Photocatalytic NO oxidation on N-doped TiO2/g-C3N4 heterojunction: Enhanced efficiency, mechanism and reaction pathway

Heterojunction photocatalysts with a high activity have been pursuit for years. In this work, we report a facile three-step approach to the synthesis of N-doped Ti-O2/g-C3N4 composite (denoted as N-TiO2/g-C3N4), in which N-TiO2 nanoplates are uniformly assemblied over g-C3N4 layers, leading to a maximization of the heterojunction effect. This resultant composite is highly efficient and durable in photocatalytic removal of ppb-level NO from a continuous air flow under visible light illumination. The photocatalytic NO removal efficiency is N-TiO2 content-dependent, and an optimal content lies at around 25 mg on 0.25 g of g-C3N4, under which the NO removal efficiency reaches 46.1%. The mechanism study reveals that the enhanced photocatalytic performance originates from the N-doping in TiO2 and the N-TiO2/g-C3N4 heterojunction construction, which promote the utilization of visible light and the separation of photoexcited electrons and holes. The active radicals of O-.(2)- and (OH)-O-. are both identified to play important roles in photocatalytic NO oxidation. The reaction pathway study of photocatalytic NO oxidation over N-TiO2/g-C3N4 by in-situ DRIFTS demonstrates that NO can be completely mineralized into nitrate. Overall, the presented work may contribute to a deeper understanding of the photocatalytic mechanism and the design of robust catalysts for air purification.