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  1. On the hydrogen bonding structure at the aqueous interface of ammonium-substituted mica: A molecular dynamics simulation
    Erschienen: 2013
    Verlag:  HAL CCSD ; Verlag der Zeitschrift Fuer Naturforschung

    Molecular dynamics (MD) computer simulations were performed for an aqueous film of 3nm thickness adsorbed at the (001) surface of ammonium-substituted muscovite mica. The results provide a detailed picture of the near-surface structure and... mehr

     

    Molecular dynamics (MD) computer simulations were performed for an aqueous film of 3nm thickness adsorbed at the (001) surface of ammonium-substituted muscovite mica. The results provide a detailed picture of the near-surface structure and topological characteristics of the interfacial hydrogen bonding network. The effects of D/H isotopic substitution in N(H/D)4+ on the dynamics and consequently on the convergence of the structural properties have also been explored. Unlike many earlier simulations, a much larger surface area representing 72 crystallographic unit cells was used, which allowed for a more realistic representation of the substrate surface with a more disordered distribution of Al/Si isomorphic substitutions in muscovite. The results clearly demonstrate that under ambient conditions both interfacial ammonium ions and the very first layer of water molecules are H-bonded only to the basal surface of muscovite, but do not form H-bonds with each other. As the distance from the surface increases, the H-bonds donated to the surface by both N(H/D)4+ and H2O are gradually replaced by the H-bonds to the neighboring water molecules, with the ammonia ions experiencing one reorientational transition region, while the H2O molecules experiencing three such distinct consecutive transitions. The hydrated N(H/D)4+ ions adsorb almost exclusively as inner-sphere surface complexes with the preferential coordination to the basal bridging oxygen atoms surrounding the Al/Si substitutions.

     

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    Sprache: Englisch
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    Übergeordneter Titel: ISSN: 0932-0784 ; Zeitschrift fur Naturforschung a ; http://hal.in2p3.fr/in2p3-00768710 ; Zeitschrift fur Naturforschung a, Verlag der Zeitschrift Fuer Naturforschung, 2013, 68, pp.91-100. ⟨10.5560/ZNA.2012-0101⟩
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry
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  2. Molecular modeling of the swelling properties and interlayer structure of Cs, Na, K-Montmorillonite: Effects of charge distribution in the clay layers
    Erschienen: 2012
    Verlag:  HAL CCSD

    Safe and sustainable management of nuclear waste poses major scientific challenges to make the environmental footprint of nuclear energy as small as possible for very long periods of time. As many other countries, France is considering the deep... mehr

     

