Directing the persulfate activation reaction pathway by control of Fe-Nx/C single-atom catalyst coordination

In the reaction systems involving peroxymonosulfate (PMS) activation, the degradation of organic pollutants is influenced by the distinct roles played by the oxidation of free radicals and non-free radicals. The synergistic effect resulting from both oxidation pathways is often more efficient compared to a single oxidation pathway, as it allows for the optimal utilization of oxidation capacity and adaptation to complex reaction environments. Nitrogen-doped carbon substrates hosting single-atom catalysts (SACs) are anticipated to serve as an optimal platform for managing the dual oxidation pathways in the PMS activation reaction. This is attributed to the availability of numerous reaction sites that meet the activation requirements. However, there's a lack of substantial reports on this subject. Herein, we synthesized a series of single-atoms Fe nitrogen-doped carbon catalysts with different coordination structures by adjusting the coordination numbers between Fe and N atoms. It is used to investigate the reaction pattern of PMS over SACs, so as to enhance the catalytic efficacy of SACs through distinct coordination structures. The experimental and theoretical results indicate that PMS functions as both an electron receiver and provider on FeNx/C catalysts. Moreover, the specific arrangement of the Fe-N-C structure influences the exchange of electrons between the catalysts and PMS. Hence, the co-oxidation pathway of free radicals (OH, SO4− and O2−) and non-free radicals (1O2) can be modulated by altering the coordination number of Fe and N atoms during PMS activation. The elimination efficiency of tetracycline hydrochloride was significantly enhanced due to the abundance of both free radical and non-free radical species generated in the FeN3/C/PMS reaction system, exhibiting a degradation kinetic constant of 0.564 min−1. In addition, it showed promising potential for application in practical wastewater degradation, exhibiting high anti-interference to general environmental disturbances (such as humic acid, chloride ions, bicarbonate ions and nitrate ions).