Cs3Sb2Br9/TiO2 composite for visible-light-driven selective epoxidation of styrene via efficient charge separation and reactive oxygen species regulation

The selective oxidation of styrene to styrene oxide (SO) is a pivotal transformation in fine chemical synthesis. Conventional thermocatalytic routes suffer from unresolved critical issues: overoxidation, poor selectivity, and environmental incompatibility. Herein, a Cs 3 Sb 2 Br 9 (CSB)/TiO 2 composite photocatalyst was constructed by coupling lead-free halide perovskite CSB with wide-bandgap semiconductor TiO 2 for highly selective styrene epoxidation under mild conditions. CSB incorporation extends the composite's photoresponse to the visible region. Mechanistic investigations confirm that under visible-light excitation (λ > 420 nm), only CSB is photoexcited. Photogenerated electrons directionally transfer from CSB to the unexcited TiO 2 (acting as an electron mediator), These electrons reduce O 2 to ·O 2 - , while holes in CSB oxidize styrene and can convert ·O 2 - to 1 O 2 , shifting the reaction from C=C cleavage to selective epoxidation. At an optimal CSB loading of 0.18 mmol, the composite achieves a total reaction rate of 27.23 mmol ·g -1 ·h -1 (9.13-fold higher than pure TiO 2 ) and an SO selectivity elevated from 42.25% to 82.28%. Concurrently, the epoxide production rate reaches 22.40 mmol ·g -1 ·h -1 , representing 17.78-fold over that of pure TiO 2 (1.26 mmol·g -1 ·h -1 ). XPS analysis reveals a positive shift in Br 3d and negative shift in Ti 2p binding energies, verifying directional electron transfer from CSB to TiO 2 . Radical quenching experiments and EPR spectroscopy demonstrate that photogenerated electrons reduce O 2 to ·O 2 -, holes further convert ·O 2 - to 1 O 2 . This regulation of reactive oxygen species shifts the reaction pathway from competitive C=C bond cleavage to selective oxygen-transfer epoxidation. This work provides a novel material design strategy and mechanistic insights for constructing efficient, highly selective photocatalytic oxidation systems.