Degradation And Mechanism Of Fluoroquinolone Antibiotics In Three Advanced Oxidation Processes

Fluoroquinolones?FQs?,as a class of commonly used pharmaceuticals and personal care products?PPCPs?,are widely used in the diseases treatment of people and animals.However,the trace of residual FQs in environment will bring the potential hazard to human and environment.Advanced oxidation processes?AOPs?can produce a large amount of reactive species with oxidizing capability,which effect on degradation and mineralization of organic pollutants.This work investigated the degradation and mechanism of three typical FQs:ciprofloxacin?CIP?,lomefloxacin?LOM?and gatifloxacin?GAT?in UV/chlorine system,Fe???-DSC/H₂O₂ system and LDH-GO/PMS system respectively,and aimed to explore the new methods about FQs degradation in AOPs.1.The degradation and mechanism of CIP in UV/chlorine system was investigated.The results showed that UV/chlorine system improve the degradation rate of CIP comparing with UV and dark chlorine system.The 10 min degradation efficiency of CIP was 100%in UV/chlorine system.The degradation of CIP in UV/chlorine system was mainly attributed to the attack of the reactive species.The relative contributions of hydrated electrons(e_aq·),hydroxyl radicals?HO·?,chlorine atoms?Cl·?and UV photolysis were calculated according to quenching experiments and competitive kinetic experiments.Under neutral condition,CIP degradation had a high pseudo first-order reaction rate constant which was about 7.4×10^-33 s^-1.In degradation,e_aq·had the highest contribution,followed by Cl·,HO·and UV photolysis.UV/chlorine system can mineralize 22.3%CIP.The inorganic products,intermediates and disinfection by-products were identified and the degradation pathway was proposed.The total organic chlorine?TOCl?and biotoxicity of CIP degradation products showed that the degradation products at 60 min had the lowest toxicity.UV/chlorine system was used in real water which can degrade CIP efficiently.2.Disodium stannous citrate?DSC?,as a Fenton-like AOPs complexing agent,was introduced into Fe???-DSC/H₂O₂ system to study the degradation of LOM.The results showed that LOM degradation rate increased with the concentration of Fe???-DSC and H₂O₂ increasing.LOM degradation efficiency was highest under acidic conditions which was 89.9%.Under neutral condition,LOM degradation efficiency was 81.7%.It was known from quenching experiments that O₂·^-and HO·were main reactive species contributing to LOM degradation.A part of Fe???was reduced by Sn?II?to form Fe?II?.The other part of Fe???reacted with H₂O₂ to generate Fe?II?and O₂·^-in Fe???-DSC/H₂O₂ system.From one aspect,O₂·^-effeacted on LOM degradation directly.From the other perspective,O₂·^-contributed to the transformation of Fe?II?/Fe???.Fe?II?reacted with H₂O₂ to generate HO·for LOM degradation.The competitive kinetic experiment showed that the second-order reaction rate constant of LOM with HO·(k_LOM-HO·)was about 5.5×10⁹ M^-1.s^-1?R²=0.90?.The defluorination and the denitrification of LOM were 17.9%and 14.3%after 60 min,perspectively.The degradation pathway of LOM in Fe???-DSC/H₂O₂ system was proposed.3.LDH-GO composites were synthesized by combining layered double hydroxide?LDH?with graphene oxide?GO?.The degradation and mechanism of GAT in LDH-GO/PMS system was studied.The results showed that LDH-GO exhibited excellent performance in the catalysis according to the synergistic effect of three different metal elements.After 45 min,GAT could be degraded completely in LDH-GO/PMS system.The mineralization and defluorination of GAT were 55.5%and 78.0%after 5 h,perspectively.T-butanol?TBA?and methanol?MeOH?were used in quenching experiments demonstrating that sulfate radicals?SO₄·^-?played a major role on GAT degradation and mineralization.It was found that a large number of surface functional groups of GO effectively immobilized the metal elements.Under acidic condition,the metal dissolution rate of LDH-GO was 32.6%of LDH.In LDH-GO/PMS system,the degradation rate of GAT under alkaline conditions was higher than that under neutral and acidic conditions.It was attributed to the protection effect of OH^-to LDH-GO and activation effect of OH^-to PMS.During the degradation process,a series of redox reactions kept a high efficiency of LDH-GO composites.As catalysts,LDH-GO showed the excellent stability and reusability.