N-doped TiO2 with stable surface Ti3+ for visible light photocatalytic hydrogen production

Pure TiO2 exhibits limited responsiveness to visible light, while the doping of Ti3+ significantly enhances its absorption efficiency in the visible spectrum, improving the efficiency of photogenerated electron utilization. However, during the direct reduction of TiO2 using NaBH4, the instability of surface Ti3+ ions and their susceptibility to oxidation in air limit their performance in photocatalytic applications. Nitrogen doping into TiO2 effectively addresses this issue, improving the stability of Ti3+ ions and significantly enhancing visible-light-driven photocatalytic activity. Experimental results indicate that reducing 1 g of TiO2 with 0.2 g of NaBH4, followed by calcination in an ammonia environment at 300℃, yields a catalyst with optimal visible-light photocatalytic hydrogen evolution activity, achieving a hydrogen production rate of 847.8 μmol h−1 g−1, representing a 177-fold enhancement over pristine anatase TiO2. After modification, the band gap of the catalyst decreased from 3.2 eV to 2.83 eV. This study elucidates the synergistic effects among Ti3+ species, nitrogen dopants, and oxygen vacancies in TiO2-based photocatalysts, demonstrating their crucial roles in enhancing visible-light-driven hydrogen evolution.