Mesoporous TiO2 photocatalysts have been synthesized using polyethylene glycol (PEG) as a template direction agent in diluted acetic acid aqueous solution. This medium slows down the hydrolysis reaction of titanium sources due to the hydrolytic retardant and the strong chelating effects of acetic acid. A hydrothermal treatment process was introduced to better control the resultant mesoporous structures. The effects of PEG molecular weight and thermal treatment temperature on the resultant structure and photoactivity were investigated. Morphological, structural and phase compositional properties of the resultant photocatalysts were systematically characterized using transmission electron microscopy, X-ray diffraction and nitrogen adsorption/desorption analysis. The mesoporous structure with diameters between 13.3 and 17.0 nm and mean porous sizes that ranged from 9.6 to 13.3 nm were obtained when the molecular weight of PEG were varied from 200 to 20,000. The mesoporous diameters were changed significantly from 9.8 to 18.4 nm with mean porous sizes slightly increasing from 8.0 to 10.0 nm when the calcination temperature was varied from 350 to 550 degrees C. The activities of the resultant TiO2 photocatalysts were evaluated using 2,4,6-tribrominated phenol as a testing compound that represents a class of toxic brominated flame retardants. The experimental results revealed that the photocatalytic activity depends on the phase and on the structural characteristics of the resultant photocatalysts. (C) 2008 Elsevier B.V. All rights reserved.