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

Abstract

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.