Synthesis of magnetic core-shell Fe3O4-Mn3O4 composite for degradation of sulfadiazine via peroxymonosulfate activation: Characterization, mechanism and toxicity analysis

Sulfate radical based AOPs (SR-AOPs) have been utilized as a promising technology for refractory organic pollutants treatment. In this research, a novel magnetic core-shell Fe3O4-Mn3O4 composite was fabricated through a two-step hydrothermal method and then its surface structure, morphology and magnetism were characterized. The composite was introduced for efficient degradation of sulfadiazine (SDZ) via peroxymonosulfate (PMS) activation. Compared with pure Fe3O4 and Mn3O4, Fe3O4-Mn3O4 exhibited higher catalytic performance to eliminate SDZ. In the batch experiments, 20 μM of SDZ could be completely removed in 20 min with 0.8 mM PMS, 0.15 g/L catalyst dosage under a pH scope of 3.0–11.0. Both Cl¯ and H2PO4¯ displayed slightly inhibition effect on SDZ degradation efficiency, while HA could significantly reduce the degradation efficiency. In the successive tests, Fe3O4-Mn3O4 exhibited outstanding stability and good reusability. Even after four runs, the SDZ degradation efficiency still reached to 94.3%. Scavenging tests and electron paramagnetic resonance (EPR) results revealed that the active species formed during the Fe3O4-Mn3O4/PMS system were SO4• and •OH. The degradation mechanism was proved to be the redox reactions between Mn(Ⅱ)/Mn(Ⅲ)/Mn(Ⅳ), Fe(Ⅱ)/Fe(Ⅲ) and the synergistic effect of Mn(Ⅲ)/Fe(Ⅱ). Moreover, six intermediates were detected and three possible SDZ degradation pathways in the Fe3O4-Mn3O4/PMS system were explored. The toxicity of SDZ and intermediates were evaluated by ECOSAR program as well.