Role of the reduction site in the fluorinated or sulfated TiO2 photocatalytic process

In this article, the effects of TiO2 surface fluorination and sulfation, on the active oxygen species formed at the reduction site in the photocatalytic process, namely O2.− and H2O2, were investigated from a new perspective. The superoxide radical, (O2.−), was determined by colorimetry of nitroblue tetrazolium, a prominent O2.− scavenger. Hydrogen peroxide (H2O2) was estimated by using the iodide-starch method. In the naked TiO2 photocatalysis, O2.−, though less reactive, was a very important intermediate. When the TiO2 surface was fluorinated, more O2.− and H2O2 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.