Effect of crystalline structure on TiO_2 photocatalysis under visible light irradiation

The effects of crystalline structure, anatase, rutile and mixing crystal, on the visible-light photocatalytic performance of TiO₂ were studied with reactive red X-3B and phenol as model pollutants. The results showed that the degradation ratio of reactive red X-3B after 80 min reaction could be as high as 100% when using anatase or mixing crystal TiO₂ as photocatalyst under the condition of Vis/O₂, but the degradation ratio was less than 15% when using rutile TiO₂ as photocatalyst. Phenol could be degraded under the condition of Vis/TiO₂ by any of the three photocatalysts; rutile form exhibited a better photocatalytic activity, and its degradation ratio could be 54% after 180 min reaction. Fluorescence spectrum analysis indicates that the reaction process is predominated by the generation of ·OH radicals in the system. In the process of TiO₂ visible-light photocatalysis, hydrogen peroxide is generated by anatase TiO₂ from a series of complex reactions, and the generated hydrogen peroxide is absorbed on the surface of TiO₂ to form active species, which is responsible for the generation of ·OH radicals and the degradation of organic pollutants under visible light irradiation.