In situ quantitative single-molecule study of site-specific photocatalytic activity and dynamics on ultrathin g-C₃N₄ nanosheets

Abstract

Graphitic carbon nitride (g-C3N4) has attracted extensive research attention in recent years due to its unique layered structure, facile synthetic route, visible-light-responsive nature, and excellent photocatalytic performance. However, an insightful investigation of site-specific catalytic activities and kinetics on g-C3N4 is still warranted. Here, we fabricated ultrathin g-C3N4 nanosheets through thermal exfoliation. The optimized sample exhibits a high specific surface area of 307.35 m2 g-1 and a remarkable H2 generation activity of 2008 μmol h-1 g-1 with an apparent quantum efficiency of 4.62% at λ = 420 nm. Single-molecule fluorescence microscopy was applied for the first time to spatially resolve the reaction heterogeneities with nanometer precision (∼10 nm). The catalytic kinetics (i.e., reactant adsorption, conversion, and product dissociation) and temporal activity fluctuations were in situ quantified at individual structural features (i.e., wrinkles, edges, and basal planes) of g-C3N4. It was found that the wrinkle and edge exhibited superior photocatalytic activity due to the intrinsic band modulation, which are 20 times and 14.8 times that of the basal plane, respectively. Moreover, due to the steric effect, the basal plane showed the highest adsorption constant and the lowest direct dissociation constant. Density functional theory (DFT) simulations unveiled the adsorption energies of reactant and product molecules on each structure of g-C3N4, which support our experimental results. Such investigation would shed more light on the fundamental understanding of site-specific catalytic dynamics on g-C3N4, which benefits the rational design of 2D layered materials for efficient solar-to-chemical energy conversion.