Preparation of mesoporous silica by the rapid gelation of Na<sub>2</sub>SiO<sub>3</sub> and H<sub>2</sub>SiF<sub>6</sub> in aqueous surfactant solution

Abstract

Microporous and mesoporous materials are used as catalyst carriers, adsorbents, and ion exchangers. In this study, mesoporous molecular sieves were prepared through the rapid reaction of Na2SiO3 and H2SiF6 in a water solution containing surfactants. Mesoporous silica (MS) precipitates were produced within 5 s and X-ray diffraction (XRD) analysis of the MS samples indicated the formation of mesoporous molecular sieves owing to the appearance of well-defined peaks at intervals of 3.8-5.2 nm. The specific surface area was 371 m(2) g(-1) when using a cationic surfactant and in the range of 959-1135 m(2) g(-1) in nonionic surfactants. The pore-size distribution of MS samples showed a constant value of 2.5-3.1 nm. The shape of the silica particles observed via scanning electron microscopy was spherical with a uniform size of similar to 0.7 mu m. Transmission electron microscopy images of the samples obtained using the nonionic surfactant showed worm-hole-shaped pores, whereas those obtained using the cationic surfactant had regular honeycomb-shaped pores. MS samples synthesized using nonionic surfactants were thermally very stable in the light of their XRD peaks being maintained at 900 degrees C. The intensity of Q(3) and Q(4) signals for the MS obtained by nonionic surfactant is double than that of cationic surfactant, proving that silicate network of MS-PL15 is lots thicker than that of MS-CTAB. MS synthesized by nonionic surfactant can be used as a catalyst support at high temperatures because they has a large specific surface area and excellent thermal stability.