Adjustable electronic performances and redox ability of a g-C3N4 monolayer by adsorbing nonmetal solute ions: a first principles study

Abstract

During the process of hydrogen generation via photocatalytic water splitting, solute ions may be adsorbed on the surface of the graphitic carbon nitride (g-C₃N₄) monolayer, modifying its electronic and optical performances, as well as its redox ability due to chemical bond relaxation. With the aid of first principles calculations, we investigated the properties of a g-C₃N₄ monolayer with a series of nonmetal (NM) ions adsorbed on its surface. The obtained results revealed that the adsorbed solute ions can form NM–N or NM–C bonds with the g-C₃N₄ monolayer and result in bond relaxation, altering the valence band maximum and conduction band minimum synchronously. The small coverage rate of Br, Cl and I ions enhances the redox ability of g-C₃N₄ synchronously, while the adsorption of the other solute ions enhances the oxidizability and weakens the reducibility. In addition, the adsorption of solute ions can alter the active sites by impacting the distribution of the highest occupied molecular orbital and the lowest unoccupied molecular orbital. Therefore, we can adjust the electronic, optical performances and redox ability of a g-C₃N₄ monolayer by selecting the suitable type and quantity of solute ions, e.g., the photocatalytic efficiency of g-C₃N₄ can be enhanced by H ions plus B, N, Si, O, P and As ions with high coverage rates plus halogen ions with low coverage rates while it is suppressed by C, S, Se and Te ions.