Distinct pathways for superoxide radical generation induced by Mn and Cu-based catalysts in electro-Fenton like...

Superoxide radicals (·O₂^-) has been regarded as one of the reactive oxygen species (ROS) for the elimination of complex contaminants via electro-Fenton like (EF-like) technology. However, the generation path of ·O₂^- is diverse, and the influence of the physicochemical properties of metals on the mechanism of ·O₂^- conversion is significant in the EF-like treatment of wastewater. Herein, metals (M = Mn, Cu) loaded zeolitic imidazolate frameworks catalytic materials (M-NC) were prepared for sulfamethoxazole (SMX) removal to analyze the effect of metals on the pathways of ·O₂^- generation. The removal kinetic rate of SMX by Cu-NC was 1.32 times higher than that of Mn-NC. Quenching experiments demonstrated that ·O₂^- is the most important oxidizing species to achieve SMX removal. The RRDE measurements and quantitative experiment on the concentration of H₂O₂ experiments indicated that Mn-NC was more inclined to generate ROS through activation of H₂O₂ and Cu-NC through other ways. Therefore, the transformation pathways of ·O₂^- in different catalytic systems were thoroughly analyzed. Electron paramagnetic resonance test and reactive oxygen species quenching experiments indicated that the pathway for ·O₂^- production of Mn-NC was O₂ → H₂O₂ → ·O₂^-, and that of Cu-NC was O₂ → ·O₂^-. The strategy of using Mn and Cu-based catalysts to investigate the mechanism of the ·O₂^- generation pathway provided a way to efficiently utilize the conversion of ·O₂^-.