Degradation of sulfamethoxazole using peroxymonosulfate activated by nitrogen-doped biochar: Insights into the active sites and activation mechanism

The advanced oxidation processes based on peroxymonosulfate (PMS) activated by nitrogen-doped biochar (NBC) have broad application prospects in the degradation of antibiotics. The changes of structure and surface functional groups caused by nitrogen doping play a key role in the catalytic activity and PMS activation mechanism of biochar. Herein, the physicochemical properties of NBC were regulated by changing the mass ratio of cellulose to melamine from 0 to 2. Under the conditions of 0.2 g L- 1 NBC-2 and 3 mM PMS, 5 mg L- 1 SMX could be completely degraded within 60 min. The synthesized NBC-2 exhibited enhanced PMS activation performance, with a 111 % increase in degradation rate constant of SMX and a 40 % increase in mineralization degree compared to undoped biochar (BC). Further studies on the mechanism of SMX degradation by NBC-2/ PMS revealed that the process was mainly dominated by non-radical pathway, especially the direct electron transfer mediated by (NBC-2-PMS)* metastable complex. Defects, C=O, and pyridinic N were considered to be the key active centers for PMS activation. These active sites acted as electron donors, achieving efficient PMS activation by accelerating electron transfer. The possible degradation pathways of SMX were speculated, and the overall toxicity of the intermediates was reduced. The NBC-2/PMS system showed high tolerance to anionic interference and pH range (3-10), along with excellent universality and cyclic stability. This study provides valuable perspectives on the activation mechanisms and structure-performance relationships of nitrogen-doped biochar in activating PMS to degrade organic pollutants.