Prepration Of Iron-carbon Electrocatalyst By Hydrothermal Method For Nitrate Reduction

Due to the rapid development of industry and agriculture,excessive nitrogen emission has resulted in the imbalance of nitrogen cycle in nature,especially in nitrate pollution in water ecosystem.Excessive nitrate seriously inhibits the biodiversity of water environment and endangers human health.Therefore,it is urgent for researchers to find an efficient and simple method to treat excessive nitrate in water system.In recent years,a variety of nitrate removal technologies have been developed,such as physical denitrification,chemical reduction denitrification,biological denitrification and electro-catalytic denitrification.Because of the advantages of mild reaction and environmental friendliness,electrocatalytic denitrification is considered to be one of the most promising technologies.The design of the catalyst is one of the most important links in the electrocatalytic denitrification process.In recent years,iron nanoparticles with high activity and low cost have been widely used in the field of electrocatalysis.Due to the high surface energy and high activity of iron nanoparticles,it is easy to agglomerate and be oxidized,which results in a significant decrease in their reaction activity and catalytic effect.Therefore,there are still many limitations in promoting the practical production of iron-based electrocatalyst materials.So how to design a simple and available synthesis method to achieve an effective spatial structure and inhibit the agglomeration of iron-based materials in the catalytic process,which can make more active sites exposed and realize high reduction ability to nitrogen?Based on the points,firstly,this paper designs a multi-step hydrothermal method with in-situ high temperature reduction,the nanostructured iron is embeded in microporous carbon spheres（Fe@C）.In addition,the large number of microporous structures are in carbon spheres,which can effectively limit the aggregation of iron nanoparticles and promote ion/charge transfer in the electrocatalytic process.At the same time,the carbon spheres can be used as an effective protective layer to slow down the oxidation process of iron nanoparticles and significantly improve the catalytic effect.The final product meets gram-scale output,which has the possibility of mass production.To explore the effect of the content of different iron salt precursors on Fe@C,it is found that Fe@C-1（iron content is 38.3 wt%）shows the most excellent nitrate removal rate of75.9%,～98%selectivity of nitrogen and outstanding nitrate removal ability 1238.6 mg N g^-1 Fe.During the whole process of material design and synthesis,iron nanoparticles play an important roles as the active materials to promote the conversion of nitrate to nitrogen,which shows the excellent catalytic performance.Because most of iron nanoparictles are located in the carbon microspheres,which is harmful to contact with NO₃^-.Therefore,the dicyandiamide is chosen as nitrogen resource,and sucrose is chosen as carbon resource,which are hydrothermalized with iron salt.Then,they are carbonized in nitrogen atmosphere to prepare iron and nitrogen co-doped mesoporous carbon sheet structure.The coordination environment of nitrogen can promote the combination with metal particles and inhibit the agglomeration of iron nanoparticles,which makes the iron species targeted on the carbon sheets and the Fe Nx was formed.Under the synergistic effect of the iron clusters and Fe Nx,more active sites were exposed to improve the selectivity of nitrogen.In addition,the obtained Fe-NC nanomaterials show rich porous structure(specific surface area:969.6～1431.6 m²g^-1),which can effectively promote the adsorption and transport of nitrate during electrocatalysis.And Fe-NC-2 exhibited stable nitrogen selectivity（～98%）and excellent nitrate removal capacity(～2291.3 mg N g^-1 Fe)with the high nitrate concentration(150mg L^-1).In summary,this project adopts an efficient,simple and relatively high-yield hydrothermal method,and through a reasonable design of the structure of the iron-carbon electrocatalyst,which exposes a large number of active sites and improves the utilization of active substances.The enhanced adsorption and transmission of nitrate guaranteed the reduction path of 5-electron,which achieves the goal of high selectivity of nitrogen and the outstanding removal performance of nitrate.