Chiral Hybrid Mesoporous Silicas: Assembly of Uniform Hollow Nanospheres and Helical Nanotubes with Tunable Diameters

Uniform helical silica nanotubes and hollow silica nanostructures with adjustable diameters have been prepared through the self-assembly of sodium dodecyl sulfate (SDS) as the surfactant, N-trimethoxysilylpropyl-N,N,N-trimethylammoniumchloride (TMAPS) as a costructure directing agent (CSDA), a binapthyl-based chiral dopant, and TEOS (Si(OEt)(4)) as the bulk silica constituent. Depending on the ratio of anionic surfactant to cationic costructure directing agent, the morphology can be tuned from hollow spheres to hollow nanotubes. At a 1:1 ratio of TMAPS/SDS, in the presence of the axially chiral dopant molecule, uniformly helical structures are obtained. The chirality of the dopant is shown to affect the sense of helicity. Under identical conditions, a monosilylated chiral dopant only leads to the formation of well dispersed uniform hollow spheres rather than helical nanotubes, which further demonstrates the importance of incorporating the chiral dopant as an integral component of the siloxane network, rather than merely as a surface group.