Nitrogen, sulfur and oxygen co-doped carbon-armored Co/Co9S8 rods (Co/Co9S8@N-S-O-C) as efficient activator of peroxymonosulfate for sulfamethoxazole degradation

In this study, nitrogen, sulfur and oxygen co-doped carbon armored cobalt sulfide (Co/Co9S8@N-S-O-C) composite was synthesized, characterized and used to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). SMX (0.04 mM) can be completely degraded within 20 min in the presence of 0.8 mM PMS and 0.1 g/L Co/Co9S8@N-S-O-C composite. The first-order kinetics constant of SMX degradation was 0.307 min-1, and the mineralization of SMX was 30.1 %. The Quenching experiments of the free radicals and the identification of degradation products demonstrated that sulfate radicals played a dominant role in SMX degradation. The degradation rate of SMX increased with temperature, and activation energy was calculated to be 48.6 kJ/mol. The degradation rate of SMX increased firstly then decreased with increase of pH. Chloridion and humic acid decreased the degradation rate of SMX no matter what their initial concentration was. The effect of carbonate on SMX degradation depended on its initial concentration. Co/Co9S8@N-S-O-C composite showed good stability, the removal efficiency of SMX was 98.4 % in the fifth experiment. Based on the characterization results of the catalyst before and after use, it was concluded that cobalt, sulfur, pyridnic N and graphitic N were responsible for PMS activation.