Preparation of Monodispersed Silica and Composite Spheres

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Nanoscale crystallites of metals or semiconductors, exhibiting unusual size-dependent electronic, magnetic, optical, and catalytic properties due to the onset of quantum effects, are being heralded as the next-generation building blocks for modern materials design. However, the high expectations for these advanced materials have been hampered by our current inability to rigorously control their size, morphology, and crystalline structures. In this report monodisperse silica spheres, and a variety of coating materials based on silica particles are prepared by a set of wet technique. Fig. 1 shows the electron micrographs of the monodispersed silica nanoparticles by reverse micelles method(fig.1a), surface limited growth method(fig.1b), and forced hydrolysis method(fig.1c). By these methods, monodisperse silica spheres, which range from several nanometers to several microns in diameter, can be synthesized. Based on the monodisperse silica spheres, the controlled coating process technique is developed to prepare single-layer and multi-layer coating composite particles, include SiO2-TiO2, SiO2-TiO2-SiO2, SiO2-Ag, SiO2-Ag-SiO2, SiO2-Co3O4, and SiO2-ZnO, etc. Fig. 2a shows the scanning electron micrograph (SEM) of silica particles coated with titania, which were then coated with thin silica layers (about 5-6nm), as shown in figure 2b. Figure 3(a) shows the TEM of silica particles coated with thin silver layers (about 5nm). ZnO/SiO2 shell/core composite nanoparticles are shown in figure 4. And Figure 5 is the electron micrograph of the hematite-coated polystyrene of ferric salt particles by the hydrolysis. The advantages of the wet chemical technique are that it is simple and efficient and controllable produces monodispere silica spheres and a uniform simple-or multi-coating of titania, silver, zinc oxide, cobalt basic carbonate, which have a wide field of potential applications in catalyst, photonic crystals, etc.

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Journal: TechConnect Briefs
Volume: 3, Technical Proceedings of the 2003 Nanotechnology Conference and Trade Show, Volume 3
Published: February 23, 2003
Pages: 262 - 265
Industry sector: Advanced Materials & Manufacturing
Topics: Advanced Materials for Engineering Applications, Composite Materials
ISBN: 0-9728422-2-5