(510x) Synthesis of Mesoporous Silicate Materials from Poly Silicate without Layered Structure

FSM (Folded Sheet Mesoporous Material), which is formed from kanemite, possesses mesopores with hexagonal shape and uniform size. Kanemite, a precursor to FSM, is generally prepared by immersing calcined sodium silicates into water at room temperature. This procedure allows sodium silicates to form silicate layers and Na+ ions exist between these layers. According to FSM formation mechanism generally discussed, these Na+ ions are exchanged by surfactants that work as a template for mesopores in FSM. The removal of surfactants leads to the formation of FSM by leaving hexagonal structure of mesopores. It is, therefore, considered from previously proposed mechanisms that the presence of layered structure in kanemite is necessary for the formation of FSM. Many works about FSM are related to those in the application field of adsorption or catalyst, but few studies have been made from fundamental aspect; how the structure of kanemite is important to the formation of FSM. The present study is aimed at correlating between the structure of kanemite and that of FSM. Special interest is focused on how the temperatures of water, in which calcined sodium silicates is immersed to make FSM precursors, affect to the formation of FSM. The results of X-ray diffraction reveal that the layered structure in kanemites gradually disappears with increasing the temperatures in water. However, the FSMs with highly developed mesopores are synthesized from FSM precursors or kanemites, irrespective as to whether the precursors possess layered structures or not. In other words, the presence of layered structure in kanemite is not necessarily required for the formation of FSM which possesses mesopores with hexagonal shape and uniform size. Previously proposed mechanisms fail to explain our results obtained in this study.