Constructing a built-in electric field in monolayer g-C3N4 by carbon and oxygen co-doping for enhanced photocatalytic oxidation of toluene to benzaldehyde activity

Abstract

The sustainable production of benzaldehyde with mild reaction conditions is challenging. Recently, carbon and oxygen co-doped g-C3N4 was experimentally discovered to enhance the performance of g-C3N4 for photocatalytic selective oxidation of toluene into benzaldehyde in the experiment. However, the microscopic mechanism of C/O co-doped g-C3N4 (COCN) to improve photocatalytic activity remains unclear. In this study, the optoelectronic properties of the COCN were investigated using density functional theory. The results show that the C and O atoms preferentially substitute for the bridge N1 and edge N2 atoms, respectively. The direct bandgap of COCN is 2.36 eV, smaller than that of Pure and Single-doped g-C3N4, which exhibits stronger absorption in the visible light region. Especially, the HOMO and LUMO of COCN are more delocalized, since the COCN forms a built-in electric field that facilitates the separation of electron-hole pairs. Moreover, the band edge positions of COCN conform to the redox potential of the efficient photocatalytic oxidation of toluene into benzaldehyde, and the synergetic effect of C/O co-doping significantly promoted the adsorption of toluene on COCN surface. This study analyzes the microscopic mechanism of non-metallic atoms co-doping to improve photocatalytic efficiency and will provide theoretical strategies for the development of other efficient photocatalysts.