Synergistic effect of PMS activation by Fe0@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 Fe0 encapsulate in Fe3O4 to prepare iron-based modified carbon composite (Fe0@Fe3O4-MC) by a facile two-step pyrolysis. Fe0@Fe3O4-MC was then used for degradation of sulfamethoxazole. The results showed that Fe0@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 Fe0@Fe3O4-MC, SMX (0.04 mM) could be completely degraded within 120 min 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 Fe0 and Fe3O4, carbon defects, graphitic N, sulfur and FeN4 also contributed to PMS activation. Fe0 oxidation was the rate-limiting step for PMS activation. Dissolved oxygen made a minor contribution to Fe0 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, Fe0@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.