Effects of defects in g-C₃N₄ on excited-state charge distribution and transfer: Potential for improved photocatalysis

Graphite phase carbon nitride (g-C₃N₄) with triazine ring structures is a polymeric metal-free semiconductor with a medium bandgap and two-dimensional layered structure. g-C₃N₄ has attracted attention because of its photocatalytic applications, such as the photodegradation of pollution and hydrogen production via water splitting. Defective elements and sites are two essential factors in rationally designing highly-efficient photocatalysts based on g-C₃N₄ at the nanoscale. When the molecule absorbs energy and enters an excited state, electrons migrate and the charge distribution changes accordingly. The properties of the excited states of g-C₃N₄ are related to its defect elements and sites. Therefore, it is necessary to understand the effects of defects on excited states in the design of g-C₃N₄ catalysts. In this paper, the excited-state characteristics of intrinsic g-C₃N₄ and g-C₃N₄ with C- and N-atom defects are analyzed by density functional theory. We apply quantum chemistry and wave function analysis to determine the hole-electron distributions and charge transfer directions. To measure and discuss the characteristics of electron excitation using quantitative numerical methods, the D, Sr, H, and t indices are calculated. Our results promote a deeper understanding of the roles of defective elements and sites in photocatalysis by g-C₃N₄.