Nitrogenase-inspired bimetallic metal organic frameworks for visible-light-driven nitrogen fixation

[Display omitted] •Nitrogenase-inspired modular synthesis is designed to construct bimetallic UiO-66.•Zr-Hf clusters are constructed to coordinate the electron transfer and utilization.•U(0.5Hf)-2SH with TPA-2SH as the ligand can absorb and utilize the visible light.•A tandem ligand-to-metal-to-metal charge transfer mechanism (LMMCT) is proposed.•The resultant bimetallic UiO-66 yields 116.1 μmol h−1 g−1 NH3 under visible light. Inspired by nitrogenase, we designed a kind of metal-organic framework (MOF) photocatalysts, U(Zr-Hf)-X, composed of bimetallic Zr-Hf nodes and different functional ligands. In the Zr-Hf bimetallic cluster, the Zr species serves as the active site of nitrogen fixation, while the Hf species acts as electron buffer tank to optimize electron transfer and utilization. In the organic ligands, the light absorption and utilization of MOFs is improved via introducing target functional groups to efficiently generate electrons. Notably, the organic ligand containing two thiol groups (-SH) can extend the absorption edge to the visible region. The optimal U(0.5Hf)-2SH (metal nodes: 0.5Zr: 0.5Hf; linkers: TPA-2SH) photocatalyst exhibits nitrogen fixation rate up to 116.1 μmol g−1 h−1 under visible-light, attributed to the ligand-to-metal-to-metal electron transfer (LMMET) pathway and Zr-based π-backbonding mechanism. Our nitrogenase-inspired strategy establishes a novel paradigm for rational design of visible-light-driven nitrogen fixation catalysts.