One-step realization of open-ended TiO2 nanotube arrays by transition of the anodizing voltage

Free-standing TiO2 nanotubes with both their ends open are required in many applications. This article reports the authors’ latest progress in meeting these requirements. Elevating the voltage at the end of an anodization process can break the adhesion of the TiO2 nanotube layer to the underlying Ti substrate and simultaneously open their bottoms. Furthermore, by modulating the value and duration of the elevated voltage, the bottom morphology of the nanotubes can also be effectively tailored. Compared with most of the related work, in which obtaining free-standing TiO2 nanotube layers and opening their bottom ends are often performed in two separate procedures, this newly-developed route features a simple one-step solution and also good controllability. Both the detachment of the nanotubes from the Ti substrate and the tailoring of their bottom ends are ascribable to the local acidification and gas evolution induced by the sudden voltage transition.