Synthesis of micrometer sized mesoporous metal oxide spheres by nanocasting

Nanocrystalline SnO2, ZrO2, Mn2O3, and Fe2O3, micrometer sized spheres with additional internal mesopores and/or macropores have been prepared by nanocasting using mesoporous silica spheres as the template. The starting silica spheres are impregnated by metal salt solutions using either water or ethanol as the solvent. The metal salts (nitrates or chlorides) were decomposed by rapid heat treatment leading to the formation of particles almost exclusively inside the mesopores of the silica mold. The silica portion is subsequently leached out in either NaOH or HF solutions. The metal oxide sphere diameter can easily be adjusted by changing the particle diameter of the starting silica spheres. Furthermore, by variation of the metal salt loading of the spheres, it is also possible to prepare hollow spheres with a porous surface. The chemical and structural properties of the materials have been characterized by using SEM-EDS, mercury porosimetry, nitrogen physisorption, and XRD. These novel materials are suggested to find applications especially in the fields of macromolecular separation, and sensor technology.