Simultaneous drying and chemical modification of hierarchically organized silica monoliths with organofunctional silanes

Abstract

Large, low density silica monoliths with a hierarchical organisation of macro- and periodically arranged mesopores are prepared by a true liquid crystal templating approach of an ethylene glycol-modified silane in the presence of a non-ionic block copolymer surfactant and subsequent drying of the wet gels with organosilanes. In this approach the silanes serve two functions: first, the silylation reactions allow for non-destructive drying of the monolithic gels and simultaneous extraction of the block copolymer template; second, they serve as surface functionalization agent. A variety of organofunctional silanes such as trimethylchlorosilane, 3-mercaptopropyltrimethoxysilane, phenyl-trimethoxysilane, 3-[(2,2-dimethyl-1-aza-2-silacyclopent-1-yl)dimethylsilyl]-1-propanamine, a cyclic silazane resulting in aminopropyldimethylsilyl groups on the silica surface, and (methylmethacryloyl)dimethyl-methoxysilane, has been successfully applied in the interfacial modification of the silica surface. The resulting silica monoliths were characterized with respect to their structure by SEM, SAXS, and nitrogen sorption and with respect to their chemical composition by elemental analysis, titrations and MAS-NMR spectroscopy.