Enhancing the decomposition of refractory contaminants on SO42--functionalized iron oxide to accommodate surface SO4- generated via radical transfer from OH
Abstract OH or SO 4 − are powerful oxidants that efficiently degrade recalcitrant contaminants. The productions of OH and SO 4 − via activation of their precursors (H 2 O 2 and Na 2 S 2 O 8 ), however, can be sustainable only after continuously feeding such precursors into the activators. Motivated by the advantages of SO 4 − over OH as an environmental cracker, this study highlighted a simple and proficient way to persist solid-supported SO 4 − 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 SO 4 − , we functionalized iron oxide surface with SO 4 2- species, which could be transformed into surface SO 4 − species via radical transfer from aqueous OH species. Specifically, a series of SO 4 2- -modified iron oxide catalysts were synthesized using SO 2 and O 2 at 300–600 °C in order to vary their surface properties such as the contents of surface Fe δ + species acting as H 2 O 2 activators to form OH, the contents of surface SO 4 2- species functioning as surface SO 4 − precursor, and the character of S O bonds innate to SO 4 2- functionalities linked to their long-term stability. In addition to the comparison of energetics between SO 4 2- functionalities and their SO 4 - analogues via computation, a kinetic assessment of reaction runs were conducted under controlled environments to gather convincing evidence that the formation of surface SO 4 − via its radical interconversion with aqueous OH was highly plausible and that surface SO 4 − 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 SO 4 2- species rigidly immobilized on iron oxide surface among all temperatures studied, thereby providing the greatest activity and recyclability to degrade phenol.