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Marie Pierre Gaigeot - One of the best experts on this subject based on the ideXlab platform.
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Electrolytes at the Hydroxylated (0001) α-Quartz/Water Interface: Location and Structural Effects on Interfacial Silanols by DFT-Based MD
Journal of Physical Chemistry C, 2016Co-Authors: Morgane Pfeiffer-laplaud, Marie Pierre GaigeotAbstract:Structural properties of NaCl, KCl, and NaI electrolytes forming an electrical double layer (EDL) at the fully hydroxylated (0001) α-quartz/liquid water interface have been investigated by means of first-principles molecular dynamics simulations (FPMD). Cations are found in inner-sphere conformations, directly bonded on two in-plane silanol groups that replace water molecules that would be present in the first solvation shell of the aqueous cations. Anions are located within the second/third water layer above the surface, fully solvated as in pure liquid water, and cation–anion adopt rather flexible solvent separated ion-pair (SSIP) geometries in the EDL. While the individual solvation shells of the aqua-ions are only slightly affected by ion-pairing at the interface, the Silanols at the quartz surface are strongly perturbed. The presence of the electrolytes in the EDL affects more deeply the Silanols’ geometrical properties than single ions do (J. Phys. Chem. C2016, 120, 4866–4880): the silanol–silanol intrasurface H-bonding that was observed at the neat interface is extremely weakened by the presence of the electrolytes. Further disordering of the surface Silanols is characterized by large changes in their orientation and covalent bond-lengths, regardless of their in-plane (IP) or out-of-plane (OP) orientations. Such structural changes of the surface Silanols are tentatively correlated here with an increase in the basicity of all surface sites.
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electrolytes at the hydroxylated 0001 α quartz water interface location and structural effects on interfacial Silanols by dft based md
Journal of Physical Chemistry C, 2016Co-Authors: Morgane Pfeifferlaplaud, Marie Pierre GaigeotAbstract:Structural properties of NaCl, KCl, and NaI electrolytes forming an electrical double layer (EDL) at the fully hydroxylated (0001) α-quartz/liquid water interface have been investigated by means of first-principles molecular dynamics simulations (FPMD). Cations are found in inner-sphere conformations, directly bonded on two in-plane silanol groups that replace water molecules that would be present in the first solvation shell of the aqueous cations. Anions are located within the second/third water layer above the surface, fully solvated as in pure liquid water, and cation–anion adopt rather flexible solvent separated ion-pair (SSIP) geometries in the EDL. While the individual solvation shells of the aqua-ions are only slightly affected by ion-pairing at the interface, the Silanols at the quartz surface are strongly perturbed. The presence of the electrolytes in the EDL affects more deeply the Silanols’ geometrical properties than single ions do (J. Phys. Chem. C 2016, 120, 4866–4880): the silanol–silanol ...
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Adsorption of Singly Charged Ions at the Hydroxylated (0001) α-Quartz/Water Interface
Journal of Physical Chemistry C, 2016Co-Authors: Morgane Pfeiffer-laplaud, Marie Pierre GaigeotAbstract:Individual alkali (Na+, K+) and halide (Cl–, I–) ion effects have been characterized at the fully hydroxylated (0001) α-quartz water interface by means of ab initio molecular dynamics simulations in the framework of the electronic DFT representation (DFT-MD). We particularly focus our analyses on the ion adsorption and solvation structures (made by water and by surface Silanols), as well as on perturbations undergone by the silanol surface sites when comparing the charged interfaces (present work) to the neat interface (our previous works, J. Chem. Theory. Comput. 2012, 8, 1037; J. Phys.: Condens. Matter 2012, 24, 124106). Both sodium and potassium cations are found adsorbed in an inner-sphere configuration, while chloride and iodide are found in between inner- and outer-sphere. Cation adsorption at the interface is found to induce more perturbation on interfacial properties than anions do. In particular, we show in details how and why the orientation of out-of-plane and in-plane surface Silanols found at the neat interface are modified by inner-sphere cations at the charged interfaces, with also consequences on the silanol–silanol intrasurface hydrogen bond network. All this detailed analysis provides a clear picture of a reduction of acidity of the surface Silanols at the quartz/water interface in the presence of the alkali/halide salts.
