Integration of TiO₂ QDs with brown TiO₂: S-scheme photocatalysts with boosted activity for simulated sunlight-driven N₂ fixation without hole quencher

An alternative strategy to solve the energy consumption and pollution problems caused by traditional ammonia production is photocatalytic N₂ fixation. Therefore, the rational design and facile synthesis of photocatalysts for the efficacious ammonia production is an active research hotspot. In this research, TiO₂ QDs (TQDs) and brown TiO₂ (BTO) nanoparticles were combined through a facile hydrothermal method. The optimal homojunction TQDs/BTO (1:1) photocatalyst with QDs size of about 4.5 nm was utilized for ammonia production, for the first time, with the activity of 11844 µmol L⁻¹ g⁻¹, which was almost 14.5, 4.46, and 3.07-folds as large as TiO₂ (P25), TQDs, and BTO materials, respectively. In addition, the presence of hydrazine intermediate in the ammonium formation pathway and the impact of hydrogen-free solvents, electron quencher, and acidic and basic solutions on ammonia production were investigated. The electrochemical and spectroscopic characterizations confirmed that the boosted ability of photocatalyst is related to the boosted adsorption of N₂ molecules and effective segregation/transfer of charge carriers. Consequently, the S-scheme TQDs/BTO (1:1) homojunction photocatalyst could be a suitable photocatalyst in N₂ fixation technology, with high stability for repeated use and a facile synthesis route.