Characterization And Mechanism Of Fluoroquinolone Degradation In Water By Electro-Fenton (like) With Electrospun Carbon Nanofibers Loaded Cobalt-iron Spinel

Fluoroquinolone antibiotics（FQs）,a class of persistent organic pollutants that are difficult to degrade,are frequently detected in aquaculture wastewater,pharmaceutical wastewater,surface water and rivers and lakes.Due to their high toxicity and long retention time,they can pose a major threat to the health of aquatic plants and animals as well as humans.Therefore,there is an urgent need to develop green and efficient technologies to degrade FQs in water bodies.Electro-Fenton（like）is an environmentally friendly and proven advanced oxidation method,in which the free radicals generated during the oxidation process can efficiently degrade antibiotics and even mineralize them without secondary pollution.The key to its technology is the preparation of high catalytic activity,high stability electrodes and the reduction of electricity consumption.Cobalt-iron spinel（Co Fe₂O₄）has the physical and chemical properties of cobalt and iron and has high catalytic activity,but it is easy to aggregate and cover the catalytic active site.In addition,it is easy to leach in strongly acidic solutions.Recent studies have shown its modification by electrostatic spinning technology.The carbon nanofibers can stabilize the catalyst and uniformly disperse the catalytic active sites,and the carbon skeleton formed after calcination can also raise the corrosion resistance,enhance the electrical conductivity and promote the two electron reduction of O₂（2e-ORR）.Moreover,the doping with multi-metal and heteroatom helps to modulate the electron transfer rate and reduce the reaction power consumption.Therefore,the technical strategy of this study is to prepare a carbon skeleton-loaded cobalt-iron spinel catalyst by electrostatic spinning method and calcination to construct a electro-Fenton（like）system to regulate the electron transfer rate through strategies such as polymetallic and heteroatom doping,of which the aim was to make the oxygen reduction reaction closer to the 2e-ORR process and promote the production of multi radicals（¹O₂,HO₂·/O₂·^-,·OH,SO₄·^-,Cl·^-,Cl₂·^-,and Cl O·）to achieve the efficient degradation of FQs in water.Systematic and in-depth study on the characteristics and mechanism of fluoroquinolone degradation in water by electrospun carbon nanofibers loaded with cobalt-iron spinel（class）electrofenton using a comparative research method.The main results obtained from the study are as follows.（1）Fe/Co/Zn@C-NCNFs-800 catalysts were prepared for the modification of cathodes by a combination of electrostatic spinning and Zeolitic Imidazolate Frameworks（ZIF）in-situ growth,and subsequently by low-temperature stabilization and high-temperature carbonization.The experimental results showed that the Fe/Co/Zn@C-NCNFs-800 catalysts had a rougher surface,better crystal shape,higher graphitization,larger specific surface area and more pore volume after calcination.In addition,it possessed better 2e-ORR capability,smaller electrochemical impedance and higher corrosion potential than the initial Fe-Co-Zn-ZIF@PAN precursor.The catalyst was loaded on carbon felt（CF）to construct a heterogeneous electro-Fenton system（hetero-EF）for the degradation of enrofloxacin（ENR）.It could achieve 99.08%ENR removal in 30 min(reaction rate constant of 0.2659 min^-1)and47.13%TOC removal in 150 min at p H 3 and current of 40 m A.Meanwhile,the system could produce up to 129.03 mg L^-1of H₂O₂and 36.39 mg L^-1of·OH in 150 min.Based on the free radical quenching and electron paramagnetic resonance（EPR）experiments,it was confirmed that ¹O₂and HO₂·/O₂·^-were the main reactive oxygen species（ROS）in the degradation of ENR.The ENR degradation process involved in ring opening of the piperazine and quinolone fractions and conversion to ciprofloxacin（CIP）.（2）In order to solve the difficulties of precise regulation of 2e-ORR and to investigate the synergistic effect between hydrogen peroxide（H₂O₂）and peroxynitrite（PMS）,the method of electrospinning synergistic low-temperature stabilization and high-temperature carbonization with ultrasonic impregnation were adopted to prepare boron（B）and sulfur（S）co-doped electrospun nanofibers containing iron and cobalt（B,S-Fe/Co@C-NCNFs-900）catalysts,and used for CF cathode modification.Then,the system of heterogeneous electro-Fenton coupled PMS activation（hetero-EF/PMS）was constructed for the degradation of levofloxacin（Levo）.The morphology,structure and electrochemical properties of B,S-Fe/Co@C-NCNFs-900 were investigated.The experimental results showed that B and S co-doping significantly promoted electron transfer and modulated H₂O₂production from the2e-ORR pathway.It could achieve 99.63%Levo degradation within 20 min at p H 4,current of 20 m A and PMS dosage of 8.0 m M,with a reaction rate as high as 0.3056 min^-1.The calculated steady-state concentrations of ¹O₂were 669.17×10^-14M,which was 15.42,29.74and 45.00 times than that of HO₂·/O₂·^-(43.40×10^-14M),·OH(22.25×10^-14M),and SO₄·^-(14.87×10^-14M)respectively,indicating that ¹O₂is the main ROS involved in Levo degradation.A total of 12 degradation intermediates of Levo were detected by mass spectrometry（LC-MS/MS）,and their ecotoxicity was simulated by quantitative structure-activity relationship（QSAR）-based method.In addition,the degradation pathways were deduced to be divided into ring opening and oxidation of the piperazine ring,piperazine ring,and oxazine group.（3）In response to the presence of large amounts of chloride ions in actual pharmaceutical wastewater and the narrow p H range inherent in the electro-Fenton reaction,CeO₂and Co Fe₂O₄catalysts were first prepared by hydrothermal method,and CeO₂/Co Fe₂O₄@C-NCNFs-800 catalysts were synthesized by electrostatic spinning with synergistic low-temperature stabilization and high-temperature carbonization for the modification of CF cathodes to construct a heterogeneous electro-Fenton coupled chloride ion（hetero-EF/Cl^-）system for the degradation of norfloxacin（NOR）.The morphology,structure and electrochemical properties of CeO₂/Co Fe₂O₄@C-NCNFs-800 were investigated,and it was found that the addition of CeO₂helped to accelerate the electron transfer rate.The experimental results showed that the degradation efficiency of NOR in this coupled system was significantly higher than that of the hetero-EF system under the same conditions,mainly because more selective oxidants with substrate specific oxidation ability were generated in the simultaneous presence of·OH and Cl^-.Under the conditions of p H=6.05,40 m A current,and0.1 M Cl^-concentration,it could achieve 99.54%NOR degradation within 20 min with a reaction rate constant of 0.3032 min^-1.According to the quenching and the probe experiments,·OH,Cl O·,and ¹O₂were confirmed to be predominance during NOR degradation,whose steady-state concentrations were 2.00×10^-11M,1.39×10^-11M,and 1.19×10^-11M,respectively.In addition,a total of 13 intermediates of NOR degradation were detected,and their degradation pathways were the oxidation of substituents,the removal of piperazine ring and the ring opening of quinolone ring.The above studies provide the development direction and technical support for the preparation of electrospun loaded cobalt-iron spinel-based electrocatalysts with high catalytic activity,and also provide some theoretical basis and technical support for their practical application in the removal of antibiotics by exploring the mechanism of ROS/RCS generation in the electro-Fenton system with the co-existence of H₂O₂ with PMS and Cl^-.