Preparation Of Nano Electrode And Behavior And Mechanism For Electrochemical Reduction Of Nitrate In Groundwater

Nitrate contamination of water resources not only endangers ecological environment,but also poses a threat to human health,which has become an increasingly problem for all over the world.Electrochemical denitrification with high efficiency,easy operation,low investment and environmental friendliness,has attracted a large of researchers'interest.However,the traditional electrochemical method has some disadvantages such as a large number of by-products and poor electrode surface activity,which restricts its application in practical engineering.In this study,TiO₂ nano electrode was fabricated by anodic oxidation with Ti electrode as the substrate material,and then active metal-modified nano electrodes were prepared by electrodeposition for electroreduction of nitrate in groundwater.The physicochemical properties of the three kinds of nano electrodes were analyzed by SEM,EDS,XPS and XRD.The reduction behavior of nitrate by nano electrodes under different conditions was discussed and the mechanism of electroreduction of nitrate by nano electrodes was revealed.TiO₂ nano electrode was prepared by anodic oxidation.Response surface method was used to optimize the preparation conditions of electrode.TiO₂ nano electrode fabricated by electrochemical oxidation for 60 min at HF concentration of 0.06 wt%,acetic acid concentration of 10%?v/v?and oxidation voltage of 23.3 V covered with tubular structures with relatively uniform pore diameter and wall thickness.The results of XPS and XRD showed that the main component of TiO₂ nano electrode was TiO2.Removal efficiency of TiO2 nano electrode for nitrate?initial concentration of50 mg-N/L?could reach 66.7%after 90 minutes,which was three times than that of Ti electrode.The nanotubes formed on TiO₂ nano electrode increased the surface area of electrode and improved electrochemical activity.The double electric layer formed on the electrode surface made it easier for nitrate ions react with the electrode,which was conducive to nitrate removal.Cu nanoparticles were loaded on the surface of TiO₂ nano electrode by electrodeposition to improve the electrochemical activity of electrode.Cu/TiO₂composite nano electrode was prepared at the current density of 2 mA/cm²,deposition solution concentration of 0.2 mol/L,and deposition time of 20 s.The surface of composite nano electrode has a regular morphology,TiO₂ nanotubes were uniformly distributed and Cu nanoparticles were evenly distributed on the electrode surface.The surface area and active sites of Cu/TiO₂ composite nano electrode were increased.XPS and XRD analysis results showed that Cu loaded on the surface of the electrode with three forms of Cu⁰,Cu₂O and CuO,improved the adsorption and reduction activity of nitrate on the electrode surface.The removal efficiency of nitrate reached83.5%,which was 1.3 times higher than TiO₂ nano electrode,significantly improved the removal efficiency of nitrate.In order to further improve the nitrate reduction efficiency,the Cu/Zn/TiO₂polymetallic nano electrode was developed by electrochemical workstation under the condition of current density of 2 mA/cm²,ratio of Cu/Zn ion in the deposition solution of 2:1?w/w?,and deposition time of 20 s.The SEM and EDS results showed that Cu and Zn nanoparticles were uniformly adhered to the nanotube,and did not destruct the tubular structure of TiO₂ nano tube array.The results of XPS and XRD indicated that Cu and Zn nanoparticles were successfully loaded on the surface of electrode,which were in zero valence and oxide form.The Cu/Zn/TiO₂ polymetallic nano electrode has a large real surface area and high electrochemical activity.Cu promoted the adsorption of nitrate and enhanced the reduction of nitrate to nitrite,while Zn strengthened the conversion of nitrite to N₂,thus improving the selectivity of N₂.Cu and Zn nanoparticles cooperated with TiO₂ nanotubes enhanced the electrochemical activity of nireate,the nireate removal efficiency was 93.6%.In addition,TiO₂ nano electrode,Cu/TiO₂ composite nano electrode and Cu/Zn/TiO₂ polymetallic nano electrode were used as cathodes and Ti/Pt as anode to construct electrochemical system.Through comparative research,it was found that Cu/Zn/TiO₂ polymetallic nano electrode has the highest electrochemical activity,could efficiently reduce nitrate with lower by-products generation rate.At the same time,the effects of different influence factors on nitrate removal were also studied.The results showed that the nitrate removal efficiency increased with increasing current density and temperature,but the initial nitrate concentration had no significant effect on nitrate removal.Adding a certain amount of NaCl as electrolyte to the three electrochemical systems could realize cathodic reduction of nitrate,meanwhile,effectively inhibited the formation of ammonium and nitrite,achieving the goal of clean and safe removal of nitrate.The three new nano electrodes prepared in this study have large specific surface area and high electrochemical activity,which can achieve harmless removal of nitrate in groundwater.Therefore,this research provides theoretical and technical support for the electrochemical removal of nitrate and has some significance value of practical application.