Impact of Phosphorus Doping on Triazine- and Triazole-Based Mesoporous C<sub>3</sub>N<sub>5</sub>, C<sub>3</sub>N<sub>6</sub>, and C<sub>3</sub>N<sub>7</sub> with Excellent Photocatalytic Hydrogen Production
Saravanan Kamalakannan, B. Natarajan, Bernaurdshaw Neppolian
Abstract
In recent years, little attention has been paid to triazine- and triazole-based mesoporous C 3 N 5, C 3 N 6, and C 3 N 7, 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. C 3 N 5, C 3 N 6, and C 3 N 7 are thermodynamically stable mesoporous materials synthesized from 5-amino-1 H -tetrazole (5-AT) at 400, 300, and 250 °C. The properties of photocatalytic H 2 production from phosphorus-doped mesoporous C 3 N 5, C 3 N 6, and C 3 N 7 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 H 2 production in P-doped mesoporous C 3 N 5, C 3 N 6, and C 3 N 7 samples was higher than that observed in undoped mesoporous C 3 N 5, C 3 N 6, and C 3 N 7 samples under light irradiation. According to the results, the 10MPC 3 N 5 reaction rate is 637.7 μmol g –1 h –1, which is 6 times higher than the MC 3 N 5 reaction rate. The excess phosphorus doping, however, interrupted the triazole and triazine units, reducing the efficiency of the photocatalytic H 2 reaction. P-doped mesoporous C 3 N 5, C 3 N 6, and C 3 N 7 effectively arranged in this study can be characterized as effective, simplistic, and promising catalysts for environmental remediation and energy applications.