Cu-Doped Titania Nanotubes for Visible-Light Photocatalytic Mineralization of Toluene

Based on hydrogen titanate nanotubes prepared by a low-temperature hydrothermal technique, Cu-doped titania nanotube (Cu-TNT) catalysts were prepared using absorption-calcination methods. They were characterized by X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (UV-Vis-DRS), and electrochemical techniques. Density functional theory (DFT) was used to calculate the nanotube band structure and density of states. Cu/Ti atomic ratios in the synthesized powders were very close to the nominal values, and the Cu-doped TiO2 lattice exhibited improved visible-light absorption. This was because the valence band, formed by hybridization of O 2p states with Cu 3d states, was negatively shifted. Thus, the band gap was reduced to 2.50-2.91 eV and the samples exhibited visible-light responses. Toluene was chosen as a model pollutant to evaluate the removal capacity and the CO2 mineralization rate of volatile organic compounds under visible light. Pure TNT displayed poor visible-light activity, and the activities of samples with >0.1% Cu doping were also weak. Samples doped with 0.1% Cu exhibited optimum visible-light photocatalytic oxidation activity, with a 77% toluene degradation efficiency and a 59% mineralization rate in 7 h.