Datensatz

Zusammenfassung

In this thesis the soft and hard templating pathways have been used to produce different kinds of ordered mesoporous silica and metal oxides. A detailed study on the surface topology of well-known ordered mesoporous silica (SBA-15, MCM-41 and KIT-6) was carried out using High Resolution Scanning Electron Microscopy (HR-SEM). Images of the MCM-41 structure were obtained at a resolution of the pore size, as well as a real space image of the gyroid silica surface of KIT-6 for two different aging temperatures, clearly revealing the differences of the aging procedures. The prepared ordered mesoporous silica was used as hard template to produce ordered mesoporous metal oxide. Cubic and hexagonal ordered mesoporous Co₃O₄ with different crystallite size and textural parameters was successfully nanocast; magnetic properties and catalytic activity of these materials in CO-oxidation were investigated. Nanostructured Co₃O₄ was found to be an excellent catalyst for low temperature CO oxidation, with the activity depending clearly on surface area and pore system of the catalysts. Additionally, the first ordered nanostructured CoO (which is not possible to produce by conventional methods) was prepared by the reduction of nanocast Co₃O₄ using glycerol as reducing agent. The reduction conditions of this new process were optimized and the structure and morphology of the materials were fully characterized.
Ordered mesoporous Co₃O₄/CoFe₂O₄ composite and ferrihydrite were also prepared for the first time via the nanocasting pathway. Structure, topology and magnetic properties of the nanostructured metal oxides were examined in detail. The Co₃O₄/CoFe₂O₄ nanocomposite behaves as an exchange coupled system with a cooperative magnetic switching and ferrihydrite shows interesting magnetic behavior with a spin glass state because of uncompensated spins due to the small structure size.
Ordered mesoporous Cr₂O₃ was also fabricated via the nanocasting pathway using cubic and hexagonal ordered mesoporous silica as hard template. Magnetic properties of the nanocast Cr₂O₃ and effect of the calcination temperature on the structure of the materials was investigated. Crystal structure refinements reveal increasing lattice parameters with increasing calcination temperatures. The magnetic studies reveal a significant increase in Néel temperature (TN), for the sample calcined at elevated temperature and a spin-flop transition at much smaller fields compared to the bulk Cr₂O₃.