Asymmetric cyano-rich crystalline carbon nitride with a powerful dipole field for efficient hydrogen peroxide photosynthesis

Abstract

The production of environmentally friendly oxidizer hydrogen peroxide (H₂O₂) through green and energy saving photocatalysis technology is an excellent solution to the environmental crisis. As an organic photocatalyst, graphitic carbon nitride (BCN) has the advantages of low cost, high stability and easy adjustable morphology and energy band structure, but it still has the problems of high surface inertness, insufficient surface-active sites and a high recombination rate of photogenerated carriers. In order to solve these problems, this work designed a modified scheme of introducing a triazole moiety (3,5-diamino-1,2,4-triazole) with a high nitrogen content into BCN fragments. And combining with the molten salt post-treatment, asymmetric cyano-rich crystalline BCN was synthesized successfully. Herein, the introduction of a triazole moiety breaks the highly symmetrical molecular structure of the BCN molecule, enhances its dipole moment, and inhibits the recombination of photogenerated carriers. The intercalation of K⁺ brought by the molten salt environment enables the construction of an interlayer channel to promote the separation and migration of photogenerated charges. The introduction of terminal cyano groups not only ameliorates the problem of insufficient light absorption, but also provides transfer channels and reaction sites for photogenerated electrons. The directional arrangement of long-range ordered structures in the plane greatly promotes the migration ability of photogenerated carriers. The photocatalytic H₂O₂ production rate of the modified sample reached 14.94 mmol g⁻¹ h⁻¹ under visible light irradiation, which was 115 times that of BCN, and the H₂O₂ accumulation can reach 60.50 mmol g⁻¹ within 8 h. This study proves that the precise design and modification of the molecular structure of BCN can effectively improve its inherent shortcomings and provides a simple and feasible idea for the modification of bulk carbon nitride.