Efficient degradation of sulfamethoxazole by a peroxymonosulfate system activated by g-C3N4@polyethylene glycol-derived carbon-nitrogen nanosheets: The key roles of N and O groups

A simultaneous thermal polymerization reaction was performed with graphitic carbon nitride and polyethylene glycol to synthesize a novel metal-free carbon-nitrogen (CN) material, and the prepared material was applied to activate a peroxymonosulfate (PMS) system. Sulfamethoxazole (SMX) removal by CN7/PMS reached 93.75 % in 10 min, which was 39.86 times higher than that achieved by PMS systems alone. Material characterization showed that the pyrolysis temperature could be adjusted to modulate the N atom and functional group contents. As determined by experimental validation and DFT calculations, C = O/C-N, graphitic N and defects were the main active sites. This finding indicates that CN7 activated PMS to produce hydroxyl radicals (center dot OH), sulfate radicals (SO4 center dot-) and singlet oxygen (1O2) through electrostatic interactions, nucleophilic addition, electron transfer and other pathways. Moreover, 1O2 was dominant, with a 91.58 % contribution. In addition, the materials maintained high catalytic stability in different water matrices and multiple cycling experiments. The present study innovatively illustrated the mechanism by which nitrogen-doped carbon materials activated PMS, providing a new insight into the development of highly active metal-free catalysts applied in PMS systems.