TiO2 nanoparticles were synthesized by sol-gel method and they were coated on alpha-alumina supports to form ultra fine layer of nanosized TiO2. The effect of synthesis parameters; molar ratio of surfactant/precursor, refiuxing temperature and refluxing time, calcination temperature and time was simultaneously investigated on crystallite size, crystalline phase content, specific surface area and photocatalytic activity of the product, using a statistical approach. The powder samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller technique (BET). The results revealed positive effect of refluxing temperature on the crystallite size and crystallinity, while a negative effect was observed on the anatase phase content. The anatase phase content was enhanced by increasing the reflux time. Increasing calcination temperature and calcination time resulted to the higher crystallite size and relative crystallinity but lower anatase phase content. Application of surfactant improved specific surface area and pore size of the crystals. The optimal synthesis conditions to achieve maximum content of anatase phase, surface area and minimum crystallite size were found to be equal molar ratio of surfactant/precursor, refluxing temperature of 60 degrees C, reflux time of 6 h, calcination temperature of 550 degrees C and calcination time of 2 h. The optimal gel product was applied for preparing TiO2 thin films by spraying the gel content on the alpha-alumina support. The photocatalytic behavior of the coated films was examined in photocatalytic degradation of acetaldehyde in gas phase batch reactor under UV irradiation and a reduction of 61% was observed for only 0.01 g coated TiO2 film on the ceramic support. (C) 2012 Elsevier B.V. All rights reserved.