Research On Preparation And Applications Of Iron And Iron Oxides Nanomaterials

Iron is one of the most abundant metallic elements in the earth's crust.Nanostructured iron and iron oxides exhibit many peculiar physico-chemical properties due to their nano-effects,which make them attractive in wide applications.However,there are many problems in the preparation technique of nanostructured iron and iron oxides,such as complicated process,high cost and low yield.Solution combustion synthesis(SCS)has emerged as an extensive employed technique to fabricate nanomaterials due to its attractive advantages of simplicity,scalability,time-and energy efficiency.In this paper,nanostructured Ca-Fe2O3,Fe3O4,amorphous FeOx/C and Fe/C composites were successfully prepared via solution combustion synthesis.By adjusting the ratio of raw materials,combustion atmosphere and heat treatment parameters,the precise control of product composition,morphology,particle size and phase state can be achieved,leading to the optimization of product electrochemical or electro-catalytic properties,which can endow the product good application prospects in the fields of lithium ion battery anode materials,fuel cell cathode catalysts,etc.The main research work in this paper focused on several aspects as follows:(1)?-Fe2O3 and Fe3O4 nanomaterials were prepared via one step solution combustion synthesis by designing a simple experimental device to reasonably control the combustion reaction atmosphere using ferric nitrate as the iron source and oxidant,glycine as the fuel and reducing agent.The effects of the ratio of glycine and ferric nitrate on the combustion reaction mechanism under oxygen-rich and-lean conditions were investigated.The results showed that with the decrease of oxygen and increase of glycine,the reaction mode tended to undergo the transition from VCS to SHS then to SCS process.On the basis of this,it was possible to control the composition,morphology,particle size and phase state of products by adjusting the glycine content and combustion reaction atmosphere.Thus,we have successfully prepared amorphous ?-Fe2O3 nanorods,crystalline ?-Fe2O3 nanosheets,?-Fe2O3/Fe3O4 nanosheets,?-Fe2O3/Fe3O4 nanoparticles,single-phase Fe3O4 nanoparticles,Fe3O4/FeO nanoparticles and amorphous FeOx/C nanosheets,etc.When they were tested as the anode material for lithium ion batteries,it can be found that the amorphous FeOx/C nanosheets displayed the best cycle stability,which maintained stable reversible specific capacity of?450 mAh g-1 after 500 cycles at the current density of 1 A g-1.(2)In order to further improve the electrochemical properties of amorphous FeOx/C nanosheets,we introduced water-soluble glucose as an organic carbon source in the ferric nitrate-glycine reaction system to optimize the phase and structure of product.It can be found that the addition of glucose could weaken the exothermic reaction between ferric nitrate and glycine,making it difficult to form a crystalline structure.Besides,with the increase of glucose content,the nanosheet structure of product became more obvious and the thickness of nanosheet decreased gradually,meanwhile,the surface porosity of product declined and the pore size distribution became more discrete.When the thickness of nanosheet was about 3 nm,the surface of nanosheet exhibited a uniform spherical bubble structure,forming an amorphous iron oxide and carbon composite with hierarchical mesoporous 3D foamed nanosheet structure.When evaluated as lithium ion battery anode material,this product exhibited a high reversible specific capacity and excellent cycle stability(maintained a reversible specific capacity of 1118 mAh g-1 after 500 cycles at the current density of 1 A g-1),which was superior to the current commercial graphite anode material.(3)The Fe/C nanocomposites were prepared by carbothermal reduction using the above amorphous FeOx/C nanosheets.The effects of glucose content and thermal temperature on product composition were investigated.It was found that with the increase of temperature,the phase of product underwent a change of Fe3O4?Fe?Fe3C,and the more glucose added,the rapid this change occurred.Then,as the pore-forming agents,sodium chloride and zinc chloride were further added in solution to prepare Na+ and Zn2+ containing FeOx-C-N nanocomposites in NH3 atmosphere.Afterwards,the composites were used as precurser for carbothermal and hydrogen reduction reactions in nitrogen-hydrogen mixed atmosphere,and finally washed with hydrogen peroxide solution and deionized water in order to obtain a hierarchical porous Fe@C-N nanosheets with large specific surface area of 478.57 m2 g-1.The product exhibited excellent electro-catalytic activity,cycle stability and resistance to methanol poisoning as an ORR catalyst for fuel cells.It can be found that after 20000 s catalytic test and methanol interference,the product maintained stable current response.Besides,the onset potential and half-wave potential of product were both?30 mV more positive than that of commercial Pt/C catalyst,meanwhile,it exhibited a?40 mV cm2 enhanced limiting current density compared to Pt/C catalyst,which were also superior to some non-precious metal ORR catalysts reported in the current literature.