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.
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