Spatially restricted strategy to construct crystalline carbon nitride nanosheet assists exciton dissociation to enhance photocatalytic hydrogen evolution activity

Two-dimensional carbon nitride nanosheets continue to attract attention in photocatalysis, but inefficient exciton dissociation and charge separation limit further improvement of their photocatalytic performance. Herein, we have prepared highly crystalline carbon nitride sheets using a integrated strategy of spatially restricted growth in solid salt media and hydrochloric acid induced exfoliation. In the confined space of the solid salt, K+ induce the ordered growth of carbon nitride and diffuse into the carbon nitride bulk phase with thermodynamically feasible paths. Pickling was also found to control the K+ concentration gradient distribution and regulate the charge characteristic of cyanoamino, thereby controlling the quantity and activity of trapped long-lived electrons. The storage free electron behavior of carbon nitride dual-functionalized with cyanoamino and K+ (KCCN) greatly facilitates the dissociation of excitons, resulting in photocatalytic hydrogen evolution efficiency of 10.78 mmol·g−1·h−1, which was 49 times higher than that of ordinary carbon nitride. KCCN had a hydrogen production quantum efficiency of 27.79%, higher than the majority of the similar materials reported. This study provides new insights into the design of more excellent carbon nitride-based photocatalysts through exciton engineering.