New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi₂MoO₆/Cs₃Sb₂Br₉ heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp³)–H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g^-1h⁻¹), which was almost two- and five-fold that of pristine CSB (1,165 μmol g^-1h⁻¹) and BiMo (482 μmol g^-1h⁻¹), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin–trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94–98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb³⁺ and Bi³⁺. This work not only provides a new visible-light-driven photocatalyst for C(sp³)–H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.