TiO2 films deposited on unheated substrates of alumina silicate glass by rf. (13.56 MHz) magnetron sputtering in the mixture of O-2 and Ar gases have been studied with X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and optical spectroscopy. Structural and optical properties of TiO2 films deposited at different O-2 concentrations and total pressures have been analyzed. Photocatalytic properties of TiO2 films were characterized by following the degradation of methylene blue molecules under UV irradiation. It was found that the rate of methylene blue decomposition strongly depends on morphology and crystallinity of the deposited films, namely on the content of the anatase phase and on the size of the anatase grains. The best photocatalytic activity was found on TiO2 films consisting of pure anatase phase with the size of grains of about 450 angstrom. With the help of those films a thin film reactor for water purification has been designed and tested. (C) 2009 Elsevier B.V. All rights reserved.