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.

The transformation of layered silicate-surfactant materials derived from a layered polysilicate kanemite into precursors for ordered mesoporous silicas was investigated. When kanemite was allowed to react with docosyltrimethylammonium (C22TMA) and docosyltriethylammonium (C22TEA) surfactants, layered C22-TMA-and C22TEA-silicate materials were formed. The 29 Si MAS NMR spectra of the layered intermediates clearly indicated that fragmented silicate sheets were present in the silicate-surfactant materials. These layered materials can be transformed by acid treatment into mesostructured precursors with threedimensional (3-d) silicate networks that afford uniform mesopores after the removal of the surfactants. Ordered mesoporous silica with a 2-d hexagonal structure (FSM-16) can be obtained by using C22TEA with a larger headgroup. The results here successfully support the proposed formation mechanism of FSM-16, which consists of assembling of fragmented layered silicate sheets with surfactants and the subsequent structural transformation to the 2-d hexagonal mesophase.

Silica-based mesostructured materials derived from a layered polysilicate kanemite were prepared by reactions with gemini-type diammonium (C16–3–16, C16–5–16, C16–3–1) surfactants. The surfactants were assembled in the two-dimensionally limited space between the silicate layers of kanemite, leading to the formation of lamellar, 2-d hexagonal, and disordered mesophases. Lamellar phases were formed by using C16–3–16 and C16–5–16 surfactants. An acid treatment of the lamellar C16–5–16–silicate complex induced the transformation into a 2-d hexagonal phase, whereas the C16–3–16–silicate complex retained its lamellar structure after the treatment. A disordered phase was obtained through the reaction of kanemite with C16–3–1 surfactants whose assembly shows a larger surface curvature. The formation of layered surfactant–silicate intermediates under various conditions and the transformation to other mesophases lead to the conclusion that the formation of ordered and disordered mesostructured materials derived from kanemite simply depends on the surfactant assemblies in the two-dimensionally limited space.

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