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

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.