Abstract: Developing highly efficient photocatalysts for nitrogen fixation remains a significant challenge due to the difficult activation of N₂ and rapid recombination of photogenerated carriers. Herein, 3D hierarchical hollow Bi/Bi₄Ti₃O₁₂ Schottky junction photocatalysts with tunable surface oxygen vacancies (OVs) are fabricated by a facile hydro/solvothermal method. Due to the synergistic effect of surface OVs and the Schottky junctions at the Bi/Bi₄Ti₃O₁₂ interface, efficient light utilization and enhanced separation and migration of photogenerated carriers are achieved. Additionally, the Schottky junctions facilitate unidirectional electron transfer from Bi₄Ti₃O₁₂ to metallic Bi NPs. The electron-rich metallic Bi serves as the active sites for N₂ reduction reaction. The optimized 1 % Bi/HBTO-OV3 composite achieves an outstanding ammonia production rate of 24.25 µmol g^-1 h^-1 in pure water without sacrificial agents, which is 5.66 times higher than that of pristine Bi₄Ti₃O₁₂. In situ experiments and DFT calculation elucidate the photocatalytic nitrogen fixation mechanism, confirming an associative distal pathway for the hydrogenation of N₂. This work provides a rational strategy for designing high-efficiency photocatalysts by integrating surface defect engineering with Schottky junctions, paving the way for sustainable solar-driven nitrogen fixation.

Key words: Photocatalytic nitrogen reduction, Bi₄Ti₃O₁₂, Surface oxygen vacancies, Bi nanoparticles, Schottky junctions