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.