Water enhances photocatalytic activity for toluene selective oxidation in acetic acid solution

Photocatalytic oxidation of hydrocarbons to value-added oxygen-containing compounds is a green and sustainable method. However, the efficient activation of C(sp³)–H bonds under mild conditions remains a significant challenge. In this study, we prepared BiOBr/Bi₂MoO₆ Z-scheme heterostructure for photocatalytic selective oxidation of toluene to benzaldehyde utilizing acetic acid as solvent. A small amount of water as an additive established an acidic environment to facilitate the formation of highly reactive hydroxyl radicals (·OH) through the O₂ →·O₂⁻ → H₂O₂ →·OH process. The ·OH together with photogenerated holes acted as reactive species dissociate C(sp³)–H bonds, which is regarded as the rate-determining step for this reaction, boosting photocatalytic activity. Compared to the reaction system without water, the conversion of toluene increased from 23.6% to 39.0%, reaching a toluene conversion rate of 6110 μmol·g^–1·h^–1. Additionally, there is a slight improvement in the selectivity of benzaldehyde.