Synthesis of shaped-controlled gold nanoparticles

Abstract

Gold (Au) used to be considered to have no catalytic activity because the inert nature of massive gold. However, in 1987 Haruta identified high activity for CO oxidation reaction when gold is supported on metal oxides in a highly dispersed state. Several effects contribute to the catalytic properties of supported nanoparticles catalysts such as particle size, shape and crystalline defects. The shape dependence of catalytic performance intrinsically results from the differences in geometric structure and electronic state of the catalyst atoms associated with different crystallographic facets. The surface facets of a catalyst nanoparticle offer different binding configurations and strengths. For a metal nanoparticle with a face-centered-cubic lattice, the three main surface facets are {100}, {111} and {110}. Each facet provides different atomic arrangements and surface coverage. The intrinsic differences in surface occupancy results in a large difference in adsorption energy or activation barrier for dissociation of a reactant molecule and consequently the catalytic activity. By tuning the shape of the nanoparticle their terminating facets and anisotropy can be easily controlled. We intend to produce gold nanoparticles with well controlled shape to understand the reactivity of the different facets during the CO oxidation reaction. The cubic, rounded and hexagonal nanoparticles will be synthesized by the solution-based seed-mediated growth method. First the gold seed will be prepared with a strong reducing agent in the presence of a surfactant. The shape of the nanoparticles will be controlled during the growth reaction by the adjust of the surfactant and weak reducing agent concentration. The nucleation and growth of the seed and the subsequent growth of the nanoparticles will be investigated by UVvis spectroscopy and SAXS. The shape and size will be investigated by X-ray and electron microscopy.