Construction of g-C3N4 with three coordinated nitrogen (N3C) vacancies for excellent photocatalytic activities of N2 fixation and H2O2 production

Nitrogen defect engineering has been confirmed to be an effective strategy to improve photocatalytic perfor-mance, and nitrogen vacancies at different positions show different effects on photocatalytic performance. Here, we prepare g-C3N4 with three-coordinate nitrogen (N3C) vacancies (g-C3N4-N3C) by a simple in situ copyrolysis method. The introduction of N3C vacancies helps to narrow the band gap, enhance the light-harvesting efficiency, accelerate the separation and transfer of photogenerated carriers, and provide more active centers. Interestingly, g-C3N4-N3C exhibits photocatalytic performance for the production of NH3 and H2O2. The optimized g-C3N4-N3C- 0.3 exhibits the best photocatalytic N2 fixation rate (1915 mu mol h-1 g-1) and photocatalytic H2O2 production rate (1098 mu mol h-1 g-1), with corresponding apparent quantum efficiency (AQE) of 7.79 % and 12.43 % at lambda = 370 nm, respectively, which are superior to most known photocatalysts. Meanwhile, density functional theory (DFT) calculations indicate that g-C3N4-N3C makes the activation and further reduction of *N2 and *O2 more ther-modynamically favorable than pure g-C3N4. This work deepens the understanding of the role of nitrogen defect engineering in enhancing the photocatalytic performance of g-C3N4, and provides a new way for the design and preparation of efficient and stable photocatalysts.

Automated summary

Nitrogen defect engineering in g-C3N4 enhances photocatalytic performance by narrowing the band gap, improving light-harvesting efficiency, accelerating carrier separation and transfer, and providing more active centers. The optimized g-C3N4-N3C-0.3 shows superior photocatalytic N2 fixation and H2O2 production rates, with high apparent quantum efficiency. DFT calculations demonstrate that g-C3N4-N3C facilitates the activation and reduction of *N2 and *O2 compared to pure g-C3N4.