Abstract:

Carbon nitride is an ideal catalyst for photocatalytic reduction of CO₂, but the recombination of photoelectron-holes has greatly limited the application of carbon nitride. Based on the strategy of heterojunction construction, graphite-phase carbon nitride/nitrogen-rich carbon nitride （C₃N₄/C₃N₅） catalysts were synthesized by high-temperature thermal polymerization-thermal reflux method using melamine and 3-amino-1, 2, 4-triazole as raw materials. The catalysts were characterized by a series of methods. The photocatalytic performance of C₃N₄/C₃N₅ catalyst for CO₂ reduction was evaluated by introducing high-purity CO₂ into the aqueous phase under 300 W xenon lamp irradiation. The results showed that only CH₄ was produced during the photocatalytic reduction of CO₂ by C₃N₄/C₃N₅ catalyst under light irradiation for 5 h, and the yield reached 2.102 8 μmol/ （g·h）, which was 9.8 times and 5.2 times that of single-component C₃N₄ and C₃N₅ catalysts, respectively. The photocatalytic performance was significantly improved. It was not only due to the increases of specific surface area and pore size after the disordered stacking of C₃N₄ and C₃N₅, but also due to the construction of Z-scheme heterojunction after the coupling of C₃N₄ and C₃N₅, which effectively promoted the separation of photoelectron-holes and promoted the transfer of charges. Active species such as photoelectrons and holes played a key role in the process of photocatalytic CO₂ reduction.

Key words: carbon nitride, Z-scheme heterojunction, CO₂ reduction, methane