Activation-conversion relay mediated by CoN4/CO enables efficient sulfite-driven radical chain reactions

Co-N 4 /C O dual sites enable relay catalysis in sulfite-based AOPs. • C O sites initiate radical chains via strong p-p hybridization with sulfite. • Co-N 4 sites promote the conversion of SO 5 •− to SO 4 •− through d-p coupling. • Flow, real wastewater, and ecotoxicity tests confirm practicality. Sulfite-based advanced oxidation processes (S(IV)-AOPs) have emerged as a promising persulfate-free and low-toxicity route for sulfate radical (SO 4 •− ) generation. However, the radical-chain nature of S(IV) oxidation, involving both SO 3 •− initiation and the subsequent conversion of SO 5 •− to SO 4 •− , makes it difficult for single-site catalysts to simultaneously achieve efficient chain initiation and downstream radical conversion. Here, we report a carbon-supported Co-N 4 /C O bifunctional catalyst that establishes a dual-site relay catalysis strategy for S(IV)-AOPs. In this architecture, spatially separated yet electronically coupled sites exhibit a clear division of labor: ketonic C O groups serve as primary activation sites for S(IV) activation to generate SO 3 •− via p-p hybridization, whereas adjacent Co-N 4 moieties act as relay sites to facilitate the conversion of SO 5 •− to SO 4 •− through d-p coupling. In situ spectroscopy, selective site-masking experiments, open-circuit potential measurements, and density functional theory calculations collectively verify this stage-specific activation-conversion relay mechanism. As a result, the Co-N 4 /C O catalyst achieves a 10.36-fold higher apparent rate constant for metronidazole degradation than its single-site Co-N 4 counterpart. Moreover, the catalytic system exhibits robust stability in continuous-flow operation and real wastewater treatment while maintaining low ecotoxicity. This work provides a strategy for radical-chain regulation in S(IV)-AOPs. Download: Download high-res image (264KB) Download: Download full-size image