CuFe3O4@ZIF-2 with oxygen vacancies and multiple reactive sites to efficiently activate peroxymonosulfate for levofloxacin degradation

In this work, CuFe3O4@ZIF-X (X = 1,2,3,4 and 5) composite catalysts with oxygen vacancies and multiple reactive sites were synthesized for the first time by Cu-doped Fe3O4-supported ZIF-X and used to efficiently activate PMS for levofloxacin (LEV) degradation. Influencing factors on LEV degradation were investigated, including the amount of CuFe3O4, pH, catalyst dosage, PMS concentration, coexisting inorganic anions and natural organic matter. In the presence of 1 mM PMS and 40 mg/L CuFe3O4@ZIF-2, 98% removal of LEV (10 mg/L) and 47% mineralization could be achieved within 10 min. The rate constants of CuFe3O4@ZIF-2/PMS were 2.9 times and 4.3 times those of ZIF and Fe3O4@ZIF, respectively. Further investigation found that the introduction of Cu-doped Fe3O4 onto ZIF significantly ameliorates the problem of the reduced catalytic performance of magnetic MOFs due to the high saturation magnetization intensity and severe hindrance of the active sites. Then, the mechanism of LEV degradation, including radical and nonradical pathways, was expounded. Furthermore, the intermediates of LEV degradation were identified, and five possible degradation pathways were proposed. CuFe3O4@ZIF-2 demonstrated a decent catalytic performance even after five consecutive recycles and low metal ion leaching after LEV degradation, greatly improving the problem of secondary contamination.