Hydrothermal Growth of Layered Titanate Nanosheet Arrays on Titanium Foil and Their Topotactic Transformation to Heterostructured TiO₂ Photocatalysts

Layered titanate nanostructures have been recognized as an important intermediate in preparing TiO 2 nanostructures due to their availability in various morphologies, among which ultrathin nanosheets have attracted particular attention due to their unique properties arising from their high surface area and confined thickness in nanoscale. Herein, we report a simple approach to fabricate heterostructured TiO 2 nanosheet array film by (1) hydrothermal growth of sodium trititanate nanosheet array on Ti foil in alkaline solution, (2) ion exchange of Na + in titanate naosheet with H +, and (3) topotactical transformation into TiO 2 nanosheet via thermal annealing. XRD and Raman as well as HRTEM analyses proved the formation of a novel anatase/TiO 2 (B) heterostructured nanosheet array with coherent interface between the two phases, which exhibited superior photocatalytic efficiency under UV illumination as compared with the relevant commercial products P25 and anode oxidized TiO 2 nanotube film of the same thickness but with greater mass of photocatalyst. The high photocatalytic activity of the TiO 2 nanosheet array film can be ascribed to the synergistic effect of large surface area and high crystallinity as well as heterojunction between TiO 2 (B) and anatase phase.