Synthesis of free-standing anatase TiO2 membrane by using two-step anodization

Free-standing titanium dioxide (TiO2) membranes with highly ordered, vertically aligned nanotube arrays were fabricated by using two step anodization of pure titanium (Ti) foil in fluorine containing ethylene glycol. TiO2 nanotubes were prepared under anodizing voltage of 50 V on Ti foil, followed by a thermal annealing at temperature of 200 °C for 10 min, and 450 °C for 2 h, respectively. Subsequently, anodization was carried out at high voltage of 70 V which directly induced detachment of the nanotube membranes from Ti substrate. The film with high-quality surface and open-ended tubes could be obtained, which was easily peeled off and transferred onto other substrates. Free-standing TiO2 membranes were characterized by field emission scanning electron microcopy (FE-SEM), X-ray diffraction (XRD), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). As a result, we found that the diameter increased while tube length decreased with increasing concentration of DI water. Additionally, the thickness of film increased with increasing anodization time.