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The amorphous silica-liquid water interface studied by ab initio molecular dynamics (AIMD): Local organization in global disorder
Journal of Physics Condensed Matter, 2014Co-Authors: Álvaro Cimas, Frederik Tielens, Marie Pierre Gaigeot, Marialore Sulpizi, Dominique CostaAbstract:The structural organization of water at a model of amorphous silica-liquid water interface is investigated by ab initio molecular dynamics (AIMD) simulations at room temperature. The amorphous surface is constructed with isolated, H-bonded vicinal and geminal Silanols. In the absence of water, the Silanols have orientations that depend on the local surface topology (i.e. presence of concave and convex zones). However, in the presence of liquid water, only the strong inter-silanol H-bonds are maintained, whereas the weaker ones are replaced by H-bonds formed with interfacial water molecules. All Silanols are found to act as H-bond donors to water. The vicinal Silanols are simultaneously found to be H-bond acceptors from water. The geminal pairs are also characterized by the formation of water H-bonded rings, which could provide special pathways for proton transfer(s) at the interface. The first water layer above the surface is overall rather disordered, with three main domains of orientations of the water molecules. We discuss the similarities and differences in the structural organization of the interfacial water layer at the surface of the amorphous silica and at the surface of the crystalline (0 0 0 1) quartz surface.
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the silica water interface how the Silanols determine the surface acidity and modulate the water properties
Journal of Chemical Theory and Computation, 2012Co-Authors: Marialore Sulpizi, Marie Pierre Gaigeot, Michiel SprikAbstract:Silica is the most abundant metal oxide and the main component of the Earth's crust. Its behavior in contact with water plays a critical role in a variety of geochemical and environmental processes. Despite its key role, the details of the aqueous silica interface at the microscopic molecular level are still elusive. Here we provide such a detailed understanding of the molecular behavior of the silica-water interface, using density functional theory based molecular dynamics (DFTMD) simulations, where a consistent treatment of the electronic structure of solvent and surface is provided. We have calculated the acidity of the silanol groups at the interface directly from the DFTMD simulations, without any fitting of parameters to the experimental data. We find two types of silanol groups at the surface of quartz: out-of-plane Silanols with a strong acidic character (pKa = 5.6), which consequently results in the formation of strong and short hydrogen bonds with water molecules at the interface, and in-plane Silanols with a pKa of 8.5, forming weak hydrogen bonds with the interfacial water molecules. Our estimate of the quartz point of zero charge (1.0) is found in good agreement with the experimental value of 1.9. We have also shown how the Silanols orientation and their hydrogen bond properties are responsible for an amphoteric behavior of the surface. A detailed analysis has identified two species of adsorbed water molecules at the solid-liquid interface, which using the language of vibrational spectroscopy can be identified as "liquid-like" and "ice-like" water or, in other words, water molecules forming respectively weak and strong H-bonds with the oxide surface. These two populations of water are in turn responsible for two distinct peaks in the infrared spectrum of interfacial water and thus provide a molecular explanation of the experimental sum frequency generation spectrum recorded in the literature. In the specific case of quartz, we show that the liquid-/ice-like behavior is the result of the silanol groups ability to donate or accept hydrogen bonds with different strengths, which consequently modulates the vibrational properties of the adsorbed water layer.
Waldemar Adam - One of the best experts on this subject based on the ideXlab platform.
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host guest chemistry in a urea matrix catalytic and selective oxidation of triorganosilanes to the corresponding Silanols by methyltrioxorhenium and the urea hydrogen peroxide adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R Sahamoller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/...
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host guest chemistry in a urea matrix catalytic and selective oxidation of triorganosilanes to the corresponding Silanols by methyltrioxorhenium and the urea hydrogen peroxide adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R Sahamoller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H2O2. It is proposed that this novel Si−H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H2O2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation of the optically active silane (S)-(α-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si−H oxygen insertion has been reported for the preparation of optically active Silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(α-Np)Ph...
