Oxide semiconductor photocatalysts based on TiO2 (band gap of 3.2 eV) are normally used to destroy organics under UV irradiation. Currently we have been focused on the aerogel synthesis of nanocrystalline photocatalysts that will destroy organic compounds such as acetaldehyde using visible and UV radiations. Herein we report the results of our attempts to synthesize mixed metal oxides of the type MTi2O5 (M=Mg, Mn, Fe, Co, Zn, and Sri). The preparation method involves the formation of a single source precursor by the condensation reaction of Ti(OPrn)(4) with M(OAc)(2), followed by their (M[O-Ti(OPi(n))(3)](2)) hydrolysis and drying under supercritical conditions by a modified aerogel process. Product compositions, oxide structure types, and morphology were characterized by powder X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDXA), and BET surface area measurements. Only for Mg, the stoichiometry MgTi2O5 with pseudo-brookite structure type was obtained, while the composites MTiO3/TiO2 were obtained for M = Fe, Co and Zn. Photocatalytic behavior of these composite oxides were tested by the decomposition of gaseous acetaldehyde under UV light (320 nm < lambda < 400 nm). Of these, CoTiO3/TiO2 showed an interesting catalytic behavior; it decomposed acetaldehyde in the dark, at room temperature. Other mixed metal oxides such as MgTi2O5, and composites such as FeTiO3/TiO2 and ZnTiO3/TiO2 decomposed acetaldehyde only under UV light (not under visible light or in the dark). The photocatalytic activity was compared with the reference degussa P25 TiO2 photocatalyst. (C) 2004 Elsevier B.V. All rights reserved.