Enhancing the decomposition of refractory contaminants on SO₄^2--functionalized iron oxide to accommodate surface SO₄^[rad]- generated via radical transfer from ^[rad]OH

^[rad]OH or SO₄^[rad]− are powerful oxidants that efficiently degrade recalcitrant contaminants. The productions of ^[rad]OH and SO₄^[rad]− via activation of their precursors (H₂O₂ and Na₂S₂O₈), however, can be sustainable only after continuously feeding such precursors into the activators. Motivated by the advantages of SO₄^[rad]− over ^[rad]OH as an environmental cracker, this study highlighted a simple and proficient way to persist solid-supported SO₄^[rad]− species used to accelerate the decomposition of recalcitrants in the presence of an electric potential. While using ubiquiotous iron oxide as a platform to accomodate SO₄^[rad]−, we functionalized iron oxide surface with SO₄^2- species, which could be transformed into surface SO₄^[rad]− species via radical transfer from aqueous ^[rad]OH species. Specifically, a series of SO₄^2--modified iron oxide catalysts were synthesized using SO₂ and O₂ at 300–600 °C in order to vary their surface properties such as the contents of surface Fe^δ+ species acting as H₂O₂ activators to form ^[rad]OH, the contents of surface SO₄^2- species functioning as surface SO₄^[rad]− precursor, and the character of S[sbnd]O bonds innate to SO₄^2- functionalities linked to their long-term stability. In addition to the comparison of energetics between SO₄^2- functionalities and their SO₄^[rad]- analogues via computation, a kinetic assessment of reaction runs were conducted under controlled environments to gather convincing evidence that the formation of surface SO₄^[rad]− via its radical interconversion with aqueous ^[rad]OH was highly plausible and that surface SO₄^[rad]− would be the major decomposer of phenol (model compound of recalcitrants). In addition, 500 °C was found to be the optimized temperature to greatly populate Fe^δ+ and SO₄^2- species rigidly immobilized on iron oxide surface among all temperatures studied, thereby providing the greatest activity and recyclability to degrade phenol.