Mechanistic insights into rapid sulfite activation with cobalt sulfide towards iohexol abatement: Contribution of sulfur conversion

Abstract

Recently, activation of sulfite for production of sulfate radical (SO4•−) has emerged for abatement of organic contaminants. Herein, with regard to the excellent activation efficacy of Co(II) and the enhanced electron donating capacity by sulfur species, cobalt sulfide (CoS) was proposed for efficient sulfite activation towards iohexol abatement via SO4•−–based advanced oxidation processes. CoS exhibited better activation performance than typical CoO and Co3O4 with a sharp decline of iohexol within 0.5 min, for which superior electron transfer efficiency of CoS was confirmed by Electrochemical impedance spectroscopy (EIS). The contribution of SO4•− and HO• to iohexol abatement was demonstrated by radical quenching experiment and Electron paramagnetic resonance (EPR). The influences of various parameters (solution pH, CoS and sulfite dosage, iohexol concentration), co-existing anions (HCO3−, HPO42−, Cl− and NO3−) and humic acid on iohexol abatement were investigated, as well as, the effect of different water matrixes on iohexol abatement was also evaluated. A possible mechanism was proposed based on ionic strength experiment, Transmission electron microscope-Energy dispersive spectrometer (TEM-EDS), X-ray photoelectron spectroscopy (XPS) and Raman. The superior activation performance of CoS could be attributed to the inner-sphere complexation between CoS and sulfite and enhanced > Co(III)/>Co(II) recycling induced by reductive sulfur species via rapid electron transfer. In addition, the iohexol degradation pathways were analyzed. This study highlights the contribution of sulfur conversion in the sulfite activation process and is expected to provide a facile CoS enhanced sulfite activation method for efficient abatement of organic contaminants.