Study Of Fe-Co Dual Metal Hollow Nanorods In Heterogeneous Electro-Fenton Degradation Of Tetrahydropyran

The electro-Fenton technologies have been widely concerned in the field of industrial wastewater treatment because of their strong oxidation ability,in-situ generation of H₂O₂and scarcely generated iron-containing sludge.However,in heterogeneous electro-Fenton systems,both the high selectivity of O₂ 2 e^-reduction at cathode surface to generate H₂O₂ and activation efficiency of H₂O₂ to generate·OH are the key roles to realizing high performance of pollutant removal.Thus,the design and synthesis of cathode materials in heterogeneous electro-Fenton systems is essential.Among them,Fe-based cathode materials exhibit high efficiency of H₂O₂ activation to produce·OH.But,they are still influenced by the solution pH and show the weak ability of 2 e^-O₂ reduction for H₂O₂ production.Some research showed that cathode materials with adding Co element can promotes the 2 e^-O₂ reduction ability and broaden the catalyst pH range in application process due to its Lewis acidity.Therefore,how to design the Fe-Co based cathode materials with the high efficiency of both 2 e^-O₂reduction to generate H₂O₂ and activation to generate·OH process is urgent for improving the performance of wastewater treatment in heterogeneous electro-Fenton systems.In this work,Fe-Co bimetallic oxide nanorods（MIL88A-Co-Co）are designed to synthesize as the cathode material for antibiotic pollutants treatment in the heterogeneous electro-Fenton system.Firstly,the electrocatalytic property of MIL88A-Co-Co materials is explored.Then,the catalytic performance of MIL88A-Co-Co loaded carbon paper as a cathode electrode for TC（Tetracycline as the model pollutant）degradation is optimized in a three-electrode electro-Fenton system.Meanwhile,the reactive oxygen species and intermediate products of TC degradation are detected in this system.This study aims to provide theoretical and technical support to design for developing cathode materials with high performance for catalytic O₂ reduction and H₂O₂ activation,which applied in heterogeneous electro-Fenton system for pollutants removal.The primary research findings are as follows:1.The precursor MIL88A is synthesized through hydrothermal method,and then the solvothermal method of secondary exchange etching reaction is used to prepare the catalyst MIL88A-Co-Co.The catalysts are deposited on carbon paper after pyrolysis to form electrodes.The scanning electron microscope（SEM）images reveal that the microscopic morphology of MIL88A-Co-Co sample is a curved hexagonal prism rosette structure.According to the detection of X-ray photoelectron spectroscopy（XPS）,the results show that Fe 2p and Co 2p peaks are analyzed as Fe²⁺/Fe³⁺and Co²⁺/Co³⁺,respectively.The TEM image clearly shows that the MIL88A-Co-Co is a hollow structure,indicating that the core of MIL-88A has been completely etched.The X-ray diffraction（XRD）pattern shows that after two etchings,the obviously Fe peak of MIL-88A disappears,which is consistent with the results observed in both SEM and TEM images.2.The effects of Fe-Co ratio,pyrolysis temperature,etching times,and temperature,deposition voltage on the catalytic performance of Fe-Co bimetallic catalysts are investigated.The Fe-Co material exhibits the best performance of TC degradation in heterogeneous electro-Fenton reaction when the prepared sample is prepared as followed condition:The atomic ratio of Fe:Co 1:2,deposition voltage 15 V for 25 min,pH=3,annealing at 600℃,and double etching.In detail,the material synthesized under this condition achieved rapid TC degradation of 10 mg/L within 5 min.3.The reaction mechanism of MIL88A—Co-Co/CP to activate O₂ for TC pollutants degradation is explored.Electron paramagnetic resonance spectroscopy（EPR）confirms that the reactive oxygen species involved in the catalytic process was mainly·OH.Combined with the test and analysis of both H₂O₂ and·OH content,the results show that the surface interface of the cathode mainly occurs 2 e^-reduction of O₂to generate H₂O₂ and then is rapidly activated to form·OH reaction.4.The influence of environmental factors（background ions,natural organic matter,etc.）on the O₂ activation to degrade TC pollutants and the performance of actual wastewater degradation are investigated in the three-electrode electro-Fenton system by using MIL88A—Co-Co/CP as cathode electrode.The results show that MIL88A-Co-Co/CP electrode has high catalytic activity over a wide pH range;NO₃^-,Cl^-and low concentration of ClO₄^-（2 mg/L）exerts insignificant effects on TC removal,while the reaction effect of high concentration of Cl^-（10 mg/L）is reduced by 40%after 10 min under acidic conditions;NO₃^-,Cl^-and ClO₄^-exert insignificant effects on TC removal under neutral conditions;NO₃^-,Cl^-and ClO₄^-（2 mg/L）all significantly inhibit degradation under alkaline conditions,probably due to increased repulsion between ions and reduced reaction rates;The competitive adsorption between natural organic matter（NOM）and pollutants also significantly inhibits the rate of TC degradation.The electro-Fenton system with MIL88A-Co-Co/CP electrode as cathode shows good performance in antibiotic pollutants and the wastewater treatment,highlighting the potential for practical environmental application.5.By evaluating the environmental adaptability and stability of the samples,the cyclic reactions at different pH values are conducted with MIL88A-Co-Co/CP electrode.The results confirm that MIL88A-Co-Co/CP electrode can maintain excellent performance in electro-Fenton System.Furthermore,through analyzing the results of inductively coupled plasma spectrometer,there is just minor leaching of iron and cobalt（lower than 10%）after usage.Thus,the results have jointly proven the stability of MIL88A-Co-Co/CP electrode in electro-Fenton System.