Solar-responsive sole TiO 2 nanotube arrays with high photocatalytic activity prepared by one-step anodic oxidation

We prepared sole TiO 2 nanotube arrays (NAs) using one-step and two-step anodic oxidation followed by annealing. These TiO 2 NAs were characterized by X-ray diffraction (XRD), Raman spectrum, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis absorption spectrum, photoluminescence spectrum (PL), and contact angle measurement. The XRD and Raman spectra results suggest only anatase TiO 2 phase formed after anodic oxidation followed by annealing. The XPS spectra showed that the surface electron density change in the TiO 2 NAs prepared by one-step anodic oxidation compared to those prepared by two-step one. Therefore, the former could absorb visible light more intensely. The PL and photocurrent measurement proved that the recombination rate of electron-hole pairs was suppressed in the sample prepared by two-step anodic oxidation followed by annealing as the degree of crystallinity increased and crystal defects decreased compared with the sample prepared by one-step anodic oxidation followed by annealing. However, the latter possessed better wettability to water and oil and thereby more active sites. The combined action made the sole TiO 2 NAs prepared by one-step anodic oxidation exhibited rather similar high photocatalytic activity in RhB degradation under the irradiation of simulated solar light to those prepared by two-step one. Therefore, solar-responsive sole TiO 2 NAs with high photocatalytic activity were possible to be prepared.