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 H2O2, 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.