Correlation between growth mechanisms and the influence of process control parameters on physical properties of titanium dioxide nanotubes in electrochemical anodisation

The growth of thin oxide films has been covered by several theories and models. The high electrical field model, Fowler-Nordheim tunneling in Metal Oxide films and Schottyky barrier Mechanisms are models which explain metal oxide formation. The growth mechanisms and process control parameters during thin film growth in electrochemical anodization play a key role in the growth process. This work explores how the growth mechanisms correlate with process control parameters to influence the growth process in electrochemical anodization of titanium dioxide nanotubes (TNTs). The theories on growth mechanism have been explained in detail. On the experimental part, TiO2 nanotubes were synthesized for photocatalytic activity using electrochemical anodization in a third generation electrolyte. The electrolyte comprised of a mixture of ethylene glycol and ammonium fluoride in little amount of water. Anodizing time and electrode separation distance were explored as process control parameters. The TNTs were analysed using SEM, XRD, Profilometer and UV-Visible spectrophotometer. Short electrode separation distance recorded fast growth, non-uniformity in TNTS, disorganisation, distortion and etching of TNTs. The TNT length, inner and outer diameters reduced with increasing electrode separation distance due to reduction of electric field, increased bulk resistance. There was no significant increase in TNT dimensions at electrode separation distance of 4.5 cm which also recorded the smallest grain size for the TNTs highest degree of crystallinity for with absorption maxima at 550 nm. TNT length, inner and outer diameters and crystallinity increased with anodising time.