Unraveling the contribution of Co(IV)and free radicals in Co^(2+)-activated Peroxymonosulfate process:Reaction mechanism,degradation pathway,and DFT calculation

The Co^(2+)and Peroxymonosulfate(PMS)reaction is a highly regarded advanced oxidation process(AOP)that has been extensively researched.The consensus regarding the relative contribution of reactive species in the Co2+/PMS system under different pH conditions has not been established.In this study,quenching experiments and electron spin resonance(ESR)tests demonstrated the coexistence of Co(IV),sulfate radical(SO_(4)^(•-)),hydroxyl radical(•OH),and singlet oxygen(1O2),and there fell to CBZ degradation were Co(IV)>SO_(4)^(•-)->•OH≈1O2 in the optimal conditions,where almost 100%of CBZ was degraded in the Co2+/PMS system within 30 min.Furthermore,Cl−would suppress the formation of Co(IV),SO_(4)^(•-),and•OH but enhance the yield of 1O2,thereby showing a trend of inhibiting CBZ degradation.The probe compound used in this study was Methyl Phenyl Sulfoxide(PMSO),while methyl phenyl sulfone(PMSO_(2))as the indicator of Co(IV),the generation efficiency of PMSO_(2)(η'[PMSO_(2)])increased with reaction time and reached 70%–98%at 40 min at all set pH values(3,4,6,and 8).These results suggest that Co(IV)played a significant role in the Co^(2+)/PMS system and its importance became more pronounced as the reaction progressed.PMSO probe and SO_(4)^(•-)quantification experiments jointly revealed that Co(IV)had the greatest performance at pH 4,and compared to other pH values,SO_(4)^(•-)had the largest contribution in the initial stage of the reaction at pH 6.The Ecological Structure Activity Relationships(ECOSAR)software was utilized to predict the toxicity of the degradation by-products.Additionally,luminescent bacteria experiments were conducted to assess the acute toxicity of the reaction solution.The results of these experiments demonstrated that the Co^(2+)/PMS process exhibited a remarkable ability to detoxify the solution.