Highly photoactive nano-sized TiO2 powder photocatalyst was prepared by a hydrothermal method at 180 degrees C for 5 It using tetrabutyl titanate (TBOT) as the precursor. The pH values of the starting suspensions were adjusted from 1 to 11 using a 1.0 M HCl or 1.0 M NH3 center dot H2O solution. The obtained TiO2 powders were characterized with X-ray diffraction (XRD), N-2 adsorption-desorption measurement, transmission electron microscopy (TEM), X-ray photoelectron spectra, Fourier transform infrared (FTIR), Raman spectra and UV-vis spectrophotometry. The photocatalytic activity was evaluated by photocatalytic oxidation decomposition of acetone in air. The results showed that the pH values of the solutions obviously influenced the microstructures and photocatalytic activity of the as-prepared TiO2 powders. With increasing pH values, the crystallization enhanced, crystallite size increased and BET specific surface areas decreased. The photocatalytic activity of TiO2 powders prepared at a pH range of 6-9 exceeded that of Degussa P-25 by a factor of more than two times. (c) 2006 Elsevier B.V. All rights reserved.