Effects of calcination temperature on the morphology, structure and photocatalytic activity of titanate nanotube thin films

"Titanate nanotube thin films were synthesized on titanium substrate via a simple hydrothermal method. The as-prepared film was composed of Na2Ti3O7, and then transformed into H2Ti4O9·H2O after acid washing process. However, H2Ti4O9·H2O was thermally unstable. The effect of calcination temperature on its morphology (nanotube, nanosheet, nanorod or a lotus-root-like appearance), structure and photocatalytic activity was carried out by annealing the films at 300–900 °C in the static air and then analyzing by X-ray diffraction, scanning electron microscope and transmission electron microscope. Based on the results, the possible evolution mechanisms were discussed for no-acid (washed with distilled water) and acid washed (washed with dilute HNO3) samples, respectively. Finally, the photocatalytic activity of acid washed films calcined at different temperatures was evaluated by photodegradation of methyl orange (MO) under ultraviolet light. The results indicated that the film obtained at 500 °C showed the highest rate for decomposing MO solution, which could be explained by its unique surface morphology and crystal structure.