Visible Light-Photocatalytic Activity of Sulfate-Doped Titanium Dioxide Prepared by the Sol-Gel Method

Sulfate-doped TiO2 was prepared from sol-gel systems containing titanium alkoxide and sulfuric acid. The time needed for gelation of the systems was significantly reduced by ultrasonic irradiation. The doped sulfate was observed by FTIR and XPS measurements. Some sulfate ions remained in the TiO2 even after heating at 300-600 degrees C. The UV and visible photocatalytic activities of the samples were confirmed by the degradation of trichloroethylene (TCE). The activity of the photocatalyst samples during the UV irradiation strongly depended on their crystallinities rather than their specific surface areas, i.e., adsorption ability. The degradation rate during the visible irradiation depended on both the adsorption ability and visible absorption of the photocatalyst samples. The visible absorption induced by the sulfate-doping was effective for the TCE degradation.