Photocatalysis research heavily emphasizes increasing photo-efficiency. This study presents the application of carbon nanotubes (CNTs) to increase the photocatalytic activity of TiO2. It elucidates the effect of CNTs dose on the decolorization efficiency of aqueous azo dye, C.I. Reactive Red 2 (RR2) determines the effects of SO42- formation and removal of total organic carbon (TOC), and measures the effects of various ultraviolet wavelengths. Scanning electron microscopy was used to elucidate the mixing phenomenon and the size of TiO2 and CNTs; X-ray diffraction was used to determine crystallinity: a BET meter was used to measure surface area and a spectrophotometry was used to determine the decolorization of RR2. Experimental results indicated significant effects of photodegradation on the combination of TiO2 with CNTs and electron transfer is higher for 410 nm irradiation than for 365 nm, revealing that solar light can be used. The electron transfer in the TiO2/CNTs composites reduced the electron/hole recombination and increased the photon efficiency and the prevenient dye-degradation mechanisms using UV/TiO2/CNTS were established. (C) 2008 Elsevier B.V. All rights reserved.