Preparation And Application Of Core-shell Type Metal-coated Micro-Nano Materials

Core-shell composite materials of micro-nanoparticles usually have unique properties such asSurface Effect, Volume effect, Quantum effect, and so on. Thus, they have special properties onmechanics, thermal, optical, electrical, magnetic and chemical, which differ from the material ofmacroscopic. Core-shell-like silver-coated silica composite-spheres were studied hotly as a novelcomposite material. There’s a variety of research about it, however, the uniformity and compactnessof the distribution on the surface of the composite-spheres and its silver particle size which have asignificant impact for the physical properties could not be guaranteed well. Thus, how to control thesize of the silver particles and to prepare the composite particles with a good uniformity andcompactness, then to get special physical properties, is an important issue worthy of further studies.And how to get optimal production with less silver used is an urgent reality.For the abovementioned problems, here come solutions. In this paper, the synthesis of baresilica is achieved based on stober method and the synthesis of SiO2@Ag has been obtained bycontrolled-reduction of silver nitrate and ammonia in absolute ethyl alcohol with PVP as a protectiveand reducing agent. The particles size, structure and composition analyses revealed that the resultantSiO2@Ag composite-spheres were monodisperse, well-proportioned and stable with a mean corediameter of255nm silica and silver-shell whose silver particle diameter is about8nm. Some furtherresearches in this paper are as follows:1. The mechanism of composite material was analyzed, and the main factors which affect thestructure and properties of silver-coated silica composite-spheres were explored. We found that theconcentration of the silver source solution, the reaction temperature and pH largely affect the densityand homogeneity of the core-shell composite-spheres. Experimental data show that: the compactnessand homogeneity of the core-shell-like silver-coated silica composite-spheres would be best whenthe concentration of silver ion is2.0mmol/L;40~50℃was regarded as the main growthtemperature of the silver nanoparticles, which was most conducive for the growth of the silvernanoparticles and forming a core-shell structure composite-sphere, the temperature above50℃wastreated as saturation temperature since there’s less silver nanoparticles deposited; it’s disadvantagefor the composite-spheres to form a perfect core-shell structure when the condition was too acid ortoo alkaline, and the perfect structure of the composite-spheres would appear at pH=12.12. 2. Compared to the absorption rate of bare silica spheres and silver nanoparticles, the silver-coated silica core-shell composite-spheres have a strong optical absorption capacity whose averageabsorption rate is about80%, and even reached over95%at where the absorption platform appeared,moreover, the absorption bandwidth of the composite spheres was broadened in the UV-visibleregion. It is due to the joint effect of both silica core and silver nanoparticles shell. The special lightabsorption properties of the composite-spheres are predicted to have a wide potential applicationprospect in fields of nonlinear optical materials, light-sensitive sensor materials, photocatalyticmaterials and so on.