Modulating electronic structures of MOF through orbital rehybridization by Cu doping promotes photocatalytic reduction of nitrate to produce ammonia

Ammonia synthesis through nitrate reduction can mitigate nitrate pollution and fulfill energy demands. However, the process still has limitations because it is a complex eight-electron reduction process with a high energy barrier. Herein, Cu2+, which is a highly electronegative element, was successfully integrated into NH2–MIL-125 (Cu–NM) using an in situ solvothermal method. This incorporation regulates the band structure of MOFs, promoting the generation and directional transfer of photogenerated charges. Furthermore, it enhances the electron density of the Cu active sites, effectively improving the catalytic activity of the catalyst s for ammonia synthesis. Density functional theory (DFT) calculations and in situ characterization further confirmed that Cu doping induces p–d hybridization between Cu 3d and NO3− O 2p orbitals. This facilitates the formation of a more stable bidentate mode adsorption structure for nitrates (NO3−) on the Cu sites, reducing the activation energy barrier of the active intermediates. Consequently, Cu–NM exhibited a high ammonia yield of 32.8 mg gcat−1.h−1 and high selectivity of 94.8%, outperforming the catalysts reported in previous studies. This study provides valuable insights into the advancement of highly active photocatalysts for nitrate reduction and ammonia production.