On the synthesis and characterizations of TiO2 nanotubes

In the present work, aligned TiO2 nanotubes have been synthesized by a simple method of electrochemical anodization of high purity, well cleaned, etched and ultrasonicated Ti-sheet (Purity approximately 99.99%) in a fluoride mediated electrolytic media consisting of a solution of 0.14 M NaF and a solution of 0.5 M/1.0 M H3PO4. Studies on the effects of anodization voltage, time and electrolyte concentration on the formation of TiO2 nanotubes have been carried out. The TiO2 nanotube arrays have been synthesized at applied anodization voltages of approximately 10 V and approximately 20 V. The anodization was carried out for 1 hour and 2 hours at each applied voltage. Structural/microstructural characterizations of TiO2 nanotubes have been carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of TiO, nanotubes showed interesting features relating to morphology, the pore size (diameter of the tubes) and the lengths of the tube. TEM investigations revealed that the as synthesized nanotubes are amorphous in nature and on electron beam annealing, these transformed to crystalline phases (rutile and brookite). The optical characterizations through UV-Visible spectroscopy exhibited that the band gap are approximately 3.03 eV and approximately 2.87 eV for tubes synthesized at applied anodization voltages of approximately 10 V and approximately 20 V respectively. A tentative mechanism for the growth of TiO2 nanotube has been put forward.