Synthesis and characterization of highly ordered mesoporous material; FSM-16, from a layered polysilicate

Development of preparation conditions of highly ordered mesoporous SiO₂materials(FSM-16) derived from a layered polysilicate has been summarized and a “folded sheets: mechanism for their formation has been presented. When Na ions in the interlayer region of kanemite were exchanged for alkyltrimethylammonium ions, organoammonium/silicate complexes were obtained and mesoporous silica materials were prepared by calcination of those complexes. When the exchange reaction was carried out at a relatively low pH(∼8.5), the exchange ratio was low and highly ordered pore structures of the mesoporous silica could not be confirmed although the formation of uniform pore size was realized. Increasing the pH(∼11.5) improved the exchange ratio and consequently realized highly porous materials with a regular hexagonal array of uniform channels. The condition of high pH(>11.5) increased a fraction of dissolved silica species. Removal of the dissolved species from the system was necessary to prepare pure FSM-16. The improvement of the reguarlity and purity of FSM-16 by increasing the pH and filtration supported the “folded sheets” mechanism for its formation. The Q⁴/Q³ratios of SiO₄tetrahedra in the silicate/organic complexes prepared by the optimum procedure were in good agreement with those calculated by the folded sheets model and the observed N₂absorption behavior suggested an uniform pore-size of FSM-16.