Electroreduction Properties Of Iron-based Nanoparticles With High Iron Content

Nitrate is a common pollutant in surface and groundwater.The accumulation of nitrate ismainly caused by anthropogenic activities,such as fossil fuel burning,excessive use of nitrogen-rich fertilizer and wastewater discharge.Nitrate has great solubility and high stability in water,which makes it difficult to remove.Concentrated nitrate may cause the eutrophication that destructs aquatic ecosystems.At present,many physical,chemical and biological technologies have been developed for nitrate reduction and transformation,each of which has its advantages and disadvantages.Electrocatalytic reduction is an economical and green method with controllable reduction products,and its core is the design and selection of electrocatalyst.Up to now,it has been found that various alloy materials（Cu Pd,etc.）and iron-based materials（nano zero-valent iron,etc.）have excellent catalytic conversion and product selectivity.Iron-based materials have attracted much attention because of their wide sources,simple preparation and low price.However,due to their intrinsic magnetism and high activity,iron-based materials are easy to agglomerate,further reducing their catalytic activity.Although iron nanoparticles can be dispersed to a certain extent by compounding iron-based materials,it will inevitably lead to the decrease of iron content and catalytic performance.Therefore,how to develop effective methods to achieve high iron content and excellent catalytic performance of the catalyst is an important direction in the research of nitrate electrocatalytic reduction.Based on this,this thesis focuses on three aspects:In chapter 1,preparation of boron-doped iron nanochains（B-Fe NCs）by reductionmethod.B-Fe NCs composites were synthesized by one-step method with sodium borohydride as reducing agent and boron source in ice bath.The obtained B-Fe NCs composites have one-dimensional nano-chain structure and high iron content（86.53 wt.%）.At the same time,the catalyst shows excellent electrocatalytic performance,in which the conversion rate of NO₃^-can reach 80%,and the corresponding selectivity of N₂can reach 99%.In chapter 2,preparation of Fe nanoparticles by electrochemical reduction of Fe₃O₄.Firstly,magnetic Fe₃O₄ nanoparticles with uniform particle size and high monodispersity were prepared as structural units by solvothermal method.Then,the prepared magnetic Fe₃O₄nanoparticles were dripped on current collector（foam nickel）,and then reduced to nano-zero-valent iron based on cathodic reduction strategy in electrochemical system.At the same time,the prepared current collector can be directly used as working electrode for electrocatalytic reduction of nitrate.The results show that the catalyst has excellent electrocatalytic activity and cycle stability after reduction at-1.6V for 10min,in which the conversion rate of NO₃^-can reach 88%,and the corresponding selectivity of NH₄⁺can reach 90%.In chapter 3,preparation of iron@mesoporous organosilicon nanocomposites byconfined reduction under a H₂ atmosphere.With magnetic Fe₃O₄ nanoparticles as structural unit and periodic mesoporous organosilicon as precursor,we designed and synthesized high-activity core-shell nanocomposites.Among them,the iron content can reach 65.49 wt.%.The optimized nanocomposite（Fe@BPMO）displays comprehensively high performance for electrocatalytic denitrification in terms of outstanding cycling stability and favorable structure integrity.Specifically,in the mixed electrolyte system of 0.02 M Na₂SO₄ and 0.02 M Na Cl with the concentration of 100mg/L NO₃^--N,Fe@BPMO demonstrates high conversion rate of NO₃^-and N₂ selectivity after continuous catalytic cycle for 240 h.At last,the whole thesis is summarized and prospected.