The photocatalytic reduction of Hg(II) in air-equilibrated aqueous suspensions of TiO2 under UV-illumination were studied. The amount of Hg(II) photo-reduced is affected by the pH of solution, the amount of the hole-scavengers, the concentration of chloride, mass of the catalyst, and incident light intensity. Hg(0) was detected during the photocatalytic reduction of Hg(H). The reduction rate of Hg(II) was controlled by the amount of Hg(II) adsorbed onto the TiO2 Powders. About 100 ppm Hg(II) is efficiently removed within 30 min from air-equilibrated solution at pH 4. The separation for Cr(VI)/Hg(II) mixtures can be achieved via UV/TiO2 photocatalysis. Photocatalytic, activities of two commercially available TiO2 (Degussa P25 and Hombikat UV 100) were also compared for different light intensities and catalyst loadings. (C) 2003 Elsevier Ltd. All rights reserved.