Mesoporous Materials with Uniform Pore Size; Synthesis and Their Applications.

Abstract

We have proposed a folding sheet mechanism to form mesoporous crystal from a layered polysilicate, kanemite. This report reviews the structure of layered polysilicates, their intercalation properties, condensation reactions between the polysilicate layers, the mechanism of forming mesoporous materials (FSM) and their applications. SiO₄-tetrahedral sheets and interlayer cations form sodium disilicate (Na₂Si₂O₅) and kanemite (NaHSi₂O₅). An exchange for organic cations gave silicate/organic c omplexes. When we used kanemite as a host material, we observed a condensation reaction between the unit sheets besides the cation exchange. Removing the organic cations by calcination formed mesoporous materials. Cation exchange at pH =12 folded the SiO₄-tetrahedral sheets without the condensation. Following pH adjustment at 8.5 promoted the condensation between adjacent sheets and gave a silicate/organic complex with hexagonal symmetry. Highly ordered crystals with uniform pores were obtained by calcination at 550°C. We call this mechanism and materials folding sheets mechanism and folded sheets mesoporous materials (FSM), respectively. Complexes with layered structure were also made by using a surfactant with cylindrical shape, or by adding an alcohol. The mesoporous crystals (FSM) are expected to be useful as adsorbents, catalysts or host materials for making nano-cluster of metals or semi-conductors.