Removal Of Nitrate From Water By The Electrocatalytic Denitrification

With the rapid development of industry and agriculture,nitrate pollution in water is increasingly serious in China,directly or indirectly harm the human health.The nitrate content in drinking water should be less than 10 mg/L according to the hygienic standard of drinking water in China.Since some byproducts are produced during the nitrate reduction process,it is difficult to convert all of nitrate into nitrogen.Therefore,the development of a highly efficient,highly selective and low-cost nitrate nitrogen treatment method has become a promising research direction.In recent years,the electrocatalytic denitrification method has been paid more and more attention by researchers.Among the cathode materials,the study of bimetallic materials gradually developed into a trend.The bimetallic electrode in the electrocatalytic activity and reaction selectivity has a high plasticity,with good application prospects.In this paper,Cu-M(M represents Bi and Sn)bimetallic electrodes were prepared by constant current electroplating method.Cu-Bi electrode was a new type of electrode in the field of electrocatalytic denitrification.The preparation conditions of the two electrodes were optimized,and the electrocatalytic denitrification performance of the two electrodes was studied.The effects of plating current density on the stability and element composition of the electrode coating were investigated.The electrolysis of sodium nitrate simulated wastewater was carried out in a single chamber reactor with control of constant current.The effects of current density,initial pH value and initial concentration of nitrate on the removal efficiency of nitrate and the composition of the products were discussed in detail.The electrocatalytic denitrification properties of Cu-Bi and Cu-Sn were compared.Through the above experimental results of the analysis and discussion,the following conclusions:(1)The electroplating current density has a great influence on the stability of the electrode coating.The optimum current density of Cu-Bi electrode is 6 mA/cm~2,and the surface of the coating is dense,uniform,stable and no charring phenomenon.The optimum current density of electroplated Cu-Sn bimetallic electrode is 4 mA/cm~2,and the surface particle of the obtained coating is uniform and the roughness is high,which is favorable for catalysis.(2)Cu-Bi bimetallic electrode was used as cathode,ruthenium iridium electrode was used as anode,the initial concentration of nitrate nitrogen was 100 mg/L,the concentration of Na2SO4 was 0.125 mol/L,the current density was 6 mA/cm~2,the initial pH value was 7,under the above condition of electrocatalytic reduction for 4 h,the removal rate of nitrate nitrogen was 87.5% and the total nitrogen removal rate was 60.7%.The concentration of nitrite was 3.74 mg/L,ammonia nitrogen concentration 17.15 mg/L,and the current efficiency was about 34%.(3)Cu-Sn bimetallic electrode was used as cathode,ruthenium iridium electrode was used as anode,the initial concentration of nitrate nitrogen was 100 mg/L,the concentration of Na2SO4 was 0.125 mol/L,the current density was 10 mA/cm~2,the solution was alkaline,under the above condition of electrocatalytic reduction for 4 h,the removal rate of nitrate nitrogen was 34%,the nitrite nitrogen was not detected in the products,the selectivity of ammonia nitrogen was 100%,and the current efficiency was 8%.(4)Cu-Bi bimetallic electrode was significantly better than Cu-Sn bimetallic electrode by electrocatalytic denitrification.The Cu-Sn electrode could convert all the nitrates into ammonia nitrogen and no other by-products.Cu-Bi electrode has better effect under neutral condition,while Cu-Sn electrode has better effect under alkaline condition.(5)Cu-Bi bimetallic electrode on the reduction of nitrate accompanied by the occurrence of hydrogen evolution reaction,Cu-Sn bimetallic electrode reduction of nitrate reaction occurred before the hydrogen evolution reaction.The increase of the content of copper in the coating is helpful to improve the electrocatalytic activity of the electrode.