Electrochemically Assisted Transition-metal-based Cathode To Activate Peroxymonsulfate For Organic Contaminant Degradation

The mass production and widespread use of antibiotics inevitably produce antibiotic-containing sewage,which would be harmful to the ecological environment or biological sewage treatment system if the sewage is discharged to the urban pipe network.The Advanced Oxidation Process（AOPs）based on activated persulfate is an effective technique to degrade this kind of contaminants.Generally peroxymonosulphate（PMS）can be activated to produce hydroxyl radicals·OH,sulfate radical SO₄^·-or singlet oxygen ¹O₂,and then effectively degrade the organic contaminants.In this paper,three kinds of transition metal-based cathode materials were synthesized on nickel foam（NF）matrix,and an electrochemically assisted activated PMS system were formed for degradation of Levofloxacin（LEV）.The main research contents are as follows:（1）A series material of Co Fe-MOF was grown in situ on NF surface to construct an electrochemically enhanced PMS activation system named as EC/Co Fe-MOF@NF/PMS.The materials were characterized by Scanning Electron Microscope,Transmission Electron Microscope,X-Ray Diffraction,X-ray Photoelectron spectroscopy,et al.,and the removal of LEV was investigated.The results showed that Co1Fe1-MOF@NF had a large surface area and the highest LEV removal.Under the conditions of 0.5 m A·cm^-2current,p H 6.0 and 15.0 mmol·L^-1PMS dosage,LEV removal in EC/Co1Fe1-MOF@NF/PMS system was 95.4%,and the removal rate of Chemical Oxygen Demand,COD was 63.0%,which was significantly better than that in the system without supplying electric field.The system also has high anti-interference to Cl^-,H₂PO₄^-,HCO₃^-and HA,and strong removal ability to a variety of antibiotics,dyes and other kinds organic contaminants.This system was found less stability during reusing,but LEV removal effect of the system could be significantly recovered after heat treatment for the cathode.The excellent contaminant degradation effect of the system was mainly due to the fact that the electric field promoted LEV adsorption on the electrode and the reduction of cobalt and iron in Co1Fe1-MOF@NF also accelerates the formation of SO₄^·-、·OH and ¹O₂.（2）Co-MOF was grown on NF surface by hydrothermal method,and it was heat treated to form Co₃O₄@NF.The morphology and structure of the materials were characterized by SEM,TEM,XRD and XPS.The synthesized materials were used as cathode to construct an electrochemically assisted PMS activation system,EC/Co₃O₄@NF/PMS,to degrade LEV.The results showed that degradation of LEV reached 95.8%at p H 3.0,PMS dosage of 3.5 mmol·L^-1,current density of 4 m A·cm^-2at40 min treatment.The COD removal was 73.3%at 55 min treatment,which was significantly better than the system without supplying electric current.This system has high anti-interference to Cl^-,H₂PO₄^-,HCO₃^-and HA interference and high reusability.It also has strong removal ability to a variety of antibiotics,dyes and other organic contaminants.The formation mechanism of active species in the system showed that the electric field promoted the activation of PMS into ¹O₂and the process of SO₄^·-and·OH free radicals by accelerating the Co³⁺—Co²⁺cycle on the surface of Co₃O₄@NF cathode,thus both non-free radical and free radical pathways for LEV degradation were enhanced.（3）A series of Zn Cu@NF materials with different Cu Zn ratios were in situ grown on NF surface and used as cathodes to construct EC/Zn Cu@NF/PMS system to degrade LEV antibiotics.The morphology and structure of the materials were characterized by SEM,TEM,XRD and XPS.Among them,EC/Zn Cu_0.15@NF/PMS showed the highest LEV removal of 94.4%and COD removal of 64.9%after 40 min treatment under the optimal conditions of 4 m A·cm^-2,p H 6.0 and 10 mmol·L^-1PMS dosage.The experiment results showed that Zn Cu_0.15@NF had a significant activation effect on PMS,and the electric field accelerated the Cu²⁺—Cu⁺cycle.On the other hand,S^2-also promoted the Cu²⁺—Cu⁺cycle by reducing Cu²⁺,thus promoted the formation of more oxygen vacancy V_Oon the cathode surface.All these processes were helpful to activate PMS to generate ¹O₂,and make the non-free radical oxidative degradation of LEV become the dominant way.