M. Benjelloun

Plugged hexagonal templated silica: a unique micro- and mesoporous composite material with internal silica nanocapsulesElectronic supplementary information (ESI) available: Fig. S1: X-ray diffractogram of a PHTS material. Fig. S2: TEM images of SBA-15 and PHTS-2. Fig. S3: hydrothermal stabilities. See http://www.rsc.org/suppdata/cc/b2/b201424f/

We describe in this paper the development of plugged hexagonal templated silicas (PHTS) which are hexagonally ordered materials, with internal microporous silica nanocapsules; they have a combined micro- and mesoporosity and a tuneable amount of both open and encapsulated mesopores and are much more stable than other tested micellar templated structures.

Reproducible synthesis of high quality MCM-48 by extraction and recuperation of the gemini surfactant

High quality MCM-48 can be repeatedly and reproducibly prepared, as a novel method for the extraction, recuperation and re-use of the gemini surfactant has been optimized. Gemini surfactants have the general formula [CnH2n+1N+(CH3)2(CH2)sN+(CH3)2CmH2m+1]·2Br, and have been shown to produce MCM-48 in a very convenient way. In each cycle, more than 95 wt% of the surfactant is extracted under mild conditions. The extracted surfactant does not degenerate during this treatment and can be re-used many times. The MCM-48 produced by this soft extraction, has a narrower mesoporous pore size distribution and a larger pore radius than materials prepared by normal temperature-programmed calcination. The surface of the extracted MCM-48 still contains sufficient silanol groups, although some silanol groups have been replaced by methoxy groups. The number of silanols on the surface of the MCM-48 has been titrated by surface reaction with hexamethyldisilazane, followed by quantification of the liberated NH3.

Template extraction from porous clay heterostructures: Influence on the porosity and the hydrothermal stability of the materials

The template extraction of two porous clay heterostructures (PCHs), derived from natural montmorillonite (PMH) and synthetic saponite (PSH), has been studied. Extraction in methanol solvent in the presence of cations (H+) removes up to 90% of the templates in a reproducible way without a subsequent calcination step for both PMH and PSH. The extracted materials have a high surface area (896 m2 g−1 for PMH and 1122 m2 g−1 for PSH) and pore volume (0.84 cm3 g−1 for PMH and 1.13 cm3 g−1 for PSH) and are structurally very stable when exposed to hydrothermal conditions. The number of silanol groups on the surface of PCH materials have been titrated by a surface reaction with hexamethyldisilazane, followed by quantification of the liberated NH3. Based on this method both extracted PMH and PSH have slightly higher silanol numbers than their calcined forms, a very important feature with respect to the amount of catalytic sites that can eventually be grafted onto the surface. The hydrothermal stability under a N2 flow containing 25% steam for 5 days at different temperatures between 400 °C and 700 °C for both calcined and extracted PMH and PSH was investigated using X-ray diffraction and N2-adsorption data. A remarkable hydrothermal stability was observed for all samples until 600 °C, a promising characteristic for applications of porous clay heterostructures.