Fabrication of TiO₂ Nanotubes and Their Advanced Nanostructures

TiO₂ is one of the most studied compounds in materials science because of the outstanding properties used in photocatalysis, dye-sensitized solar cells, and biomedical devices. Its tubular and advanced nanostructures have recently been synthesized and characterized with different electrolytes. In this paper, we reviewed the fabrication of traditional morphologies of highly ordered TiO₂ nanotube (TNT) arrays made by anodic oxidation of titanium in different kinds of electrolytes, such as fluoride-based, fluoride salt-based, other acids-based electrolytes. Furthermore, we further reviewed the ability to fabricate TiO₂ tube-like arrays of different shape, such as TIT nanostructures, double-walled, bamboo-type, multipodal, V-like hollow and branched TNT arrays, by varying anodization parameters including electrolyte concentration, pH, voltage, and bath temperature, with fabrication and crystallization variables discussed in reference to a nanotube array growth model. These advanced material architectures have proven to be of great interest for use in water photoelectrolysis, photocatalysis, heterojunction solar cells, and gas sensing.