Synergistic effect of PMS activation by Fe-0@Fe3O4 anchored on N, S, O co-doped carbon composite for degradation of sulfamethoxazole

High efficient activator is highly desired in the field of persulfate-based advanced oxidation process. In comparison with the previous studies, this study adopted nitrogen, sulfur and oxygen co-doped carbon material to support Fe-0 encapsulate in Fe3O4 to prepare iron-based modified carbon composite (Fe-0@Fe3O4-MC) by a facile two-step pyrolysis. Fe-0@Fe3O4-MC was then used for degradation of sulfamethoxazole. The results showed that Fe-0@Fe3O4-MC had superior catalytic activity for PMS activation due to the synergistic effect of iron-based compound and modified carbon. In the presence of 0.1 g/L of Fe-0@Fe3O4-MC, SMX (0.04 mM) could be completely degraded within 120 mM at pH 3.4 and 3 mM of PMS. The SMX degradation followed pseudo first-order kinetic model, with the rate constant of 0.12 min(-1), and the mineralization of SMX achieved 48.4%. Sulfate radicals dominated in the SMX degradation. In addition to Fe-0 and Fe3O4, carbon defects, graphitic N, sulfur and FeN4 also contributed to PMS activation. Fe-0 oxidation was the rate-limiting step for PMS activation. Dissolved oxygen made a minor contribution to Fe-0 oxidation. The intermediate products of SMX degradation were identified, and two pathways of SMX degradation were proposed. The influencing factors on SMX degradation were studied, including pH, temperature, PMS concentration, Fe-0@Fe3O4-MC dosage, chloridion, carbonate and humic acids, and the influencing mechanism was discussed. This study could provide an efficient PMS activator for the degradation of emerging organic pollutants in water and wastewater.