Processing and morphological control of titania nanotubes (TiO2) by single and multi-step anodization processes using HF/EG electrolytes

Abstract

Titania or TiO2 nanotube arrays (TNAs) are of great interest for a wide range of technological and biological applications, especially due to their high surface-to-volume ratios and size dependent properties. The possibility to achieve alterations in nanotubular dimensions (pore diameter, tubular length, wall thickness etc.) and surface morphology are important features that enable the use of such nanostructures for a variety of applications. Subtle differences in the above parameters can control the use of these tubular structures in applications as diverse as solar cells to biomedical implants. This thesis work is an attempt to elucidate the anodization processing conditions and electrolyte chemistry (nature and composition) that helps to achieve control over the dimensional and morphological parameters of titania nanotubes. In the technique of anodization, the choice of the electrolyte, ie., aqueous or non-aqueous, concentration and type of fluoride ion, composition of the electrolyte and thereby its pH and conductivity; all these are parameters that provide uniqueness to the dimensional features and thus, the properties of titania nanotubes generated. An appropriate choice of the electrolyte medium,in addition to the applied voltage and anodization duration, affect the characteristics of the oxide layer that form during anodization. It is important that the electrolyte system selected is not aggressive towards the growing oxide to avoid its dissolution during the process; but guarantee a higher oxide growth rate over the rate of dissolution. Thus, the nature and composition of electrolytes used in anodization have a marked influence in the formation of titania nanotubes. Researchers have explored various types of electrolytes to study the influence of electrolytic parameters in controlling the anodization process. However, how it drives the formation process and what will be the contribution of the nature and composition of electrolytes in controlling the dimensional and morphological parameters of nanotubes