Structural evolution of anodized TiO2 nanotubes and their solar energy applications

TiO₂ is one of the most important materials in modern industrial societies because of its outstanding chemical and electrical properties. Many properties of TiO₂, including its charge transport behaviors, grain boundaries, surface-to-volume ratio, and contact with surrounding systems, are strongly influenced by its nanoscale architecture. In this regard, TiO₂ nanotubes produced by anodization have received extensive attention as a promising TiO₂ architecture because of their unique one-dimensional configuration that includes well-defined nanostructures with a vertical orientation. These architectural features enable efficient charge transport along the axial direction. However, early anodized TiO₂ nanotubes suffered several drawbacks including limited substrate and singly open-ended nanostructure restrict their further applications. To address these challenges, researchers have developed advanced TiO₂ nanotubes, and several TiO₂ nanotube structures, including freestanding membranes, doubly open-ended nanotubes, and hierarchical structures, have been reported, and these TiO₂ nanotubes have exhibited enhanced performance in various applications. In this article, we review recent advances in the structural developments of anodized TiO₂ nanotubes and the applications of these materials in the field of solar energy.

Graphical abstract

Schematic diagram of the characteristics and applications of TiO₂ nanotubes.