Simultaneous degradation of amoxicillin and norfloxacin by TiO2@nZVI composites coupling with persulfate: Synergistic effect, products and mechanism

Abstract

• Persulfate (PS) significantly enhanced AMX removal by TiO 2 @nZVI/UV process. • The decomposition rate of PS in TiO 2 @nZVI/PS/UV process was the highest. • Both HO• and SO 4 •− were the dominant radicals in TiO 2 @nZVI/PS/UV process. • AMX was effectively degraded through hydroxylation and deamination reactions. • A mechanism for the simultaneous removals of AMX and NOF was proposed. In recent years, a serious threat of antibiotic residues in aquatic environments to human health and ecological security has become increasingly widespread attention. In this study, this is the first report on an alternative strategy on enhanced degradation of amoxicillin (AMX) and norfloxacin (NOF) by TiO 2 @nZVI/persulfate (PS) process under UV irradiation. Results revealed that a signficantly synergistic effect on AMX degradation had been achieved in TiO 2 @nZVI/PS/UV process due to the photocatalysis and Fenton-like reactions. NO 3 – , HCO 3 – , PO 4 3- and humic acid exhibited inhibitory effects on AMX degradation, whereas Cl - was negligible on that. The degradation of AMX decreased as the addition of Cr(VI) concentrations increased, whereas the correspond values were enhanced when a low Cu(II) concentration was introduced. TiO 2 @nZVI/PS/UV process was the most efficient for activating PS decomposition. HO•, SO 4 •− and 1 O 2 were all generated in TiO 2 @nZVI/PS/UV process, but HO• and SO 4 •− were the dominant radical species for AMX degradation. The AMX intermediates products identified by LC-MS system confirmed AMX was effectively degraded through hydroxylation and deamination reactions. A better performance on the simultaneous removals of AMX and NOF by TiO 2 @nZVI/PS/UV process could be achieved at lower concentration conditions, and the simultaneous reaction mechanism was thereby proposed base on expriment results.