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

Superoxide radicals (·O 2 − ) 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 ·O 2 − is diverse, and the influence of the physicochemical properties of metals on the mechanism of ·O 2 − 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 ·O 2 − generation. The removal kinetic rate of SMX by Cu–NC was 1.32 times higher than that of Mn–NC. Quenching experiments demonstrated that ·O 2 − is the most important oxidizing species to achieve SMX removal. The RRDE measurements and quantitative experiment on the concentration of H 2 O 2 experiments indicated that Mn–NC was more inclined to generate ROS through activation of H 2 O 2 and Cu–NC through other ways. Therefore, the transformation pathways of ·O 2 − in different catalytic systems were thoroughly analyzed. Electron paramagnetic resonance test and reactive oxygen species quenching experiments indicated that the pathway for ·O 2 − production of Mn–NC was O 2 → H 2 O 2 → ·O 2 − , and that of Cu–NC was O 2 → ·O 2 − . The strategy of using Mn and Cu-based catalysts to investigate the mechanism of the ·O 2 − generation pathway provided a way to efficiently utilize the conversion of ·O 2 − .