TiO2 nanotubes, nanofibers and nanowires were prepared by the hydrothermal treatment of TiO2 nanoparticles with different NaOH concentrations (5, 10 and 12 N) at 120, 140 and 180 degrees C; afterwards, HCl was added until reaching pH 2. Both the crystalline phase and coordination of the TiO2 nanotubes, nanofibers and nanowires were composed principally of H2Ti3O7, H2Ti4O9 center dot H2O and H(2)Ti(5)O11 center dot H2O. Likewise, the surface area, pore volume and pore size of the TiO2 nanotubes, nanofibers and nanowires changed with the NaOH rinsing treatment. The photocatalytic activities for methylene blue and methyl orange degradation were strongly enhanced by the nanotubes and nanoparticles in the basic and acid media, respectively, showing a relationship between their structure and the medium. (C) 2015 Elsevier B.V. All rights reserved.