Colloidal stability of nanosized titania aqueous suspensions

In this work the colloidal behaviour of three different TiO2 nanopowders in water is studied. A commercial powder of anatase and another of rutile were used for this study. For comparison purposes, a cryogel of anatase synthesised by a particulate sol–gel route and freeze-dried was also studied. All three powders were characterised by scanning electron microscopy, specific surface area measurements and X-ray diffraction. Diluted aqueous suspensions were prepared and characterised in terms of particle size distribution and zeta potential, using dynamic light scattering and laser Doppler velocimetry principles, respectively. All suspensions were prepared using an ultrasounds probe for mixing times ranging from 0 to 5 min. Colloidal stability was studied as a function of pH, type and concentration of dispersants (polyacrylic-based deflocculant and citric acid) and mixing time. Stable suspensions of commercial nanosized powders were obtained with polyelectrolyte contents of 1.0–1.5 wt.%. No stable suspensions of the cryogel were obtained with polyelectrolyte, requiring in this case the use of citric acid as deflocculant. It was observed that neither the size distribution nor the zeta potential values were affected by the sonication time.