Efficient Activation Of Persulfate By Spinel Composites For Degradation Of Fluoroquinolone Antibiotics In Water

Fluoroquinolones?FQs?have been widely distributed in environment,which even at trace level have potential threat to the human health and the whole eco-system.Persulfate?PS?involved advanced oxidation process?AOP?shows strong capacity in decomposing emerging contaminants owing to its high oxidization ability for a wide range of refractory organics.In consideration for the practical utilization and operation cost,the activation of PS by heterogeneous-based catalysts provides an alternative route for pollution removal in aqueous solution,in which the enhanced efficiencies of PS activation and contaminants degradation can be achieved.However,the poor catalytic efficiency and stability restrict the practical application of single heterogeneous catalysts.Thus,in this thesis,?-Fe₂O₃/Mn₃O₄?CuO/MnFe₂O₄?AC@CoFe-LDH?AC@CoFe₂O₄ which belonged to spinel and spinel precursor composites were fabricated and used as PS activators for the degradation of FQs.Besides,the mechanism of FQs degradation was clarified.The main works of this thesis are as follows:In order to improve the catalytic activity and stability of the single catalysts,?-Fe₂O₃/Mn₃O₄ and CuO/MnFe₂O₄ were synthesized and optimized through the co-participation methods.Then the physiochemical properties of the catalysts were systemically characterized and the catalytic performances of them were evaluated via the activation of PS for levofloxacin?LVF?removal.Moreover,the effects of operating parameters and the roles of reactive species in reaction system as well as the reaction mechanism were studied.The reusability and stability of?-Fe₂O₃/Mn₃O₄ and CuO/MnFe₂O₄ were also investigated.Results indicated that?-Fe₂O₃/Mn₃O₄-1:3nanocomposites revealed a higher catalytic performance than pure?-Fe₂O₃,pure Mn₃O₄ and other fabricated?-Fe₂O₃/Mn₃O₄ nanocomposites.And under the optimized conditions of 1 g·L^-1 catalyst and PS dosage at pH 5.0 and 25 ^oC,90.8%of LVF could be decomposed by?-Fe₂O₃/Mn₃O₄-1:3 within 150 min.Meanwhile,free radical quenching experiments implied SO₄?^-and?OH were involved in the system and SO₄?^-played a key role in LVF decomposition.As for the CuO/MnFe₂O₄/PS system,it could be found that CuO/MnFe₂O₄-9%exhibited the best catalytic activities,where92.2%of LVF was removed in 120 min with the following conditions:PS and catalyst concentration of 1 g·L^-1,reaction temperature of 25 ^oC and pH value of 9.0.Both SO₄?^-and?OH were the main dominant radical species involved in the system.Based on the results of the intermediates detected,three decomposition pathways of LVF were proposed.Especially,the?-Fe₂O₃/Mn₃O₄ and CuO/MnFe₂O₄ nanocomposites showed good stability and could be easily separated by external magnet,which might make sense to the development of environmental catalysts for practical use.For further enhancing the PS activation efficiency,the AC@CoFe-LDH and AC@CoFe₂O₄ nanocomposites were fabricated by coupling AC with spinel/spinel precursor composites.Subsequently,the physiochemical properties of them were characterized.The catalytic performances of as-synthesized AC@CoFe-LDH and AC@CoFe₂O₄ were investigated towards PS activation for the degradation of lomefloxacin?LMF?.Besides,the degradation behaviors of LMF were investigated in terms of reaction kinetics,effects of reaction parameters,catalytic stability,the possible degradation pathways and degradation mechanism.Results indicated that AC@CoFe-LDH-1:2 and AC@CoFe₂O₄-1:1 showed higher catalytic performances for LMF removal than their pure catalysts and other composites,which might be attributed to the abundant active sites as well as the large surface area of the catalysts after the introduction of Co/Fe materials to AC.Under the optimized operation conditions of 0.2 g·L^-1 of catalyst and 1 g·L^-1 of PS,pH of 5.0 and reaction temperature of 25 ^oC,the maximum LMF degradation of 89.9%and 94.6%were achieved by AC@CoFe-LDH-1:2 and AC@CoFe₂O₄-1:1,respectively.The free radical quenching experiments implied the SO₄?^-and?OH were the predominant radicals responsible for LMF degradation.Moreover,several oxidation intermediates were identified and four suggested pathways were proposed to reveal the reaction mechanism,indicating a comprehensive route of LMF decomposition via the activation of PS.Further in order to remove CIP in water,four as-prepared catalysts were used as heterogeneous PS activators for the degradation of CIP.Besides,the influenced factors of the degradation process such as pH,PS concertation,catalyst dosage,CIP concentration,common anions in water and common organic compounds in water were systemically investigated.Moreover,the kinetics of these reactions were also clarified.Results showed that the spinel composites exhibited good activities of PS activation,with the CIP removal efficiencies followed the order:AC@CoFe₂O₄-1:1>AC@CoFe-LDH-1:2>CuO/MnFe₂O₄-9%>?-Fe₂O₃/Mn₃O₄-1:3.The degradation processes fitted the pseudo-first-order reaction kinetics model.Moreover,several degradation intermediates and proposed decomposition pathways of CIP were identified according to the UPLC-MS results.Combining with the degradation processes of LVF and LMF,the degradation pathways of three kinds of FQs via PS based AOP were systemically induced.