Fabrication of highly-ordered TiO2 nanocolumns by two-step anodizing of an Al/Ti layer in etidronic acid

TiO2 nanocolumns were fabricated by a two-step anodizing process of an Al/Ti bilayer system and using as electrolyte 0.3 M etidronic acid at 40 °C. To prepare the Al/Ti bilayer samples, two different procedures were employed, obtaining either nanocolumns with or without highly-ordered. It was found that the titania nanocolumns were chemically stable after selective alumina dissolution in 0.05 M KOH at 50 °C. Nanocolumns of different heights were obtained, height averages ranged between 170 and 689 nm, depending on the potentiodynamic rate and the final voltage employed in the second anodizing step. The diameter of the nanocolumns, in all cases, was about 286 nm. Raman and X-ray diffraction analysis confirmed that after heat treatment at 600 °C for 3 h, the TiO2 nanocolumns have a crystalline structure composed of both anatase and rutile phases.