Study On The Efficient Removal Of Nitrate From Groundwater By NiO/TiO₂ Nano Electrode

Nitrate contamination in groundwater is a wordwide environmental problem due to its harmfulness to human health threatening drinking water safety.Various methods have been developed to remove nitrate in groundwater.Compared with other treatment methods,electrochemical method has the advantages of simple operation,low cost and environmental friendliness.However,the removal efficiency of tradtional electrochemical method for removing nitrete from water is low with poor selectivity of electrode to products and short lifespan.Therefore,the development of new electrodes is required to remove nitrate from groundwater efficiently.In this study,Ti plate was used as the electrode material to prepare the TiO₂ nanoelectrode by redox method.On the basis of this,NiO/TiO₂ nanoelectrode was successfully developed by the chemical water bath method.The NiO/TiO₂ nanoelectrode was successfully developed.The optimization of electrode preparation showed that the NiO/TiO₂ nano-electrode prepared at a water bath time for 10 min and a calcination temperature of 500? had a nitrate removal rate of 90.4%.Through various characterization methods,it was found that there were a large number of TiO₂ nanopores and a small amount of metal Ni on the surface.The effect of current density,initial concentration,temperature and pH on nitrate removal efficiency was studied by using Pt electrode as anode and NiO/TiO₂ nanoeiectrode as cathode.The results showed that:?1?when the current density was between 10 and 50 mA/cm2,the nitrate removal effciency increased with the increase of current density;?2?when the initial concentration of nitrate was between 10-100 mg/L,the removal efficiency of nitrate increased with the increase of initial concentration;?3?when the experimental temperature was controlled at 0-60?,the removal efficiency of nitrate increased with the increase of temperature;?4?when the pH of the solution varied between 3 and 11,that the removal efficiency of nitrate is higer under alkaline conditions;?5?when IrO₂ was used as the anode and NiO/TiO₂ nanoeiectrode as the cathode,adding NaCl concentration of 0.3 mg/L,the major product of the electrolysis products was N2,and the generation of ammonia nitrogen and nitrite was negligible.The reaction surface method was used to optimize the reaction conditions for the removal of nitrate by electrochemical method.The Box-Behnken design-method was used by selecting the three major factors including current density,reaction time and sodium chloride addition as independent variables.Nitrate removal rate and ammonia nitrogen production amount were used as the dependent variables.The model was established by Design Expert 8 Application software.The results showed that the condition with current density 36.68 mA/cm2,reaction time 95.65 min,and NaCl addition amount 0.27 g/L was the best condition with 97.63%of nitrate removal efficiency and 0.04 mg/L ammonia nitrogen production,which is consistant with the results from modelling demonstrating that the method could be used for optimization of nitrate removal by NiO/TiO₂ electrode and prediction of nitrate removal efficiency and ammonia generation.The mechanism of the electrodes as a cathode to removal nitrate was investigated by an electrochemical worksation.NiO/TiO₂ electrode reduction peak appeared around-0.65 V,higher than TiO₂ nano-electrode.Its reduction voltage was higher than those of Ti electrode and nano-electrode showing higher nitrate removal efficiency.The enhanced electrochemical system by NiO/TiO₂ nano-electrode is an effective method for nitrate removal in groundwater compared with Ti electrode and TiO₂ nano-electrode.