Corrugation Matters: Structure Models of Single Layer Heptazine-Based Graphitic Carbon Nitride from First-Principles Studies
Qian Gao, Xinying Zhuang, Shuanglin Hu, Zhenpeng Hu
Abstract
The graphitic carbon nitride (g-C3N4) nanosheets have attracted much attention for its excellent performance in photocatalysis, but the verification of the detailed experimental geometry structure is under debate. Here we present a theoretical study of several structure models for single layer heptazine-based g-C3N4 with different conformations. In all the investigated conformations, the planar structured carbon nitride (1 × 1-p-CN) is energetically unstable, whereas the corrugated ones (1 × 1-c-, 3 × 3-, 2 × 3-, and 2 × 2-CN) are identified to be in lower energy, which is linked to the repulsion between the lone electron pairs of close nitrogen atoms. The repulsion distorts the C6N8 units connected by the central nitrogen atoms, thus having a great influence on the overall structures. Except for 1 × 1-p-CN, all the corrugated conformations exhibit different geometric reconstructions but similar direct band gaps, which are comparable with the experimental results. Meanwhile, the corrugated conformations are identified to be dynamically stable from phonon dispersion calculations, while the planar one is not. We also find that the structure corrugations have great influence on the values of conduction band minimum (CBM) and valence band maximum (VBM), which indicate different photocatalytic activity. As a key factor of a chemical reaction, the binding energy of the Pt atom embedded in different conformations are found to have evident influences on the thermodynamic properties. On the basis of this research, we would suggest that as large as the supercell size, at least some rational large size of model systems with proper corrugations should be used in the calculations for a reasonable result. It is believed that this work would benefit further theoretical studies related with the heptazine-based g-C3N4.