Synthesis of CdS quantum-dot sensitized TiO2 nanowires with high photocatalytic activity for water splitting

We report on the direct growth of uniform TiO2 nanowires via a facile thermal oxidation treatment of titanium substrates assisted by inorganic salts in the presence of H2O vapor. The effect of temperature, different salts and the amount of KF on the morphologies of the formed TiO2 nanostructures were systematically investigated. Scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscope (TEM), UV-Vis absorbance spectroscopy and X-ray photoelectron spectroscopy (XPS) were employed to characterize the microstructures and composition of the as-synthesized TiO2 nanowires. Our studies reveal that large-volume TiO2 nanowires were directly grown on the Ti substrate in the presence of KF at temperatures above 450 degrees C. In contrast, there were no TiO2 nanowires observed in the samples that were prepared using either KNO3 or KCl. Our XPS results indicate that K+ and F- were doped into TiO2 nanowires. The TiO2 nanowires that were prepared at 600 degrees C exhibited the highest photocurrent response. The as-synthesized TiO2 nanowires were further modified with CdS quantum clots, which significantly increased the photocurrents. The formed CdS quantum dot-TiO2 nanocomposites also demonstrated strong visible light response, which is very promising for the efficient utilization of solar energy. (C) 2012 Elsevier B.V. All rights reserved.