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

Abstract

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[PMo4V8O40] (PMo4V8) 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 % (PMo4V8). The introduction of POMs provides new insights for the design of high‐performance photocatalyst nanomaterials to reduce N2.

Polyoxometalates (POMs): from electroactive clusters to energy materials

“…Recently, Li et al used a typical MOF material, zeolitic imidazolate framework-67 (ZIF-67) with network tetrahedral topologies to adsorb N 2 on its porous structure. 274 The ZIF-67 was combined with various transition-metal-substituted…”

“…Figure 19 (a) NH 3 yield of various ZIF-67/POMs hybrids. (b) Energy levels and electron-transfer mechanism for ZIF-67 and POMs composite photocatalyst 274. …”

A Review of MOFs and Their Composites‐Based Photocatalysts: Synthesis and Applications

“…In the same year, the polyoxometalates/MOFs (POMs/ZIF‐67) composites photocatalysts were successfully fabricated for ammonia synthesis by Li and co‐workers. [ 313 ] The combination of POMs with ZIF‐67 can enhance the visible light absorption ability, restrain the recombination of photogenerated carrier charge, as well as improve the structural stability. The POMs/ZIF‐67 photocatalyst presented an excellent NH 3 yield of 149 µmol L −1 h −1 , which is much higher than that of pure POMs and ZIF‐67.…”

“…[ 309–311 ] Among many functional materials, MOFs and their composites‐based photocatalysts draw much attention in photocatalytic NRR since their good light‐harvesting ability and unique porous structure. [ 312–314 ]…”

Recent Advances in MOF‐Based Materials for Photocatalytic Nitrogen Fixation

“…introduced polyoxometalates (POMs) into the porous structure of MOF through in situ synthesis and prepared a series of ZIF‐67@POMs materials (Figure 11). [112] POMs have been considered as a promising optoelectronic material because of its unique semiconductor characteristics [113] . Unfortunately, POMs is an unstable catalyst that can be dissolved in water and lost from the carrier.…”