Preparation Of Iron-based Carbon Nanofibers And Their Applications In Electrocatalytic Nitrate Reduction

Excessive nitrate existed in water poses a huge threat to the ecological environment and human health.Therefore,there is an urgent need for a green and environment-friendly technology to reduce nitrate to non-toxic,harmless and directly emitted nitrogen.Among various nitrate reduction technologies,the electrocatalytic reduction method has been considered to be the most promising nitrate treatment technology because of its simple operation,low cost,and no secondary pollution.Abundant reserves,low price and non-toxic nano-zero-valent iron gradually replacing precious metals and becoming a popular catalyst because of its attractive nitrate reduction activity,.However,poor dispersibility,easily to be corroded and oxidized,the low selectivity to nitrogen restricts its further development.Therefore,exploring iron-based composite materials suitable for electrocatalytic nitrate reduction has become an important issue.In this paper,in order to design iron-based composite catalysts with excellent electrocatalytic nitrate reduction performance,we selected different iron sources to prepare nitrogen（N）-doped carbon nanofibers loaded with different iron-containing active ingredients through electrospinning combined with spatially thermal reduction strategies.The experimental results show that the synthesized iron-based electrocatalyst can improve the removal activity of nitrate,increase the conversion percentage of nitrate and can obtain ultra-high nitrogen selectivity.The main research contents are as follows:（1）We synthesized N-rich carbon nanofibers decorated with Fe/Fe₃C nanoparticles （Fe/Fe₃C-NCNFs）which confined in carbonaceous matrix evenly embedded in carbon nanofiber through electrospinning and spatial thermal reduction strategy by selecting Prussian Blue（PB）as the iron source.In addition,we compared and analyzed the effects of different iron content and calcination temperature on electrocatalytic nitrate reduction.The results reveal that the good dispersibility of Fe/Fe₃C nanoparticles,the synergistic catalysis of active iron species Fe and Fe₃C,the N-rich doping sites and the continuous one-dimensional carbon skeleton structure can play an important role in improving the electrocatalytic nitrate removal capacity（mg N/g Fe）and nitrogen selectivity.（2）The bimetallic Cu/Fe nanoparticles embedded N-doped carbon nanofibers （Cu/Fe@NCNFs）was synthesized through combining electrospinning with pyrolysis reduction strategy at appropriate temperature by using Cu Fe Prussian Blue Analogue（Cu Fe PBA）as the metal source.The combination of metal Cu and metal Fe with complementary activities not only promote the ability of the catalyst to convert nitrate to nitrite and ammonium,but also maintain high nitrogen selectivity and exhibit better catalytic activity than single metal catalysts by means of comparing and analyzing the electrocatalytic nitrate reduction performance of different control samples.In addition,heteroatom N-doped carbon nanofibers can further enhance the nitrate reduction activity through the adsorption effect of nitrate.（3）The carbon nanofibers with ultra-high iron content（62%）was obtained through adjusting the Fe₃O₄content in the spinning solution and controlling the calcination temperature（FFC@NCNFs）.The electrochemical performance tests show that increasing the iron content can effectively improve the nitrate conversion percentage.In addition,the Cu²⁺contained in the electrolyte can be converted into copper element through ion replacement reaction and combined with Fe/Fe₃C to form copper-doped iron-based carbon nanofibers（FFCC@NCNFs）.The experimental results exhibit that the incorporation of elemental copper further improve the electrocatalytic nitrate reduction activity of iron-based carbon nanofibers with high iron content at low salt concentrations.In summary,we designed and synthesized nitrogen-doped carbon nanofiber modified with different iron-containing active ingredients and explored their electrocatalytic nitrate reduction performance.This research provides broad potential for the further development of designing iron-based carbon nanofiber suitable for electrocatalytic nitrate reduction.