A New Role for Fe3+ in TiO2 Hydrosol: Accelerated Photodegradation of Dyes under Visible Light

The effect of Fe3+ on the photocatalytic activity of TiO2 hydrosol prepared through a low-temperature route has been investigated under visible light irradiation. The total reactive oxygen species (ROS) level and the accumulation of Fe2+ during the photodegradation process were detected to examine the role of Fe3+. In contrast to an aqueous TiO2 dispersion where Fe3+ strongly inhibited the photoactivity of TiO2 via suppressing the reduction of O2 and decreasing the production of ROS, Fe3+ accelerated the photodegradation of all dyes examined in the hydrosol through increasing the yield of oxidative ROS. The influence of the prebound hydroxyl groups on the surface of TiO2 was compared to that of free alcohols in aqueous solution, which revealed the cooperative function of the surface hydroxyl groups. The thoroughly contrary effect of Fe3+ on the photocatalysis of TiO2 hydrosol and TiO2 powder, which are all anatase nanocrystallites but are synthesized with different procedures, was ascribed to the complexation of the hydroxyl groups bound to TiO2 surface with Fe3+. The formation of such complexes has resulted in an altered electron-transfer pathway of the dye-sensitized photocatalysis under visible light irradiation.