Highly Ordered Titania Nanotube Arrays Synthesized via One-faced and Single-step Anodization

Abstract

Highly ordered titania (TiO₂) nanotube arrays were synthesized via one-faced and single-step anodization method. Titanium foils were anodized in ethylene glycol based electrolytes containing 0.25 wt% NH₄F, 2 vol% H₂O, and doped with various concentrations of K₃[Fe(CN)₆] at applied voltage of 50 V for 2 h at room temperature. As-anodized samples were annealed at 450 °C for 2 h in order to transform the amorphous titania to nanocrytalline anatase. Highly ordered titania nanotube arrays were obtained after K₃[Fe(CN)₆] at different concentrations was introduced. The surfaces of TiO₂ nanotubes were smoother after increasing concentrations of K₃[Fe(CN)₆], confirmed by AFM investigation. Doping of K₃[Fe(CN)₆] successfully extended the absorption spectrum of samples in range of 200 to 375 nm and slightly increased their band gap energy. Doping with 0.20 wt% K₃[Fe(CN)₆] caused Ti 2p shift towards lower binding energy due to the reduction of Ti⁴⁺ to Ti³⁺, thus improving the electrochemical performance of titania nanotubes. This work suggests an alternative method for fine tuning the size of TiO₂ nanotube arrays that widely applied in the field of energy conversion materials.