Monolayered Metal-Organic Framework Unlocks Integration of Shaped Nanoparticles for Synergistic Photocatalysis

Metal-organic frameworks (MOFs) with ordered structures and high surface areas are promising supports for metal nanoparticles (MNPs) in synergistic catalysis. However, their limited pore sizes restrict integration to small spherical MNPs, excluding shaped MNPs that are critical for exposing specific lattice surfaces and achieving a superior catalytic performance. In this work, we address this limitation by reducing MOFs to monolayers, enabling the integration of shaped MNPs onto their surfaces to significantly enhance the catalytic efficiency. The monolayered MOF (monoMOF), Hf₁₂-Ir, with a thickness of ∼1.8 nm, was synthesized using photosensitizing DBB-Ir-F linkers. Freshly synthesized cubic Cu nanoparticles (Cu-NPs, ∼35 nm) were functionalized with thioctic acid (TA) via Cu-S coordination and integrated onto the surface of Hf₁₂-Ir through carboxylate-Hf₁₂ coordination, forming the Cu/Hf₁₂-Ir composite. Upon light irradiation, Cu/Hf₁₂-Ir achieved exceptional CO₂-to-CO conversion with a turnover frequency of 82.9 mmol g_Cu^-1 h^-1 and a CO selectivity of 98.3%. This catalytic performance was over an order of magnitude higher than that of the homogeneous system (Cu-NPs and H₂DBB-Ir-F) and the small spherical MNPs-based composite (S-Cu/Hf₁₂-Ir). Mechanistic studies revealed a synergistic effect between the Cu-NPs and Hf₁₂-Ir, where their proximity enhanced electron transfer from the photoexcited DBB-Ir-F centers to the Cu-NPs. This work demonstrates a straightforward strategy for constructing MNP-monoMOF composites and highlights the critical charge transfer pathway between the photosensitizing monoMOF and catalytic MNPs.