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 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.