A Secondary Oxidant Generating System Based on Anatase/Porphyrin/Bromide for Aerobic Oxidation of Organic Compounds With the Intermediacy of Bromine

In order to increase the photocatalytic activity of TiO₂-anchored meso-tetrakis(4-carboxyphenyl)porphyrin (H₂TCPP), TiO₂@H₂TCPP, in the aerobic oxidation of sulfides in water, KBr has been used as a source for the formation of the secondary oxidant, bromine. The change in the nature of reactive oxidant from superoxide anion radical to molecular bromine led to a significant increase in the efficiency of oxidation of the sulfide as well as the oxidative stability of the porphyrin photosensitizer. The contribution from different reactive oxygen species, hole and electron in the formation of sulfone as the sole product, has been studied using the scavengers of hydroxyl radical, superoxide anion radical, hole, electron, and singlet oxygen, and accordingly, a mechanism was proposed. Using sodium bromate instead of KBr led to a similar increase in the photocatalytic activity of TiO₂@H₂TCPP, which was attributed to the reduction of bromate to bromide under the reaction conditions.