Controlled Synthesis Of Iron-based Nanocompound And Their Performance

Fe-based nanocompound has been widely used in eletrode materials,drug delivery,magnetic resonance imaging and bioseparation for its specila magnetic,electrochemical performance and biocompatibility.Among them,FeF₂ nanoparticles?NPs?is a common antiferromagetic material,while the iron carbide?Fe-C?NPs is the typical ferromagetic material.It is important to study the preparation and their performance.The physical and chemical properties of NPs are closely related to their size and morphology.Therefore,controlled synthesis of monodispersed Fe-based NPs with a special structure have attracted great attention in recent years.By controlling the nucleation and growth process,thermal decomposition could adjust the morphology perfectly.Here we used this method to synthesis FeF₂ NPs and Fe-C NPs.The dissertation aims to synthesize FeF₂ and Fe-C nanomaterials with a novel morphological structure by appropriate means and study their properties in MRI and Lithium-ion batteries.A study was conducted for the structure,morphological,and properties of the synthesized nanomaterials tested by such test methods as X-ray diffraction?XRD??Transmission Electron Microscope?TEM??X-ray Photoelectron Spectroscopy?XPS??Cyclic voltammograms?CV??Electrochemical Impedance Spectroscopy?EIS?.The result is as follows:?1?FeF₂ nanoparticles with a controllable size and morphology were prepared by the thermal decomposition method with acetylacetone iron as precursor,ammonium fluoride as reactants,and oil amine as solvents,surfactants and reducing agent.By adjusting the reaction time and temperature under inert gas protection,100-200 nm FeF₂ nano-cubic clusters were obtained.Notably,F^-ion in the system was acted as adhesive agent to form the cluster structure.Surfactant was also critical for the morphology.10 nm FeF₂ NPs were collected when added certain oleic acid into the reacting system.Longitudinal relaxation effectiveness in magnetic resonance imaging?MRI?of FeF₂ nanoparticles with 100 nm in size was tested,which exhibited the value was 1.08 m M^-1s^-1,indicating that FeF₂ NPs were ideal candidate for T₁-MRI contrast agents.?2?The electrochemical performance of FeF₂ nanocluster as cathode material for lithium ion battery was investigated,and the influence of the introduction of carbon for battery performance was also studied.Two ways for carbonization of FeF₂ NPs was applied,by either mixing the NPs with organica precusor for sintering or sonication of NPs with graphene in hexane solution.When selected PS to mix with the FeF₂ NPs,a carbon layer was sucessfully introduced on the surface,which could effectively enchanced the conductivity and cycling stability.Moreover,the charge transfer reaction resistance?Rct?was reduced to 140?,and the capacity rentention could be 65%even after 30 cycles compared with rough FeF₂ NPs.However,a reduce of initical capacity to 213 m Ah g^-1,which was only 37%of its theoretical capacity,was observed,accounting for the introduction of iron oxides NPs when treating at the high temperature.In contrast,the methode of sonication with graphene can also increase the conductivity and cycling stability.Rct value was decreased to be 60?,and the initial discharge capacity was as high as 475 m Ah g^-1,which is 83%of its theoretical capacity.?3?Fe₂C?hexagonal system,monoclinic system?and Fe₅C₂?monoclinic system?were prepared by using carbonyl iron as precursor,oil amine as surfactants,octadecylamine as solvent with a two-step method.The addition of halogen ions is the key to control the phase of Fe-C during carbonization process.The phases of Fe₂C NPs could be controlled by direct phase transformation in the drastic thermal driven procedure?defined as thermodynamical manner?.Within the range 260-300?,hexagonal system of FeF₂ was obtained,then,it transformed to monoclinic system when the temperature reached to 310?.While,the selective absorption of halogen ions weakened the bonding between Fe and C atoms,thus interfering the penetration of C atoms to form less carbon content Fe₅C₂ NPs.It has no influence on the phase by changing the concentration of carbonyl iron,carbonization time,the concentration of halogen ions.The transverse relaxation effectiveness as T₂-MRI contrast agents of Fe₂C and Fe₅C₂ were tested,which exhibited the values were 357 m M^-1s^-1and 192m M^-1s^-1 respectivley,and both of these values were higher than the commercial available contrast agent iron oxide NPs.