Size tailoring of TiO2 anatase nanoparticles in aqueous medium and synthesis of nanocomposites. Characterization by Raman spectroscopy

Nanoparticles of anatase with mean size in the range 5-10 nm were prepared by precipitation of TiCl4 in aqueous medium in the range 2 less than or equal to pH less than or equal to 6. Hydroxylation of TiCl4 at room temperature leads instantaneously to an amorphous titanium oxyhydroxide phase which crystallizes as anatase upon aging at 60 degreesC in suspension. Small amounts of brookite or rutile are concurrently obtained depending on the acidity. The size of anatase particles was characterized by X-ray diffraction, electron microscopy and Raman spectroscopy. The latter was also used to determine the particle size and to characterize the crystallinity of particles through the phonon confinement effect. The particle size, dependent on the acidity, is closely related to the electrostatic surface charge density of particles. The size variation was interpreted as resulting from a lowering of the interfacial tension due to the protonation of particle surface groups. Composite materials were synthesized by polymerisation of silica in aqueous sols of anatase. The dispersed anatase nanoparticles are stable against the transformation to rutile up to 1000 degreesC.