Encapsulation of Gold Nanoclusters in Silica Materials via an Inverse Micelle/Sol-Gel Synthesis

Nanometer-sized gold particles were encapsulated in the micropores of xerogels and aerogels. The synthesis involves the sequential reduction of a gold salt followed by sol-gel processing in an inverse micelle solution. The inverse micelle solution solubilizes the metal salt and provides a microreactor for the nucleation, growth, and stabilization of the nanometer-sized clusters. Hydrolysis and condensation of an added siloxane precursor produces a wet gel embedding the particles. Characterization of the particle size and composition and the particle growth process was completed with transmission electron microscopy (TEM), electron diffraction, and UV-visible absorption spectrometry. Characterization of the gel surface areas was completed with N₂ porosimetry. Material properties determined as a function of the gel precursor (TEOS vs a prehydrolyzed form of TEOS), the water to gel precursor reaction stoichiometry, and surfactant concentration are discussed in terms of the unique solution chemistry occurring in the microheterogeneous inverse micelle solutions.