Self-Construction of Core-Shell TiO2: A Colloidal-Molecular Mediated Recrystallization Process

TiO2 with hierarchical core-shell polyhedral architecture was prepared by a one-pot hydrothermal route in the presence of fluorine ions and hydrogen peroxide. Detailed investigations on samples at different preparation stages revealed that the growth of the complex crystalline geometrical structure follows a colloidal-molecular mediated recrystallization process. The whole process can be described by the following successive steps. (1) Primary amorphous TiO2 spheres undergo oriented aggregation to yield colloidal-molecules. (2) Single crystal anatase plates start to nucleate at specific sites defined by the colloidal-molecular. (3) The anatase shell grows into single crystalline plates via Ostwald ripening by consuming the core, and meanwhile, the core recrystallizes into nanorods assembly with hollow interior. Fluorine ions and H2O2 were both found to have important roles in the formation of this hierarchical polyhedron architecture. The present work adds new useful information for the understanding of site specific growth of crystal and may provide a versatile approach for bottom-up construction of 3D architectures in micro- to nanometer scale.