Fast anodically growth of long, small diameter TiO2 nanotubes by electropolishing of Ti foils in an ethanol-containing solution

Abstract Anodic growth of TiO 2 nanotubes with length of several 10 µm in fluoride containing electrolytes conventionally leads to tube diameter of ca. 90–100 nm with an undesired nanograss appearance on the surface of tubular array. Fabrication of nanotubes with diameters smaller than 50 nm needs mild anodization conditions that lead to tubes shorter than 7 µm. In the present work, we introduce a simple and fast approach for fabrication of highly ordered, long nanotubes, 23 µm, with dramatically small diameter of ca. 29 nm, free of nanograss and top porous layer just by 2 h anodization. This method is based on the creation of small diameter semi-spheres on the Ti surface by electropolishing in an ethanol-containing electrolyte. Besides pretreatment of Ti foil, we show that controlled stirring speed and temperature of the electrolyte during anodization are crucial factors to achieve this novel morphology.