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

Electro-Fenton reaction was limited by the generation of H 2 O 2 and the circulation of Fe(Ⅱ)/Fe(Ⅲ). Herein, an efficient electro-Fenton-like process was constructed based on Fe 3 O 4 –CaO 2 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 Fe 3 O 4 –CaO 2 exhibited good stability in the recycles due that CaO 2 was covered by Fe 3 O 4 , which inhibited the rapid release of H 2 O 2 . Mechanism analysis indicated that CaO 2 could not only replace H 2 O 2 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 Fe 3 O 4 in electro-Fenton reaction. Meanwhile, the hydrolyzed product of Ca(OH) 2 reacted with Fe(Ⅲ) in the presence of H 2 O 2 and converted into CaO 2 . Thus, the self-circulation of CaO 2 /Ca(OH) 2 and Fe(Ⅲ)/Fe(Ⅱ) was realized, which accelerated the generation of active species, such as, ·OH, O 2 · - and 1 O 2 . This work first proposed a self-circulating electro-Fenton-like system and demonstrated the potential application of Fe 3 O 4 –CaO 2 in the treatment of wastewater.