(396g) Single-Step Synthesis of Metal/Porous Support Nanocomposite Materials in Mixed Surfactant Mesophase

Gold/porous silica and platinum/porous titania, have been synthesized in a bicontinuous surfactant mesophase systems by simultaneous hydrolysis/condensation of a support precursor present in the oil phase along with reduction of the metal precursor in the aqueous phase. The bicontinuous phase is formed by adding water to an isooctane solution containing AOT and lecithin. TMOS or TIP (titanium isopropoxide) is solubilized in the organic phase, while HAuCl4 or PtCl4 are the metal precursors dissolved in the aqueous phase. The high viscosity of this multicomponent system immobilizes metallic nanoparticles once they are formed throughout the aqueous domains, thus preventing agglomeration. Pore size, specific surface area, as well as nanoparticle loading can be controlled using this technique. Highly facetted and size tunable gold nanoparticles were also synthesized in-situ in the same system. This was done without adding additional reducing agents ? the surfactants donate electrons, reduce the metal ions and adsorb onto preferred planes of the growing nanocrystal leading to hexagonal and triangular plates with dimensions of the order of microns, but thickness of a few nanometers. These experiments provide a new pathway for the formation of catalyst-support composite materials with well-dispersed metal nanoparticles inside the support material, as well as a robust technique for producing nanoparticles of highly controlled morphology.