Enhanced photocatalytic nitrogen fixation on defect-engineered Ni-doped MIL-101(Fe) via nitrogen-coordinated activation

Abstract

Defect engineering is a promising strategy for overcoming the challenges associated with rapid charge recombination and N₂ activation. In this study, MIL-101(Fe/Ni)-X% catalysts with different oxygen vacancy concentrations were synthesized by introducing Ni²⁺ into MIL-101(Fe) systems for photocatalytic nitrogen fixation. The optimal catalyst, MIL-101(Fe/Ni)-15%, achieved an ammonia production rate of 66.3 μmol g⁻¹ h⁻¹, which was much greater than that of MIL-101(Fe). The characterization results indicate that Ni doping can induce the lattice distortion and the absence of oxygen coordinated with Fe, facilitating the generation of Fe²⁺ species and oxygen vacancies. The unsaturated Fe²⁺ coordination site can effectively adsorb and activate N₂. Moreover, vacuum heat treatment regulates the oxygen vacancy concentration. An appropriate amount of oxygen vacancies is conducive to optimizing the utilization of interface holes and the separation of photogenerated charges. This work offers a novel approach for photocatalytic nitrogen fixation by synergistically modifying MOF materials through metal doping and defect engineering.