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Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R. Saha-möller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H2O2. It is proposed that this novel Si−H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H2O2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation of the optically active silane (S)-(α-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si−H oxygen insertion has been reported for the preparation of optically active Silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(α-Np)Ph...
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synthesis and reactivity of silicon transition metal complexes 33 metallo Silanols and metallo siloxanes 8 metallo silanole vom typ c5r5 oc 2 me3p m siph2oh m cr mo w darstellung nach der dimethyldioxiran methode und uberfuhrung in funktionalisierte
Chemische Berichte, 1995Co-Authors: Wolfgang Malisch, Siegfried Schmitzer, Reiner Lankat, Michael Neumayer, Frank Prechtl, Waldemar AdamAbstract:Synthesis and Reactivity of Silicon Transition Metal Complexes, 331 . — Metallo Silanols and Metallo Siloxanes, 82 . — Metallo Silanols of the Type C5R5(OC)2(Me3P)M-SiPh2OH (M = Cr, Mo, W): Preparation According to the Dimethyldioxirane Route and Conversion into Metallo Disiloxanes3 The metallo silanes C5R5(OC)2(Me3P)M-SiPh2H (4a-c), are converted into the corresponding metallo Silanols C5R5(OC)2-(Me3P)M-SiPh2OH [R = H, M = Cr (6a); R = Me, M = Mo (6b); M = W (6c)] by oxofunctionalization with dimethyldioxirane (5). Treatment of 6b, c with the chlorosilanes Me2Si(R)Cl [R = H (3b), [R = Cl (3c)] in the presence of triethylamine gives access to the metallo disiloxanes C5Me5(OC)2(Me3P)M-SiPh2OSiMe2R (M = Mo, R = H (7a); M = W, R = Cl (7b)]. The structure of tungsten silanol 6c is determined by X-ray diffraction analysis.
Oliver Weichold - One of the best experts on this subject based on the ideXlab platform.
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host guest chemistry in a urea matrix catalytic and selective oxidation of triorganosilanes to the corresponding Silanols by methyltrioxorhenium and the urea hydrogen peroxide adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R Sahamoller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/...
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host guest chemistry in a urea matrix catalytic and selective oxidation of triorganosilanes to the corresponding Silanols by methyltrioxorhenium and the urea hydrogen peroxide adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R Sahamoller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H2O2. It is proposed that this novel Si−H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H2O2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation of the optically active silane (S)-(α-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si−H oxygen insertion has been reported for the preparation of optically active Silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(α-Np)Ph...
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Host−Guest Chemistry in a Urea Matrix: Catalytic and Selective Oxidation of Triorganosilanes to the Corresponding Silanols by Methyltrioxorhenium and the Urea/Hydrogen Peroxide Adduct
Journal of the American Chemical Society, 1999Co-Authors: Waldemar Adam, Catherine M Mitchell, Chantu R. Saha-möller, Oliver WeicholdAbstract:The oxidation of silanes to Silanols, catalyzed by methyltrioxorhenium (MTO), proceeds in high conversions and excellent selectivities in favor of the silanol (no disiloxane product) when the urea/hydrogen peroxide adduct (UHP) is used as oxygen source instead of 85% aqueous H2O2. It is proposed that this novel Si−H oxidation takes place in the helical urea channels, in which the urea matrix serves as host for the silane substrate, the H2O2 oxygen source, and the MTO metal catalyst as guests. In this confined environment, the metal catalyst is stabilized against decomposition, and this enhances higher conversions while condensation of the silanol to its disiloxane is avoided for steric reasons. The oxidation of the optically active silane (S)-(α-Np)PhMeSiH proceeds with retention of configuration in excellent yield. To date, no catalytic Si−H oxygen insertion has been reported for the preparation of optically active Silanols. In analogy with the stereoselectivity in the dioxirane oxidation of (+)-(α-Np)Ph...
