Periodic Mesoporous Organosilica in Confined Environments

Abstract

Periodic mesoporous organosilica (PMO) mesophases based on bis(triethoxysilyl)ethane (BTSE) were synthesized within the confined tubular environment of anodic alumina membrane (AAM) channels. The resulting mesophases were investigated by transmission small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), nitrogen sorption, and transmission electron microscopy (TEM). Two different surfactants--nonionic Brij 56 and ionic cetyltrimethylammonium bromide (CTAB)--were used in an acid-catalyzed evaporation-induced self-assembly (EISA) process. Brij 56 as the structure-directing agent (SDA) resulted in the formation of either the hexagonal circular or the cubic mesophase. While the hexagonal circular mesophase is common for such kinds of composites, the cubic mesophase has never been reported before. The template could be removed from the mesophases by template extraction and calcination after annealing the samples. When using CTAB as the SDA during EISA, the only mesophase observed was the hexagonal circular structure. This is in contrast to previous experiments and reports on pure silica mesophases, where the only mesophase formed with CTAB is hexagonal columnar.

Hierarchically structured biphenylene-bridged periodic mesoporous organosilica

“…5A), similar to recent observations with other PMO and mesoporous polymer phases in AAM hosts. 43,57 The formation of a cubic mesostructure was also confirmed by the following TEM micrographs. A plan-view TEM micrograph obtained from F127-cubic-200 Bp-PMO is displayed in Fig.…”

“…This can be contrasted to our previous results on CTAB/ethane-bridged PMO/AAM composites that form a 2D-hexagonal circular mesophase. 43 This difference could be related to the different character of the organic bridges of the siloxane precursor, such as the hydrophobicity, the flexibility and the size of the bridges, which might lead to different interactions between the SDA (structure directing agents) and the organosilane precursor and thus lead to the formation of different mesophases. 2D small angle X-ray scattering (2D-SAXS) and transmission electron microscopy (TEM) were performed to characterize the mesostructure of the CTAB-columnar-lamellar system.…”

“…S2A †) for the as-prepared F127-circular sample shows both in-plane and out-of-plane reflections that can be assigned to a circular hexagonal structure. 42,43 In order to obtain an open pore system, the sample was calcined in air at 250 C for 10 h to remove the surfactant template molecules from the mesophase. After calcination, the F127-circular-250 Bp-PMO (F127-circular sample calcined at 250 C) features a highly ordered mesostructure as observed by 2D-SAXS (Fig.…”

“…43 The isotherm shape (hysteresis loop) suggests the existence of ink-bottle shaped pores. This can be confirmed by comparing the DFT poresize distribution from the adsorption branch (av.…”

Funktionsmaterialien: von harten zu weichen porösen Netzwerken

“…In den ersten Jahren nach der Entdeckung einer neuen Klasse von porösen Materialien, seien es geordnete meso- [ 165] A [168,169,[171][172][173] Membranen [174] oder Monolithen [175,176] [177] Zum Schluss soll noch angemerkt werden, dass die Herstellung eines bestimmten funktionellen porösen Materials meistens keineswegs trivial ist. Für jede anvisierte Funktion, die in ein poröses Material eingebracht werden soll, kann es nötig sein, neue Synthesemethoden zu entwickeln.…”