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Water intrusion-extrusion isotherms performed at room temperature on hydrophobic pure silica chabazite have shown that the water-Si-CHA system exhibit real spring behavior. The studies have shown that Si-OH clusters have behaved like a real water trap at the origin of two water populations, where a first layer of water has strongly hydrogen bonded with the silanols of the framework and a subsequent layer of liquidlike physisorbed water molecules in interaction with the first layer.

The structure determined from molecular modeling and Rietveld analysis on synchroton data of AlPo4-SOD dehydrated under vacuum at 100 degree Celsius together with some solid state NMR experiments of the rehydrated product is presented. The dehydration/rehydration of AlPo4-SOD, however, is a reversible but very slow process.

AlPO4-SOD, a microporous aluminophosphate, is synthesized in a quasi-nonaqueous medium using dimethylformamide as solvent and template. The as-synthesized, dehydrated, and calcined materials and the corresponding rehydrated phases are investigated by various solid-state NMR and powder X-ray diffraction techniques.

Issues concerning the reflection of the three-dimensional arrangement of P2O(sub 7)(super 4-) units in the TiP2O7 structure in various one- and two-dimensional 31P MAS NMR experiments are discussed. The 31P MAS NMR properties of the isostructural phases TiP2O7 and SiP2O7 are compared.

Binding of antibiotics to clay minerals can decrease both their physical and biological availability in soils. To elucidate the binding mechanisms of tetracycline antibiotics on smectite clays as a function of pH, we probed the interactions of oxytetracycline (OTC) with Na-montmorillonite (MONT) using X-ray diffraction (XRD), infrared (IR), and solid-state nuclear magnetic resonance (NMR) spectroscopies, and Monte Carlo molecular simulations. The XRD patterns demonstrate the presence of OTC in the MONT interlayer space at acidic pH whereas complexation of OTC by external basal and edge sites seems to prevail at pH 8. At both pH, the 1H-13C NMR profile indicates restricted mobility of the adsorbed OTC species; and, -CH3 deformation and C-N stretching IR vibration bands confirm a binding mechanism involving the protonated dimethylamino group of OTC. Changes in the 23Na NMR environments are consistent with cation-exchange and cation complexation reactions at the different sites of adsorption. Molecular simulations indicate that MONT interlayer spacing and structural charge localization dictate favorable binding conformations of the intercalated OTC, facilitating multiple interactions in agreement with the spectroscopic data. Our results present complementary insights into the mechanisms of adsorption of TETs on smectites important for their retention in natural and engineered soil environments. [ABSTRACT FROM AUTHOR]

The structure of AlPO4-SOD, a microporous aluminophosphate synthesized in a quasi-nonaqueous system using dimethylformamide as template and solvent, was previously reported. Then, various solid state nuclear magnetic resonance techniques applied on the dehydrated compound at 200 °C were performed and suggested a rearrangement of one-third of the template molecules inside the sodalite cages and a tripling of the unit cell parameter c. We present here the structure determined from molecular modeling and Rietveld analysis on synchrotron data of AlPO4-SOD dehydrated under vacuum at 100 °C together with some solid state NMR experiments of the rehydrated product. [ABSTRACT FROM AUTHOR]

Discusses the characterization of the structure of LiNi1-yCoyCoO2 phases (0=

We have explored in this work the stability and the reactivity of multiarm cyclam-grafted mesoporous silica samples in aqueous solution. A series of hybrid materials have been prepared by grafting silylated cyclam molecules bearing one, two, or four silyl groups onto both amorphous silica gel (K60) and ordered mesoporous silica (SBA15). Under these conditions, cyclam moieties are attached to the silica walls via one, two, or four arms. Various physicochemical techniques have been applied to characterize the functionalized solids (elemental analysis, 1H-29Si and 1H-13C CPMAS NMR, and N2 adsorption-desorption isotherms). The interest in two and four arms for improving the chemical stability in solution, by comparison with the system displaying only one arm, has been demonstrated by using a set of complementary experiments involving pH measurements and silicon determination with ICP-AES. Then, the investigation of their protonation and binding properties toward copper(II) has revealed a significant decrease in the reactivity of these hybrids as a consequence of multiarm tethering. A comparison of amorphous and ordered materials has permitted us to point out the influence of mesostructuration on the reactivity of these functionalized solids, especially from a kinetic point of view.

The mechanism of formation of a MSU-type siliceous material from tetraethyl orthosilicate (TEOS) in the presence of the nonionic surfactant tergitol T-15-S-12, sulfuric acid, and sodium fluoride has been investigated using mainly fluorescence probing techniques and, to a lesser extent, dynamic light scattering (DLS) and 29Si NMR spectroscopy. The tergitol micelles present in the systems obtained by progressively generating the reaction mixture giving rise to the mesostructured material by adding to an appropriate tergitol solution sulfuric acid, TEOS, and NaF were characterized by fluorescence probing (micelle aggregation number, micropolarity, and microviscosity) and also by dynamic light scattering (apparent micelle diameter). 29Si NMR experiments were also performed on selected systems after hydrolysis of the TEOS. The fluorescence probing techniques were also used to follow the changes of micelle characteristics with time during the evolution of the full reaction mixture from a limpid solution to a system containing a minor amount of condensed siliceous material. The synthesized solid material was characterized by X-ray diffraction and nitrogen adsorption-desorption analyses. The micelle aggregation number N was found to change only little, and the micropolarity remained constant when going from the tergitol solution to the full reaction mixture. The results of DLS measurements agree with this finding. Besides, while the condensation of silica took place after addition of NaF, the N value increased only very little with time up to the point where a small amount of mesostructured material precipitated out. These results indicate that the interaction between tergitol micelles and the siliceous species formed in the system by the hydrolysis of TEOS and also between micelles and the growing siliceous species must be very weak. As in our previous studies of the mechanism of formation of MCM41-type material from sodium silicate in the presence of cetyltrimethylammonium bromide, it appears that the locus of formation of the mesostructured material is not the micelle surface but the bulk phase. Micelles only act as reservoirs of surfactant providing surfactant monomer that binds to the growing siliceous species.