Co single-atom catalyst for efficient and long-acting activation of peroxymonosulfate: Formation of Co-N₄ site and insight into the activation mechanism

While single-atom catalysts (SACs) have been extensively investigated as a high-atom-efficiency heterogeneous catalyst for peroxymonosulfate (PMS) oxidation reaction, the stable constructing and activation efficacy of the reaction sites remains less clarified. Herein, we employed gelatin as a N,O-bidentate ligand for Co (II) to form for a N-doped carbon precursor, while introducing NaCl as a template agent to induce the adoption of a Co-N conformation and disorganize the Co-O moiety. This approach facilitates uniform spatial isolation and atomic-level dispersion of Co atoms within the aerogel, effectively inhibiting the aggregation of Co during synthesis and enabling precise and controllable preparation of Co single-atom catalysts (SACs). As a result, the obtained SCAs/PMS system rapidly eliminated more than 99.6 % of 40 mg/L commercial dye in 10 min. Experimental and theoretical results reveal that the Co-N₄ site can trigger facilitative dissociation/desorption of reaction intermediates and reduce energy barrier for SO₅* and H* form, thereby redirecting the dissociation pathway from direct contiguous electron transfer to ROS-mediated degradation. Importantly, Co-N₄ not only enhances the chemical adsorption and electron transfer between PMS and catalysts, but also functions as an interface electron bridge to facilitate internal electron hopping. As a beneficial effect that collectively endows the alternating of Co-N₄ sites and ultimately improve the long-term catalytic stability. This study provides a comprehensive understanding of the Co-N₄ sites and PMS activation mechanism in Co-SACs, shedding light on the structural-property correlation for PMS activation.