Two percent Cu-doped TiO2 nanoparticles were prepared by a modified ammonia-evaporation-induced synthetic method, calcined at 450 degrees C, and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, ESR spectroscopy, scanning electron microscopy, UV-visible diffuse reflectance spectrum, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Doping shifts the optical absorption edge to the visible region but increases the charge-transfer resistance and decreases the capacitance. Under visible light, the composite nanoparticles very efficiently catalyze the disinfection of Escherichia coli. The prepared oxide is selective in photocatalysis; under UV light, its photocatalytic activity to degrade sunset yellow, rhodamine B. and methylene blue dyes is less than that of the undoped one. (C) 2010 Elsevier Inc. All rights reserved.