Formation mechanism of the rutile-phase of TiO₂ nanorods on Ti foil substrate by gel-calcination method

A formation mechanism that leads to the synthesis of rutile-phase TiO₂ nanorods at high temperatures on Ti foil by NaOH-based gel-calcination is discussed based on a series of experimental investigations. TiO₂ nanostructures are prepared on Ti foil following two steps, namely gelation and calcination. It is shown that the use of an alkali-based solution during gelation, such as NaOH and KOH, leads to the formation of faceted TiO₂ nanorods upon calcination at high temperature (~800 °C). When an acidic solution that does not contain an alkali element, such as H₂O_2, is used during gelation, the shape of the nanostructures upon calcination at high temperature does not display the faceted nanorod shape. The following formation mechanism is suggested: the high temperature calcination of the Na based amorphous network of dendritic structures (formed on the Ti surface during a 24-h soak in NaOH solution) converts it into Na-titanate in the shape of nanorods. This in turn converts into nanorods of rutile-phase TiO₂ when Na evaporates in the form of an oxide.