Degradation of sulfamethoxazole using PMS activated by cobalt sulfides encapsulated in nitrogen and sulfur co-doped graphene

In this study cobalt sulfides (Co9S8) coated on the nitrogen and sulfur co-doped graphene (Co9S8@S-N-RG) was firstly prepared and used for degradation of antibiotic sulfamethoxazole (SMX). The results showed that SMX could be completely degraded by Co9S8@S-N-RG-activated peroxymonosulfate (PMS) within 20 min with its mineralization efficiency of 38.7%. The SMX degradation rate followed pseudo first-order kinetics with kinetic constant of 0.377 min-1 that was higher than that induced by Co9S8, N-RG, S-N-RG and Co9S8@S-RG, indicating Co9S8@S-N-RG had superior catalytic activity. Co9S8@S-N-RG can activate PMS to produce sulfate radicals and hydroxyl radicals, while sulfate radicals played major role. Co9S8 participated in PMS activation in which Co2+ was involved in sulfate radicals formation, while sulfur species facilitated the conversion of Co3+ to Co2+. In addition, carbon defects, CO, pyridinic N and pyrrolic N also contributed to PMS activation.The superior catalytic activity was attributed to the synergistic effect of Co9S8 and S-N-RG. This study could provide an efficient and stable PMS activator, and insight into the PMS activation mechanism by Co9S8@S-N-RG.