i-Silica: Nanostructured silica hybrid materials containing imidazolium groups by hydrolysis-polycondensation of disilylated bis-N,N′-alkyl-imidazolium halides

We report the synthesis of silica hybrid materials from the ionic bis-N,N'-(3-triethoxysilyl)propyl imidazolium chloride precursor. This precursor shows very particular behaviour in template directed hydrolysis polycondensation procedures due to its ionic nature. Nanostructured phases were obtained by sol-gel transformation of this precursor in the presence of anionic surfactants. In contrast, hydrolysis-polycondensation under standard reaction conditions using usually applied templating methods with cationic or neutral surfactants led to the formation of amorphous materials. Detailed insight in the hydrolysis polycondensation behaviour of this precursor was obtained via co-condensation reactions of the ionic precursor with a silica network former tetraethoxysilane (TEOS). It appears that the formation of nanostructured phases in the presence of anionic surfactants can be explained by ionic interactions between the template and the organo-cationic substructure of the imidazolium precursor in the hydrolysis polycondensation mixture. These results point a new templating mechanism for the formation of nanostructured silica hybrid materials. (C) 2010 Elsevier Inc. All rights reserved.