Removal of levofloxacin by H2O2 and PMS co-activation by sulfide-supported oxalate zero-valent iron enhanced with simultaneous catalysis of SO4-• and 1O2: Major free radicals, synergistic effects and mechanism exploration

It is reported in the literature that sulfide and oxalate are promising ways to modify zero-valent iron (ZVI) for the degradation of antibiotics, but the synergistic activation mechanism of H2O2 and PMS is still unclear. In order to explore this effect, a new type of oxalated and sulfided ZVI (OA-S-ZVI) was synthesized in this study, and levofloxacin (LEV) was degraded in H2O2, PMS and H2O2/PMS systems. The batch experiments confirmed that the removal ability of OA-S-ZVI/H2O2/PMS was 1.65–10 times that of other systems. This result was achieved by modifying ZVI surface catalytic sites and cooperating with H2O2/PMS. At the same time, the synergistic factor S (1.74) confirmed that the composite system H2O2/PMS can capture electrons from the catalyst Fe0 to Fe2+ and adsorb active sites of the catalyst, such as ≡Fe-C2O4-, ≡Fe-OH/OOH and ≡Fe-S. Further calculation and analysis revealed that the binding energy of singlet oxygen (1O2) and sulfate radical (SO4-•) in the composite system decreased and multiple molecular orbitals participated in the removal process. The characterization experiments and EPR experiments explained the transfer free radicals to non-free radicals from a single system to a composite system. This study provides a new perspective on modifying ZVI and utilizing multi-system synergy to effectively remove organic micropollutants from water.