Facile synthesis of silver core – silica shell composite nanoparticles

Combining metal nanoparticles and dielectrics (e.g. silica) to produce composite materials with high dielectric constant is motivated by application in energy storage. Control over dielectric properties and their uniformity throughout the composite material is best accomplished if the composite is comprised of metal core – dielectric shell structured nanoparticles with tunable dimensions. We have synthesized silver nanoparticles in the range of 40–100 nm average size using low concentration of saccharide simultaneously as the reducing agent and electrostatic stabilizer. Coating these silver particles with silica from tetraalkoxysilanes has different outcomes depending on the alcoholic solvent and the silver particle concentration. A common issue in solution-based synthesis of core–shell particles is heterogeneous nucleation whereupon two populations are formed: the desired core–shell particles and undesired coreless particles of the shell material. We report the formation of Ag@SiO2 core–shell particles without coreless silica particles as the byproduct in 2-propanol. In ethanol, it depends on the silver surface area available whether homogeneous nucleation of silica on silver is achieved. In methanol and 1-butanol, core–shell particles did not form. This demonstrates the significance of controlling the tetraalkoxysilane hydrolysis rate when growing silica shells on silver nanoparticles.

Ag@SiO2 core–shell particle formation and the occurrence of byproducts depend on the alcoholic solvent used as well as available silver surface area.Figure optionsDownload high-quality image (65 K)Download as PowerPoint slideResearch highlights
► Monodisperse silver nanoparticles in the range of 40–100 nm average size are synthesized using saccharides (glucose or maltose) simultaneously as the reducing agent and electrostatic stabilizer.
► When coating of silver nanoparticles with silica from tetraalkoxysilanes, the alcoholic solvent used determines the products.
► The desired Ag@SiO2 core–shell particles are obtained in 2-propanol as well as in ethanol, where silver particle concentration determines the occurrence of coreless silica byproduct.