    Safe and sustainable management of nuclear waste poses major scientific challenges to make the environmental footprint of nuclear energy as small as possible for very long periods of time. As many other countries, France is considering the deep geological disposal (in the Callovo-Oxfordian (COx) argillite formations of the Paris basin) as a reliable way of storing high-level radioactive waste in order to provide adequate protection for humans and the environment. In addition to being proven geologically stable for million years, the natural and engineered clay barriers can benefit from many favorable properties, such as low permeability, high sorption capacity, etc. The mineralogical composition of the Callovo-Oxfordian argillite shows about 41% of clay minerals (23% of interstratified illite/smectite, 14% of illite-type minerals, 2% kaolinite and 2% chlorite) [1,2]. A non-negligible amount of organic matter is also present (~1%) [3], and it is known that the interaction of natural organic matter (NOM) with radionuclides and clays can affect the solubility and toxicity of trace elements in natural aqueous environments [4,5]. Reliable prediction of the behaviour of radionuclides and their transport and retention in clayey formations at nuclear waste repositories requires detailed molecular scale understanding of these complex multicomponent systems. Computational molecular modelling has already become an important tool in the study of thermodynamic, structural and transport properties of hydrated clays (e.g., [6-8]). As the first step in our study of the effects of organic molecules on the adsorption and transport of radionuclides in hydrated clay systems we have investigated the effects of the ordering in charge distributions on the swelling behavior of simulated clays. Montmorillonite was chosen as a model of smectite clay. Montmorillonite structure consists of aluminum-oxygen octahedral sheet sandwiched between two opposing silicon-oxygen tetrahedral sheets giving rise to a 2:1 clay mineral. Isomorphic substitutions in the tetrahedral and octahedral sheets are responsible of the negative layer charge of montmorillonite clay minerals having the chemical composition (Si8-xXx)(Al4-yYy)O20(OH)4 where X = Al, Y = Mg, Fe.[9]. The montmorillonite models for our study are based on a pyrophillite unit cell structure (5.16Å×8.966Å×9.347Å) obtained from the crystallographic data of Lee et al. [10]. The 4×4×2 simulation supercells were built and substitutions were made in the pyrophillite structure in order to approximate as close as possible the chemical composition of Wyoming montmorillonite M24(Si248Al8)(Al112Mg16)O640(OH)128, where M is either Cs+, Na+, or K+ [9]. We explored three different models of substitution distributions. In the first model, the substitutions were uniformly and orderly distributed within the tetrahedral and octahedral sheets. In the second model, the substituted positions were kept ordered in the octahedral sheets but made disordered in the tetrahedral one. In the third model, the substituted positions of the octahedral sites were additionally made disordered. In order to study the swelling behavior of these montmorillonites, molecular dynamics (MD) simulations were run in the NPzT statistical ensemble (T = 298 K, Pz = 1 bar) for each of the three different substitution models and with 22 different hydration states ranging from 0 to 700 mgwater/gclay (from 0 to 42 H2O molecules per one monovalent cation). All MD runs were performed for a total of 2 ns using the CLAYFF force field [11]. At the beginning of the simulations, the cations were placed at the midplane of the clay interlayer space and water molecules were added randomly. After the system reached equilibrium, the last 1ns of each MD trajectory was used to compute the clay basal spacing and the swelling thermodynamic properties: hydration energy, immersion energy, isosteric heat of adsorption. The MD simulation results indicate that in addition to the commonly observed 1-layer and 2-layer hydrates, stable hydration states corresponding to 3-layer and 4-layer hydrates can also be distinguished. The stable states corresponding to the minima of hydration energy were then selected to run further 500 ps NVT-ensemble MD simulations at the same temperature and with the volume fixed at the average value resulting from the corresponding previous NPzT simulation. The equilibrium parts of these NVT-simulated trajectories were then used to calculate the structural (radial distribution functions, atomic density profiles) and dynamical (diffusion coefficient) properties of the hydrated montmorillonite. References [1] ERM (1997) Echantillons d'argiles du forage EST104 : Etude minéralogique approfondie. Rapport ANDRA n° D.RP.0ERM.97.008 [2] ERM (1996b) Caractérisation d'échantillons d'argiles du forage EST103. Rapport ANDRA n° B.RP.0ERM.96.003 [3] ANDRA (2005) Dossier 2005 Argile, Référentiel du site de Meuse Haute Marne. C.R.P.ADS.04.0022 Andra : Paris [4] Buffle, J. (1988) Complexation Reactions in Aquatic Systems: An Analytical Approach; Ellis Horwood Ltd.:Chichester, p 692. [5] Tipping, E. (2002) Cation Binding by Humic Substances, Cambridge University Press: Cambridge, p 434. [6] Smith, D.E., Langmuir, 14, 5959-5967 (1998). [7] Rotenberg, B., Marry, V., Vuilleumier, R., Malikova, N., Simon, C., Turq, P., Geochim. Cosmochim. Acta, 71, 5089-5101 (2007). [8] Liu, X.D., Lu, X.C., Wang, R.C., Zhou, H.Q. Geochim. Cosmochim. Acta, 72, 1837-1847 (2008). [9] Tsipursky, S.I., Drits, V.A. Clay Minerals, 19, 177-193 (1984). [10] Lee, J.H. and Guggenheim, S. American Mineralogist, 66, 350-357 (1981). [11] Cygan, R.T., Liang, J.J., Kalinichev, A.G. Journal of Physical Chemistry B, 108, 1255-1266 (2004).

