Modulating Adsorption–Redox Sites and Charge Separation of Cs₃Bi₂Br9–x@AgBr Core–Shell Heterostructure for Selective Toluene Photooxidation

Constructing vacancy-decorated heterojunction photocatalysts is a feasible strategy for highly efficient photooxidation of toluene to benzaldehyde. However, poor interface interaction and vacancy-triggered mismatched redox kinetics seriously impede photocatalytic activity improvement. Herein, a chemically bonded Cs3Bi2Br9–x@AgBr core–shell heterojunction with unified adsorption-redox sites is fabricated via an in-situ light-assisted Ag+ insertion method. Experiments and theoretical calculations demonstrate that the type-II band alignment with interfacial Bi–Br–Ag bonds boosts the charge separation. Moreover, because of the greater oxygen adsorption energy and the steric-hindrance effect of the AgBr shell, the preferred adsorption site of O2 is modulated from Br vacancy (VBr, trapping holes) to its corresponding reduction site (AgBr, gathering electrons), thereby ensuring VBr-enhancing toluene adsorption/oxidation on Cs3Bi2Br9. Therefore, Cs3Bi2Br9–x@AgBr exhibits an improved benzaldehyde production rate of 5.61 mmol g–1 h–1 (selectivity: 91%), outperforming pure Cs3Bi2Br9 by a factor of 6. This work underlines the importance of the rational design of vacancy-decorated heterointerface and redox sites at the atomic level in photocatalysis.