Solar-responsive sole TiO2 nanotube arrays with high photocatalytic activity prepared by one-step anodic oxidation

Abstract

We prepared sole TiO2 nanotube arrays (NAs) using one-step and two-step anodic oxidation followed by annealing. These TiO2 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 TiO2 phase formed after anodic oxidation followed by annealing. The XPS spectra showed that the surface electron density change in the TiO2 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 TiO2 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 TiO2 NAs with high photocatalytic activity were possible to be prepared.