     

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    Quelle: BASE Fachausschnitt AVL
    Sprache: Englisch
    Medientyp: Konferenzveröffentlichung; Weitere
    Format: Online
    Übergeordneter Titel: 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement" ; http://hal.in2p3.fr/in2p3-00769152 ; 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement", Oct 2012, Montpellier, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  3. Effects of surface cations on the structure and dynamics of the hydrogen-bonding network at the illite-water interface: A molecular dynamics simulation study
    Erschienen: 2012
    Verlag:  HAL CCSD

    Safe and sustainable management of nuclear energy poses major scientific and engineering challenges, one of which is the necessity to make the environmental impacts of the long-term nuclear waste storage as small as possible. This requires detailed... mehr

     

    Safe and sustainable management of nuclear energy poses major scientific and engineering challenges, one of which is the necessity to make the environmental impacts of the long-term nuclear waste storage as small as possible. This requires detailed understanding and prediction of the behaviour of radionuclides and their migration and retention properties in the geological formations of nuclear waste repositories. The Callovo-Oxfordien rock formation of the French nuclear repository site is mainly composed of clay minerals (illite, smectite and interstratified illite/smectite), quartz, calcite, with some non-negligible amount of organic matter. The adsorption of water can change the properties of mineral surfaces, including protonation state, surface charge, structure, and reactivity [1]. Similarly, the properties of interfacial water are strongly affected by the mineral substrate structure and composition. Recent advances in experimental techniques such as FTIR [2], ellipsometry [3], synchrotron X-ray scattering [4], sum-frequency vibrational spectroscopy [5] are capable of probing the properties of mineral-water interfaces at different levels of hydration. However, the surface-specific results of these experiments are often difficult to quantitatively interpret without having a reliable molecular scale picture of the underlying physical and chemical processes. Molecular computer simulations have become one of the most important tools in the study of such interfacial systems and phenomena by providing invaluable atomistic information on the underlying chemical and physical processes. The present study is aimed at investigating the structural and dynamics effects of three different cations (K+, NH4+, and H3O+) exchanged at the hydrated surface of muscovite mica, which is taken here as a model illite. Molecular dynamics computer simulations were performed using the CLAYFF force field [6] to investigate the important differences of the H-bonding configurations formed by the sorbed species, including H2O, H3O+, and NH4+, in contrast to the behavior of spherical metal ions, such as K+. At the muscovite (001) surface, H2O can donate 2 H-bonds (to other H2O and/or to the surface O atoms) and accept 2 H-bonds (from other H2O), but it can also partially replace surface K+, because the hydrogens of H2O bear some positive charge. This behavior was observed in previous MD simulations of the mica surface [7]. Such surface-adsorbed H2O molecules have their negatively charged oxygen atoms exposed to the fluid phase and accessible for either H-bond acceptance from other H2Os or hydration of metal cations in outer-sphere coordination. For surface H3O+, the charges on the hydrogens are slightly higher than those of H2O, but the oxygen atom of hydronium is now almost hydrophobic, and cannot participate in a H-bond network (e.g., [8]). In contrast, NH4+ can equally well donate H-bonds to the surface O atoms and to the neighboring H2O molecules, but it cannot participate in the hydration shell of a displaced metal cation. Thus, three similar species (H2O - two HB donors and 2 HB acceptors; H3O+ - 3 HB donors and no acceptors; NH4+ - 4 HB donors, no acceptors) can provide for three greatly different structural, energetic, and dynamical situations at the muscovite-water interface. Since the hydrogen-bonding network in any aqueous media provides a natural mechanism of forming low-barrier reaction paths for proton transfer in such systems, it is also an important phenomenon controlling the surface reactivity under various pH conditions. In addition, a detailed study of the structural characteristics of surface-adsorbed NH4+ provides a way for better understanding of the mechanisms of adsorption for organic molecules having amino-groups in their structure, which is quite common for natural organic matter (e.g., [9]). Each of the three systems was simulated at 7 different hydration states providing information on the structure and dynamics of the adsorbed water film in a wide range of relative humidity conditions. The atomic density profiles of water show significant layering at all hydration levels and the layering strongly depends upon the nature of the ionic species present on the surface. Our studies support the fact that the H3O+ ion is less strongly bound when compared to K+ on the muscovite surface as observed in earlier studies [7]. At muscovite surfaces, both NH4+ and H3O+ cations establish strong hydrogen bonds with the surface bridging oxygen atoms and also with the neighbouring H2O molecules at all hydration levels. However, we observed that the interactions are different for both species at low hydration levels (<< molecular monolayer). At low hydration levels, H3O+ prefers to strongly bind as 3-cordinated species to the surface than with the neighbouring waters molecules. However, as the hydration levels increase, H3O+ binds as 2-cordinated species with the surface as is indicated by hydrogen bonding analysis (Figure 1). In contrast, irrespective of the hydration levels, NH4+ ion strongly interacts with the surface as 3-cordinated species because of its tetrahedral geometry. At the same time, we observe from hydrogen bond analysis that the hydrogen bonding network of water has been strongly influenced by the nature of the surface cations present at the mineral-water interface. The dynamics of water molecules were examined by self-diffusion coefficients from the mean square displacement of water oxygen. The diffusion mechanism is similar for K+ and NH4+ but was different for H3O+, in particular at the low hydration states. Furthermore, the spatial and orientation distributions of H2O and ions at the muscovite-water surface are analyzed in quantitative detail. All the simulation results are compared with available experimental data and the results of previous molecular simulations to provide reliable molecular view of the ions and water at the muscovite surface. References [1] Henderson, M. A. Surf. Sci. Rep. 2002, 46, 5-308. [2] Cantrell and G. E. Ewing. J. Phys. Chem. B, 2001, 105, 5434-5439. [3] Beaglehole, D and Christenson, H. K. J. Phys. Chem, 1992, 96, 3395-3403. [4] Fenter, P. and Sturchio, N. C. Progress in Surface Science, 2004, 77, 171-258. [5] Shen, Y. R. and Ostroverkhov, V. Chem. Rev., 2006, 106, 1140-1154. [6] Cygan, R.T., Liang, J.J., and Kalinichev, A.G. J. Phys. Chem. B, 2004, 108, 1255-1266. [7] Wang, J., Kalinichev, A., Kirkpatrick, R., Cygan, R. J. Phys. Chem B., 2005, 109, 15893-15905. [8] Petersen, P.B. and Saykally, R.J. J. Phys. Chem. B, 2005, 109, 7976-7980. [9] Leenheer, J.A. Annals of Environmental Science, 2009, 3, 1-130.

