A self-circulating electro-fenton-like process over Fe₃O₄-CaO₂ cathode for highly efficient degradation of...

Electro-Fenton reaction was limited by the generation of H₂O₂ and the circulation of Fe(Ⅱ)/Fe(Ⅲ). Herein, an efficient electro-Fenton-like process was constructed based on Fe₃O₄-CaO₂ cathode promoted by peroxymonosulfate (PMS). Levofloxacin (LEV) could be efficiently degraded (92.1%) and mineralized with the TOC removal of 74.5% in this self-circulating process. More importantly, the Fe₃O₄-CaO₂ exhibited good stability in the recycles due that CaO₂ was covered by Fe₃O₄, which inhibited the rapid release of H₂O₂. Mechanism analysis indicated that CaO₂ could not only replace H₂O₂ to accelerate the oxidation of Fe(Ⅱ) to Fe(Ⅲ), but also could form complexes with Fe(Ⅲ) and PMS to transfer electrons from ligands to metals, thereby enhancing the reduction of Fe(Ⅲ) to Fe(Ⅱ). As a result, the electrical consumption was significantly reduced, which was only 5.0% of the Fe₃O₄ in electro-Fenton reaction. Meanwhile, the hydrolyzed product of Ca(OH)₂ reacted with Fe(Ⅲ) in the presence of H₂O₂ and converted into CaO₂. Thus, the self-circulation of CaO₂/Ca(OH)₂ and Fe(Ⅲ)/Fe(Ⅱ) was realized, which accelerated the generation of active species, such as, ·OH, O₂·^- and ¹O₂. This work first proposed a self-circulating electro-Fenton-like system and demonstrated the potential application of Fe₃O₄-CaO₂ in the treatment of wastewater.