The Performance And Mechanisms The Degradation Of Antibiotic Ciprofloxacin By Photoelectro-Fenton Process:Effect Of The Formation Of Fe³⁺-CIP Chelates

At present,the water pollution by the low concentration of antibiotics is widespread,its effective removal has become a serious concern in the field of water treatment.Ciprofloxacin(CIP),a synthetic third-generation fluoroquinolone(FQ)antibiotic,is widely used for the treatment of human infections because of its broad spectrum antimicrobial activity and good oral absorption,and it has been detected in surface water and secondary effluent from wastewater treatment plants(WWTPs).Moreover,even at trace concentrations,residual CIP may chelate with metal ions to form metal-ligand complexes,which may change CIP chemical properties and affect its degradation behaviors.Therefore,it is significant to develop efficient degradation technologies treating antibiotic wastewater.In this thesis,CIP was chosen as a model pollutant,we studied on the chelation mechanism of CIP with metal ions(Fe2+/Fe3+/Cu2+),and the effect of chelating behavior on CIP degradation in electro-Fenton(EF)process,including degradation kinetics,mineralization efficiencies,and the formation of intermediate products.Meanwhile,the effect of chelating behavior on CIP degradation in light xenon lamp photoelectro-Fenton(Xe-PEF)process had also been investigated.The main research are as follows:(1)The chelating behavior of CIP with metal ions(Fe2+/Fe3+/Cu2+):The results indicated that Fe3+/Cu2+ was likely complex with CIP.After the absorbance value was refined by AAbs method to preclude the weak absorption of the free CIP and Fe3+,the vibration of absorbance value was found in the mixed solution of CIP and Fe3+/Cu2+.A saturation complexation ratio of about 2:1(CIP:Fe3+)in acid solution was measured by Job's method,while the optimal saturation complexation ratio of CIP-Cu2+ chelate was mutable.pH-value in aqueous solution did also affect the chelating behavior.(2)The effect of chelating behavior on CIP degradation in EF process:The optimal initial Fe2+ and Fe3+ contents were both verified to be 1.50 mM,in which 73%and 72%of initial TOC were eliminated after 360 min electrolysis,respectively.And the corresponding apparent kinetic constants(kapp-value)were 0.046 min-1(R2 = 0.998)and 0.053 min-1(R2 = 0.990)for Fe2+/Fe3+ conditions in 90 min electrolysis,respectively.Faster CIP decay and slightly lower TOC removal were observed under initial Fe3+conditions during EF process.RuO2/Ti electrode exhibited strong Fe2+ oxidation and weak Fe3+ reduction in AO process.About 35%of initial 1.50 mM Fe3+ were reduced to Fe2+ by activated carbon fiber(ACF)felt cathode at 18 mA cm-2 in 200 mg L-1 CIP solutions during 30 min pre-aeration of EF process,while higher Fe2+ concentration was maintained for initial 1.50 mM Fe3+ during CIP degradation.Eight aromatic intermediates were identified using UPLC-QTOF-MS/MS during CIP degradation in EF process,and a feasible mineralization pathway was proposed.(3)The effect of chelating behavior on CIP degradation in Xe-PEF process:The optimal initial Fe2+ and Fe3+ contents were both verified to be 1.00 mM,in which 80%and 84%of initial TOC were eliminated after 360 min electrolysis,respectively.And the corresponding kapp-value were 0.072 min-1(R2 = 0.997)and 0.064 min-1(R2 =0.997)for Fe2+/Fe3+ conditions,respectively.This behavior indicated that Fe2+/Fe3+catalyst could be utilized more efficiently in EF treatment by xenon lamp radiation.Under initial Fe3+ conditions,efficient TOC removal was achieved during Xe-PEF process.The mutual transformation of Fe2+/Fe3+ was no longer affected by the formation of CIP-Fe3+ chelate during CIP degradation,and the ratio of Fe3+ reduction during 30 min pre-aeration of Xe-PEF process increased from 35%to 48%by ACF felt cathode at 10 mA cm-2 in 200 mg L-1 CIP solutions.This behavior suggested that the complexes of CIP with Fe3+ were too weak to Xe-PEF system.Eight aromatic intermediates,which were the same as EF process,had been identified by UPLC-QTOF-MS/MS analysis during CIP degradation in Xe-PEF process,and the relative peak area of products showed significant differences,indicating that Xe-PEF system favored pathwaylof proposed feasible mineralization route of CIP during Xe-PEF process.This phenomenon indicated that the mineralization pathway of CIP degradation in EF process was unlikely to be transformed by xenon lamp radiation,but the reaction rate of different degradation pathways would.