Effective sulfite activation with atomically dispersed cobalt loaded SBA-15 for iohexol abatement

Abstract

Cobalt-based heterogeneous catalysts receive research interests in the sulfite activation to generate reactive radicals for abatement of organic contaminants in the aquatic environments, yet the sulfite activation efficacy is compromised by the limited utilization of available active cobalt sites. To address this problem, the atomically dispersed cobalt loaded on mesoporous silica SBA-15 (simplified as Co/SBA-15) is constructed for sulfite activation process regarding the incorporation of cobalt species into the confined space abundant with silicon hydroxyl groups in SBA-15. Co/SBA-15 exhibits excellent sulfite activation efficacy, in which iohexol can be completely degraded within 30 min. Sulfate radical (SO4•−) and hydroxyl radical (HO•) are the dominant reactive radicals responsible for iohexol abatement, in which 7.15 μM of SO4•− and 2.23 μM of HO• are produced. The excellent electron transfer efficiency of Co/SBA-15 is demonstrated by electrochemical impedance spectroscopy (EIS). Structural characterization and valence analysis suggest that the formation of atomically dispersed cobalt species facilitates the sulfite activation and Lewis acid sites on Co/SBA-15 can adsorb organic molecular fragments to realize the rapid conversion from >Co(III) to >Co(II) by electron transfer. The iohexol degradation pathways are also proposed based on UPLC-QTOF-MS analysis. In addition, the effects of various influencing factors including the reactant dosage, coexisting anions, humic acid and the different real water backgrounds on iohexol abatement are systematically investigated. This study is expected to provide an efficient heterogeneous catalyst for sulfite activation to achieve the rapid abatement of organic contaminants.