Pseudomorphe Transformation mesostrukturierter Silikagele zu anderen Metalloxiden

Abstract

Porous materials with high surface areas, well-defined pore sizes and long-range ordering of the packing of pores are of great importance in many applications. Sol-gel processing is a great tool towards the synthesis of highly porous featuring the above mentioned properties. The aim of this work is the formation of macroporous magnesium oxide or titanium dioxide through one-step or multi-step gas-solid displacement reactions, using hierarchically organized silica monoliths as hard template. In the first step, monolithic SiO2-preforms were prepared through sol-gel processing by using tetrakis(2-hydroxyethoxy)silane (EGMS) as precursor and the commercially available triblock copolymer Pluronic P123 (ethylene oxide)EO20(propylene oxide)PO70(ethylene oxide)EO20 as the structure-directing agent. The obtained SiO2-gels were dried by surface silylation treatment with trimethylchlorosilane and calcined at 650 °C. For the transformation reactions magnesium powder or titanium(IV)fluoride were used as reagent. The influence of different reaction temperatures and conversion times were tested. The resulting chemical composition was analyzed by X-ray diffraction. The gel morphology and porosity were characterized by scanning and transmission electron microscopy and nitrogen physisorption.