Construction of a TiO2/Ti-MOF/MXene ternary heterojunction for enhanced photocatalytic nitrogen fixation

Abstract

In this work, a ternary heterojunction photocatalyst with oxygen vacancies, TiO₂@MIL-125(Ti)/MXene (MM-350), was successfully designed and synthesized. TiO₂ nanoparticles were generated in situ via the co-oxidation of MIL-125(Ti) and MXene, uniformly coated around the MIL-125(Ti)/MXene (MM) composite to form a stable ternary heterojunction structure. MM-350, along with enhanced structural stability, achieved a remarkable photocatalytic nitrogen fixation rate of 76.92 μmol g⁻¹ h⁻¹, which was nearly double that of MM (44.78 μmol g⁻¹ h⁻¹). Mechanistic studies revealed that the superior performance of MM-350 originates from the synergistic effects of an S-scheme heterojunction between TiO₂ and MIL-125(Ti) and a Schottky junction between MIL-125(Ti) and MXene. The intrinsic built-in electric field at the TiO₂/MIL-125(Ti) interface drives directional charge migration from TiO₂ to MIL-125(Ti), and MXene serves as an efficient electron reservoir, promoting electron accumulation and N₂ activation at Ti active sites. The presence of dual charge transfer routes significantly promotes photogenerated carrier separation and utilization, thereby enabling effective N₂ reduction under visible light. This work provides a rational design strategy for constructing multi-interface heterostructures with synergistic charge transfer for efficient photocatalytic nitrogen fixation.