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 electron-hole 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.