Electro-generation Of H₂O₂ And Degradation Of Norfloxacin Using Modified Carbon Fiber Felt

Recently,organic pollutants such as pharmaceuticals and personal care products（PPCPs）have become the subject of attention among environmental researchers due to their potential biological activity and unknown effects on the water environment.At present,Electro-Fenton（EF）technology stands out as an advanced oxidation technology（AOPs）due to its cleanliness,efficiency and non-selectivity.In this process,H₂O₂ generated by two electron oxygen reduction reaction（2e^–-ORR）reacts with Fe²⁺in solution to form strong oxidizing·OH to remove organic contaminants from wastewater.The EF technical challenge lies in how to produce H₂O₂ efficiently on the cathode surface.Therefore,the development of EF cathode materials with high catalytic activity is the key to improve the removal efficiency of pollutants.In this work,carbon fiber felt（CF）was used as the EF cathode material,and via simple and low-cost modification methods to improve the catalytic activity of the cathode.The specific research contents are as follows:（1）PAN-based CF and viscose based CF were used as EF catalytic electrodes,respectively.SEM,Optical Contact Angle Measuring Device,XRD and Raman were used to characterize the two kinds of CF.The electrochemical properties of CF were analyzed by EIS,LSV and CV.The activity of 2e^–-ORR was characterized by electrochemical generation of H₂O₂concentrations at different cathode potentials.The results showed that the surface inertia of the viscose based CF with high graphitization was strong,which reduced the accumulation of oxygen active substances and hindered the progress of 2e^–-ORR.In contrast,PAN-based CF had a larger electroactive area,which was conducive to the electrosynthesis of H₂O₂.Under the conditions of p H 3,applied potential-0.85 V（SCE）and O₂ flow rate 300 m L L^–1,H₂O₂ yield can reach 160.7 mg L^–1 and the current efficiency can reach 65.4%at 90 min.（2）PAN-based CF with the better performance in（1）was selected for the following study.The surface of CF was electrochemical modified with organic acid（oxalic acid-citric acid）as anodic oxidation solution.The CF before and after modification was characterized by SEM,Optical Contact Angle Measuring Device,Raman and XPS.The electrochemical properties of CF before and after modification were measured by CV and LSV.The results showed that the surface of the modified CF was more hydrophilic and introduced a large number of defect sites and oxygen-containing groups,which lead to a larger electroactive area and stronger 2e^–-ORR ability.The effects of oxalic acid-citric acid mass ratio and oxidation time on the CF cathode were investigated.As a result,H₂O₂ electrogeneration was 1.6 times as much as that of virgin CF counterpart at the mass oxalic-citric acid ratio of 2:1 oxidation for 40 min.However,overoxidation also impaired the electrical production of H₂O₂.Finally,the effects of cathode potential and p H on the properties of the cathode were optimized.Under the conditions of-0.85V（SCE）,O₂ flow rate of 400 m L min^–1 and p H 3,the maximum generation rate of H₂O₂ can reach 4.5 mg h^–1 cm^–2,and the current efficiency can reach 75%.The modified cathode maintained stable H₂O₂ generation performance during 8 cycles.（3）The CF by anodizing and HNO₃ ultrasonic integrated treatment was used as cathode to degrade norfloxacin.The modified cathodes were characterized by SEM,XRD,BET,Raman,XPS and Optical Contact Angle Measuring Device.CV and LSV were used to test the electrochemical properties of the modified cathodes.The results showed that the synergistic modification effect could produce more defective active sites（DASs）on the cathode surface and improve the 2e^–-ORR activity compared with the single modification method.Free radical quenching experiments showed that H₂O₂ could be co-activated by Fe²⁺and DASs to generate·OH_{（ads and free）}and·O₂^-degrade norfloxacin.The effects of anodic oxidation time,HNO₃ultrasonic time,cathode potential,Fe²⁺concentration,p H and O₂flow rate on norfloxacin degradation were systematically investigated.Under the optimal conditions,when 50 mg L^-1norfloxacin was continuously degraded for 120 min,the removal rate was 93%and the mineralization rate reached 63%.According to the mineralization rate of the system,the operating cost is calculated and analyzed.The degradation products of norfloxacin were determined by LC-MS and the possible degradation pathways were proposed,including decarboxylation,defluorination,piperazine ring breakage and nalidixic ring transformation.The biotoxicity of norfloxacin was analyzed by T.E.S.T.software.The results showed that the degradation process of norfloxacin was accompanied by detoxification effect.