Degradation Of Ciprofloxacin By Activated Persulfate From Iron-Containing LDHs-Based Materials

Antibiotics are commonly used to treat infectious diseases in humans and animals,such as farm and aquatic animals.The mass production and overuse of antibiotics has led to ecological disruption and new threats to human health through the circulation of surface and groundwater.Among these,ciprofloxacin（CIP）is the most commonly detected quinolone antibiotic in the environment.Due to its stable chemical structure and poor biodegradability,CIP cannot be effectively removed by conventional wastewater treatment technologies,which makes it a potential threat to the environment and human health.Advanced oxidation technology based on peroxodisulfate（PDS）is one of the effective technologies for treatment of wastewater contaminated with ECs due to its high selectivity and simple reaction conditions.However,most of the inhomogeneous catalysts for PDS activation are composed of transition metals such as Co²⁺,Cu²⁺,Ni²⁺,and others,which will inevitably lead to the washout of metal ions and secondary pollution when used for PDS activation to treat wastewater contaminated with ECs.Therefore,in this dissertation,MgAlFe-LDHs,an environmentally friendly MgAlFe hydrotalcite,was used to improve the performance of PDS activation for CIP degradation by the specific structure of LDHs and to elucidate the related reaction mechanism.The main research results are as follows:（1）MgAlFe-LDHs（S₂O₈·LDHs）for PDS intercalation were prepared by a simple one-step co-precipitation method to optimise the elemental Fe content of LDH laminates and to modulate the catalytic activity of S₂O₈·LDHs.Fe-S₂O₈·LDH-0.2 with Fe/（Al+Fe）=0.2 had superior CIP removal performance,and a Fe-S₂O₈·LDH-0.2 dosage of 1.0 g/L degraded 99.55%of CIP within 60min.By investigation of the mechanism of CIP removal by Fe-S₂O₈·LDH-0.2,the contribution of SO₄^·-、·OH、O₂^·-and ¹O₂ to CIP degradation was excluded,and electron transfer was shown to be the cause of CIP degradation.The electron transfer mechanism was theoretically verified with Density Functional Theory（DFT）.Due to the space limitation within the layers of LDH,the O-O bond of the interlayer S₂O₈^2-is in a more active state,and the laminate of LDH transfers electrons from the piperazine ring of CIP to the S₂O₈^2-within the layers upon contact with CIP,which leads to the oxidative degradation of CIP.The degradation intermediates were identified by liquid chromatography quadrupole time-of-flight mass spectrometry（LC-Q-TOF-MS）,which suggested that the degradation pathway of CIP is dominated by the cleavage and oxidation of the piperazine ring and the cleavage of the cyclopropyl group.Fe-S₂O₈·LDH-0.2also showed efficient removal of other quinolones,while Cl^-,NO₃^-,HCO₃^-/CO₃^2-and natural organic matter on Fe-S₂O₈·LDH-0.2 had little effect on the performance of activated PDS.This work not only provides an in-depth study of the degradation of ECs by PDS-intercalated LDHs,but also provides some new insights into the non-radical mechanism.（2）MgAlFe·CO₃-LDH precursors with CO₃^2-intercalation were prepared by co-precipitation method,and the layered composite metal oxides（LDO）were obtained by calcination to enhance the ability of their surface metal active sites to activate PDS for CIP removal.LDO-700 was obtained at a calcination temperature of 700℃with the best performance of activated PDS for CIP removal,and 79.7%of CIP could be removed within 60 min.Identification of active species,electrochemical tests and X-ray photoelectron spectroscopy analysis showed that LDO-700 activated PDS degraded CIP by a non-radical mechanism based on electron transfer.Contact between PDS and LDO-700 The contact of PDS with LDO-700 puts it in a more active state,and the CIP in solution provides electrons to the active PDS through electron transfer from the surface metal active site of LDO,which results in CIP degradation and PDS decomposition.The prepared LDO-700 has excellent anti-interference ability in activation of PDS to remove CIP,and the presence of common anions Cl^-,NO₃^-and natural organic matter in water has negligible effect on CIP removal.