Preparation And Surface Coated Treatment Research Of Metal Nanoparticles

Metal nanoparticles have different physical and chemical properties compared to traditional materials,such as the small-size effect,the surface effect,the quantum size effect and the quantum tunneling effect, therefore, metal nanomaterials have potential applications in catalysis, consider light, optical absorption material, medicine, magnetic media, and new materials,etc. However, due to the small size of nanoparticles, large surface area and high surface atoms share the high surface energy, high chemical activity, metal nanoparticles are particularly sensitive to their environment, easy to interact with the gas molecules in the environment,and easily oxidized exposed in air,which causes the poor stability and dispersion of the nanoparticles, easily agglomerated, seriously affecting its storage and application. In order to overcome these limitations, depositing a protective shell has been recommended as one prospective method to improve the chemical stability of metal nanoparticles.The novel structures not only prevent their oxidation and environment degradation, and effectively resist their agglomeration and resolve the problem of metal nanoparticles can not steadily conservation under atmospheric conditions, but also provides a chance to synthesize advanced functional materials with new microstructures and novel physical properties.Firstly, we have an overview to the preparation methods, character, applications of metal nanomaterials and core-shell structure nanomaterials in this thesis.Next, to overcome particle aggregation, not controllable parameters and morphology,low yield and other defects,we made a meaningful improvement to the direct current arc plasma preparation technology.And then the carbon encapsulated Ni nanoparticles were succesfully prepared by improved direct current arc plasma method, and We also conducted a preliminary analysis of the formation mechanism of the carbon encapsulated Ni nanoparticles. The products were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM), high—resolution transmission electron microscopy(HRTEM) and X-ray energy dispersive spectrometry(XEDS) to determine the chemical composition,morphology,crystal structure,particle size,and particle size distribution of carbon encapsulated Ni nanoparticles. The results show that the carbon encapsulated Ni nanoparticles possess clear core-shell structure, the core of the particles is face centered cubic structure Ni, and the shell of the particles is disorder carbons. The particles are scattered homogeneously in spherical or ellipsoidal shapes. The particle size of the nanocapsules ranges from15nm to40nm, with an averaged value about30nm, and the diameter of metal core is about18nm, the thickness of the shells is about6-8nm.Secondly, the nickel nanopowders prepared by direct current arc discharge plasma method were used as the source, the silica encapsulated Ni core-shell structure nanoparticles were successfully prepared by Sol-gel method. The composition, morphology, microstructure, particle size of the products and magnetic properties were investigated via X-ray diffraction (XRD), transmission electron microscopy (TEM), high magnification transmission electron microscopy, selected area electron diffraction(SAED) and vibration sample magnetometer (VSM). The results show that the silica encapsulated Ni nanoparticles possess clear core-shell structure, the core of the particles is face centered cubic structure Ni, and the shell of the particles is disorder silica. The average particle size of the nanocapsules is about30nm, the thickness of the shell is about4nm. The as-prepared silica encapsulated Ni nanoparticles which showed an unique magnetic properties exhibited weak ferromagnetism in room temperature. A saturation magnetization of Ms=33.40emu/g and a coercive force of Hc=78.27Oe were achieved for the nanoparticles. This method also provide a new and simple way to prepare other oxide coated magnetic metal nanomaterials.In the last, the silver nanowires including a small amount of folded structure of silver nanowires, were synthesized by hydrothermal method under the polyol system combined with traces of sodium chloride. the crystal structure of the as-prepared Ag nanowires was fcc structure with uniform width, smooth surface, t The folded structure Ag nanowires with diameter of110-150nm were composed of3-7joints.The folded structure of silver nanowires synthesized were due to the straight silver nanowires were connected in an end-to-end manner, with obvious spacing between them.