The present thesis concerns the synthesis and characterization of three mesoporoussemiconducting metal oxides ZnO, In2O3 and SnO2 which possess large specific surface areasand ordered pore systems. Such systems are, due to their high surface-to-volume ratios,particularly of great interest in fields of catalysis, gas sensing and electrochemistry.Generally two synthesis strategies are described in the recent literature which facilitate theapproach to those systems by the utilization of templates. The application of supramolecularaggregates of amphiphilic molecules as structure-directing agents in the liquid phase enableprimarily the synthesis of mesoporous silica materials, inorganic/organic hybrid materials aswell as the fabrication of a few metal oxides. Owing to low synthesis temperatures and thelow rigidity of these structure directors, that synthesis route is not transferable to the mostmetal oxide systems. Furthermore, the resulting materials are often amorphous and possessonly a low temperature stability, which limit potential applications. The second synthesisstrategy, nanocasting, avoid these disadvantages, originated from low synthesistemperatures, by the employment of rigid structure matrices with higher temperaturestability. In case of the one-step nanocasting , the pores of a 3-D highly interconnected silicamatrix are initially filled with a suitable metal oxide precursor species (frequently used: metalnitrates), followed by a thermal in situ conversion into the respective metal oxide. Finally, thestructure matrix is removed by etching with HF or NaOH solution. Hence this route enablesthe synthesis of only those metal oxides, which withstand the template removal procedure.For those metal oxides which are not stable towards NaOH and HF, the utilization ofmesoporous carbon as template represents a promising alternative, since they can easily beremoved by combustion. The carbon matrices are generally synthesized using mesoporoussilica as templates. In case of that two-step nanocasting three problems become apparent:(i) impregnation of the highly hydrophobic carbon matrix with polar precursor species, (ii) theconversion into the oxide without structural loss of the carbon matrix and (iii) removal of thecarbon template at high temperatures still retaining the structural integrity of the resultantmetal oxide.
Verknüpfung zu Publikationen oder weiteren Datensätzen
