Fabrication of Free Standing Anodic Titanium Oxide Membranes with Clean Surface Using Recycling Process

Large area of self-organized, free standing anodic titanium oxide (ATO) nanotube membranes with clean surfaces were facilely prepared to desired lengths via electrochemical anodization of highly pure Ti sheets in an ethylene glycol electrolyte, with a small amount of NH₄F and H₂O at 50 V, followed by self-detachment of the ATO membrane from the Ti substrate using recycling processes. In the first anodization step, the nanowire oxide layer existed over the well-arranged ATO nanotube. After sufficiently rinsing with water, the whole ATO layer was removed from the Ti sheet by high pressure N₂ gas, and a well-patterned dimple layer with a thickness of about 30 nm existed on the Ti substrate. By using these naturally formed nano-scale pits as templates, in the second and third anodization process, highly ordered, vertically aligned, and free standing ATO membranes with the anodic aluminum oxide (AAO)-like clean surface were obtained. The inter-pore distance and diameter was 154 ± 2 nm and 91 ± 2 nm, the tube arrays lengths for 25 and 46 hours were 44 and 70 μm, respectively. The present study demonstrates a simple approach to producing high quality, length controllable, large area TiO₂ membrane.