Ordered Mesoporous Silica Derived from Layered Silicates

Abstract

Here, the development of ordered mesoporous silica prepared by the reaction of layered silicates with organoammonium surfactants is reviewed. The specific features of mesoporous silica are discussed with relation to the probable formation mechanisms. The recent understanding of the unusual structural changes from the 2D structure to periodic 3D mesostructures is presented. The formation of mesophase silicates from layered silicates with single silicate sheets depends on combined factors including the reactivity of layered silicates, the presence of layered intermediates, the variation of the silicate sheets, and the assemblies of surfactant molecules in the interlayer spaces. FSM‐16‐type (p6mm) mesoporous silica is formed via layered intermediates composed of fragmented silicate sheets and alkyltrimethylammonium (CnTMA) cations. KSW‐2‐type (c2mm) mesoporous silica can be prepared through the bending of the individual silicate sheets with intralayer and interlayer condensation. Although the structure of the silicate sheets changes during the reactions with CnTMA cations in a complex manner, the structural units caused by kanemite in the frameworks are retained. Recent development of the structural design in the silicate framework is very important for obtaining KSW‐2‐based mesoporous silica with molecularly ordered frameworks. The structural units originating from layered silicates are chemically designed and structurally stabilized by direct silylation of as‐synthesized KSW‐2. Some proposed applications using these mesoporous silica are also summarized with some remarks on the uniqueness of the use of layered silicates by comparison with MCM‐type mesoporous silica.

Effect of the template ion exchange behaviors of chromium into FSM-16 on the oxidative dehydrogenation of isobutane

“…It is generally accepted that FSM-16 is formed via layered intermediates composed of fragmented silicate sheets and alkyltrimethylammonium cations. 9) Hence, the formation mechanism is different from that of MCM-41, resulting in unique catalytic activities on silicious or metalcontaining FSM-16. 9) Also, it is generally accepted that the preparation of MCM-41 requires hydrothermal conditions that result in the formation of thermally unstable mesoporous silica.…”

Reactivity and applications of layered silicates and layered double hydroxides

“…Another example is the FSM-16-type mesoporous silica with a hexagonal array of channels, 94,95 which is formed via layered intermediates composed of fragmented silicate sheets and CTMA ions. 57 Moreover, lamellar and FSM-16 materials have also been synthesized using docosyltrimethylammonium-kanemite and docosyltriethylammonium-kanemite complexes, respectively. 96,97 On the other hand, mesoporous silica with square channels (KSW-2) 98,99 has been obtained by adjusting the pH of the layered CTMAkanemite complex to a pH of 4.0-6.0 with 1 M acetic acid.…”

“…49 Moreover, they are well-suited for use as precursors for the synthesis of various materials including novel layered silicates, 50,51 pillared layered silicates, 52,53 already known and new zeolites 54 and mesoporous materials. [55][56][57] Fig. 4 depicts the possibilities for the preparation of various advanced functional and catalytic materials using layered sodium silicates as precursors.…”

“…Discussion of their synthesis conditions, structures and applications can be found in several review articles. [55][56][57] A typical example of a mesoporous material obtained from a layered precursor is KSW-1 93 (mesoporous silica derived from Kanemite Sheets at Waseda University). It was first synthesized by intercalation of the layered sodium silicate kanemite with long-chain cetyltrimethylammonium (CTMA) ions at 70°C, followed by adjustment of the pH of the suspension to 8.5 and then calcination of the resulting CTMA-kanemite complex at 550°C in air.…”

Recent progress in mesoporous titania materials: adjusting morphology for innovative applications

“…The International Union of Pure and Applied Chemistry (IUPAC) classifies porous materials into three types depending on their pore sizes: microporous materials with pore sizes below 2 nm, mesoporous materials with pore sizes between 2 and 50 nm, and macroporous materials with pore sizes larger than 50 nm [1][2][3]. Mesoporous materials exhibit several geometric mesostructures (lamellar, two-dimensional (2D) hexagonal, three-dimensional (3D) hexagonal and cubic), morphologies (powder, nanoparticles and film), and framework compositions (inorganics, organics, metals and metal oxides; figure 1).…”