The influence of the concentration of aqueous TiCl4 solution on the phase formation, morphology and particle size of the titanium dioxide hydrolysis product was investigated by XRD and TEM. Significant features, observed in the Raman spectra of the TiCl4 solutions with a concentration >3 M, demonstrated that the TiCl4 had hydrolysed. As the formal concentration of TiCl4 decreased from 4.98 to 1 M, the Raman spectra changed qualitatively. Despite the changes in the Raman spectra of these precursor solutions, the TiO2 product was mainly rutile in all cases. However, at low TiCl4 concentrations small amounts of anatase were also observed. Electron microscopy suggested that the anatase particles were significantly smaller than the rutile and also indicated increasing aggregation of the product from the more dilute TiCl4 solutions. The optical properties and photoactivities of the TiO2 powders prepared at different concentrations were also investigated. The powder synthesized from 5 M TiCl4 showed the highest UV extinction. The photoactivity of the product, determined by the photocatalytic oxidation of propan-2-ol (isopropanol) to propanone (acetone), was not significantly modified by changes in the concentration of the starting TiCl4. The possibility that the relatively low area of most rutiles contributes to the reported photocatalytic activity of rutile being lower than that of anatase is discussed. (C) 2014 Elsevier B.V. All rights reserved.