Structural Construction Of Fe-Based Self-Supporting Electrodes And Their Electro-Fenton Degradation Performance

Electro-Fenton（EF）,one of the electrochemical advanced oxidation processes,has attracted widespread attention in the field of water treatment,wherein the key challenge is to synthesize efficient and stable electrocatalytic materials.Self-supporting electrodes became the popular material due to advantages such as low internal resistance,high activity and easy operation.As for the active component,transition metal Fe has been widely used for in situ growth on self-supporting electrodes because of low cost,wide source and high efficiency.However,for already fabricated Fe based-self-supporting electrodes,the complex preparation methods,agglomeration and shedding of surface components,and weak catalytic activity severely limits their development.In view of above problems,it will be of great application value and guiding significance to develop efficient and durable Fe-based electrodes.In this study,a three-layer structured self-supporting electrode（CFP@PANI@Fe₃O₄）was firstly prepared by electrodeposition combined with solvothermal method,in which carbon fiber papers（CFP）was used as conductive substrate,polyaniline（PANI）was used as the intermediate transition layer and Fe₃O₄ spherical nanoparticle was used as the active component that in suit growth on the surface.The prepared electrode was characterized to reveal the morphology,chemical composition and electrochemical performance,and showed excellent electro-Fenton activity for p-nitrophenol（4-NP）degradation.After 60 min of reaction,20 mg L^-1 4-NP was completely degraded,and the TOC removal was 51.2%.Moreover,it has higher current efficiency and lower energy consumption compared with CFP and CFP@PANI electrodes.Reasonable reaction mechanism and performance improvement mechanism were also proposed through mechanism exploration experiment.Secondly,functional design and modification was implemented toward the outer iron oxide,in which the Fe-containing metal-organic framework（MIL-101（Fe））was selected as the template and precursor of active Fe species.The quasi-MOF derivative electrode（CFP@PANI@MIL-101（400））was prepared by controlled pyrolysis method,and exhibited excellent removal efficiency for higher concentration of organic pollutants.More importantly,the performance of stability was greatly improved with up to 92%removal efficiency even after ten consecutive runs.It was confirmed that the induced active Fe-O bond and in-situ Fe₃O₄ nanoparticles coated with carbon layer contribute to enhance the catalytic activity and stability of the electrode.On the basis of the above research,further design and development of electrode material was carried out.The intermediate transition layer of Mn O₂ was prepared by electrodeposition method,thus,the bimetal-based self-supported electrode（CFP@Mn O₂-Fe₃O₄/C）was fabricated.The prepared intermediate layer can not only promote the directional growth of the outer component,but also show good EF catalytic activity.The CFP@Mn O₂-Fe₃O₄/C possessed prominent degradation performance and stability for several typical organic pollutants.Remarkably,a high removal efficiency was achieved in the EF treatment of shale gas fracturing flowback wastewater.The residual COD is 80 mg L^-1 after reaction 4 h with a low specific energy consumption of 6.9 k Wh kg^-1COD^-1.In order to obtain more efficient self-supporting electrode via simpler preparation method,a highly active Fe single atoms-based self-supporting electrode（CFP@Fe SAs-N-C）was finally successfully prepared by simple electrodeposition and pyrolysis method,in which the active site can directly anchor on the conductive substrate.The uniformly dispersed Fe atomic sites exert excellent atomic-scale effect,which can effectively promote the production of highly active·OH in the system,thus,improving the reaction efficiency of EF.The prepared electrode can effectively degrade aromatic organic pollutants,and the residual COD and TOC values of treated actual shale gas fracturing flowback wastewater were under 60 mg L^-1 and 10 mg L^-1.It shows excellent stability and catalytic activity,becoming an iron-based electrode material with great development potential in the field of water treatment.