Co single-atom C2N3 activates peroxymonosulfate for efficient degradation of sulfamethoxazole at 4 °C: A combined experimental and density functional theory study

The Fenton-like reactions for antibiotic degradation become very slow at low temperatures. To overcome this inadequacy, we prepared a rare CxNy allotrope, C2N3, by pyrolysis of HNO3 pretreated melamine and loaded with ultrahigh-density Co single atom (SA) to activate peroxymonosulfate (PMS) to remove sulfamethoxazole (SMX). Results showed that the removal rate of SMX reached 100 % at 4 °C within 8 min. The Co/C2N3-650 + PMS system achieved excellent degradation efficiency for simulated wastewater experiments and various interference factors. The catalyst could efficiently degrade a variety of antibiotics, and achieved more efficient degradation rate in alkaline wastewater. Electron paramagnetic resonance (EPR) measurements and quenching tests confirmed the primary role of singlet oxygen (1O2) in SMX degradation with PMS. Density functional theory (DFT) calculation verified the binding energy of CoN3 site and activation pathway for the different oxygen sites of PMS. The linear sweep voltammetry (LSV) and chronopotentiometry analysis revealed that the electrons of PMS were transferred to the CoN3 sites to form SO5•- intermediates, and proved the generation of 1O2 via the SO5•- self-reaction. This work reveals a new mechanism for the formation of 1O2 and opens up novel approach for SA heterogeneous catalysts in advanced oxidation processes (AOPs).