Synthesis, characterization, and electrophoretic concentration of titanium dioxide nanoparticles in AOT...

Stable organosols of TiO₂ nanoparticles were prepared by hydrolysis of titanium tetraisopropoxide (TTIP) in microemulsions of sodium bis(2-ethylhexyl)sulfoxynate (АОТ) in n-decane with increasing the content of aqueous pseudophase from 0.15 to 0.85 vol.%. As the water content increased, the hydrodynamic diameter of nanoparticles grew from 10 to 225 nm, and the  ζ-potential, from -6 to 18 mV (the surface of TiO₂ nanoparticles was recharged when the water content was 0.45 vol.%). Nonaqueous electrophoresis in a capacitor-type cell made it possible to concentrate nanoparticles with a diameter of 60 to 225 nm (concentration factor was 10), separate 20 nm and 225 nm particles, and decrease the content of АОТ in organosol by an order of magnitude. Preparation of a concentrate of nanoparticles with a low content (0.015 M) of AOT included the following stages: (i) electrophoresis after synthesis; (ii) sampling of the concentrate and its twenty-fold dilution with pure n-decane; and (iii) repeated electrophoresis. In situ laser and spectrophotometric scanning of the interelectrode space showed the formation of a sharp boundary between the raffinate and the layer of moving nanoparticles during electrophoresis.