One-Step Microheterogeneous Formation of Rutile@Anatase Core-Shell Nanostructured Microspheres Discovered by Precise Phase Mapping

Nanostructured core–shell microspheres with a rough rutile core and a thin anatase shell are synthesized via a one-step heterogeneous templated hydrolysis process of TiCl4 vapor on the aerosol water–air interface. The rutile-in-anatase core–shell structure has been evidenced by different electron microscopy techniques, including electron energy-loss spectroscopy and 3D electron tomography. A new mechanism for the formation of a crystalline rutile core inside the anatase shell is proposed based on a statistical evaluation of a large number of electron microscopy data. We found that the control over the TiCl4 vapor pressure, the ratio between TiCl4 and H2O aerosol, and the reaction conditions plays a crucial role in the formation of the core–shell morphology and increases the yield of nanostructured microspheres.