Preparation of noble metal nanoparticles in supercritical carbon dioxide

Silver, palladium, and silver–palladium nanoparticles have been prepared by reduction of silver acetylacetonate and palladium acetate with dimethylamine–borane in the presence of a fluorinated surfactant (FOMBLIN HC/P2-1000) in supercritical carbon dioxide. The sizes of silver and palladium nanoparticles increases with increasing concentrations of both the soluble precursors and FOMBLIN. The size of silver nanoparticles obtained is 3–12 nm, while that of palladium nanoparticles is 3–6 nm. For preparation of silver–palladium nanoparticles, the particle size is ranged between 4 and 5 nm and dependent on the feed molar ratio of palladium acetate. It is found that silver–palladium nanoparticles consist of a core-shell structure with enriched palladium in the surface.