Comparison between microwave and muffle annealing of self-organized TiO2 nanotubes into crystalline anatase

• Microwave annealing converts amorphous TiO2 nanotubes into crystalline anatase.
• The microwave annealed TiO2 nanotubes present adequate electrical properties.
• The morphological properties of the TiO2 nanotubesare not altered by the annealing.
• Improved donor density value is attained comparatively to muffle furnace annealing.
• Microwave annealing of TiO2 nanotubes is a rapid and facile crystallization option.

For the first time, the electrical and morphological properties of self-organized TiO2 nanotubular samples annealed (for only 2 min) in a microwave oven through hybrid thermal heating (MO–TiO2) are assessed comparatively to those of samples conventionally annealed (for 30 min) in a muffle furnace (MF–TiO2). This comparative assessment was carried out through scanning electron micrographs, cyclic voltammetry and photocurrent density curves, as well as determinations of band-gap energy, donor density, and flat-band potential values. No differences in bang-gap energy and morphology were observed; MO–TiO2 presented a small improvement in the donor density value, which, however, did not lead to higher photocurrent densities in comparison to MF–TiO2. Hence, considering that the morphological and electrical properties of the differently annealed TiO2 nanotubular samples are similar, clearly microwave annealing is an advantageous option to convert amorphous TiO2 nanotubes into the crystalline anatase phase, especially because this procedure is very rapid and facile.