Thickness regulation of graphitic carbon nitride and its influence on the photocatalytic performance towards CO2 reduction

Graphitic carbon nitride (g-C3N4) has been widely investigated in photocatalysis due to its excellent semiconductor properties. Though various strategies have been used to optimize the catalytic activity of g-C3N4, the influence of thickness itself on the photoelectric properties and CO2 reduction activity of g-C3N4 is still unclear. In this work, g-C3N4 with various thickness were successfully prepared by high-temperature exfoliation, and applied for the photoreduction of CO2. It was found that the conduction band (CB) of g-C3N4 samples shifted to negative position with decreasing thickness due to quantum confinement effect. Meanwhile, the more negative CB position endowed g-C3N4 with higher reduction potential that favors the reduction of CO2. Moreover, the specific surface area remarkably increased with higher exfoliation degree accompanied by more exposed active sites. The thinner g-C3N4 thickness also led to the exposure of ample edge amino groups that are beneficial for CO2 adsorption. Furthermore, the high-temperature exfoliation were also benefit for optimizing the crystal structure of g-C3N4 and reducing defect structures, which significantly inhibits the recombination of electronhole pairs and facilitates the migration of charge carriers. These merits of g-C3N4 with high exfoliation degree synergistically catalyze the photoreduction of CO2 with high efficiency.