A study of the solubility and separation of alkanethiol stabilized gold nanoparticles in supercritical fluids

This thesis is a record of a series of studies into the solubility of alkanethiol stabilized gold nanoparticles of various sizes in supercritical ethane at a range of pressures. In order to perform this study it was first necessary to discover a simple synthetic technique for the preparation of gold nanoparticles that disperse easily in supercritical ethane. In order to do this a number of different stabilizing ligands were tested, it was found that dodecanethiol stabilised gold nanoparticles purified by soxhlet extraction were most suitable due to compatibility with the fluid (supercritical ethane) and the excellent stability ofthese nanoparticles. The dodecanethiol stabilized gold nanoparticles prepared for the first part of the study were found to be rather polydisperse from TEM measurements. It was shown that selectively dissolving certain sizes in supercritical ethane (by variation of fluid pressure) resulted in the isolation of small quantities of more monodisperse size fractions from the sample. Further study ofthis technique is required for a more accurate 'fractionation' process. Monodisperse dodecanethiol stabilised gold nanoparticles were prepared by synthesising gold nanoparticles functionalized by a thioether terminated polymer followed by a simple ligand exchange reaction with dodecanethioi. Some of these samples were then used in simple solubility tests in supercritical ethane. A quantitative consideration of the solubility behaviour of these particles shows that they behave in a similar manner to other solids in supercritical fluids at low mole fractions. The calculation of accurate theoretical Henry's Law constants for the nanoparticles was impossible; this is believed to be due differences between the solubility behaviour of nanoparticles dissolved in supercritical fluids and the solubility behaviour of gases dissolved in fluids. The pressure dependent solubility of gold nanoparticles in the 2-4 nm size range was found to be in the region of 3.5-5 x 10-18 moI.ba.EThOS - Electronic Theses Online ServiceGBUnited Kingdo