Highly efficient activation of peroxymonosulfate by cobalt sulfide hollow nanospheres for fast ciprofloxacin degradation

We reported a facile preparation of CoS2, Co3S4, and Co9S8 hollow nanospheres (HNSs) and their use as peroxymonosulfate (PMS) activators for ciprofloxacin (CIP) degradation. The CIP degradation efficiency follows the order of CoS2> Co3S4 > Co9S8. The Co2+ is proved to be active site for PMS activation and reactive oxygen species generation. The effect of operating parameters on performance of CoS2 HNSs/PMS system was explored. CoS2 HNSs exhibited highly catalytic activity in a wide pH range of 3 - 10. Complete removal of 10 mg/L CIP was achieved by CoS2 HNSs in 3 min at initial pH of 8.0 with 62.6% CIP mineralization. Three other organic pollutants (rhodamine B, methylene blue and tetracycline) were also degraded to evaluate the universality of the CoS2 HNSs/PMS system. The catalytic performance dropped in the presence of chloride, phosphate, nitrate ions and humic acid. Above 97% CIP removal was achieved even in the sixth run. The degradation pathway of CIP was proposed based on HPLC-MS/MS analysis of CIP intermediates, and two new intermediates, namely, C15H18O4N3F (m/z 323) and C29H31O4N6F (m/z 546), were identified for the first time. Both OH center dot and SO4 center dot- were generated and the latter played a key role in CIP degradation.