Mechanism insight into the photocatalytic degradation of fluoroquinolone antibiotics by the ZIF-8@Bi2MoO6 heterojunction

This work reports a comprehensive study on the mechanisms for material formation, charge separation, persulfate activation, and photocatalytic degradation of fluoroquinolone antibiotics (e.g., ofloxacin (OFX), levofloxacin (LFX), and ciprofloxacin (CFX)) under LED visible light using the ZIF-8@Bi2MoO6 (BIZ) heterojunction. The BIZ heterojunction was synthesized by the combination of solvothermal and sol-gel methods and characterized by SEM, TEM, XRD, EDX, FTIR, PL, EIS, BET, TGA, and UV-vis DRS analyses. The results show that using 500 mg L-1 BIZ (10% ZIF-8) with 500 mg L-1 Na2S2O8, at unadjusted pH for 25 min of irradiation results in an excellent photocatalytic activity with a degradation efficiency of 56.52% CFX, 85.70% LFX, and 96.36% OFX. The OFX degradation rate constant by BIZ was 3.2 and 23.3 times higher than those by Bi2MoO6 and ZIF-8, respectively. These high efficiencies are attributed to the high charge separation rates for the photo-generated carriers in the heterojunction structure. The activity of radicals in the photocatalytic process as well as their role in the OFX removal was in the order of SO4- > O-2(-) > h(+) > O-1(2) > HO. The mechanisms of charge separation, persulfate activation, and degradation pathway were then proposed for the photocatalytic removal of OFX using the BIZ heterojunction under visible light.