Theoretical insight into the mechanism of photoreduction of CO2 to CO by graphitic carbon nitride

Abstract

Graphitic carbon nitride (g-C₃N₄) is a promising photocatalyst for the reduction of CO₂ into fuels. However, the reduction mechanism of CO₂ using g-C₃N₄ is not clear in the literature. In the present study, the fixation of CO₂ and the formation of carbamate on the nitrogen atom at the edge of g-C₃N₄ were investigated using first-principles density functional theory. The calculated results shows that two adjacent bare nitrogen atoms at the edge of g-C₃N₄ could be the activation sites for the proton and CO₂ molecule respectively, which are crucial to the formation of carbamate. The calculated energy barrier of carbamate formation is 0.95 eV for a preferential pathway. From studies on these micro processes, we propose a mechanism with proton assistance for the g-C₃N₄-catalyzed photoreduction of CO₂ to CO.