Optimization of Silica Content in Initial Sol−Gel Grain Particles for the Low Temperature Hydrothermal Synthesis of Titania Nanotubes

Abstract

High purity anatase titania nanotubes were prepared by a low temperature hydrothermal process from anatase TiO2 nanoparticles synthesized by a sol−gel process, and the optimization of titania/silica ratios at initial synthetic sol−gel processes is elucidated in detail. It was observed that a high titania/silica ratio (50:50) in the initial sol−gel synthetic process does not allow titania nanotubes to form; rather, a lamellar structure of protonic lepidocrocite titanates is obtained after hydrothermal treatment with 8 M aqueous alkali solution, and without silica in the initial grains at the sol−gel stage, high crystalline shorter nanorods with dominant rutile phases were observed. However, with titania/silica ratios of 90:10, only pure anatase titania nanotubes of diameter ∼8 nm and length of 500−900 nm were observed. The anatase nanotubes were of good quality and clean surface with no phase observation of sodium titanate and protonic titanates. The nanotube purity was confirmed by field-emission scanning electron microscopy, high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis in TEM, X-ray diffraction, Raman spectroscopy, photoluminescence, and BET surface area techniques.