Enhanced photoelectrochemical performance of CdO-TiO2 nanotubes prepared by direct impregnation

A direct impregnation technique was adopted to prepare a series of CdO-TiO2 nanotubes. Self-organized TiO2 nanotubes were prepared using an optimized two-step anodization process. The morphology, crystallinity, elemental composition, and photoelectrochemical properties of the CdO-TiO2 nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis diffuse reflection spectra (UV-Vis DRS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoelectric cell (PEC) measurements. At lower Cd(NO3)(2) concentration, no obvious CdO crystalline particle formed on the TiO2 NTbs surface, while the EDS and XPS measurements shows the increasing doping amount of CdO as the Cd(NO3)(2) concentration increasing. At a relatively high precursor concentration (800 mM), the formation of particle clusters and nanocrystals on the surface of the TiO2 nanotubes could be easily detected, and the sample presented XRD diffraction peaks indicative of CdTiO3. Meanwhile, the Ti 2p XPS spectra displayed an obvious shift (similar to 0.3 eV), which could be attributed to the change in the lattice structure. A negative shift in the flatband potential (V-fb) and a decrease in charge carrier density were observed after doping. The maximum incident photon to charge carrier efficiency (IPCE) value calculated for the CdO-TiO2 nanotubes was 10.16%, much higher than that of pure TiO2 nanotubes.