The Z-Scheme MIL-88B(Fe)/BiOBr Heterojunction Promotes Fe(III)/Fe(II) Cycling and Photocatalytic-Fenton-Like Synergistically Enhances the Degradation of Ciprofloxacin

The Z-scheme MIL-88B/BiOBr (referred to as MxBy, whereas x and y are the mass of MIL-88B(Fe) and BiOBr) heterojunction photocatalysts are successfully prepared by a facile ball milling method. By adding low concentration H2O2 under visible light irradiation, the Z-scheme heterojunction and photocatalytic-Fenton-like reaction synergistically enhance the degradation and mineralization of ciprofloxacin (CIP). Among them, M50B150 showed efficient photodegradation efficiency and excellent cycling stability, with 94.6% removal of CIP (10 mg L-1) by M50B150 (0.2 g L-1) under 90 min of visible light. In the MxBy heterojunctions, the rapid transfer of photo-generated electrons not only directly decomposed H2O2 to generate center dot OH, but also improved the cycle of Fe3+/Fe2+ pairs, which facilitated the reaction with H2O2 to generate center dot OH and center dot O2- radicals. In addition, the effects of photocatalyst dosages, pH of CIP solution, and coexisting substances on CIP removal are systematically investigated. It is found that the photocatalytic- Fenton-like reaction can be carried out at a pH close to neutral conditions. Finally, the charge transfer mechanism of the Z-scheme is verified by electron spin resonance (ESR) signals. The ecotoxicity of CIP degradation products is estimated by the T.E.S.T tool, indicating that the constructed photocatalysis-Fenton-like system is a green wastewater treatment technology. This research reveals the synergistic effect of photo-Fenton and Z-type heterojunction of MIL-88B(Fe)/BiOBr in the degradation of CIP. Cyclic conversion of Fe(III)/Fe(II) and selective activation of H2O2 are achieved by the Z-type heterojunction structure. MIL-88B(Fe)/BiOBr shows superior photocatalytic-Fenton-like performance for CIP degradation at near-neutral-pH (5.7) and low H2O2 (0.5 mM) conditions, which is valuable for practical applications.image