Enhanced visible light sensitized photoreaction by mixed phase titania nanotubes

In this work, we demonstrate the synthesis of mixed crystalline TiO2 nanotubes (TiNT) using a rapid breakdown anodization process and investigate its application in visible light photocatalytic degradation of rhodamine-B (RhB) dye pollutant. Nanotubes with different anatase to rutile crystalline phases were achieved during ther­mal annealing by tuning the amount of perchlorate ions. Increasing the rutile content decreased the nanotubes’ bandgap and surface area. Photocatalytic studies of TiNT with different crystalline phase ratios revealed promising RhB degradation under visible light compared to commercial TiO2. Herein we propose the humidity conditioning (99% relative humidity) of TiNT as a surface modification method to enhance the –OH group on the oxygen defective sites. FTIR and XPS analysis of the TiNT before and after surface modification showed signif­icant change in the surface –OH groups. The surface area normalized apparent-first order kinetic rate constant was higher for all the TiNTs than commercial TiO2. We report for the first time the higher photocatalytic activity of the humidity conditioned nanotubes with high –OH groups compared to the respective catalyst with less –OH group. The simple method proposed for –OH group incorporation shows a possible way of developing an efficient photocatalyst without complex surface modification techniques.