| Nitrate pollution has emerged in the water bodies of various countries and has become a worldwide environmental issue as industry and agriculture advanced.When the nitrate in the water body exceeds the standard,it will cause problems such as eutrophication and the changes in the diversity of plants and animals in the water body.After people drink water containing nitrate that exceeds the standard,it will increase the risk of cancer and cause serious threat to our health.Among the many methods for the treatment of nitrates,the electroreduction method has the advantages of fast reaction rate,strong controllability,no sludge generation,and not effected by environmental conditions,so it is favored by researchers.However,in this technology,the cathode material is very important for the removal rate of nitrate and the production of by-product ammonia nitrogen and nitrite.Therefore,it is of great significance to find an electrode that can efficiently remove nitrate and improve the selectivity of nitrogen for the treatment of nitrate.In this study,two kinds of electrodes,Ni-TiO2 and Bi-TiO2 nanotube arrays,were prepared by electrodeposition method with a high proportion of TiO2 nanotubes as substrates.The influence of different treatment methods on titanium surface,plating time of nickel and bismuth,and calcination temperature of nanotubes on the reduction of nitrate were studied,and the preparation parameters of the electrode with the best nitrogen removal performance were determined.Afterwards,the optimized electrode was subjected to the experiment of influencing factors,and the affect of various factors on nitrate removal rate、nitrite nitrogen and ammonia nitrogen transfer quantity,the removal of total nitrogen and the selectivity of nitrogen was analyzed.Finally,the kinetic models of nitrate removal of the two electrodes were respectively determined by analyzing the removal rate of nitrate nitrogen at different concentrations,the influence of different experimental conditions on the rate constant of nitrate reduction was analyzed.Finally,respectively analyze the removal process of nitrate nitrogen of two electrodes.The results of the study indicate that:(1)The introduction of Ni and Bi greatly enhances the reduction activity of the nanotube electrode to nitrate.The optimized parameters of Ni-TiO2 electrode:the titanium substrate was treated with 5000 mesh sandpaper,the plating time of nickel was 5 min,and the calcination temperature was 500℃;the optimized parameters of Bi-TiO2 electrode:the plating time of Bi was 8 min,the calcination temperature was 500℃.(2)When the Ni-TNA electrode was used as cathode for removing nitrate,under the optimal processing condition:current density of 25 mA/cm2,pH value of 11.0,NaCl concentration of 0.75 g/L,and stirring speed of 450 rad/min.after 2 hours of reduction,the removal rate of 50 mg/L nitrate was 86.33%,the content of nitrite nitrogen and ammonia nitrogen in the solution were close to zero,the removal rate of total nitrogen was 86.21%,and selectivity of nitrogen was 99.86%.(3)When the Bi-TNA electrode was used as cathode to remove nitrate,under the optimal operating conditions:current density of 30 mA/cm2,pH value of 8.5,NaCl concentration of 1.25 g/L,after 2 hours of reduction,the removal rate of 50 mg/L nitrate was 93.52%,the amount of nitrite nitrogen and ammonia nitrogen were almost zero,the removal rate of total nitrogen was 93.40%,and the selectivity of nitrogen was 99.87%.(4)The reduction process of nitrate by Ni-TNA and Bi-TNA electrodes followed the first-order reaction kinetics of the Langmuir-Hinshelwood model.Ni-TNA and Bi-TNA electrodes remove total nitrogen from the solution,including reduction of nitrate and oxidation of ammonia nitrogen.The results of this study provide a theoretical basis for the preparation and application of cathode in electrochemical reduction of nitrate. |
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