Facile synthesis of ZnO/TiO2 core-shell nanostructures and their photocatalytic activities.

We reveal a new strategy for synthesizing ZnO/TiO2 core-shell nanostructures with different TiO2 shell thickness by wet chemical method. This is a facile and rapid process, requires inexpensive precursors with excellent fidelity. The thickness of a typical core-shell nanostructure ranges from 20-50 nm in size with TiO2 shell thickness of 3-6 nm which were confirmed by Transmission electron microscopy (TEM). X-ray diffraction peaks intensity of TiO2 gradually increased while we increase precursor ratio which confirmed the increase of shell thickness. X-ray photoelectron spectroscopy (XPS) results indicated that zinc ions did not enter TiO, lattice and more likely to bonded with oxygen atoms to form TiO2 coupled on the surface of ZnO. However, the PL intensity gradually increased with the increase of the TiO2 shell thickness, indicating charge transfer between the two materials of the ZnO/TiO2 core-shell nanostructures. Further investigation, revealed that the core-shell nanostructures possessed significantly higher solar light photocatalytic activity which was twice than that of original 1-D ZnO nanostructures. The mechanism of the optimal TiO2 shell thickness to reach the maximum photocatalytic activity in the ZnO/TiO2 core-shell nanostructures are proposed and discussed. It is believed that this facile, rapid wet chemical process is scalable and can be applied to synthesize other (oxide/oxide) core-shell nanostructures for various applications.