A novel supercritical CO2 synthesis of amorphous hydrous zirconia nanoparticles, and their calcination to zirconia

A novel synthesis of amorphous hydrous zirconia nanoparticles was performed in a supercritical carbon dioxide (scCO(2)) reverse microemulsion, converting a high concentration of a very inexpensive starting material (zirconyl nitrate hydrate) into a product that was then calcined to yield monoclinic zirconia nanoparticles. The amorphous hydrous zirconia precursor particles were obtained by simply adding a precipitating agent to [Zr-(aq)(4+)]/perfluoropolyether/scCO(2). Calcination converts the amorphous hydrous zirconia precursor into the oxide, and the corresponding phase changes that occur were confirmed by differential thermal analysis. Some control of particle size and shape (ellipticity) could be achieved by selecting the reaction pressure from within the range over which stable microemulsions are obtained (13.9-17.3 MPa): a higher reaction pressure yields smaller and more spherical particles. This novel route for the synthesis of zirconia nanoparticles is both green (environmentally friendly) and economical.