In situ decomposition of bromine-substituted catechol to increase the activity of titanium dioxide catalyst for visible-light-induced aerobic conversion of toluene to benzaldehyde

Abstract

Photocatalytic oxidation is an attractive approach for environmentally benign fine chemical synthesis. In addition, semiconductors have been intensively explored as photocatalysts for selective organic synthesis. In this study, we found that the photolysis of tetrabromocatechol on titanium dioxide produced surface-modified titanium dioxide, which showed higher activity than bare titanium dioxide in the aerobic conversion of toluene to benzaldehyde under visible light irradiation. When tetrabromocatechol was added to titanium dioxide dispersed in toluene, the titanium dioxide powder became orange in color due to the complex formation between tetrabromocatechol and titanium dioxide on the surface. The tetrabromocatechol was decomposed by visible light irradiation, and colorless titanium dioxide powder was obtained. We found that the apparent quantum yield of benzaldehyde formation determined by using the recycled colorless titanium dioxide powder at 450 nm was about eight times higher than that of bare titanium dioxide.