Synthese und Funktionalisierung nanostrukturierter Silicagele durch Kombination von Sol-Gel Prozess und Klick-Chemie

Abstract

Sol-gel processing in combination with Click-chemistry, specifically the azide-alkyne Cu(I)-catalyzed 1,3-dipolar cycloaddition, has been applied to synthesize nanostructured inorganic-organic hybrid materials based on a silicamatrix. Combining the enormous variation potential of organic groups with the advantages of thermally stable and robust inorganic substrates is particularly attractive to broaden the areas of application of inorganic materials e.g. in chromatography, catalysis or in their function as nanoreactors. Hierarchically organized porous silica monoliths with bimodal pore size distribution and high specific surface areas were obtained by sol-gel processing of tetrakis-(2-hydroxyethoxy)-silane in the presence of P123 as structure-directing agent. The material exhibit a cellular network built up with interconnected macropores comprising a well organized mesostructure with periodically arranged mesopores. To functionalize the silica-network a co-condensation reaction with trialkoxysilanes containing chloromethyl- and alternatively chloropropylgroups has been used. Subsequent conversion of the chloro groups via nucleophilic substitution with NaN3 in N,N-dimethylformamide to the corresponding azido moieties was successfully conducted. These samples then were reacted Cu(I)-catalyzed with molecules holding terminal acetylenes to get 1,2,3-triazoles with different organic groups attached on the silica surface and confirmed through 13C-CPMAS-NMR, IR-ATR spectroscopy and elemental analyses. The structure of the silica monoliths is changed for the better with respect to an enlargement of the lattice constant and the periodic repeating unit as well as an increase of the pore volume and the pore diameter with simultaneously reduction of the pore wall thickness, which was confirmed by N2-sorption analysis, SAXS, TEM and SEM. Further investigations point out that the structural changes are caused by the azide that is used for nucleophilic substitution.