Peroxymonosulfate activation by Co9S8@ S and N co‐doped biochar for sulfamethoxazole degradation

High efficient and stable activator is desired for the sulfate radical-based wastewater treatment. Cobalt sulfide and cobalt oxide have high catalytic activity for peroxymonosulfate (PMS), but poor stability. Here, a novel composite, nano Co9S8 and CoO encapsulated by nitrogen and sulfur co-doped sludge-derived biochar (CoO/Co9S8@N-S-BC) was synthesized, characterized and applied for activating PMS. The results showed that CoO/Co9S8@N-S-BC can effectively activate PMS for sulfamethoxazole (SMX) degradation, and 0.08 mM of SMX could be completely degraded within 10 min. The influencing factors, such as pH, temperature, chloridion, carbonate and humic acid were investigated. The SMX degradation conformed to pseudo first-order kinetics with rate constant of 0.379 min−1. Sulfate radicals (dominant) and hydroxyl radicals contributed to SMX degradation. Carbon defects, pyridinic N, quaternary N, the carbon atoms next to pyridinic N, CO groups, -C-S-C and Co(II), all contributed to PMS activation.