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

In this study cobalt sulfides (CoS) coated on the nitrogen and sulfur co-doped graphene (CoS@S-N-RG) was firstly prepared and used for degradation of antibiotic sulfamethoxazole (SMX). The results showed that SMX could be completely degraded by CoS@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 that was higher than that induced by CoS, N-RG, S-N-RG and CoS@S-RG, indicating CoS@S-N-RG had superior catalytic activity. CoS@S-N-RG can activate PMS to produce sulfate radicals and hydroxyl radicals, while sulfate radicals played major role. CoS participated in PMS activation in which Co was involved in sulfate radicals formation, while sulfur species facilitated the conversion of Co to Co. 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 CoS and S-N-RG. This study could provide an efficient and stable PMS activator, and insight into the PMS activation mechanism by CoS@S-N-RG.