Enhancing the decomposition of refractory contaminants on SO42--functionalized iron oxide to accommodate surface SO4 center dot - generated via radical transfer from (OH)-O-center dot

Abstract

(OH)-O-center dot or SO4 center dot- are powerful oxidants that efficiently degrade recalcitrant contaminants. The productions of (OH)-O-center dot and SO4 center dot- 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 center dot- over (OH)-O-center dot as an environmental cracker, this study highlighted a simple and proficient way to persist solid-supported SO4 center dot- 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 center dot-, we functionalized iron oxide surface with SO42- species, which could be transformed into surface SO4 center dot- species via radical transfer from aqueous (OH)-O-center dot species. Specifically, a series of SO42--modified iron oxide catalysts were synthesized using SO2 and O-2 at 300-600 degrees C in order to vary their surface properties such as the contents of surface Fe delta+ species acting as H2O2 activators to form (OH)-O-center dot, the contents of surface SO42- species functioning as surface SO4 center dot- precursor, and the character of S-O bonds innate to SO42- functionalities linked to their long-term stability. In addition to the comparison of energetics between SO42- functionalities and their SO4 center dot - analogues via computation, a kinetic assessment of reaction runs were conducted under controlled environments to gather convincing evidence that the formation of surface SO4 center dot- via its radical interconversion with aqueous (OH)-O-center dot was highly plausible and that surface SO4 center dot- would be the major decomposer of phenol (model compound of recalcitrants). In addition, 500 degrees C was found to be the optimized temperature to greatly populate Fe delta+ and SO42- species rigidly immobilized on iron oxide surface among all temperatures studied, thereby providing the greatest activity and recyclability to degrade phenol.