A solution-based processing method has been used to synthesize nanocrystalline TiO2 powders by controlling the hydrolysis of TiCl4 in an aqueous solution in both anatase and rutile phases. The primary particle sizes of the powders were in the range of 5-15 nm. To determine the crystal phase composition and size of the prepared photocatalysts, X-ray diffraction (XRD) measurements were used. We also studied the photocatalytic removal of the herbicide, Bentazon, from contaminated water in the presence of synthesized nanocrystalline TiO2 powders under UV light illumination (30 W). The removal efficiency of Bentazon was 16% when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic operational parameters such as the different kinds of TiO2, amount of TiO2, irradiation time and initial concentration of Bentazon on the photocatalytic removal efficiency of Bentazon. Our results indicated that 99% removal of the herbicide from the solution containing 15 ppm of Bentazon after selecting desired operational parameters could be achieved in a relatively short time, about 90 min. A kinetic model was successfully established for the prediction of removal of Bentazon by the UV/TiO2 system with any concentration of the herbicide. In this work, we also compared the photocatalytic activity between the commercial TiO2 and synthesized nanocrystalline TiO2 powders. The photocatalytic activities of different photocatalysts were tested using the herbicide solution. (C) 2009 Elsevier B.V. All rights reserved.