Facet effect of metal-organic frameworks on supporting co-catalysts for photocatalytic hydrogen peroxide production

The facet effect of metal-organic frameworks (MOF) on regulating the property of loaded co-catalysts is an important but unexplored issue in the field of photocatalysis. In this work, a series of MIL-125-NH₂ polyhedrons (MIL = Materials Institute Lavoisier) with facet exposure of {001}, {001}/{111} and {111} are synthesized and used to load Pd-based co-catalysts for photocatalytic oxygen reduction reaction (ORR) toward H₂O₂ production. The different facets with distinct chemical environments (Ti-O clusters on {111} facets and carboxyl ligands on {001} facets) result in the selective loading of Pd⁰ and PdO dominated cocatalysts on {001} and {111} facets, respectively. The {001}/{111} co-exposed MIL-125-NH₂ thus enables the spatially separated loading of Pd⁰ and PdO dual cocatalysts respectively. Pd⁰ efficiently traps the photoexcited electrons and PdO trends to capture the holes, collaboratively promoting the directional separation of photogenerated electron-hole pairs. As a result, the photocatalytic ORR activity is significantly enhanced with a H₂O₂ production rate of 128.6 mmol L^-1 g^-1 h^-1, superior than pristine and single cocatalyst modified MIL-125-NH₂ samples. Our findings provide new insight into the design of high-performance photocatalysts.