High-efficiency oxidation of norfloxacin by Fe3+/H2O2 process enhanced via vacuum ultraviolet irradiation: Role of newly formed Fe2

Abstract

Fluoroquinolones in water environments have caused worldwide concern due to negative effects on human health and ecological environment. Heretofore, synergistic mechanisms of Fe³⁺/H₂O₂ process enhanced via vacuum ultraviolet (VUV) irradiation for fluoroquinolones removal, and generation ways and contribution evaluations of reactive oxygen species (ROS) in integrated VUV/Fe³⁺/H₂O₂ were not reported systematically. This work comparatively investigated norfloxacin (NOR, typical fluoroquinolones) degradation in VUV/Fe³⁺/H₂O₂ and its sub-processes. Compared with its sub-processes, VUV/Fe³⁺/H₂O₂ process could not only increase degradation rate constant by 2.1-10.2 times and increase mineralization rate by 14.5%-49.5%, but also reduce energy consumption by 53.1%-89.9% and reduce economic cost by 33.3%-68.0%. Effect mechanisms of Fe³⁺ and H₂O₂ doses on decontamination capability of VUV/Fe²⁺/H₂O₂ were elaborated, and 3 mM H₂O₂ and 90 μM Fe³⁺ were determined as optimal doses. The synergetic factor in integrated VUV/Fe³⁺/H₂O₂ was 3.33, which was mainly ascribed to VUV photons accelerating iron cycle. In VUV/Fe³⁺/H₂O₂ process, superoxide radical and hydroxyl radical were confirmed as primary ROS, contributing 20.86% and 76.32% to NOR oxidation, separately. Organic and inorganic products of NOR and its degradation pathways in integrated VUV/Fe³⁺/H₂O₂ were also investigated. Besides, the synergistic reaction pathways in VUV/Fe³⁺/H₂O₂ were elaborated. Effects of water matrices on decontamination capability of VUV/Fe³⁺/H₂O₂ were also studied. All results indicated VUV/Fe³⁺/H₂O₂ as an efficient and cost-effective process suitable for NOR removal.

Keywords: Advanced oxidation process; Fenton-like reaction; Norfloxacin; Reactive oxygen species; Synergistic mechanism.