The adsorption and photocatalytic reduction of toxic Hg(II) in aqueous solutions were investigated at different temperatures using synthesized TiO2 nanoparticles and TiO2/montmorillonite. The synthesized materials were tested by TGA, BET, TEM and XRD methods. High-purity anatase TiO2 nanoparticles with an average diameter of 9.10 nm were produced by the acid catalyzed sol-gel method at 500 degrees C, and the specific surface area of synthesized TiO2 nanoparticles was in excess of 200 m(2) g(-1). TiO2/montmorillonite was prepared by slurry reactions, resulting in average pore size of 3.10 nm with TiO2 nanoparticles on the montmorillonite surface. TiO2/ montmorillonite with a 22 wt% TiO2 load exhibited a specific surface area of 239 m(2) g(-1). Removal of Hg(II) in aqueous solutions at 25, 35 and 45 degrees C in darkness and under UV illumination showed that the photocatalytic reduction of Hg(II) increased with increasing temperature, and a decline in adsorption was observed for a rise in temperature from 25 to 45 degrees C, following the exothermicity of the adsorption process. The adsorption behavior of Hg(II) on TiO2 nanoparticles was well described by the Langmuir isotherm model, and the rates were simulated by the Elovich equation. A first-order reaction model was used to simulate the photocatalytic reduction reaction of Hg(II) in aqueous solutions, and a good fit was obtained with the experimental data. (C) 2010 Elsevier BM. All rights reserved.