Free-standing TiO2 nanotube membranes from electrochemical anodization

In this paper, a series of electrochemical anodization experiments have been carried out to understand the formation mechanism and to increase control over the morphology of free-standing TiO₂ nanotube membranes. Immobilized TiO₂ nanotube arrays with ordered structure on Ti substrates were prepared under anodization with low voltage (≤60V). High anodization voltage (>;80V) directly induces detachment of the nanotube membranes from Ti substrate, but the surface of membrane is covered by many disordered nanowires. A facile two-step anodic route has been developed to solve this problem. By taking advantage of conventional anodization of Ti substrates, followed by a thermal treatment and further low voltage anodization, a free-standing crystallized membrane with ordered TiO₂ nanotube arrays has been synthesized. The resulting membrane is mechanically robust and with a large area. The ability to fabricate this free-standing TiO₂ nanotube membrane is an essential step towards the exploitation of extended applications.