Transition metal-doped TiO2, electrodes were prepared by re-anodization and characterized. The structure of these electrodes was investigated by X-ray diffraction and electron diffraction, which mainly showed typical characteristic anatase reflections without any dopant-related peaks. The amount of transition metal dopant in TiO2 was kept at approximately 1.0 at.%, as measured by energy dispersive X-ray spectroscopy. The effects of different types of dopants on the photocatalytic activity were revealed by measuring the degradation of an organic aqueous solution containing a dye (acid red G) using a combination of ultraviolet (UV) light energy in the presence of these electrodes. The photocatalytic efficiency was remarkably enhanced by the incorporation of Mn2+ and Cr3+. Mn2+ showed the most significant enhancement. However, CO2+ accelerated the rate of acid red G degradation only slightly. Langmuir-Hinshelwood rate expression was employed for the degradation of acid red G by UV/TiO2 electrodes system. The adsorption equilibrium constant, the rate constant, and the initial degradation rate were determined for different electrodes. The effect of the concentration of Mn2+ on the degradation of acid red G was also investigated and the results showed that there is an optimal value (about 1.0 at.%) of the concentration of Mn2+ for inducing faster degradation of the dye. The enhanced photocatalytic degradation rate of acid red G in the presence of transition metals is attributed to the increase of the charge separation in these systems. (c) 2007 Elsevier B.V. All rights reserved.