The effect of water on the structural, electronic and photocatalytic properties of graphitic carbon nitride

Abstract

g-C₃N₄, as a typical metal-free catalyst for water splitting, has attracted special attention. The structural and electronic properties of water adsorption on g-C₃N₄ play a key role in understanding the water splitting mechanism at the atomic level. The properties of a single g-C₃N₄ sheet and the water adsorption on a single g-C₃N₄ sheet were thoroughly explored based on density functional theory (DFT) calculations. The results show that water adsorption on one side of the single g-C₃N₄ sheet will lead the initial flat structure to change to a buckle one, while water molecule adsorption on both sides of g-C₃N₄ will not disturb the flat structure. The flat g-C₃N₄ is an indirect semiconductor, and interestingly the band structure of g-C₃N₄ changes from an indirect to a direct one during the flat structure transformation from flat to buckle because of the water adsorption. Water molecules prefer to adsorb around the intrinsic vacancy of the single g-C₃N₄ sheet at low coverage, and further adsorbed water molecules stay around the intrinsic vacancy. Water adsorption also affects the band edge position of g-C₃N₄ for water splitting. These results provide a deep insight into the structure and adsorption properties of g-C₃N₄ in the water environment, which will greatly help to design a new type of metal-free catalyst for water-splitting.