Persulfate Oxidation of Sulfamethoxazole by Magnetic Iron-Char Composites via Nonradical Pathways: Fe(IV) Versus Surface-Mediated Electron Transfer.

Abstract

Despite the vital roles of reactive radical species in the coupled iron-carbon composite/persulfate (PS) system for eliminating pollutants, nonradical contributions are typically overlooked. Herein, we developed two efficient magnetic iron-char composites via low-temperature (BCFe-400) and high-temperature (BCFe-700) pyrolysis. The two composites activated PS through nonradical pathways for sulfamethoxazole (SMX) degradation. In the BCFe-400/PS system, high-valent iron Fe(IV) was the dominant active species for the oxidation, evidenced by methyl phenyl sulfoxide-based probe tests, Mössbauer spectroscopy, and in situ Raman analyses with kinetic evaluation. In the BCFe-700/PS system, surface-mediated electron transfer dominated the oxidation, and the nonradical regime was probed by the electrochemical test and in situ Raman analysis. Furthermore, the BCFe-400/PS system maintained high efficiency in continuous degradation of SMX due to the feasible Fe2+generation toward Fe(IV) formation. In the BCFe-700/PS system, the stability of the system was limited due to the hindered electron transfer between the surface reactive complex (i.e., BCFe-700-PS*) and SMX, and thermal treatment would help recover the reactivity. Both BCFe-400/PS and BCFe-700/PS systems exhibited high performances for SMX removal in the presence of chloride and humic acid and in real water matrixes (e.g., seawater, piggery wastewater, and landfill leachate), exhibiting the great merits of the nonradical system. Overall, the study would provide new insights into PS activation by iron-loaded catalysts to efficiently degrade pollutants via nonradical pathways.