Construction of a BiOBr-Vo/MIL-101(Fe)-F microsphere heterostructure for photocatalytic nitrogen fixation

Photocatalytic ammonia synthesis represents a highly promising and environmentally sustainable strategy for nitrogen fixation. In this study, a novel type II heterojunction MOF-based composite BiOBr-Vo/MIL-101(Fe)-F was successfully constructed. The introduction of oxygen vacancies on BiOBr <i>via</i> a thermal calcination strategy, and <i>in situ</i> doping with F-modified MIL-101(Fe) using the solvothermal method, facilitated the adsorption and activation of nitrogen in the photocatalytic nitrogen fixation. The fluorine modification in MIL-101(Fe) can effectively promote the separation of charge carriers, thereby further enhancing the photocatalytic efficiency. Photocatalytic experiments reveal that the BiOBr-Vo/MIL-101(Fe)-F (10 wt% doping) composite achieves an optimal nitrogen fixation rate of 80.9 μmol_NH₃ g_cat^-1 h^-1 under visible light (≥420 nm), which is 2.8 times higher than that of the hybridised materials without F modification and 21 times higher than that of pristine BiOBr. The type II heterojunction also effectively suppresses the recombination of photogenerated electron-hole (e^--h⁺) pairs, resulting in an efficient separation of the charge carriers and an enhanced photocatalytic activity for the reduction of nitrogen. Continuously stable catalytic activity over 8 cycles (lifetime ≥ 32 h) shows negligible activity loss, which is attributed to the robust coordination structure of BiOBr-Vo/MIL-101(Fe)-F. This finding carries significant implications for the development of novel nitrogen reduction photocatalysts that exhibit both high efficiency and stability.