Internal electric field construction on dual oxygen group-doped carbon nitride for enhanced photodegradation of pollutants under visible light irradiation

Graphitic carbon nitride (g-C3N4), as metal-free and visible-light-driven photocatalyst, has been a promising alternative to replace the traditional inorganic photocatalyst. Herein, a dual oxygen group (C-O-C and C = O) doped carbon nitride (ACN*) was prepared by a two-step thermal treatment process. The photocatalyst showed high and stable photocatalytic activity for the degradation and mineralization of refractory organic pollutants under visible light irradiation, as demonstrated with bisphenol A, phenol, 2-chlorphenol and diphenhydramine. By electron paramagnetic resonance spectroscopy and density functional theory calculations, higher valence-electron densities were formed around the O atoms of C-O-C and C = O groups than around C and N atoms, constructing an internal electric field in ACN*, which was enhanced by light irradiation and the adsorption of pollutants by hydrogen bond and n-n bond interactions. Correspondingly, transfer processes of photogenerated carriers were proposed based on all experimental information obtained for pollutant photodegradation, including transfer of photoexcited electrons to the region around O atoms in the two types of oxygen groups, reaction with O-2 to form center dot O- 2, and donation of electrons from adsorbed pollutants to electron-poor tri-s-triazine motifs in ACN*. The synergetic oxidation by the two processes contributed to higher photodegradation of pollutants. This correlation between the transfer of photogenerated carries and pollutant degradation shed a new light on the construction of internal electric field in carbon nitride photocatalysis.