Synthesis of Large-Pore Mesostructured Micelle-Templated Silicas as Discrete Spheres

The synthesis of large-pore micelle-templated silica (MTS) materials as discrete spheres by pseudomorphic synthesis solves the double challenge: enlarging the pore size of MTS beyond the diameter of the micelles and controlling the morphology and the size of the particles. The pseudomorphic transformation of silica beads of the desired size into MTS is one of the more suitable routes to control both nanometric and micrometric scales of MTS synthesis. The most employed method to enlarge pore diameter of MTS synthesized from alkyltrimethylammonium surfactants is to use 1,3,5-trimethylbenzene (TMB) as a swelling agent in the micelles. Unfortunately this method leads to particle aggregation. By means of the pseudomorphic route combining an original set of chemical compositions (C 18 TAB/decane/TMB/NaI), under mild conditions (low temperature, without autoclaving), we successfully synthesized nonaggregated MTS beads of 10 μm with pore diameter ranging from 7 to 9 nm, 900 m 2 /g specific surface area, and 1.5 mL/g pore volume. To accommodate the large pore volume developed by large-pore MTS, highly porous silica beads of 10 μm and 300 m 2 /g specific surface area have previously been synthesized by means of an emulsion/polymerization procedure. The control at nanometric scale, by means of surfactants, leads to improved textural properties compared to optimized silica gels, whereas the control of the micrometric morphology (discrete spheres) makes these supports suitable for column packing and chromatographic evaluation.