Effects of ion exchange and calcinations on the structure and photocatalytic activity of hydrothermally prepared titanate nanotubes

Titanate nanotubes (TiNTs) were prepared by alkaline hydrothermal processing. The TiNTs are thermodynamically unstable and easily transformed to the titania phase by heat or acid treatment. These phase transformations are affected by the preparation conditions. In this study, we investigated the effects of using the washing process to modify the sodium content of the TiNTs. After an alkaline hydrothermal process was used to prepare the TiNTs, the resulting suspensions were washed with weak acid solution and distilled water until the pH value of the wash solution reached approximately 1 or 7, and the products were identified as H-TiNTs or Na-TiNTs, respectively. The characteristics and photocatalytic activities of the H-TiNTs and Na-TiNTs were compared for various calcination temperatures. The H-TiNTs were transformed completely to anatase-type TiO ₂ by dehydration during calcination, while the crystallinity of the Na-TiNTs increased with calcination temperature. However, the photocatalytic H ₂ production rates on calcined H-TiNTs were much higher than on Na-TiNTs, which could be attributed to the crystalline anatase phase.