Structural features of nanotubes synthesized from NaOH treatment on TiO₂ with different post-treatments

We demonstrated that nanotubes synthesized from a NaOH treatment on TiO₂ with subsequent acid washing could proceed with repeatable crystalline-structure transformation through a simple acid-base washing step. By providing the unit cell parameters, we identified a divalent salt titanate (Na₂Ti₂O₅H₂O) with a layered structure as the structure formed after the NaOH treatment. With the increase in acidity during the post-treatment acid washing, the layered titaniate transformed into a nanotube through Na⁺-H⁺ substitution, and eventually transformed into anatase TiO₂. Crystalline-structure analysis has shown the feasibility of this titanate - titania transformation occuring through a simple structural rearrangement. A complete scheme for the formation and transformation of nanotubes induced by the NaOH treatment and the post-treatment washing was proposed.