Direct synthesis and characterization of gold and other noble metal nanodispersions in sol-gel-derived organically modified silicates

A general approach to prepare nanodispersions of noble metals in organically modified silicates is presented with particular emphasis on the synthesis of gold nanodispersion and its characterization. Organically modified sol-gel monomers containing amine functional groups are used to stabilize the metal salts before the reduction step and to cap and prevent coagulation of the metal sol after reduction and through gel formation, drying, and aging. Uniform spherical metal nanodispersions of Au, Pt, and Pd with average diameter of 4-6 nm were obtained. The particle size distribution and the average size of silver nanoparticles prepared by the same method were considerably larger. This was attributed to the lower stability of the silver-amine complex and to the lower affinity of amines to silver surfaces. Stable aqueous colloidal solutions and supported metal nanodispersions in porous films and monoliths can be prepared by this route.