关键词: 密度泛函理论, g-C₃N₄, 碱金属改性, 氮气吸附

Abstract: The effect of alkali metal modification on g-C₃N₄ photocatalyst was systematically studied. The density functional theory is used to explain the microscopic mechanism of different alkali metal modification on improving photocatalytic activity from the various angles of geometry and electronic structure. The results show that the binding energies of alkali metals and g-C₃N₄ become weaker and weaker with the increase of the number of extra-nuclear electronic layers of Li, Na, K and Rb atoms, and the influence on the structure of g-C₃N₄ is weaker and weaker. The electronic structure analysis shows that Li, Na, and K atoms have an activation effect on g-C₃N₄, and Rb atoms have a passivation effect on the surface of g-C₃N₄. At the same time, the adsorption of N₂ molecules on M-g-C₃N₄ (M=Li, Na, K, Rb) is simulated, and the interaction mechanism between N₂ molecules and alkali metals is understood. By analyzing the adsorption energy, structural parameters and electronic properties of N₂ adsorption, it is found that the influence of Li and Na atoms on N₂ adsorption is greater. The N—N bond of N₂ is elongated, and the K and Rb atoms have little effect on N₂. Alkali metal modified g-C₃N₄ is more beneficial for the adsorption of N₂ molecules than pure g-C₃N₄, but as the atomic radius of the alkali metal increases, the adsorption capacity becomes weaker and weaker, and the electron transfer becomes less and less. That is to say, the ability of activating N₂ molecule decreases in the order of Li, Na, K and Rb.

Key words: Density functional theory, Graphite phase carbon nitride, Alkali metal modification, N₂ molecular adsorption