Carmine Dagostino - One of the best experts on this subject based on the ideXlab platform.
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effect of al content on the strength of terminal silanol species in zsm 5 zeolite catalysts a quantitative drifts study without the use of molar extinction coefficients
Physical Chemistry Chemical Physics, 2018Co-Authors: Pierre Brauer, Olivia Situmorang, Carmine DagostinoAbstract:The strength of terminal hydroxyl Si-OH groups (Silanols) in zeolites is important for many non-size-selective catalytic reactions occurring onto the external surface of the zeolite crystals and may often be responsible for catalyst deactivation, e.g., coke formation. A quantitative analysis of Si–OH strength and its link with the Al content, hence varying silica-to-alumina ratio (SAR = SiO2/Al2O3), has not been established yet. Various hypotheses have been proposed in the literature; nonetheless, the role of Al content in determining silanol strength remains still unclear and the object of speculation. In this work, we have systematically investigated the effect of the Al content on the strength of terminal silanol sites in ZSM-5 zeolite catalysts with varying SAR using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) at variable temperatures without molar extinction coefficients. Two base probe molecules with different proton affinity values, pyridine and collidine, were used. To quantify the strength of terminal silanol sites the change of the terminal silanol peak in the OH stretching region, together with data on elemental analysis, was used. With this experimental protocol, unlike most IR studies, the use of molar extinction coefficients, often difficult to obtain, is not needed for quantification. The results reported here show for the first time that for ZSM-5 zeolite catalysts the fraction of occupied terminal silanol acid sites for both pyridine and collidine increases with increasing concentration of external Bronsted acid sites, hence establishing a clear link between the two types of acid sites. In summary, this work shows that the use of DRIFTS without molar extinction coefficients is able to quantitatively probe the strength of terminal silanol acid sites and establishes a link between the external Bronsted Al content and the strength of terminal silanol species in ZSM-5 zeolites with varying SAR at elevated temperatures.
Ota Bludský - One of the best experts on this subject based on the ideXlab platform.
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Theoretical investigation of layered zeolite frameworks: Surface properties of 2D zeolites
Catalysis Today, 2014Co-Authors: Jan Hermann, Michal Trachta, Petr Nachtigall, Ota BludskýAbstract:Abstract Surface properties of layered zeolite frameworks, or 2D zeolites, derived from zeolites UTL and ITH are probed by interaction with several small molecules (CH4, CO2, H2O, H2, N2). The dominant feature of the 2D zeolites is the dense grid of the surface silanol groups formed after dissolution of the double 4-member ring building units of the parent 3D zeolites. Compared to the original 3D zeolite frameworks, several distinctive effects contribute to the changes in binding energies: (i) hydrogen-bond and electrostatic interactions with surface Silanols, (ii) the confined space effect enhancing dispersion interactions in 3D zeolites and (iii) structural flexibility of 2D zeolites.
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theoretical investigation of layered zeolite frameworks interaction between ipc 1p layers derived from zeolite utl
Catalysis Today, 2013Co-Authors: Lukas Grajciar, Ota Bludský, Wieslaw J Roth, Petr NachtigallAbstract:Abstract Interaction between layers of layered zeolite framework IPC-1P was investigated computationally. The inter-layer interaction is controlled by inter-layer hydrogen bonds formed between Silanols on adjacent layers. Due to a relatively large concentration of surface Silanols in IPC-1P the inter-layer hydrogen bonds account for about 80% of inter-layer interactions. Large number of possible arrangements of neighboring layers exist; the stability of individual arrangements depends primarily on the number of inter-layer hydrogen bonds and their strength. The most stable structure is formed when silanol groups are all parallel with the ac plane and forming a hydrogen-bonded analogue of 10R channel along b direction. Several different arrangements were found with similar interaction energies (within 2.5 kJ mol −1 per surface silanol). The reliability of computational methods was also investigated. The non-local vdW-DF2 exchange-correlation functional was found to give very accurate description of inter-layer interactions.