Peroxymonosulfate-assisted photocatalytic degradation of antibiotic norfloxacin by a calcium-based Ag3PO4 composite in water: Reactivity, products and mechanism

Nowadays, environmental problems caused by residual antibiotics are getting increasing attention. In the present work, peroxymonosulfate (PMS) was firstly employed for the enhanced degradation of norfloxacin (NOF) by a calcium-based Ag3PO4 composite (Ca-Ag3PO4) under visible light irradiation. Experiment results show that NOF removal in Ca-Ag3PO4/PMS/visible light process was higher than the sum of that in Ca-Ag3PO4/visible light and Ca-Ag3PO4/PMS processes. This significant enhancement of NOF removal was mainly due to a synergistic effect between photocatalysis of Ca-Ag3PO4/visible light process and Fenton reaction of Ca-Ag3PO4/PMS process. The inhibitory effects of water quality components on NOF removal followed: Humic acid (HA) > PO43-> HCO3−> NO3−> Cl−. NOF and co-existing heavy metals (ie., Cr(VI) and Ni(II)) or organic compounds like tetracycline (TC) could be simultaneously removed. Both PMS and H2O2 exhibit positive effects on the removal of NOF, but PMS could more effectively improve NOF removal compared with H2O2. An excellent PMS decomposition had been achieved in Ca-Ag3PO4/PMS/visible light process. HO•, SO4•− and 1O2 all took part in NOF degradation by Ca-Ag3PO4/PMS/visible light process, but both HO• and SO4•− might be primary species for NOF degradation. A plausible degradation pathway of NOF in Ca-Ag3PO4/PMS/visible light process was thereby proposed to proceed through ring-opening cracking hydroxylation and elimination reactions reactions. The enhanced reaction mechanism for the degradation of NOF in Ca-Ag3PO4/PMS/visible light process was also proposed.