Large pore methylene-bridged periodic mesoporous organosilicas: Synthesis, bifunctionalization and their use as nanotemplates

Large pore, methylene-bridged, periodic mesoporous organosilicas (PMO-Me's) have been synthesized using the nonionic surfactant P123 (EO ₂₀PO₇₀EO₂₀) as a structure-directing agent under acidic conditions. The morphology of the PMO-Me materials was observed to be strongly dependent on the acidity of the solution used in each preparation. Modification of the PMO-Me surface with 3-mercaptopropyltrimeth-oxysilane (MPTS), via a supercritical fluid grafting reaction, resulted in the formation of a bifunctionalized organosilica (SH-PMO-Me). These SH-PMO-Me materials, coated with Au clusters, were subsequently utilized as templates for the supercritical fluid deposition of germanium nanocrystals. The highly hydrophobic surfaces of the SH-PMO-Me templates, and the effective penetrating power of the supercritical fluid, resulted in rapid diffusion of the germanium precursor into the mesopores to produce highly crystalline nanoparticles and nanorods. These nanocomposite materials were found to be significantly more crystalline than those formed from functionalized Au-coated mesoporous silica templates (SH-SBA-15), highlighting the benefits of using PMOs as hosts for the encapsulation of semiconductor nanomaterials.