In situ studies of structural stability and proton conductivity of titanate nanotubes

Abstract

Titanate nanotubes were prepared by hydrothermal treatment of anatase TiO₂ with concentrated NaOH solution. In situsynchrotron X-ray diffraction studies revealed that the nanotubes are thermally unstable at temperatures above 360 °C and can transform directly to anatase via a dehydration and recrystallization process. This indicated that the titanate nanotubes possess an orthorhombic lepidocrocite (γ-FeOOH)-type layered structure. An aggregate of the as-prepared nanotubes showed an electric conductivity of about 1 × 10⁻⁶ S cm⁻¹ at 50 °C in humid atmospheres. The conductivity depended on humidity of the atmosphere and decreased with increasing temperatures, suggesting that the proton conduction in the titanate nanotubes might correlate with the interlayer H₃O⁺ ions.