Modeling for Ligand-Capped Metallic Nanoparticles in a Gas-Expanded Liquids System: Surface Fraction Model

Abstract

Gas-expanded liquids (GXLs) are mixtures of gas dissolved in organic solvents and compressed up to pure gas vapor pressure. GXLs are the most commonly used and investigated class in particle separation processes. By employing both CO2-expanded hexane and ethylene-expanded hexane, gold as well as silver nanoparticles were precipitated at 303 K under various gas pressures ranging from 2.07 to 4.82 MPa. The cascaded-vessel apparatus applied in this study allowed fractionation of nanoparticles into a narrow range of fractions in a faster and dependable manner. The mean sizes of metal particles obtained in a GXL system can be adjusted simply by varying the gas pressure. To investigate the effects of ligand length and surface coverage on the production of precipitates, a thermodynamic model developed for the fractionation of ligand-capped nanoparticles in GXLs was applied. Specifically, a surface fraction model with an effective ligand surface area ratio was employed, and the reliability of the modeling results was shown quantitatively. It is worth noting that the results of thermogravimetric analysis led to good estimates of the surface coverage.