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.

All-inorganic halide perovskite (IHP) has been deemed promising in photocatalysis due to tunable bandgap and long lifetime of charge carriers. However, unsatisfactory photocatalytic activity and low stability prevent its practical applications. Rational construction of heterojunctions has been proved to be an efficient way to circumvent these obstacles. Herein, g-C₃N₄ nanosheet was employed to construct a 2D/2D (2D: two-dimensional) heterostructure with Cs₃Bi₂Br₉ through an electrostatic self-assembly process. Owing to the efficient transfer of photogenerated charge carriers, the activity of Cs₃Bi₂Br₉ was boosted with enhanced generation of carbon centered radicals. The optimized 10% Cs₃Bi₂Br₉/g-C₃N₄ composite displays the highest benzaldehyde formation rate of 4.53 mmol·h⁻¹·g⁻¹ under visible light, which is 41.8 and 2.3 times that of individual g-C₃N₄ and Cs₃Bi₂Br₉, respectively. The stability of Cs₃Bi₂Br₉ nanosheets and its selectivity for benzaldehyde (from 65% of Cs₃Bi₂Br₉ to 90% of the composite) was enhanced by reducing its surface energy and tuning the reaction pathway, respectively.