Pegie Cool

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.

The relation between the synthesis of pillared clays and their resulting porosity

Abstract Clays can be converted to stable microporous materials by the incorporation of pillars. The type of pillars determine to a large extent the porosity features of the pillared clays. Different pillaring species (Al, Ti, Zr, Fe) were investigated and discussed in terms of pore volume, pore size and pore size distribution. The porosity induced by pillaring can be further modified by small modifications during the synthesis. More meso- and macroporosity can be achieved by choosing clays with smaller clay layer sizes (laponite compared to montmorillonite) or by the way of drying (air or freeze drying). Incorporation of Zr and Cr in the Fe-pillars creates mixed oxide pillared clays and pillared clays with new properties were obtained. The adsorption strength strongly increased resulting in higher adsorption capacities as demonstrated for gases (O2, N2 , CO2, CO and CH4) and chlorinated hydrocarbons. Pre-adsorption of amines effectively reduces the pillar density (Fe-PILL) and distributes the pillars more homogeneously between the layers (Al- and Ti-PILC) creating higher pore volumes and higher adsorption strength. Amines were also useful for the orientation of laponite clay layers to more regularly ordered face-to-face stacked pillared laponite clays which exhibit significant increased pore volumes.

Is there any microporosity in ordered mesoporous silicas

The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

Enhanced Brönsted acidity created upon Al-grafting of porous clay heterostructures ia aluminium acetylacetonate adsorption

Montmorillonite-PCH (porous clay heterostructure) and saponite-PCH are inorganic silica-like materials with large surface areas (∽1000 m2 g−1) and pore volumes (0.7 cm3 g−1). They are obtained by introducing a surfactant template in-between the clay plates and subsequently polymerizing a silica source around them. The acidity of porous clay heterostructures has been improved. Based on the ‘ molecular designed dispersion’ method, the Al-grafting onto the PCH surface using aluminium acetylacetonate complex is carried out, involving interaction between the surface silanol groups of the PCH-support and the complex, followed by a calcination step. In this way, stable Bronsted acid sites are created, remaining even after thermal treatment as high as 300°C. Evaluation of this acidity has been performed by NH3 and acetonitrile-d3 (CD3CN) adsorptions.

Acidic porous clay heterostructures : study of their cation exchange capacity

Abstract The cation exchange capacities (CECs) of two porous clay heterostructures (PCHs), derived from natural montmorillonite (PMH) and synthetic saponite (PSH), have been studied. Both materials are highly porous, with surface areas of 997 m 2 /g (PMH) and 1118 m 2 /g (PSH). In order to obtain exchangeable ammonium cations in the pore structures of the PCHs, different modifications are performed on calcined and extracted PMH and PSH. Three methods for the formation of NH 4 + -exchanged PCH forms are described and evaluated: (1) adsorption of ammonia under a gas flow on calcined and extracted PCHs in acidified methanol; (2) direct exchange in NH 4 Cl solution; (3) solvent extraction with NH 4 Ac/EtOH/H 2 O. The obtained ammonium containing materials are subsequently exchanged for K + cations in aqueous solution in order to determine the CEC of the PCH solids. With Kj-N analysis and infrared-DRIFT technique, evidence is found for the presence of ammonium cations on the surface of PCHs. The stability (crystallinity and porosity) of the porous solids under the different treatments has been investigated using X-ray diffraction and N 2 -adsorption isotherms. The adsorption under NH 3 gas flow proves to be the best method for maintaining the porosity of the studied PCHs. Maximal K + loadings of 0.55 mmol/g (PMH) and 0.37 mmol/g (PSH) are obtained for ammonia-loaded and extracted PCH samples in MeOH/HCl.

Influence of polymer matrix and adsorption onto silica materials on the migration of α-tocopherol into 95% ethanol from active packaging

In this study, the effect of polymer materials with different polarity, namely low density polyethylene (LDPE) and ethylene vinyl acetate (EVA), on the migration behaviour of α-tocopherol from active packaging was investigated. The antioxidant was also adsorbed onto silica materials, namely SBA-15 (Santa Barbara-15) and Syloblock, in order to protect the antioxidant during extrusion and to ensure a controlled and sufficient release during the shelf-life of the food product. Migration experiments were performed at 7.0 ± 0.5°C and 95% ethanol was used as fatty food simulant. All films contained a high concentration of α-tocopherol, ∼ 2000 mg kg−1, to obtain an active packaging. Polymer matrix had a small influence on the migration profile. The migration of 80% of total migrated amount of antioxidant was retarded for 2.4 days by using LDPE instead of EVA. When α-tocopherol was adsorbed onto both silica materials, the migration of 80% of total migrated amount of antioxidant was retarded for 3.4 days in comparison to pure α-tocopherol. No difference was seen between the migration profiles of α-tocopherol adsorbed onto both silica materials. In the case of pure α-tocopherol, 82% of the initial amount of α-tocopherol in the film migrated into the food simulant at a rather fast migration rate. In the case of adsorption on silica materials, a total migration was observed. These antioxidative films can have positive food applications.

Pillared Clays: Preparation, Characterization and Applications

Pillared Clays (PILCs) are an interesting class of 2-dimensional microporous materials. Due to their high surface area and permanent porosity they are very attractive solids for adsorption and catalysis purposes. Since their porosity can be localized in the larger micropore region, these substrates form a bridge between the microporous zeolites on one hand and the inorganic meso- and macroporous solids (e.g. silica, alumina) on the other. The history of PILCs started in 1955, but the first extensive studies appeared only around 1980. During this pioneering work, mainly organic cations and organometal pillars were used. Now, the inorganic polyoxycations are of greatest interest because of their high thermal stability. By changing the nature and, hence, the size of the pillars, different pore-sizes are obtained. In this way, it becomes possible to tune the porosity. This porosity combined with the properties of both pillar and host are very important for certain applications, such as selective gas adsorptions, catalytic reactions, etc.

Structure of nanoscale mesoporous silica spheres

Hexagonal MCM-41 can be transformed into cubic MCM-48 and finally into spherical particles by the addition of alcohol during the synthesis of a mesoporous silica material. X-ray diffraction suggests that the structure of these spherical particles is of the MCM-41 type. Transmission electron microscopy however reveals that the structure of the mesoporous silica spherical particles consists of a core in the form of a truncated octahedron with an MCM-48 cubic structure and radial pores grown on the surfaces of the truncated octahedron. Spherical MCM particles therefore consist of a mixture of cubic and hexagonally arranged pores.

Controlled formation of amine-templated mesostructured zirconia with remarkably high thermal stability

In order to control the reactivity of the inorganic precursor and the hybrid formation, the evaporation induced self-assembly procedure (EISA) has been applied to direct alkyl amines into zirconia hybrid composites. It is demonstrated that, with controlled water amounts, a mesostructured wormhole-like high-surface-area zirconia can be formed but the mesostructure collapses due to massive crystallisation of the zirconia walls into tetragonal zirconia as the calcination temperature rises to 400 °C. To overcome the lack in thermal stability, zirconia hybrids are treated in aqueous ammonia to protect the primary particles in the zirconia walls against uncontrolled particle growth and crystallisation. The growth of the initially amorphous zirconia particles in the walls is limited by increasing the condensation degree upon ammonia treatment resulting in mesostructured zirconia consisting of nanosized ‘tetragonal’ particles at higher temperatures. It is shown that the alkaline-treated zirconias have a remarkable thermal stability with retention of most physical characteristics such as high surface area, pore volume and mesoporosity up to a temperature of 800 °C.

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.