Synergetic mechanism of defective g-C 3 N 4 activated persulfate on removal of antibiotics and resistant bacteria: ROSs transformation, electron transfer and noncovalent interaction.

The environmental hazards of antibiotics and the resulting antibiotic-resistant bacteria (ARB) have attracted more and more attention. In this study, an efficient synergistic system constructed by vacancy g-C ₃ N ₄ (CN _V0.8 ) and persulfate (PS) showed excellent oxidation performance to degrade aztreonam (AZT) and Escherichia coli (E. coli) screened from wastewater treatment plant (WWTP), as the typical β-lactam antibiotic and ARB. As the recombination of electron and hole was effectively inhibited and the interaction with PS was enhanced after the introduction of defects, CN _V0.8 showed superior PS activation ability compared with bulk-g-C ₃ N ₄ (BCN). The synergistic mechanism was systematically analyzed at three levels step by step. Firstly, the conversion of reactive oxygen radicals (ROSs) was studied using electron spin resonance (ESR) and quenching experiments. Then based on the DFT simulation, the enhancement of adsorption energy between catalysts and PS from -8.924 eV (BCN) to -11.190 eV (CN _V0.8 ) and the elongation of O-O bond in PS (from 1.496 Å to 1.505 Å) indicated CN _V0.8 had better activation performance for PS compared with BCN. The electron transfer results observed by deformation charge density showed that more electrons could be transferred from the CN _V0.8 layer to the surrounding of PS for its own activation in the synergistic mechanism. Thirdly, the noncovalent interaction of PS/CN _V0.8 belonged to the region of van der Waals force which was defined by the reduced density gradient (RDG) analysis. The intermediate products in the degradation of AZT were first studied in detail using Fukui function calculations and HPLC-QTOF-MS analysis. Subsequently, the environmental practicability of the oxidation system was investigated through wastewater simulation. This research provides a possible strategy for the effective removal of micropollutants and promotes the development of the sulfate radical-advanced oxidation processes (SR-AOPs) in the field of wastewater treatment.
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