An anode fabricated by Co electrodeposition on ZIF-8/CNTs/CF for peroxymonosulfate (PMS) activation

A Co@ZIF-8/CNTs-CF anode for PMS activation was prepared by Co electrodeposition on carbon felt (CF) modified with ZIF-8 and carbon nanotubes (CNTs). The results showed that the fabricated Co@ZIF-8/CNTs-CF anode was an effective peroxymonosulfate (PMS) activator toward tetracycline (TC) removal. Compared with that in reaction system of bare CF anode + PMS, the reaction system of Co@ZIF-8/CNTs-CF anode + PMS exhibited 3.08 times decrease in the activation energy demanded and 4.21 times increase in the reaction rate constant (k), resulting in a kinetic favorable process of PMS activation by the Co@ZIF-8/CNTs-CF anode. The enhanced activation performance of the fabricated anode was ascribed to the high contents of the pyrrolic N and low valence state of Co in the Co@ZIF-8/CNTs-CF anode. Furthermore, the influence factors on the characteristics of transformation among the generated reactive species during the anodic PMS activation process were comprehensively investigated by the quenching experiments and the electron paramagnetic resonance (EPR) tests. The results showed that the SO₄^•- and reactive oxygen-containing reactive species (O₂^•- and ¹O₂) were generated during the activation of PMS by anode and became the major contributors toward TC removal. The production of ¹O₂ was through the dismutation of O₂^•-. In addition, the EPR experiments demonstrated that O₂^•- was generated mainly through the anodic PMS activation but the electrochemically driven molecular oxygen reduction reaction (ORR) process. The fabricated Co@ZIF-8/CNTs-CF anode for PMS activation provided a reference for the wastewater treatment based on the electrochemical advanced oxidation processes (EAOPs).