Synthesis of highly-ordered TiO₂ nanotube arrays with tunable sizes

Vertically-oriented one-dimensional TiO₂ nanotube (TNT) arrays have been fabricated by anodic oxidation using different electrolyte solvents, including ethylene glycol (EG), diethylene glycol (DEG), and dimethyl sulfoxide (DMSO), in the presence of hydrofluoric acid (HF) or ammonium fluoride (NH₄F). The influence of synthetic conditions, including the nature of the electrolyte and anodization voltage, on nanotube microstructure has been systematically investigated. Highly-ordered TNTs with tube length of ∼0.5-26.7 μm, inner diameter of ∼13-201 nm, and outer diameter of ∼28-250 nm have been obtained. The conversion of as-prepared TNT arrays from amorphous phase to crystalline structure has been achieved by a postsynthetic annealing at 500 °C for 3 h in oxygen ambient. The TNT arrays with tunable sizes and structures are attractive for use as electrode materials in fabrication of thin film solar cells and highly active photocatalysts.