Mixed phase titania photocatalysts, such as Degussa P25, typically show higher photocatalytic activity than pure phase titania, as reported by many researchers. Our previous experimental results indicate that the solid-solid interface is a key factor in enhancing the photocatalytic reactivity of mixed phase titania and may be the location of catalytic "hot spots". In this study, titania photocatalysts consisting of varying amount of anatase and rutile phases are prepared by reactive dc magnetron sputtering and by a modified solgel method. These titania materials are characterized with a variety of techniques and are tested in the photocatalytic degradation of acetaldehyde. Mixed phase titania thin films prepared by magnetron sputtering have a high density of anatase-rutile interfaces and display the highest photocatalytic activity among the catalysts tested. Studies by electron paramagnetic resonance spectroscopy show a unique distribution of charge trapping sites which are characteristic of the sputtered films. The role of anatase-rutile interface to separate charge and improve the photoactivity of mixed phase materials is discussed. (c) 2007 Elsevier B.V. All rights reserved.