Tuning the Optical Property and Photocatalytic Performance of Titanate Nanotube toward Selective Oxidation of Alcohols under Ambient Conditions

Titanate nanotube (TNT) represents one class of novel one-dimensional semiconducting nanomaterials that can be used as photocatalyst for given applications. However, TNT is only UV-light photoactive because of its intrinsic limitation of light absorption in the UV region. Here, we report a facile approach to tune the optical property and photocatalytic performance of TNT by doping various metal ions (Cu(2+), Co(2+), Ni(2+), Fe(2+), and Mn(2+)) via an ion-exchange method in an aqueous phase. The optical properties of TNT can be finely tuned by incorporating different kinds of metal ions into its tubular framework. In particular, the incorporation of metal ions into the matrix of TNT is able to extend its light absorption to the visible-light region, thus making TNT have the visible-light photoactivity. Activity testing on photocatalytic selective oxidation of a variety of benzylic and allylic alcohols under mild conditions demonstrates that these metal-ion-doped TNTs exhibit markedly enhanced catalytic performance as compared to the undoped TNTs under both the irradiation of UV light and visible light. Such an enhancement of photocatalytic activity with regard to metal-ion-doped TNT is primarily attributed to the prolonged lifetime of photogenerated electron-hole pairs in comparison with that of undoped TNT. Our current research work demonstrates the tunable optical property of TNT by doping metal ions and, more significantly, opens promising prospects of one-dimensional nanotubular TNT or TNT-based materials as visible-light-driven photocatalyst in the area of selective transformation using molecular oxygen as benign oxidant under ambient conditions.