Interfacial synergy of Pd sites and defective BiOBr for promoting the solar-driven selective oxidation of toluene

Metal-modified semiconductors are being deemed as one of the most promising photocatalysts for various applications. Although great efforts have been devoted to developing a variety of metal-modified semiconductor photocatalysts, the exact functions of their interfaces in governing photocatalytic processes still remain elusive. Herein, the interfacial synergy of metal sites and defective semiconductor with oxygen vacancies (VOs) was investigated toward the photocatalytic selective oxidation of toluene, by taking the Pd/BiOBr photocatalyst as an example. The presence of Pd induces the generation of more VOs on the BiOBr surface due to the electronic interaction at the Pd–BiOBr interface. The coexistence of the Pd and VO sites on BiOBr enables the favorable adsorption of O2 and toluene molecules. The Pd–BiOBr interface governs the charge separation and prompts the activation of O2 and toluene, leading to 1.5 times the activity of BiOBr–VO for the photocatalytic selective oxidation of toluene to benzaldehyde with a high selectivity (>99%). Moreover, the typical influencing factors, such as the illumination intensity and toluene concentration, were optimized to improve the photocatalytic efficiency. The active species and intermediates in the photocatalytic reaction were identified by a series of controlled experiments, as well as in situ ESR measurements. Therefore, both experimental and theoretical results provide the direct evidence to understand the key roles of the interfacial Pd and VO sites in enhancing photocatalysis toward the selective oxidation of toluene.