Defect-engineered Mn–Fe₂O₃ catalysts enable heterogeneous Fe^IV=O formation for enhanced Fe(VI)/H₂O₂ oxidation of organic pollutants

Iron-based catalysts are generally used to activate oxidizing species, such as hydrogen peroxide by increasing homogeneous active substances like free radicals, to promote the degradation of organic matter. However, less attention has been paid to the reactions on the surface or the generation of heterogeneous metal-oxo species. Herein, oxygen vacancies (Vo) were introduced into Fe oxides by a calcination-induced hetero-atom doping modification. The characteristic peak of the heterogeneous hypervalent iron-oxo [≡Fe^IV=O] species in the UV–Vis spectrum at 371 nm was observed. In the context of electrochemical experiment, Vo-rich Mn-Fe₂O₃ significantly enhanced the electron conduction of sulfamethoxazole and H₂O₂, while simultaneously inhibiting the self-decomposition of potassium ferrate (Fe(VI)). Regarding the H₂O₂ generated during the self-decomposition process of Fe(VI), Vo-rich Mn-Fe₂O₃ can accelerate the degradation of sulfamethoxazole, increasing the reaction rate to 0.1081 min⁻¹ (with a 30.05 % improvement in removal efficiency). Density functional theory calculations indicate that Vo leads to an enhanced capture of O atoms by the low-coordinated Fe atoms, promoting the anchoring of H₂O₂ and the formation of the active ≡Fe^IV=O with a higher spin state. This work proposes heterogeneous reactive species on the surface of metal oxidase, constructing Vo as the O atom capture sites in iron-based oxides to facilitate the formation of ≡Fe^IV=O and the degradation of organic compounds.