Kinetically Controlled Formation of Supported Nanoparticles in Low Temperature Supercritical Media for the Development of Advanced Nanostructured Materials

Abstract

The formation of surface nanostructures allows assemblies of materials at different scales, opening new routes toward the design of advanced nanostructured materials. The decoration of surfaces with shape- and size-controlled metal nanoparticles can be achieved through the reduction of hexafluoroacetylacetonate complexes [M(hfac)x] with H2 in supercritical CO2/alcohol at low temperature with neither catalyst nor surface prefunctionalization. This paper investigates the influence of different alcohols, methanol, ethanol, and isopropanol, used as cosolvent on the reduction kinetics of Cu(hfac)2·H20 in the supercritical CO2/alcohol/H2 mixtures. The results are applied to the modeling of the decoration process of silica spheres, used as a model substrate, with copper nanoparticles (5−17 nm). The model, using the decomposition kinetics of the precursor, is based on a bimodal process: (i) an initial homogeneous nucleation in the supercritical media and (ii) a fast heterogeneous growth by coalescence on the surface of the silica particles. We demonstrate good agreements between the simulated results and the experimental data showing an advanced kinetically controlled size of the supported nanoparticles in the range of temperature 100−125 °C and residence time 0−120 min.