Electrocatalytic Reductive Dechlorination Of 2,4-dichlorophenoxyacetic Acid On NiCo₂O₄ Interlayer Modified Palladium/nickel Foam Electrode

Chlorinated organic compounds?COCs?are ofen widely used as herbicides,plant growth regulators and chemical raw materials in agriculture,chemical industry,biomedicine and other industries.They present the characteristics of difficult degradation,bioaccumulation,high toxicity and long-distance migration.Once enter the environment,they will cause serious damage to soil,surface water and groundwater.2,4-dichlorophenoxyacetic acid?2,4-D?is a typical kind of COCs,and its toxicity is mainly determined by chlorine substituent functional groups.Therefore,it is of great significance and value to study the dechlorination behavior of 2,4-D in the field of environmental protection and other related fields.Among these methods,electrocatalytic reduction dechlorination has been widely studied by researchers due to its advantages of high efficiency,low cost and green process with no secondary pollution.Therefore,the development of a new efficient low cost catalytic materials as cathode and the corresponding dechlorination mechanism have become the most important part in this research area.In this paper,the Pd/Ni foam electrode was modified by adding a NiCo₂O₄nanosheet interlayer,the physical and chemical properties of the electrode were analyzed by various characterization methods,such as glancing incidence X-ray diffraction?GIXRD?,field emission scanning electron microscopy?FE-SEM?and transmission electron microscopy?TEM/HRTEM?.The Pd load on the electrode surface was 0.68mg measured by atomic absorption spectrophotometer?AAS?.The formation and immigration of active atomic hydrogen(H*_ads)is very important in the dechlorination process.Therefore,in this work,the hydrogen binding energy?HBE?values on Pd?111?,NiCo₂O₄?311?and ML Pd-NiCo₂O₄?311?surfaces were calculated using density functional theory?DFT?.The similar HBE values on Pd?111?and ML Pd-NiCo₂O₄?111?surfaces indicating the possibility of NiCo₂O₄ interlayer modified Pd/Ni foam keeps the dechlorination efficienty at a lower precious metal Pd loading.The prepared composite electrode was used as the cathode for electrocatalytic reduction of dechlorination 2,4-D.When the applied cathode potential was-1.0 V,the removal efficiency of 2,4-D on Pd/Ni foam electrode was 17.1%after 75 min of electrocatalytic dechlorination.And the Pd/NiCo₂O₄/Ni foam electrode with the same Pd loading showed a higher removal efficiency of 2,4-D,which was 97.6%.The Pd/NiCo₂O₄/Ni foam electrode reacted the maximum current efficiency?CE?of 5.2%at-1.0 V after 60min.The high activity of the electrode could be maintained after five consecutive cycles of dechlorination reaction,indicating the good stability of electrode.Comparing the Pd load of Pd/Ni electrode used for dechlorination,it showed that NiCo₂O₄ interlayer was beneficial to save the cost.Through the analysis of electrode dechlorination efficiency and intermediates in the process of dechlorination,it was concluded that the dechlorination mechanism of Pd/NiCo₂O₄/Ni foam electrode was an indirect electrocatalytic dechlorination process in which the generated H*_ads to attack 2,4-D,and the dechlorination pathway was mainly 2,4-D was removed a chlorine atom to intermediate o-CPA,and then the final product PA was generated by further dechlorination by o-CPA.In addition,the effects of cathode potential,reaction temperature,initial 2,4-D concentration and initial p H were compared for the dechlorination efficiency on Pd/NiCo₂O₄/Ni foam electrode.