Preparation Of Co₃O₄ Electrode By Electrodeposition Method And The Study Of Its Performance On Nitrate Electroreduction

Nitrate is a common chemical contaminant in the world largely resulting from industrial discharge,animal manure and atmospheric deposition.Excessive nitrate accumulation in water may cause damage to the environment and health risks to human beings.Various techniques have been researched and full-scale applied for nitrate contamination remediation.Among these techniques,electrochemical reduction seems to attract more and more attention in the past few years,especially for refractory industrial wastewater treatment.Furthermore,cathode material plays an important role during the process of electrochemical denitrification.The purpose of this study is to investigate the effects of cathode catalysts including catalysts type and catalyst microstructure and electrochemical reaction conditions on electrochemical NO₃^-reduction rate for high-salt（chlorine）industrial wastewater.The electrochemical denitrification performance of Ti,Ni,Co and Cu as cathodes is firstly compared.Furthermore,Cu O,Fe₂O_3,Co₃O₄and Ni O film are synthesized through electrodeposition method and are used as cathode in NO₃^--N electrochemical reduction and the performance comparison of these electrodes was under the same experimental conditions.The experimental results show that the differences among the performance of Cu,Fe,Co and their corresponding oxides are not obvious,while Ni and corresponding oxide has the worst NO₃^--N reduction performance.Co₃O₄ nanosheet film is synthesized through electrodeposition and used as cathode in electrochemical NO₃^-removal.The electrodeposition conditions are optimized and the NO₃^-removal rate is enhanced by 1.7times in comparison with Co₃O₄solid particle cathode,which mainly results from its large surface area and high efficient electron transfer and utilization capacities.The effects of reaction temperature and current are then deeply investigated.NO₃^-removal rate is enhanced from 0.00667 min^-1to 0.0156min^-1at 0.08 A with reaction temperature rising from 5 ^oC to 45 ^oC,and it can further be enhanced to 0.0220 min^-1with current increasing to 0.16 A.Furthermore,the physical properties of Co₃O₄nanosheet cathode are more stable during the reaction at high temperature.Low reaction temperature tend to have electrode self-reaction.Although high temperature and high current could facilitate the NO₃^--N reduction rate,this condition may promote the conversion of NH₄⁺-N to NH₃which would escape into the air.Almost 60%TN removal is obtained under 0.16 A,however,most of which is obtained through NH₃escape instead of N₂generation.Adjusting the pH around neutral condition during the reaction can effectively fix NH₄⁺in solution.The NH₄⁺can then be oxidized to N₂in the presence of certain amount of Cl^-and achieve total nitrate reduction process.