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

The photocatalytic reduction of N-2 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 N-2 reduction. ZIF-67 can effectively fix N-2 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 N-2. The reduced POMs can recover their oxidation state through contact with an oxidant, which forms a self-recoverable and recyclable photocatalytic fixing N-2 system. The photocatalytic activity enhances with the increasing number V substitutions in the POMs. Satisfactorily, ZIF-67@K-11[PMo4V8O40] (PMo4V8) displays the most significant photocatalytic N-2 activity with a NH3 yield of 149.0 mu mol L-1 h(-1), which is improved by 83.5 % (ZIF-67) and 78.9 % (PMo4V8). The introduction of POMs provides new insights for the design of high-performance photocatalyst nanomaterials to reduce N-2.