Nanostructured TiO2 ultratine powder (Ti-SG) 100% anatase phase prepared by the sol-get method was used as a photocatalyst in the decomposition reaction of a basic dye, Crystal Violet (hexamethyl-p-rosaniline chloride), in water under UV light irradiation. Optimization of the photocatalyst's performance as a function of irradiation time, catalyst concentration, and solution pH was performed. The photoactivity was greatly dependent on the solution pH and it was effective for Crystal Violet to be degraded under basic conditions. The extent of photooxidation or -reduction of CV was discussed in terms of the Langmuir-Hinshelwood model. Results also indicated that the proper addition of H2O2 could improve the degradation rate, but excess H2O2 quenched the formation of OHcenter dot. Textural and photocatalytic characteristics of sol-gel derived TiO2 (Ti-SG) were compared with those of commercial P25, TiO2. The relative photonic efficiency of sol-gel derived TiO2 was found to be 2.77 with reference to phenol. (c) 2005 Elsevier Inc. All rights reserved.