Important role of carbon doping in photocatalytic peroxymonosulfate activation of carbon nitride for efficient 4-Chlorophenol degradation

In order to improve the photocatalytic activity of pristine carbon nitride while maintaining its metal-free property to achieve the activation of peroxymonosulfate (PMS), a series of carbon-doped g-C3N4 (BCN) with different carbon contents were synthesized in this paper by adding benzotriazole to urea. The catalyst obtained by this approach significantly promoted PMS activation and enhanced the degradation efficiency of 4-chlorophenol (4-CP). Experiments and theoretical calculations showed that the introduction of carbon not only narrowed the band gap, but also accelerated the separation of photoinduced electron-hole pairs, which greatly improved the photocatalytic activity of g-C3N4. In the degradation of pollutants, free radicals and non-free radicals acted simultaneously, with non-free radicals playing a dominant role. This study explained the origin of 1O2 by Density functional theory (DFT) calculations, visible light excited photocatalysts to form holes, while carbon introduction decreased the valence-electron density around the area, inducing electron transfer from PMS toward g-C3N4 directed to generate 1O2. The 1O2-dominated degradation process improved the application of the catalysts in complex aqueous matrices. In addition, we proposed 4-CP degradation pathways, and the toxicity of intermediates derived from 4-CP degradation process reduced.