Mineralization Enhancement of Pharmaceutical Contaminants by Radical-Based Oxidation Promoted by Oxide-Bound Metal Ions.

While the use of transition metal oxides in catalyzing advanced oxidation reactions has been widely investigated, very few reports have focused on how the preliminary contact of oxides with target compounds may affect the succession of reaction. In this study, we examined the adsorption and electron transfer reactions of two fluoroquinolones, flumequine (FLU), and norfloxacin (NOR), with goethite (α-FeOOH) or manganese (Mn) oxide, and their impact on the subsequent mineralization of target compounds using H2O2 or S2O82- under UVA irradiation. Intriguingly, higher total organic carbon (TOC) removal was achieved when antibiotics and metal oxides were allowed for preequilibration before starting the oxidation reaction. The rate and extent of TOC removal are strongly dependent on the molecule structure and the redox-active mineral used, and much less on the preequilibration time. This high efficiency can be ascribed to the presence of reduced metal ions, chemically or photochemically generated during the first stage, onto oxide minerals. Oxide-bound MnII plays a crucial role in catalyzing oxidant decomposition and then producing greater amounts of radical species through a photoassisted redox cycle, regardless of the underlying surface, MnIVO2 or MnIIIOOH. This finding will be of fundamental and practical significance to Mn-based oxidation reactions and wastewater treatment processes.

Use of laterite as a sustainable catalyst for removal of fluoroquinolone antibiotics from contaminated water.

Although there is a growing interest in Fenton oxidation processes based on natural catalysts, the use of laterite soil to promote sequential adsorption/oxidation treatments of fluoroquinolone antibiotics has been scarcely investigated. In this work, the ability of an african laterite containing goethite and hematite to remove flumequine (FLU), used as a representative compound of fluoroquinolone antibiotics, was evaluated under dark and UVA irradiation. Batch experiments and liquid chromatography analyses showed that the presence of laterite can enhance FLU removal from heavily contaminated water through both sorption and oxidation reactions (up to 94% removal of 77 µmol L-1 of FLU and 72% of mineralization). The heterogeneous reaction rate is dominated by the rate of intrinsic surface chemical reactions including sorption and oxidation of FLU, and light-induced reduction of FeIII sites to produce FeII. Based on the probe and scavenging experiments, OH radicals were mainly involved in the heterogeneous oxidation reaction. The photo-assisted Fenton process showed a high efficiency of FLU removal even in the presence of a second fluoroquinolone antibiotic, norfloxacin (NOR), which can be co-found with FLU in affected environments. Determinations of kinetic rate constants and total organic carbon (TOC) for five sequential adsorption/oxidation cycles showed that laterite exhibited no deactivation of surface sites and an excellent catalytic stability. This cost-effective and environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.

Activation of persulfate by irradiated laterite for removal of fluoroquinolones in multi-component systems.

Although several emerging contaminants (e.g. fluoro(quinolones) (FQs)) have been simultaneously detected in environmental systems, there is very limited information on their elimination from contaminated waters in multi-component systems. In this study, removal of three FQs including flumequine (FLU), ciprofloxacin (CIP) and norfloxacin (NOR) were investigated in single and mixture systems, using natural laterite soil and persulfate (PS) under UVA irradiation. Both sorption and oxidation reactions contribute to the removal of FQs from aqueous phase, whereas quenching experiments showed that SO4- is mainly responsible for the FQs oxidation. The kinetic rate constants can be ranked as follows: CIP > NOR > FLU, regardless of whether the compound was alone or in mixture. The higher degradation rate constant of CIP relative to those of NOR and FLU could be explained by the high reactivity of SO4- radical with cyclopropane-ring containing compounds. Fall in oxidation performance was observed in synthetic wastewater, probably due to sulfate radical scavenging by wastewater components. However, degradation rate constants of CIP in wastewater remains unchanged in mixture systems as compared to single ones. This environmentally friendly remediation technology may appear as a promising way for the removal of fluoroquinolone antibiotics from multi-contaminated waters.