Aligned metal oxide nanotube arrays: key-aspects of anodic TiO2 nanotube formation and properties

TL;DR

This review discusses the fundamental principles, growth mechanisms, morphologies, and functional enhancements of self-aligned TiO2 nanotubes, highlighting their potential in energy, environmental, and biomedical applications.

Contribution

It provides a comprehensive overview of the mechanistic aspects of TiO2 nanotube formation and how growth approaches can tailor their properties for specific high-performance applications.

Findings

Different morphologies of TiO2 nanotubes are characterized.

Double- and single-walled nanotubes can be detached for membranes.

Growth methods influence nanotube properties like electron mobility and doping.

Abstract

Over the past ten years, self-aligned TiO2 nanotubes have attracted tremendous scientific and technological interest due to their anticipated impact on energy conversion, environment remediation and biocompatibility. In the present manuscript, we review fundamental principles that govern the self-organized initiation of anodic TiO2 nanotubes. We start with the fundamental question: Why is self-organization taking place? We illustrate the inherent key mechanistic aspects that lead to tube growth in various different morphologies, such as rippled-walled tubes, smooth tubes, stacks and bamboo-type tubes, and importantly the formation of double-walled TiO2 nanotubes versus single-walled tubes, and the drastic difference in their physical and chemical properties. We show how both double- and single-walled tube layers can be detached from the metallic substrate and exploited for the preparation of robust self-standing membranes. Finally, we show how by selecting the right growth approach to TiO2 nanotubes specific functional features can be significantly improved, e.g., an enhanced electron mobility, intrinsic doping, or crystallization into pure anatase at extremely high temperatures can be achieved. This in turn can be exploited in constructing high performance devices based on anodic TiO2 in a wide range of applications.