Impact of Phosphorus Doping on Triazine- and Triazole-Based Mesoporous C3N5, C3N6, and C3N7 with Excellent Photocatalytic Hydrogen Production

In recent years, little attention has been paid to triazine- and triazole-based mesoporous C₃N₅, C₃N₆, and C₃N₇, which are potential catalysts. High-N/C atomic ratio carbon nitrides (>2) may possess unique electronic properties. To synthesize these nanostructures, however, many portions of the carbon nitride frameworks in the C-N have to be replaced with N-N frameworks that are thermodynamically less stable. C₃N₅, C₃N₆, and C₃N₇ are thermodynamically stable mesoporous materials synthesized from 5-amino-1H-tetrazole (5-AT) at 400, 300, and 250 °C. The properties of photocatalytic H₂ production from phosphorus-doped mesoporous C₃N₅, C₃N₆, and C₃N₇ were investigated for the first time with triazine and triazole units. Based on our study, we found that phosphorus (P) replaced carbon to form P-N/P═N bonds through four coordinations, which form the P 2p-level donor positions in the band gap, thereby enhancing light absorption and reducing charge separation. Photocatalytic H₂ production in P-doped mesoporous C₃N₅, C₃N₆, and C₃N₇ samples was higher than that observed in undoped mesoporous C₃N₅, C₃N₆, and C₃N₇ samples under light irradiation. According to the results, the 10MPC₃N₅ reaction rate is 637.7 μmol g^-1 h^-1, which is 6 times higher than the MC₃N₅ reaction rate. The excess phosphorus doping, however, interrupted the triazole and triazine units, reducing the efficiency of the photocatalytic H₂ reaction. P-doped mesoporous C₃N₅, C₃N₆, and C₃N₇ effectively arranged in this study can be characterized as effective, simplistic, and promising catalysts for environmental remediation and energy applications.