Degradation of iopamidol by silicate-based microfiltration membrane activated peroxymonosulfate in aqueous solution: Efficiency, mechanism and degradation pathway

Iopamidol (IPM) was frequently detected in drinking water and effluents from wastewater treatment plants (WWTPs). A silicate-based microfiltration membrane (SFM) was successfully synthesized using silicate cement as raw material and pore-forming agent. In this study, peroxymonosulfate (PMS) was activated by SFM for the first time to effectively degrade and mineralize IPM. The removal efficiency and mineralization rate of IPM were 99.7% and 49.5% respectively within 30 min in the SFM/PMS process, which were higher than those obtained by PMS oxidation only (12.8% and 1.26%) and SFM adsorption (negligible). The effects of solution pH, PMS dosage, reaction temperature, natural organic matter (NOM), chloride ion (Cl−), bicarbonate (HCO− 3), and water matrixes on the degradation of IPM were systematically evaluated. Based on radical inhibition examinations and X-ray photoelectron spectroscopy (XPS) analysis, the potential activation mechanism was elucidated. It was found that the Fe(II) and alkaline hydration products on the surface of SFM could promote the activation of PMS. Radical scavenging tests and electron spin resonance (ESR) experiments suggested that hydroxyl radicals (•OH), sulfate radicals (SO4·−), singlet oxygen (1O2) and superoxide radicals (O2·−) generated in SFM/PMS system played a critical role for IPM degradation. Finally, eleven intermediates in the degradation process of IPM were identified and five degradation pathways were proposed, mainly including hydroxyl oxidation, amide hydrolysis, amino oxidation, hydroxyl substitution and dehydroxylation. The results show that the SFM/PMS process with its excellent catalytic activity is a promising strategy for effectively removing and mineralizing organic contaminants.