Keggin-Type Polyoxometalate-Based ZIF-67 for Enhanced Photocatalytic Nitrogen Fixation

The photocatalytic reduction of N₂ to NH₃ is considered a promising strategy to alleviate human need for accessible nitrogen and environmental pollution, for which developing a photocatalyst is an effective method to complete the transformation of this process. We firstly design a series of highly efficient and stable polyoxometalates (POMs)-based zeolitic imidazolate framework-67 (ZIF-67) photocatalysts for N₂ reduction. ZIF-67 can effectively fix N₂ owing to its porosity. Integration of POMs cluster contributes enormous advantages in terms of broadening the absorption spectrum to improve sunlight utilization, enhance the stability of the materials, effectively inhibit the recombination of photo-generated electron-hole pairs, and reduce charge-transfer impedance. POMs can absorb light to convert into reduced POMs, which have stronger reducing ability to provide ample electrons to reduce N₂ . The reduced POMs can recover their oxidation state through contact with an oxidant, which forms a self-recoverable and recyclable photocatalytic fixing N₂ system. The photocatalytic activity enhances with the increasing number V substitutions in the POMs. Satisfactorily, ZIF-67@K₁₁ [PMo₄ V₈ O₄₀ ] (PMo₄ V₈ ) displays the most significant photocatalytic N₂ activity with a NH₃ yield of 149.0 μmol L^-1  h^-1 , which is improved by 83.5 % (ZIF-67) and 78.9 % (PMo₄ V₈ ). The introduction of POMs provides new insights for the design of high-performance photocatalyst nanomaterials to reduce N₂ .