The pretreatment of TiO2-photocatalysts in solutions of H2O2 was studied by examining the decolorization of methylene blue in the dark. Incubation of TiO2 particles in H2O2 solutions increased the oxidizing capacity of TiO2. Methylene blue (0.3 mM) was degraded in the presence of pretreated TiO2, and a decolorizing ratio of 47% was obtained after a 48-h incubation period in the presence of 5.0 g/L pretreated TiO2. Titanium peroxide as a stable oxidant, which can be synthesized with the reaction of titanium sulfate and H2O2, was studied in the decolorizing process of methylene blue. Concentrations of methylene blue were significantly reduced in the presence of titanium peroxide, and a greater extent of decolorization was obtained with larger amounts of titanium peroxide. A 63% decrease in methylene blue concentration was achieved in 5 h incubation in the presence of 4.0 g/L titanium peroxide. H2O2 accelerated the decolorizing process in the presence of titanium peroxide. The addition of 100 mM H2O2 to a methylene blue solution containing 2.0 g/L titanium peroxide increased the decolorizing ratio to 85% after 5 h incubation. The addition of a hydroxyl radical scavenger, dimethyl sulfoxide, significantly decreased the decolorizing ratio, indicating the role of hydroxyl radicals in the oxidation process. (c) 2007 Elsevier B.V. All rights reserved.