Identification of Superoxide Contribution through the Quenching Method and Model System

Abstract

The quenching method is widely utilized to evaluate the contribution of reactive species; however, its validity has recently been questioned. The primary role of superoxide (O₂^•–) in pollutant degradation remains controversial due to its low reactivity. To ascertain the suitability of the quenching method and the degradation ability of O₂^•–, a simple and efficient O₂^•– generation system was built using p-benzoquinone (p-BQ) as the probe with disodium hydrogen phosphate–dimethyl sulfoxide (DHP–DMSO). The results demonstrated that O₂^•– is accountable for p-BQ transformation in DHP–DMSO, and can also be generated in various alkaline-organic solvent (methanol, ethanol, iso-propanol, tert-butanol, acetonitrile, acetone, chloroform, and tetrahydrofuran) systems, revealing that these reagents do not scavenge O₂^•–. Superoxide dismutase has limited ability on O₂^•– quenching in the presence of hydroxyl radicals (^•OH). Some organic solvents can produce organic radicals when stimulated by ^•OH. This serves as a reminder to exercise caution when employing these quenchers. O₂^•– exhibited insufficient degradation capability for the majority of the eight organic pollutants tested. The relevance of O₂^•– in pollutant degradation can be quickly discerned by DHP–DMSO. This study holds significant importance in accurately evaluating the contribution of reactive species.