Insight into the activation mechanism of sulfite over amorphous Fe1-xCoxS: Key role of Fe3+/Fe2+ self-cycling and oxysulfur radicals generation

Abstract

Sulfite activation has been considered as a promising advanced oxidation technique for treating organic pollutants in water. In this work, a series of cobalt-doped FeS (Fe1-xCoxS) samples were synthesized via ultrasonic-assisted precipitation route and applied them in sulfite activation and Rhodamine B (RhB) removal in water at the same time, and their physical properties were characterized by XRD, SEM, TEM, XPS and electrochemical analysis. Benefiting from its high electron density, low corrosion voltage and impedance that beneficial to accelerate the electron transfer rate in the Fe1-xCoxS/sulfite system and the reducing sulfur species rich in electrons which beneficial to promote the self-cycling of Fe3+/Fe2+, the activity of Fe1-xCoxS for sulfite activation on the RhB removal was better than that of FeS in both acidic and neutral conditions. The redox cycle of metal ions on the surface of Fe1-xCoxS efficiently triggered sulfite activation. The hydroxyl radical (·OH), resulting from the conversion of oxysulfur radicals, plays a crucial role in the degradation of RhB. Additionally, a non-radical activation pathway of sulfite has been proposed. The present study provided a new idea and effective strategy for sulfite activation to environmental removal of organic matter in water.