Mechanism insight into the photocatalytic degradation of fluoroquinolone antibiotics by the ZIF-8@Bi ₂MoO ₆ heterojunction

Abstract

Mechanism for the photocatalytic removal of ofloxacin under visible light and persulfate activation.

Abstract

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@Bi ₂MoO ₆ (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 Na ₂S ₂O ₈, 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 Bi ₂MoO ₆ 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 SO ₄˙ ⁻ > O ₂˙ ⁻ > h ⁺ > ¹O 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.