In this paper, 3.0 mol% lanthanide europium ion modified TiO2 sol (Eu3+-TiO2) was fabricated by chemical coprecipitation-peptization method with TiCl4 as precursor. Eu3+-TiO2 Sol particles were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), transmission electron microscope (TEM) and particle size distribution (PSD). Eu3+-TiO2 sol particles prepared at low temperature (70 degreesC) had anatase semicrystalline structure. Eu3+-TiO2 sol sample homogeneously dispersed in the aqueous medium and presented narrow distribution characterization with 7 nm in mean size. Interfacial adsorption experiment shows that small particle size and positive charge of Sol particles contributed to the good adsorption of X-3B dye on the TiO2, surface. The photoelectrochemical property was investigated about electrons transfer efficiency between dye molecule and TiO2 particles. A novel hydrosol reaction system was designed to conduct X-3B photodegradation reaction. The excellent photocatalytic activity for X-3B degradation under visible light irradiation was ascribed to effective scavenging electrons by Eu3+ ion. Moreover, X-3B photocatalytic degradation mechanism under visible light excitation was proposed as photosensitization-photocatalysis. (C) 2004 Elsevier Ltd. All rights reserved.