| High nitrate concentrations in water ecosystems pose a serious threat to ecological balance and human health.In order to minimize this adverse effect,many methods have been used to eliminate nitrate from water.Electrochemical treatment plays an important role in the nitrate reduction reaction,and the most ideal solution for nitrate removal is to selectively reduce it to reusable ammonia nitrogen,but the current metal electrodes of noble metal type,although possessing good activity as well as stability,however,their high preparation cost limits their popular application for practical wastewater treatment.After literature research,it was found that electrode materials with higher activity and better stability can be obtained by modifying trace amounts of metals on inexpensive carrier materials.Therefore,for the solution of electrode cost we chose inexpensive and easily available cerium oxide nanorods with good electrical conductivity as the carrier,and then loaded with small amounts of common metals nickel and iron to prepare an efficient catalyst for electrocatalytic reduction of nitrate wastewater to recover ammonia,as follows:(1)Cerium oxide nanorods were synthesized by hydrothermal method,and then Ni-CeO2 was prepared by impregnation method with cerium oxide as a carrier,which was applied to electrocatalytic nitrate reduction reaction.Firstly,the composition and structural morphology of cerium oxide loaded with nickel metal were verified by XRD,SEM and TEM,and the experimental conditions were optimized.Meanwhile,the reduction activity of Ni-CeO2 electrode was tested in electrolytes with different nitrate initial concentrations,which proved that the preparation of the electrode has a certain range of pollutant concentration applicable.In addition to the activity,the stability of the electrode is another key evaluation index of the electrode material,so the stability test of the Ni-CeO2 electrode was conducted,and the results showed that the reduction performance of the electrode continued to be energized for 25 hours with almost no decay.Finally,the reason for the enhanced nitrate reduction activity of the nano-rod-shaped cerium oxide after loading with metallic nickel was investigated.(2)Although the activity of the prepared catalyst(Ni-CeO2)for nitrate reduction was improved after the modification of nickel,we further modified other metallic materials based on the study of cerium oxide loaded nickel in order to obtain a more desirable reduction effect.According to the literature research,iron,as an environment-friendly metal,has its own ability to reduce nitrate nitrogen,so we tried to conduct experiments on electrocatalytic reduction of nitrate nitrogen with metallic iron modified cerium oxide in nanorods as a catalyst.The experimental results showed that the Faraday efficiency of the cerium oxide loaded iron electrode in the reduction of nitrate nitrogen to recover ammonia could reach more than 90%,and the recovery of ammonia nitrogen was up to 99%,and the cerium oxide loaded iron electrode showed better activity and stability of electrocatalytic reduction of nitrate nitrogen to recover ammonia compared with the cerium oxide loaded nickel electrode.The effect of different nitrate-nitrogen concentrations on its Faraday efficiency for ammonia recovery by reduction of nitrate-nitrogen was also investigated,and the experimental results revealed that the prepared electrodes have some universality for different pollutant(nitrate-nitrogen)concentrations in a wide range of concentrations.In addition,the reduction of nitrate to ammonia nitrogen process was analyzed by electrochemical tests such as LSV and bilayer capacitance to further investigate the reason for its enhanced activity.It provides a reference for the efficient electrochemical reduction of nitrate to ammonia nitrogen. |
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