Efficient sulfite activation with Mn(II)-doped γ-Fe2O3 enriched by surface oxygen vacancy for rapid iohexol abatement

[Display omitted] •Manganese species is doped into γ-Fe2O3 for surface oxygen vacancy regulation.•The Mn-γ-Fe2O3/sulfite process achieves an effective iohexol removal.•SO4•− and HO• is responsible for the iohexol abatement.•The oxygen vacancy and > Mn(II) can accelerate the > Fe(II)/Fe(III) transformation. Advanced oxidation processes (AOPs) based on sulfite activation have been demonstrated to achieve cost-effective and highly efficient abatement of organic pollutants. In this work, the manganese-doped γ-Fe2O3 catalyst (Mn-γ-Fe2O3) is constructed based on the properties of Mn(II) with surface oxygen vacancy regulation and as an active site for sulfite activation. The increase of the Mn(II) doping ratio is favorable for the generation of surface oxygen vacancy with the content being enhanced more than two times when the Mn(II) doping ratio is 0.09 compared with that of γ-Fe2O3. The iohexol (IOX) abatement efficacy by sulfite activation with Mn-γ-Fe2O3 is positively correlated with the oxygen vacancy content, in which SO4•− is the major free radical responsible for IOX degradation and HO• plays a secondary role. The presence of surface oxygen vacancy on the Mn-γ-Fe2O3 exhibits low electrochemical resistance. The theoretical calculations support the enhancement of the electron transfer between Mn-γ-Fe2O3 and sulfite with more negative adsorption energy and strong interaction of iron and manganese atoms. By analyzing the valence variation before and after the reaction, both > Mn(II) and > Fe(III) can participate in the acceleration of sulfite autoxidation process to generate radicals. Application of surface oxygen vacancy enriched Mn-γ-Fe2O3 for sulfite activation exhibits good adaptability to different real water matrices and thus have some potential for practical applications.