Study On The Preparation Of Multistage Copper Nanoelectrode And The Application In Nitrate Removal By Electrochemical Reduction

Water pollution has become an urgent problem in developing countries,especially the quality indicators of NO3--N and total nitrogen.Over-discharge of nitrogen oxides from domestic sewage,agricultural wastewater,industrial wastewater and fossil fuel combustion has resulted in serious imbalance of global nitrogen cycle,resulting in excessive nitrate content in groundwater,rivers and lakes.This serious situation urgently requires us to seek effective strategies for nitrate degradation.Electrochemical reduction is considered as a promising and environmentally friendly candidate method,which has attracted great attention in the past decades.However,the degradation of NO3-to harmless nitrogen is a major challenge in the field of water treatment.In this paper,Cu/NF,Cuchem/NF,Cuelectro/NF,Cuod300/NF and Cuod500/NF electrodes were prepared by electrodeposition and different oxidation method,and Cu-Ni/NF,Cu-Co/NF,Cu-NiCo/NF,Cu-P/NF and Cu-S/NF modified by non-precious metals and non-metals,but the results were not satisfactory.Finally,3D self-supported hierarchical Cuocl50/NF electrode composed of ultra-thin Cu nanosheets-assembled micro-columns on porous nickel foam was prepared by three steps,including electrodeposition of CuCl-Cu,thermal oxidation into CuCl-CuO and electrochemical reduction into Cu.Benefitting from the advantages of large surface area and highly active interface as well as fast electron-transfer path,CuOCl50/NF exhibits the significant positive-shift of potential and higher current density than other Cu-based electrodes in the electrochemical reduction of NO3-(NO3--ER).Not only that,an extremely high sensitivi of nitrate reduction response up to 11.23 mA mM-1 cm-2 was obtained by chronoamperometric test,which is much higher than those of previously reported works.By exploring the effects of supporting electrolyte,current density,chloride ion content,electrolysis time,plate spacing and flow rate on the results of cathodic reduction of NO3-,as well as the effects of liquid pH value,initial ammonia nitrogen concentration and chloride ion concentration on the anodic oxidation of ammonium to harmless nitrogen gas,the most suitable experimental conditions were found to achieve the best applied results of NO3--ER.When the cathode consists of 2 g/L NaCl in electrolytic solution,the distance between plates is 2 cm,the current efficiency of constant current electrolysis at high current density-200 mA for 2 h is over 50%and the selectivity of nitrogen is 61.1%.Besides,the selectivity of nitrogen can be as high as 99.8%with the increase of electrolytic time.Under the optimum conditions of 50 mM initial ammonia nitrogen concentration and 2 M chloride ion concentration,the current efficiency in alkaline solution is 80%and the conversion rate is 99%in the anodic oxidation of ammonia nitrogen,which is better than that in neutral solution.Finally,the conversion percentage of 99.7%for NO3--ER was achieved on CuOCl50/NF cathode in NO3--ER experiments.Through the cathodic reduction of NO3-coupled with the anodic oxidation of Cl-,and the subsequent chemical reaction of NH4+and CIO-,the highly efficient degradation of NO3-into N2 with selectivity as high as 97.9%was realized.This work provides a highly efficient CuOCl50/NF electrode and a promising way for degradation of NO3-into N2.