Nanocrystal Arrested Precipitation in Supercritical Carbon Dioxide

Fluorocarbon-coated silver, iridium, and platinum nanocrystals ranging in size from 20 to 120 Å in diameter are synthesized in supercritical (sc)-CO 2 by arrested precipitation from soluble organometallic precursors. The synthesis is performed in a single CO 2 phase by reduction with H 2 at elevated temperatures ranging from 60 to 100 °C. Precursor degradation and particle nucleation occur in the presence of stabilizing perfluorooctanethiol ligands, which bind to the surface of the metal agglomerates and quench particle growth. The ligands are sufficiently solvated by CO 2 to provide a steric barrier to uncontrollable aggregation during synthesis. The particles redisperse in acetone and fluorinated solvents. The dominant mechanism to particle growth is through cluster agglomeration followed by ligand passivation, leading to self-similar size distributions with a standard deviation of ±47%. Additionally, the nanocrystal size is tunable with precursor concentration, with higher precursor loadings resulting in larger nanocrystal sizes.