Surface-bound radicals enhancing detoxification of enrofloxacin during peroxymonosulfate oxidation: Activated carbon vs. alumina as catalyst carriers

Recent studies have found the presence of surface-bound radicals (Surf-R) during the heterogeneously catalyzed peroxymonosulfate (PMS), especially when the catalyst carriers possess a high adsorption capacity. However, the effects of Surf-R on the toxicity of transformation products (TPs) are still not well elucidated. In this study, Co and Mn were loaded onto commonly used carriers: activated carbon and alumina (CoMn@AC vs CoMn@Al2O3) to create comparable catalytic centers but distinct adsorption capacity, which was proved by material characterization (SEM, EDS, BET, XPS), adsorption and catalytic tests. Both images and quantitative analysis with 3D excitation-emission matrix fluorescence spectroscopy demonstrated that the reaction solutions of enrofloxacin from two catalysts composed differently when a same degradation efficiency was achieved. It was further found that the respiratory inhibition of CoMn@AC catalyzed samples was only 7~36% of the counterpart. 50 TPs were identified with UPLC-MS/MS, among which 31 TPs were possibly more toxic than enrofloxacin according to the calculation with the Toxicity Estimation Software Tool. CoMn@Al2O3 produced 14 unique toxic TPs while CoMn@AC only 4. The analysis with EPR revealed that both catalysts generated SO4•-, •OH, and 1O2; quenching tests proved a lot of Surf-R with CoMn@AC but not with CoMn@Al2O3. This study demonstrates the high potential of Surf-R to enhance the detoxification of organic contaminants during PMS oxidation and thus provides a reference for designing novel catalysts to achieve efficient contaminant degradation and detoxification.