Carbon vacancies and hydrogen bonds in graphitic carbon nitride: Enhanced charge transfer and photocatalytic hydrogen evolution

Abstract

Accelerating the separation and transfer of photogenerated electron to the active site is an effective strategy for enhancing the photocatalytic hydrogen evolution. However, it is generally limited by the scarcity of active sites, as well as the sluggish photogenerated electron transfer kinetics. Herein, a g-C3N4 catalyst with controllable carbon vacancy and hydrogen bond was prepared using a hot–cold cycles heat treatment. It is demonstrated that after hot–cold cycles, abundant carbon vacancies were introduced into the catalyst and hydrogen bonds were broken. The abundant carbon vacancies not only provide additional electron-active sites, affords more opportunities for photogenerated electron to transfer to the active site, but also optimize the reaction environment for photogenerated electrons by regulating the hydrogen adsorption kinetics of the photocatalyst. Additionally, the broken hydrogen bonds promotes electron transfer to the active site. The combined action of the two effectively enhances the separation and transfer of photogenerated electron to the optimal active site, ultimately leading to a significant increase in photocatalytic hydrogen evolution. Consequently, the g-C3N4 resulting from the fourth cycles (CN-4) demonstrates a substantial improvement in the performance of photocatalytic hydrogen evolution under visible light irradiation (1.69 mmol·g−1·h−1), which is 4.05 times higher than initial g-C3N4. This work may provide new insights into the defect and hydrogen bond regulation design of g-C3N4.