| Dye wastewater has deep chromaticity and poor biodegradability.Traditional water treatment processes such as adsorption,membrane filtration and biological treatment are difficult to effectively degrade mineralized dye molecules,which poses a serious threat to human health and ecological environment.Electro Fenton technology can generate non selective strong oxidized hydroxyl groups（·OH）in situ by double electron oxygen reduction（2e-ORR）.It is one of the effective methods to treat dye wastewater.However,the poor performance of H2O2synthesis,low current efficiency,high energy consumption and the demand for metal catalysts limit the practical application of electro Fenton.Based on heterogeneous electro Fenton technology,this paper used two-step carbonization method to make nitrogen doped peanut shell biochar（NPSB）from waste biomass.Then,NPSB was loaded on carbon felt by calcination bonding method to form composite carbon electrode.The degradation effect of metal free electro Fenton cathode on methyl orange dye wastewater was studied.According to scanning electron microscope X-ray energy spectrum（SEM-EDS）,NPSB had rich pore structure and the percentage of N atoms reaches 2.67%.X-ray photoelectron spectroscopy（XPS）showed that NPSB had many nitrogen and oxygen structures.The above characterization analysis showed that the composite electrode could effectively improve the activity and selectivity of 2e-ORR,which may be due to nitrogen and oxygen doping.X-ray diffraction（XRD）showed that amorphous carbon was mainly found in NPSB and NPSB-CF.The contact angle（CA）of NPSB-CF was 108.01°,indicating that the composite electrode had strong hydrophobicity.According to the results of specific surface area test（BET）,the specific surface area of NPSB-CF electrode modified by NPSB（700.87 m2/g）was significantly increased to443.39 m2/g.In addition,cyclic voltammetry（CV）test showed that the ion migration rate of NPSB was fast.When loaded on carbon felt,it improved the current response of the composite electrode and had stronger oxygen reduction activity.Rotating ring disk test（RRDE）showed that NPSB had high 2e-ORR selectivity.According to the linear sweep voltammetry（LSV）,NPSB-CF electrode had higher current response.The fitting results of electrochemical impedance spectroscopy（EIS）showed that the resistance of NPSB-CF was 7.132Ω.The above test results showed that the electrochemical oxygen reduction performance of NPSB-CF was enhanced.The single factor optimization experiments of current density,initial molybdenum concentration,electrolyte concentration and aeration rate were carried out,and the operating parameters of electro Fenton process were determined.The 90 min cumulative H2O2concentration of this electro Fenton system was 196.08 mg/L,and the removal rate of 20 mg/L MO solution is more than 98%.The calculated initial current efficiency and electric energy consumption were 12%and 0.26224 k Wh/g（COD）respectively.Adsorption experiments,fluorescence detection and free radical masking experiments showed that·OH was the main active material for the removal of molybdenum.Finally,the intermediate products produced in the degradation of molybdenum simulated wastewater were analyzed by high performance liquid chromatography-mass spectrometry（HPLC-MS）,and the possible degradation pathways were put forward.In this study,nitrogen doped biochar was used to modify the carbon felt,a metal free cathode was constructed,and the wastewater containing MO was successfully degraded,which provided theoretical support for the application of electro Fenton technology in dye wastewater treatment. |
