Cs3Bi2Br9/BiOBr S-scheme heterojunction for selective oxidation of benzylic C−H bonds

Converting hydrocarbons into aldehydes in a green and environmentally benign way is of great significance in fine chemistry. In this work, all-inorganic Cs3Bi2Br9 perovskite nanoparticles were uniformly loaded on BiOBr nanosheets via an in-situ growth method, which can selectivity photoactivate aromatic C(sp3)−H bond of toluene to generate benzaldehyde. According to the in-situ X-ray photoelectron spectroscopy characterization, the photogenerated electrons of BiOBr transfer to Cs3Bi2Br9 enforced by the internal electric field under light irradiation, resulting in S-scheme heterojunction. Furthermore, theoretical calculations indicate that toluene molecules are inclined to adsorb on the BiOBr surface, subsequently involving the oxidation reaction to generate benzyl radical (PhCH2•) by using the energetic holes of BiOBr, while the remaining photoinduced electrons in the conduction band (CB) of Cs3Bi2Br9 with powerful reduction ability reduce O2 into •O2−, which is the vital oxidative active species working on toluene selective oxidation process. Such an unexceptionable charge carrier utilization mode and tendentious adsorption behavior of reactants contribute to the optimized Cs3Bi2Br9/BiOBr heterojunction with excellent photocatalytic performance, achieving a maximum of 22.5% toluene conversion and 96.2% selectivity towards benzaldehyde formation. This work provides a rational photocatalyst heterojunction construction protocol for the selective oxidation of saturated aromatic C−H bonds.