Role of the reduction site in the fluorinated or sulfated TiO 2 photocatalytic process

Abstract

Abstract In this article, the effects of TiO 2 surface fluorination and sulfation, on the active oxygen species formed at the reduction site in the photocatalytic process, namely O 2.− and H 2O 2, were investigated from a new perspective. The superoxide radical, (O 2.−), was determined by colorimetry of nitroblue tetrazolium, a prominent O 2.− scavenger. Hydrogen peroxide (H 2O 2) was estimated by using the iodide-starch method. In the naked TiO 2 photocatalysis, O 2.−, though less reactive, was a very important intermediate. When the TiO 2 surface was fluorinated, more O 2.− and H 2O 2 were produced, which indicated that the surface modification could greatly reduce the recombination of photogenerated electrons and holes, thus enhancing the photocatalytic rate. In the sulfated system, photocatalysis proceeded with a more complicated mechanism. These results added support to the view of fluoride-induced enhancement and sulfide's nonappreciable inhibition effect.