Influence of nonmetal dopants on charge separation of graphitic carbon nitride by time-dependent density functional theory

Abstract

Photocatalysts are crucial materials for green energy production and environmental purification. Non-metal doped graphitic carbon nitride (g-C 3 N 4 ) has attracted much attention in recent years because of low-cost and desired photocatalytic performance characteristics such as high charge separation efficiency and broad visible light absorption. In this study, we used time-dependent density functional theory and wave function analysis to evaluate the charge separation characteristics of phosphorus-, oxygen-and sulfur-doped g-C 3 N 4 upon photon excitation based on electron-hole pair distances, electron-hole pair overlaps, and charge transfer amounts. The lowest unoccupied molecular orbital of doped heptazine rings was shifted downward to facilitate electron transfer from undoped to doped heptazine rings upon photon excitation. Generally, the phosphorus dopant yielded relatively high charge transfer, high electron-hole pair separations, and low electron-hole overlap compared with the oxygen and sulfur dopants. In a low concentration, the sulfur dopant had the similar performance as the phosphorus dopant did. Furthermore, the phosphorus dopant attracted photon excited electrons, whereas the oxygen and sulfur dopants contributed to electron-hole pair separation. The dopants concentrated in one heptazine ring exhibited high charge separation performance than those dopants distributed among multiple heptazine rings in g-C 3 N 4 ; the simulation results suggested that doping configurations are more crucial than doping concentrations with respect to charge separation efficiency in nonmetal-doped g-C 3 N 4 . Fig. S1 The optimized ground state structure of the single-phosphorus-doped HT where the phosphorus atom was located at (a) the corner and (b) the bay positions.

Toward Quantum Confinement in Graphitic Carbon Nitride-Based Polymeric Monolayers

“…Armed with the results presented herein, the preferred sites for the HER and OER are identified and generally correspond to the nitrogen atoms (or HOMO) and carbon atoms (or LUMO), respectively. The results presented in this work also provide the most suitable sites for chemical doping studies involving g -C 3 N 4 building blocks, where modifications of the electronic structure are essential to achieve a given set of desired properties . Likewise, this study is ongoing and will be followed up by systematic doping studies of the n -mel and n -hept monolayers identified in this work.…”

“…The results presented in this work also provide the most suitable sites for chemical doping studies involving g-C 3 N 4 building blocks, where modifications of the electronic structure are essential to achieve a given set of desired properties. 93 Likewise, this study is ongoing and will be followed up by systematic doping studies of the n-mel and nhept monolayers identified in this work.…”

Influence of Phosphorus Doping on Triazole-Based g-C3N5 Nanosheets for Enhanced Photoelectrochemical and Photocatalytic Performance

“…The peak at around 455 nm decreased significantly with increasing phosphorus doping (Figure S4a–c), in agreement with the above argument that charge recombination is inhibited because extra donor states are created by the P 2p levels as a result of P-doping. Additionally, the previous study demonstrated that phosphorus doping in g-C 3 N 4 could not only improve the charge separation but also reduce the overlap and lengthen the distances between electron–hole pairs compared to the use of oxygen or sulfur as dopants. , …”

“…Subsequently, Pdoped triazole-based g-C 3 N 5 was produced through condensation polymerization via the elimination of HCl and NH 3 at a temperature of approximately 550 °C. Based on the XPS results, the P-substitution at C sites was randomly distributed throughout the structure; this substitution would not only result in more electron donation but also attract photoexcited charges 21 to enhance the photocatalytic activity.…”

“…Many studies have reported that g-C 3 N 4 and g-C 3 N 5 with a mesoporous structure and nanosheet-like and rod-like configurations , show promise as photocatalysts in terms of structural engineering. Additionally, the photocatalytic activity of g-C 3 N 4 can also be significantly improved by doping with nonmetallic ions, such as phosphorus, sulfur, oxygen, nitrogen, boron, and iodide, to reduce the recombination of photoinduced electron–hole pairs and increase their lifetime while maintaining its nonmetallic nature. − Particularly, the phosphorus doping of g-C 3 N 4 can not only facilitate charge separation by downshifting the lowest unoccupied molecular orbital of the P-doped heptazine rings upon light irradiation but also induce lower electron–hole overlap compared to oxygen or sulfur doping. − Texture and electronic properties of g-C 3 N 4 can be modified via a nonmetal doping, which can be either interstitially or substitutionally doped at different sites of its structure. − However, to the best of our knowledge, there are no reports related to P-doped triazole-based g-C 3 N 5 and the correlation between its structural features and photocatalytic activity; this topic is worthy of exploration.…”