A kind of novel and efficient catalyst, mesoporous TiO2 (anatase) modified by two transition metal-monosubstituted polyoxometalates (POMs), i.e., K-5[Ni(H2O)PW11O39] (PW11Ni) and K-5[Co(H2O)PW11O39] (PW11Co), was used to photodegrade an organochlorine pesticide, hexachlorobenzene (HCB), and three kinds of different dyes under UV irradiation. These dyes have various chemical structures, either azoic (Congo red (CR), methyl orange (MO)), or anthraquinonic (Alizarin S (AS)) or fluorescent (neutral red (NR)). TiO2 (anatase) was prepared by combined sol-gel and programmed temperature hydrothermal methods at a lower temperature (200degreesC), and these as-synthesized TiO2 particles were further functionalized by 3-aminopropyltriethoxysilane (APS). Amine-functionalized TiO2 materials impregnated with monosubstituted polyoxometalates were prepared by coordination of Ni or Co in the units of polyoxometalates with surface amine groups in TiO2. The resulting materials have been characterized by several methods, including UV diffuse reflectance spectroscopy (UV/DRS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-AES), P-31 magic-angle spinning nuclear magnetic resonance (MAS NMR), transmission electron microscopy (TEM), and nitrogen adsorption. The conversions of organochlorine pesticide (HCB) and dyes (CR, MO, AS and NR) remarkably increased on UV-irradiating these as-prepared catalysts compared with the results over traditional anatase TiO2; in particular, HCB conversion reached above 98% after UV-irradiating the catalysts for 60 min. With good photocatalytic activity under UV irradiation and the ability to be readily separated from the reaction system, this novel kind of catalyst exhibited the potential to be effective in the treatment of organic pollutants in aqueous systems. (C) 2004 Elsevier B.V. All rights reserved.