One-pot synthesis of phenyl- and amine-functionalized silica fibers through the use of anthracenic and phenazinic organogelators

Abstract

In a typical one-pot synthesis procedure, hybrid organosilica fibers were grown by templating the co-condensation between TEOS and selected organotrialkoxysilanes (20 mol% of phenyltriethoxysilane, PTES, or aminopropyltriethoxysilane, APTES) through the use of DDOA (2,3-bis(n-decyloxy)anthracene) and DUOP (2,3-bis(n-undecyloxy)phenazine) organogelators in a compatible solvent (ethanol or acetonitrile, respectively). Interestingly, the successful replication of organogelator fibrous assemblies was accomplished working at low pH values (ca. 2–3) in acid catalysed conditions. By SEM and TEM characterizations the hybrid organosilicas were seen to consist of submicronic fibers (100–200 nm) aggregated into highly anisotropic fibrous bundles (1–15 µm thick). In addition, molecular and/or supramolecular interactions between the organogelator and the growing organosiloxane network proved to have an important effect on fiber thickness and on fiber aggregation (intertwined/co-aligned, lamellar- or ribbon-like fibrous bundles). After removal of the organogelator (by calcination or by Soxhlet washing), the fibrous morphologies were perfectly conserved, and the presence of phenyl and amine moieties was confirmed by FTIR spectroscopy and also by elemental chemical analysis. The formation of a well-condensed and interconnected organosiloxane network was proven by ²⁹Si MAS NMR spectroscopy. Moreover, the accessibility and reactivity of the grafted amine groups were also corroborated by performing a simple post-functionalization heterogeneous reaction with diluted benzaldehyde.