Hierarchical Integration of ZnO Nanocrystals into Multishelled Superstructures

We have demonstrated a 'bottom-up' paradigm to effectively fabricate multishelled ZnO hollow superstructures in solution phase containing acetone, isopropanol, water, and propanoic acid. These hierarchical shells are composed of closely packed ZnO nanorods. The one-pot solvothermal method provides a mesoscale crystallization process, in which the morphology of ZnO superstructures can be facilely modulated by varying experimental parameters such as reaction time and solvent. Time-dependent synthetic experiments confirm that Ostwald ripening is responsible for the crystallization of multilevel homogeneous ZnO core shell structure. The hierarchical ripening effect depends on the spatial distribution and solution process of primary crystallites. Porous ZnO hexagonal crystals are achieved without the assistance of propanoic acid, and macroporous ZnO spherical crystals are also yielded in the absence of a defined amount of water. We believe that the chemical technique will further motivate theoretical and experimental researches of the chemical self-transformation hollowing process and can be of general applicability in the fabrication of a wide range of nanoparticle-based hollow architectures.