In situ, time-resolved energy-dispersive X-ray diffraction has been used to investigate the formation of the mesoporous silicates FSM-16 and MCM-41. The data suggest that the silicasurfactant mesophases formed are highly dependent on the reactant medium, the effect of the silica source being one of the main determining factors. Kanemite, a layered polysilicate, proves to be an excellent silicate source, giving rise to relatively ordered mesophases and subsequent highly ordered mesoporous silicate products. The time-resolved in situ X-ray diffraction data of the kanemite-alkytrimethylammonium system indicated that the silicasurfactant mesophase precursor to FSM-16 forms from a medium containing a number of intercalated silicate phases, while in contrast, the hexagonal mesophase precursor to MCM-41 forms from a medium containing no other ordered silicate-surfactant phases detectable by in situ X-ray diffraction.

Lamellar organoammonium silicates with variable silicon environments have been synthesized by the reaction of a layered polysilicate kanemite with aqueous solutions of hexadecyltrimethylammonium (C16TMA) chloride. While the structure of kanemite is composed of only Q 3 silicate species ((SiO)3SiO), SiO4 units with both Q 3 and Q 4 ((SiO)4Si) environments were present in the silicate frameworks of the lamellar C16TMA silicates. The Q 4 species mainly formed by intralayer condensation of the Q 3 species in the individual silicate sheets in kanemite rather than by interlayer condensation between the adjacent sheets. The intralayer condensation can be suppressed by lowering the reaction temperature and/or shortening the reaction time, which results in the relative retention of the silicate framework of kanemite in the lamellar C16TMA silicates.

Real-time in situ energy dispersive synchrotron X-ray powder diffraction data provides evidence for the formation of an intermediate lamellar silica-surfactant intercalate during the synthesis of the hexagonal mesophase derived from the layered polysilicate kanemite, whereas n o intermediate phases are observed during the formation of the silica-surfactant mesophase that leads t o the mesoporous material MCM-41.