Improved methods for producing colloidal dispersions of
cerium-containing
oxide nanoparticles in substantially non-polar solvents is disclosed. The
cerium-containing
oxide nanoparticles of an aqueous
colloid are transferred to a substantially non-polar liquid comprising one or more amphiphilic materials, one or more low-polarity solvents, and, optionally, one or more glycol
ether promoter materials. The transfer is achieved by mixing the aqueous and substantially non-polar materials, forming an
emulsion, followed by a phase separation into a remnant polar
solution phase and a substantially non-polar organic
colloid phase. The organic
colloid phase is then collected. The
promoter functions to speed the transfer of nanoparticles to the low-polarity phase. The
promoter accelerates the phase separation, and also provides improved colloidal stability of the final substantially non-polar colloidal dispersion. The glycol
ether promoter reduces the temperature necessary to achieve the phase separation, while providing high extraction yield of nanoparticles into the low-polarity organic phase. In addition, use of particular amphiphilic materials, such as
heptanoic acid or octanoic acid, enable efficient extractions at ambient temperatures without the use of a glycol
ether promoter.