Nanocrystal Arrested Precipitation in Supercritical Carbon Dioxide

Abstract

Fluorocarbon-coated silver, iridium, and platinum nanocrystals ranging in size from 20 to 120 Å in diameter are synthesized in supercritical (sc)-CO2 by arrested precipitation from soluble organometallic precursors. The synthesis is performed in a single CO2 phase by reduction with H2 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 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.

The evolution of pseudo-spherical silicon nanocrystals to tetrahedra, mediated by phosphonic acid surfactants

“…It has been demonstrated that hydrocarbon ligands provide some degree of steric stabilization in the formation of nanocrystals in sc-CO 2 . [32] The repulsive forces of the surface passivated nanoparticles are determined by the surface coverage of the capping ligands, the length of the ligand tail and the solvent quality. [19] In the context of this study, a poor solvent such as sc-CO 2 would cause the ligand tails to collapse partially, augmenting the overall attractive forces and increasing the aggregation of nuclei during the reaction.…”

In situ Synthesis of Gold Nanoparticles inside the Pores of MCM‐48 in Supercritical Carbon Dioxide and its Catalytic Application

“…In a recent approach, a sonochemical method was used to diffuse the nanoparticle through the solvent inside the pores of the mesoporous material, which was undesirably slow due to the low diffusivity of the medium. [14] The potential use of supercritical carbon dioxide (scCO 2 ) has attracted much interest as a sustainable and "green" medium for material synthesis. It can be handled easily because it is non-toxic, non-flammable and inexpensive.…”

Gold nanoparticles protected by fluorinated ligands: Syntheses, properties and applications

“…Supercritical CO 2 also proved to be a good solvent for fluorous nanoparticles synthesis by using suitable organometallic precursors and hydrogen as reducing agent [21,22].…”