Composite photocatalysts TiO2 immobilized on granular activated carbons with different porosities (TiO2/AC) were prepared by a novel approach, dip-hydrothermal method using peroxotitanate as precursor. The TiO2/AC composites were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and the nitrogen absorption. Their photocatalytic activity was evaluated by degradation of methyl orange (MO). The results showed that nano-TiO2 particles of anatase type were well deposited on the activated carbon surface. The porosity of activated carbon had significant influence on the adsorption, the amount of TiO2 deposited on the external surface of AC and the activity of composite photocatalysts. The composite TiO2/AC made from proper mesoporosity AC exhibited higher catalytic activity than the mixture of powdered TiO2 with AC. Furthermore, the mechanism of synergistic effect of AC adsorption and TiO2 photocatalysis was discussed. (c) 2009 Elsevier B.V. All rights reserved.