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 (Na2Ti2O5·H2O) 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.