An enhanced Bi/nZVI activated molecular oxygen process for the degradation of sulfonamide antibiotics in a citrate buffering system.

Citric acid (CA) and sodium citrate (NaCA) have been effectively employed to synergize with bismuth-doped nanoscale zero-valent iron (Bi/nZVI) to degrade sulfonamide antibiotics (SAs) without the need for additional H2O2. In the integrated Bi/nZVI-CA/NaCA system, excellent oxidation activity of sulfamethazine (SM2), sulfadiazine (SD) and sulfamethoxazole (SMX) in the mixed solution was obtained. The bimetallic enhancement alongside ligand complexation significantly promoted Bi/nZVI to catalyze molecular oxygen and was conducive to the spontaneous generation of H2O2. Fe(II)[Cit]- was formed in the CA/NaCA system, and then underwent a Fenton-like reaction with spontaneously produced H2O2 to achieve the oxidation of SAs. Long service life was confirmed by the results of characterization, electrochemical analysis, utilization rate (UR), electronic efficiency (EE) and cycling degradation experiments. In the Bi/nZVI-CA/NaCA system, two comparable degradation pathways (hydroxylation and SO2 extrusion) for SM2, SMX and SD were obtained, while another degradation pathway for SMX was reflected in the opening of the N-O bond on the benzene ring. Additionally, post-reactive solution toxicity was assessed to ensure environmental safety. Overall, our findings provide a theoretical research basis for the effective elimination of SAs from contaminated environments.