Preparation of Silver Nanoparticles via Reduction of a Highly CO2-Soluble Hydrocarbon-Based Metal Precursor

Silver bis(3,5,5-trimethyl-1-hexyl) sulfosuccinate, Ag-AOT-TMH, exhibits 1.2 wt % solubility in dense CO2 at 40 °C and 52 MPa. This is a remarkably high CO2 solubility value for a nonfluorous organometallic compound. Silver nanoparticles were produced by reducing the supercritical CO2 solution containing 0.06 wt % Ag-AOT-TMH and 0.5 wt % perfluorooctanethiol (stabilizing ligand) using a reducing agent of NaBH4. Silver nanoparticles ranging in size from 1 to 6 nm were characterized by transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS). Although silver nanoparticles have been previously formed by a similar technique using silver acetylacetonate, that precursor is far less CO2-philic, exhibiting a CO2 solubility of <<0.01 wt % at 40 °C and 70 MPa. Attempts to produce silver nanoparticles from Ag-AOT-TMH in a completely nonfluorous system were unsuccessful because stabilization could not be attained with silicone-, PEG-, or hydrocarbon-based thiols; only the fluorinated thiols provided nanoparticle dispersion.