The Preparation Of Efficient Co₃O₄/Fe₂O₃-Ti Cathodes And The Study Of Their Performances On Nitrate Electroreduction

Since nitrate has great harm to natural water and human health,several methods have been developed to treat nitrate contamination,among which electrochemical reduction of nitrate has received more and more attention due to its convenience,environmental friendly and low cost.Meanwhile,most industrial wastewaters always contain large amount of inorganic salts,resulting in high conductivity and no more electrolyte needs to add during electrochemical reduction accordingly.So,it's suitable to take electrochemical method to treat these kinds of wastewater.Co₃O₄ film and Fe₂O₃ film coated on Ti substrate are prepared using sol-gel method and applied as cathode material for electrochemical denitrification in this research.Preparation conditions including precursor coating times and calcination temperature are optimized based on NO₃^--N removal,NO₂^--N generation,NH₄⁺-N generation and total nitrogen?TN?removal efficiencies.The influences of electrolysis parameters such as current density and NO₃^--N initial concentration are also investigated.Though NO₃^--N and TN removal efficiencies increase with current density increasing,electro energy utilization efficiency is low at high current density.Meanwhile,the absolute NO₃^--N and TN removal amounts enhance with the increase of NO₃^--N initial concentration.In comparison with other common researched cathodes?Ti,Cu and Fe₂O₃/Ti?,Co₃O₄/Ti exhibits better TN removal efficiencies.In order to remove NO₃^--N completely from water,Cl^-is added to help further oxidize NH₄⁺-N to N₂.With the increase of Cl^-from 0 mg L^-1 to 500,1000and 1500 mg L^-1,TN removal after 3 h treatment increases from 65%to 80%,90%and 96%by Co₃O₄/Ti cathode,from 49%to 61%,75%and 84%by Fe₂O₃/Ti cathode.Meanwhile,rising current density can also help improve TN removal when the Cl^-concentration is at low level.The mechanism of NO₃^--N reduction on cathode and NH₄⁺-N oxidation on anode in the absence and presence of Cl^-is also investigated in a double-cell reactor.Nano rod Co₃O₄/Ti?NRCo₃O₄/Ti?cathode prepared by hydrothermal method.Under same condition,if there's no Cl^-in the solution,Co₃O₄/Ti has better nitrate reduction performance than NRCo₃O₄/Ti;if there is 1000 mg L^-11 Cl^-in the solution,NRCo₃O₄/Ti has better electrochemical denitrification performance.Finally,actual textile wastewater containing both NO₃^-and Cl^-was also treated and the Co₃O₄/Ti cathode exhibits excellent stability and reliability.More NO₃^--N will be removed if the wastewater is first pretreated with Fe₂SO₄-Fenton to remove the extra COD.It is interesting to find out that changing Fe₂SO₄ to FeCl₂ is more benefit for next-step electrochemical NO₃^--N complete removal.In comparison with Fe₂SO₄-Fenton pretreatment,TN removal enhances from 61%to 85%after 3 h treatment.