| The preparation of organically functionalized MSU-2 silica mesostructures was achieved by direct synthesis by co-condensation of tetraethoxysilane (TEOS) and a variety of functional groups such as 3-mercaptopropyltrimethoxysilane (MPTMS), N-((trimethoxysilyl)propyl)-N,N,N-trimethylammonium (PrTMA-TMS) and N-((trimethoxysilyl)propyl)-N,N,N,-tri-n-butylammonium (PrTBA-TMS). These syntheses were carried out in mildly acidified solutions of a structure-directing non-ionic surfactant (Igepal CA-720) followed by fluoride-mediated hydrolysis/cross-linking and surfactant extraction. The influence of synthesis temperature and organosilane loading on the framework order, pore structure, and particle size was investigated. The lattice spacings, pore volumes, and pore diameters were found to systematically increase as a function of increasing synthesis temperature for the MSU-2 synthesized in the presence of MPTMS. Incorporation of cationic functional groups (PrTMA-TMS and PrTBA-TMS) resulted in very disordered material where a loading of only 1% (in respect to total silane) failed to exhibit microspherical morphology. PrTMA-TMS and PrTBA-TMS were observed to be disrupting functional groups, although PrTBA-TMS was found to be less disrupting due to its more amphiphilic character. In addition, MPTMS was observed to act as a directing group because its incorporation lead to materials of higher order structure. |
