The layer silicate Cs2SnIVSi6O15

Single crystals of Cs2SnSi6O15, dicaesium tin(IV) hexasilicate, were serendipitously obtained from a CsCl/NaCl flux at 923 K, starting from mixtures of CaO, SnO and TeO2 in a closed silica ampoule. The crystal structure of Cs2SnSi6O15 is constructed from {Si6O15}6– layers extending parallel to (101), and CsI cations with a coordination number of eleven as well as isolated [SnO6] octahedra situated between the silicate layers. Each of the nine different SiO4 tetrahedra in the silicate layer has a connectedness of Q 3 (three bridging and one terminal O atom), which leads to the formation of five- and eight-membered rings. The same type of silicate layer is found in the crystal structure of the mineral zeravshanite. Comparison with other silicates of the type Cs2 M IVSi6O15 (M IV = Ti, Zr, Th, U) revealed a klassengleiche group–subgroup relationship of index 2 between Cs2ZrSi6O15 (Z = 6, space group C2/m) and Cs2SnSi6O15 (Z = 12, space group I2/c).

Supramolecular exfoliation of layer silicate clay by novel cationic pillar[5]arene intercalants

Clays are multi-layered inorganic materials that can be used to prepare nanocomposite fillers. Because the multi-layered structure is thermodynamically stable, it is difficult to change a multi-layered material into single layers to improve its dispersity. Previously, clays were modified with dodecylammonium cations to promote complexation with nylon 6, nylon 66, polypropylene, polyethylene, polystyrene, and polycaprolactone to increase the mechanical strength (and/or thermal stability) of the composite material; however, complete exfoliation could not be achieved in these composites. In this study, pillar[5]arenes are synthesized and functionalized with ten cationic substituents as novel intercalants for modifying bentonite clay, which is a multi-layered metal-cation-containing silicate. The pillar[5]arenes exfoliate the clay by forming polyrotaxanes with poly(ethylene glycol) through host–guest interactions.

New zeolite-like RUB-5 and its related hydrous layer silicate RUB-6 structurally characterized by electron microscopy

This study made use of a recently developed combination of advanced methods to reveal the atomic structure of a disordered nanocrystalline zeolite using exit wave reconstruction, automated diffraction tomography, disorder modelling and diffraction pattern simulation. By applying these methods, it was possible to determine the so far unknown structures of the hydrous layer silicate RUB-6 and the related zeolite-like material RUB-5. The structures of RUB-5 and RUB-6 contain the same dense layer-like building units (LLBUs). In the case of RUB-5, these building units are interconnected via additional SiO4/2 tetrahedra, giving rise to a framework structure with a 2D pore system consisting of intersecting 8-ring channels. In contrast, RUB-6 contains these LLBUs as separate silicate layers terminated by silanol/siloxy groups. Both RUB-6 and RUB-5 show stacking disorder with intergrowths of different polymorphs. The unique structure of RUB-6, together with the possibility for an interlayer expansion reaction to form RUB-5, make it a promising candidate for interlayer expansion with various metal sources to include catalytically active reaction centres.

Adsorption of Uranium (VI) from Aqueous Solutions by Amino-functionalized Clay Minerals

Silylation of clay minerals from Cherkasy deposit (Ukraine) montmorillonite (layer silicate) and palygorskite (fibrous silicate) was performed using organosilane (3-aminopropyl)triethoxysilane (APTES). Solvents with different polarity (ethanol, toluene) were used in synthesis. The structure of modified minerals was characterized by complex of methods (X-ray powder diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption at −196 °C and thermal analysis). Studies of adsorption characteristics of APTES-modified clay minerals were carried out in relation to uranium (VI). The results indicated that modified montmorillonite and palygorskite were effective materials for water purification from UO22+.

Caesium desorption from layer silicate minerals using quaternary ammonium salts

ABSTRACTThe adsorption and desorption of cesium onto layered minerals, zeolite and geochemical reference samples were studied. 0.5 g of bentonite and mica were able to adsorb 71.2 and 51.5 mg of cesium, respectively, from 50 mL of deionized water containing 200 mg/L of cesium under neutral pH condition. These amounts of cesium adsorption were greater than those reported for vermiculites (8.9 and 5.6 mg, respectively). Additionally, the cesium adsorption on mica and vermiculite remained essentially unchanged under seawater conditions, but it decreased drastically on zeolite. The cesium desorption from the layered minerals was promoted by the addition of ammonium ions, namely trioctylmethylammonium chloride and zephiramine. These ammonium ions desorb cesium from the interlayers of the minerals without destroying the mineral structure. The cesium desorption procedure using quaternary ammonium ions would be extremely useful for decontamination of soil containing the layered minerals with adsorbed radioactive cesium.

Thermal behaviour of stevensite at temperatures up to 800°C.

Stevensite is a Mg-trioctahedral smectite with layer charge stemming from vacancies in the octahedral sheet. In the present work we studied the thermal behavior of Jbel Ghassoul stevensite from Morocco, known as Ghassoulite or Rhassoulite, free of talc layers. The clay fraction of the material was separated by sedimentation, it was subsequently heated from 250° to 800° C and the end products were examined with X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. The influence of heating on the stevensite structure begins at 400°C and is completed at 500°C. It involves irreversible collapse of the layers at ~10Å, which do not re-expand in ethylene glycol (EG) vapors. In contrast, heating at lower temperatures does not affect the stevensite layers, which expand completely in EG. The FTIR spectra indicate the formation of talc-like (kerolite) layers after heating at temperatures exceeding 400°C. Within the current experimental setup, the transition to kerolite layers takes place without the formation of an intermediate mixed-layer stevensite/talc phase. Heating at higher temperatures does not change the transformation pattern, until 800°C where complete dehydroxylation of the 2:1 layer takes place, which is associated with the formation of enstatite. The results of this study clearly demonstrate that opposite to common trioctahedral and dioctahedral smectites, stevensite converts to another layer silicate prior to dehydroxylation.

Structure and properties of ITQ-8: a hydrous layer silicate with microporous silicate layers

ITQ-8 contains levyne-type silicate layers with 8-ring pores and is a very interesting precursor for the preparation of microporous framework silicates.