Nanotube formation from a sodium titanate powder via low-temperature acid treatment

Through structure-monitoring of nanotube formation from a lamellar sodium titanate, the present work explicitly elucidated the structure of the titanate nanotubes obtained from hydrothermal treatment of TiO₂ with NaOH. A new compound of an orthorhombic lepidocrocite-type sodium titanate was synthesized from calcination of a solid-state mixture of TiO₂ anatase and Na₂CO₃ powders followed by hydrothermal treatment with NaOH. By treating with acid at 25°C for Na₊ exchange with H₃O₊, the titanate compound exfoliated and then proceeded with sheet-scrolling to form nanotubes, which had a structure and morphology very close to those of the nanotubes derived from NaOH treatment on TiO ₂. During the low-temperature acid treatment, the lepidocrocite-type titanate is transformed from the orthorhombic C-base-centered symmetry to the body-centered symmetry. This transformation, accompanied by a size-contraction of TiO₆-octahedron units, was critical for the formation of nanotubes. The present work provides direct evidence, for the first time, that the widely reported TiO₂-derived titanate nanotubes can be obtained at low temperatures by scrolling the sheets exfoliated from the orthorhombic lepidocrocite-type titanate.