The overlooked role of Co(OH)2 in Co3O4 activated PMS system: Suppression of Co2+ leaching and enhanced degradation performance of antibiotics with rGO

Cobalt oxide (Co 3 O 4 ) activated peroxymonosulfate (PMS) system was extensively studied due to its excellent catalytic performance. However, the relatively high cobalt (Co 2+ ) leaching (up to 2 mg/L) would pose high ecotoxicological risks. Herein, we identified the existence of Co(OH) 2 on the surface of Co 3 O 4 were the major source of Co 2+ leaching in the Co 3 O 4 activated PMS system. Furthermore, the Co 2+ leaching was effectively suppressed by converting Co(OH) 2 to Co 3 O 4 via pyrolysis treatment. In addition, reduced graphene oxide (rGO) was engaged to enhance the degradation performance of antibiotics in the Co 3 O 4 activated PMS system. The oxygen functionalities of rGO would catalyze PMS to generate sulfate radicals (SO 4 − ) and trigger the non-radical pathway of singlet oxygen ( 1 O 2 ). We have achieved outstanding catalytic performance for carbamazepine (CAZ) degradation with low Co 2+ leaching, as CAZ (5 mg/L) could be completely degraded in 30 min. Combining experimental investigation and theoretical calculation, we also revealed the degradation pathways and mechanisms that CAZ would be oxidized and detoxified by 1 O 2 and SO 4 − . We have provided a simple approach to inhibit the Co 2+ leaching and enhance the catalytic performance of Co 3 O 4 activated PMS system for the effective control of antibiotics.