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 TiO₂ 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.