Transformation of Layered Docosyltrimethyl- and Docosyltriethylammonium Silicates Derived from Kanemite into Precursors for Ordered Mesoporous Silicas

Abstract

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.

Catalytic oxidation of cyclohexene over metalloporphyrin supported on mesoporous molecular sieves of FSM-16 type—Steric effects induced by nanospace constraints

“…It is worthwhile to note that the reported catalytic results and the conclusions concerning the distribution of Al in FSM-16 solids have important implications for understanding the mechanism of FSM-16 formation. In particular, they represent an indirect evidence for the postulated occurrence of fragmentation of kanemite layers [10][11][12][13], since only then a preferential accumulation of Al at the inner pore walls of directly aluminated solids is conceivable. This issue will be discussed in detail in our forthcoming paper.…”

“…The present work reports the results of catalytic oxidation of cyclohexene with iodosylbenzene over metalloporphyrin supported on aluminated mesoporous silicas of FSM-16 type, which are materials obtained from synthetic layered mineral kanemite [9]. It has been demonstrated that the kanemitederived materials are formed via mechanism essentially different from that of MCM-41, despite the use in both cases of cationic surfactants as structure directing agents [10][11][12][13]. It has been proposed that, after intercalation of the surfactant cations between the silicate layers, a transformation occurs to a layered mesophase containing fragmented silicate sheets, which is the actual precursor of the FSM-16 structure.…”

Reactivity and applications of layered silicates and layered double hydroxides

“…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. The formation mechanism of KSW-2 is different from that found in FSM-16, and proceeds mainly through the bending of individual silicate sheets and subsequent intralayer and interlayer condensation.…”

Ordered Mesoporous Silica Derived from Layered Silicates

“…On the basis of these previous studies, we tried to prepare FSM-16 using C 22 TMA surfactant, which tends to be assembled as a lamellar phase. [71] Both the presence of a layered C 22 TMA-silicate intermediate composed of fragmented silicate sheets and the subsequent transformation into a 2D hexagonal phase during acid treatment were ascertained. We elucidated experimentally that FSM-16-type mesoporous silica is formed via layered intermediates composed of fragmented silicate sheets and C n TMA cations.…”

“…[69,70] The formation mechanisms of the ordered mesoporous silica derived from kanemite have been proven only recently on the basis of experimental results. [71] An ordered mesoporous silica with an unusual mesostructure (KSW-2), which is not defined by using the geometrical packing of hexadecyltrimethylammonium (C 16 TMA) ions, was also discovered in one of the kanemite-surfactant systems. [72] The structural units of kanemite are retained in the silicate framework.…”