Co(CO3)0.5(OH)•0.11H2O as superior peroxymonosulfate activator for ciprofloxacin degradation via co-acting mechanism of low & high-valent cobalt and oxygen vacancy

Abstract

In this study, oxygen vacancies-rich (OVs-rich) Co(CO3)0.5(OH)•0.11H2O catalyst was prepared by a hydrothermal process, which was used to activate peroxymonosulfate (PMS) and degrade ciprofloxacin (CIP). Although its specific surface area was only 46.2 m2 g−1, the Co(CO3)0.5(OH)•0.11H2O catalyst exhibited high performance. Under its natural pH, 91.0% of CIP (50 ppm) was degraded and chemical oxygen demand removal reached 70% in 10 min. The rapid degradation reaction followed Behnajady-Modirshahla-Ghnbery kinetic model. The research on catalytic mechanism indicated that three coexisting catalytic pathways resulted in the efficient degradation of CIP. (1) The low-valent Co2+ in Co(CO3)0.5(OH)•0.11H2O activate PMS to generate four kinds reactive oxygen species such as SO4•−, •OH, O2•− and 1O2. (2) The dissolved oxygen was adsorbed on Co(CO3)0.5(OH)•0.11H2O surface and the abundant localized electrons of OVs made them easily endow electrons to O2, reducing O2 to O2•− and then to 1O2. (3) The reaction between the Co2+ and PMS resulted in the high-valent Co4+(O) species, which possessed outstanding oxidation ability for CIP degradation.