Uncovering the multifaceted roles of nitrogen defects in graphitic carbon nitride for selective photocatalytic carbon dioxide reduction: a density functional theory study

Surface defect engineering on the nanoscale has attracted extensive research attention lately; however, its role in modulating the properties and catalytic performance of a semiconducting material has not been comprehensively covered. Here, we systematically unraveled the effect of defect engineering towards textural, electronic and optical properties of graphitic carbon nitride (g-C 3 N 4 ), as well as its photocatalytic mechanism of CO 2 reduction using first-principle calculations by density functional theory through the introduction of various defect sites. Among the five unique atoms in g-C 3 N 4 , the vacancy site was found to be the most feasible at the two-coordinated nitrogen, N2. By initiating N2 point defects, an asymmetric electron density distribution was engendered around the vacancy region, which resulted in an evolution of semiconducting properties. We also discovered an improved charge separation efficiency and CO 2 adsorption affinity in g-C 3 N 4 , which rendered a more thermodynamically feasible pathway for CO 2 reduction to CO, CH 3 OH and CH 4 fuels. This theoretical finding is hoped to shed light on the importance of the defect engineering strategy towards photocatalytic enhancement in g-C 3 N 4 . Nitrogen defect-engineered g-C 3 N 4 with high electron localization at the vacancy site manifested stronger interaction with CO 2 molecules and concomitantly enhanced the reaction specificity towards CO, CH 3 OH and CH 4 generations from CO 2 reduction.