Research On Preparation And Properties Of Carbon-encapsulated Metal Nanoparticles Based On Microwave-induced Metal Discharge

As a new functional composite material,carbon-encapsulated metal nanoparticles,not only have unique electrical,magnetic,optical and chemical properties of metal nanoparticles,but also combine the excellent stability,biocompatibility and dielectric properties of graphitized carbon layer,which have great potential in energy,environment,medicine,etc.However,the problem such as high impurities and low yield of product in the preparation limits the application of this carbon nanocomposite.This thesis puts forward a technology roadmap of the preparation of carbon-encapsulated metal nanoparticles by microwave-induced metal discharge.Firstly,with ferrocene as the metal source,this thesis studied how different organic solvents,microwave irradiation power,irradiation time,material ratio and the dispersant impact the yield,morphology and structure of nanocomposites.Under the optimal parameters,the stability,magnetic properties and electromagnetic wave absorption performance of the product were tested.Meanwhile,carbon-encapsulated Fe/Fe3O4 nanoparticles were synthetized on the basis of the preparation of carbon-encapsulated Fe/Fe3C nanoparticles,and the electrochemical performance of lithium-ion battery anode was tested.Secondly,the carbon-encapsulated Ni-based and Co-based nanoparticles were prepared under the same condition,and the morphology,structure and property of the two were studied.Lastly,based on the literature review and the verification experiment,this thesis deduced the formation mechanism of carbon-encapsulated metal nanoparticles under microwave-induced metal discharge.The results show that the carbon-encapsulated Fe/Fe3C nanoparticles with high purity,complete core-shell structure and uniform size distribution can be quickly prepared by microwave-induced metal discharge.During the preparation,it is easier to synthesize the nanoparticles by using organic solvents that can be soluble with metal source,and thiophene can effectively improve the dispersion of nanoparticles.Compared with other synthetic methods,this method also has obvious yield advantages,the solid yield is generally 25-30wt%of the ferrocene content in the raw material.More importantly,carbon-encapsulated Fe/Fe3C nanoparticles can be oxidized into carbon-encapsulated Fe/Fe3O4 nanoparticles under certain condition.When the new product is used as anode material for lithium-ion batteries,it exhibits great charge/discharge cycle and rate performance,and has larger reversible capacity than commercial Fe3O4 nanoparticles.The complete core-shelled carbon-encapsulated Ni-based and Co-based nanoparticles also can be prepared by microwave-induced metal discharge,which shows the applicability of this method.The performance results indicate that carbon-encapsulated Ni-based and Co-based nanoparticles have excellent corrosion resistance and thermal oxidation stability,and their maximum antioxidant temperature is 420?and 300? respectively.At the same time,the two has the characteristics of wide-range of bandwidth,thin absorption coating and strong absorption,which meets the requirements of modern industry for microwave absorption materials.Moreover,all the three nanomaterials are superparamagnetic and can be rapidly separated when used as catalysts.The coupling of multiple effects of microwave-induced metal discharge can induce micro-discharge of metallic elements in organic metal compounds.This phenomenon,together with the high temperature environment created by microwave-induced metal discharge,promotes the formation and growth of carbon-encapsulated metal nanoparticles.