Monolayered Metal-Organic Frameworks as Fully Exposed Supports for Ligand-Free Photodeposition of Ultrasmall Metal Nanoparticles.

Loading active metal nanoparticles (NPs) onto heterogeneous supports is a widely adopted strategy to suppress particle migration and coalescence while enabling heterogeneous catalysis. However, conventional support materials often struggle to simultaneously achieve high metal exposure, large specific surface area, and efficient interfacial reactivity. Here, we introduce monolayered metal-organic frameworks (monoMOFs) as a new class of monolayer supports for the ligand-free photodeposition of ultrasmall metal NPs. Owing to their ultrathin (∼1.8 nm), fully exposed architecture and the integration of photosensitizing linkers, monoMOFs enable spatially confined photoreduction of metal precursors at the monolayer surface, leading to uniform nucleation and effective stabilization of ultrasmall metal NPs (2-4 nm) without the use of surface-capping ligands under dilute precursor conditions. This photodeposition strategy is general across different metals, including Pt, Rh, and Pd. Using Pt as a representative example, the resulting Pt/monoMOF exhibits an exceptionally high metal loading of up to 64.6 wt % together with outstanding photocatalytic hydrogen evolution activity (1381.4 mmol·g-1·h-1), demonstrating the effectiveness of this monolayer support strategy for constructing highly efficient supported nanocatalysts.