Nanostuctured mesoporous materials from different silica sources using fluorinated surfactants as templates

Abstract

We report here the synthesis of mesoporous silica materials from various fluorinated-based systems using as the inorganic precursor either sodium silicate solution or silicate ions produced from the dissolution of silica under basic conditions. The properties of the materials are compared with the ones of the mesostructures prepared from tetramethoxysilane as silica source. Results show that whatever the silica source, well-ordered hexagonal materials with a narrow pore size distribution are obtained. Nevertheless, the pH has a great influence on the properties of the recovered materials since it governs the interactions between the surfactant and the inorganic precursor and the pH range for which the hexagonal mesopore ordering is obtained, depends on the silica source. Using sodium silicate, hexagonal mesostructured materials with high specific surface area (≥800m2/g) and narrow pore size distribution (4nm) are recovered for pH from 0.3 to 5. It should be noted that the formation of organized mesoporous silica under acidic conditions with this precursor is barely reported in literature. Replacing sodium silicate by silica fumed, the pH range leading to a hexagonal mesopore ordering is reduced to 0.3–1.5. When the organosilane is used the ordered mesoporous materials are recovered regardless the pH. In addition in that case a better control of the self assembly between the surfactant and the silica species allows tuning the particles’ morphology. Under acidic conditions tetramethoxysilane gives rise to gyroids or toroids and favors the formation of submicrometer particles, while irregularly shaped particles are produced with sodium silicate or silica fumed under alkaline conditions. Results also show that neither the specific surface area, nor the cell parameter strongly depend on the silica precursor as long as the hexagonal structure is kept.