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 (Co3O4) activated peroxymonosulfate (PMS) system was extensively studied due to its excellent catalytic performance. However, the relatively high cobalt (Co2+) leaching (up to 2 mg/L) would pose high ecotoxicological risks. Herein, we identified the existence of Co(OH)2 on the surface of Co3O4 were the major source of Co2+ leaching in the Co3O4 activated PMS system. Furthermore, the Co2+ leaching was effectively suppressed by converting Co(OH)2 to Co3O4 via pyrolysis treatment. In addition, reduced graphene oxide (rGO) was engaged to enhance the degradation performance of antibiotics in the Co3O4 activated PMS system. The oxygen functionalities of rGO would catalyze PMS to generate sulfate radicals (SO4−) and trigger the non-radical pathway of singlet oxygen (1O2). We have achieved outstanding catalytic performance for carbamazepine (CAZ) degradation with low Co2+ 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 1O2 and SO4−. We have provided a simple approach to inhibit the Co2+ leaching and enhance the catalytic performance of Co3O4 activated PMS system for the effective control of antibiotics.