Titania nanotubes prepared through a modified hydrothermal method were functionalized with CuO in order to create a composite photocatalyst with enhanced reactivity. Their structural and morphological stability was monitored using X-ray diffraction and scanning and transmission electron microscopy. The X-ray photoelectron spectroscopy analysis indicated the presence of CuO in the titania matrix, which enhanced the anatase to rutile phase transformation. The morphological stability and photoactivity of titania nanotubes depend on the amount of CuO incorporated into the material matrix. The photocatalytic activity of the materials displays two maxima and a minimum and is the result of complex structural and electronic interactions and competing mechanisms. (C) 2015 Elsevier B.V. All rights reserved.