Rational design of Na, O co-doped carbon nitride/selenium S-Scheme heterojunction for efficient H2O2 photoproduction

Graphitic carbon nitride (g-C 3 N 5 ) exhibits great potential for photocatalytic hydrogen peroxide (H₂O₂) production due to its narrow band gap and tunable electronic structure. However, its photocatalytic activity is limited by drawbacks such as low light utilization efficiency and rapid recombination of photogenerated carriers. In this work, an S-Scheme Se/Na, O co-doped g-C 3 N 5 heterojunction (Se/NaOCN) is successfully prepared by one-step calcination of the mixture of 3-Amino-1,2,4-triazole, NaOH, and Se powder, which is then applied as the catalyst for H 2 O 2 photoproduction. Under high-temperature alkaline conditions, abundant defect sites (cyano groups and nitrogen vacancies) and Na + ions/O heteroatoms are introduced into the g-C 3 N 5 structure, gaining also an expanded specific surface area and extended optical absorption. Furthermore, the close-contact interface and the building of S-Scheme heterostructure between Se and NaOCN significantly reduces the recombination of photogenerated carriers, improves charge transfer efficiency, and retains strong redox ability. Under visible light, the yield of H 2 O 2 over the optimal photocatalyst (Se/NaOCN-0.5) reaches 2.86 mM H 2 O 2 within 90 min, which is 13 times that of pristine g-C 3 N 5 . Furthermore, the Se/NaOCN-0.5 composite exhibits strong catalytic activity and superior structural stability throughout four cycles. Mechanistic studies revealed that a two-step single-electron O 2 reduction reaction is the main pathway for H₂O₂ generation. This study highlights the significant potential of doping strategies and heterojunction engineering in designing carbon nitride-based photocatalysts for solar-driven H₂O₂ synthesis.