Nanocrystal arrested precipitation in supercritical carbon dioxide

Fluorocarbon-coated silver, iridium, and platinum nanocrystals ranging in size from 20 to 120 Angstrom in diameter are synthesized in supercritical (sc)-CO2 by arrested precipitation from soluble organometallic precursors. The synthesis is performed in single CO2 phase by reduction with H-2 at elevated temperatures ranging from 60 to 100 degreesC. Precursor degradation and particle nucleation occur in the presence of stabilizing perfluoro-octanethiol ligands, which bind to the surface of the metal agglomerates and quench particle growth. The ligands are sufficiently solvated by CO2 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.