped TiO2 under visible light irradiation

W–S–N-tri-doped TiO₂ photocatalysts (WSNTiO₂) were prepared by a simple sol–gel method. Tungstic acid, sodium sulfate and urea were used as tungsten, sulfur and nitrogen sources, respectively. The morphology and microstructure characteristics of the photocatalysts were evidenced by means of XRD, BET, TEM, SEM and UV–vis DRS techniques. The XRD results show that the main crystal phase of samples is anatase. It was also found that the tri-doping of TiO₂ increases its BET specific surface area from 95 to 121 m²·g⁻¹. Besides, it was shown that tri-doping narrows the band gap of TiO₂ effectively, which has greatly improved the photocatalytic activity in the visible light region. The photocatalytic activity of tri-doped TiO₂ powders was compared to that of bi-doped ones through the degradation of Congo Red (CR) under visible irradiation. Thus, the prepared 0.5% W–N–S–TiO₂ heat treated at 450 °C showed the best photocatalytic activity compared to the prepared pure TiO₂, Degussa P25, and co-doped samples (WNTiO₂ and WSTiO₂). In particular, a Congo Red degradation rate of approximately 99% was reached after only 35 min of visible light irradiation in the presence of 0.5% of WNSTiO₂. Total organic carbon (TOC) removal of CR was up to 72% and confirmed its significant mineralization in the presence of 0.5% of WNSTiO₂ photocatalyst.