     

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    Format: Online
    Übergeordneter Titel: 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement" ; http://hal.in2p3.fr/in2p3-00769153 ; 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement", Oct 2012, Montpellier, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  4. Ethylene glycol intercalation in smectites. Molecular dynamics simulation studies
    Erschienen: 2012
    Verlag:  HAL CCSD

    Intercalation of ethylene glycol in smectites (glycolation) is widely used to discriminate smectites and vermiculites from other clays and among themselves. During this process, ethylene glycol molecules enter into the interlayer spaces of the... mehr

     

    Intercalation of ethylene glycol in smectites (glycolation) is widely used to discriminate smectites and vermiculites from other clays and among themselves. During this process, ethylene glycol molecules enter into the interlayer spaces of the swelling clays, leading to the formation of two-layer structure (~17 Å) in the case of smectites, or one-layer structure (~14 Å) in the case of vermiculites. In spite of the relatively broad literature on the understanding/characterization of ethylene glycol/water-clays complexes, the simplified structure of this complex presented by Reynolds (1965) is still used in the contemporary X-ray diffraction computer programs, which simulate structures of smectite and illite-smectite. The monolayer structure is only approximated using the assumption of the interlayer cation and ethylene glycol molecules lying in the middle of interlayer spaces. This study was therefore undertaken to investigate the structure of ethylene glycol/water-clays complex in more detail using molecular dynamics simulation. The structural models of smectites were built on the basis of pyrophyllite crystal structure (Lee and Guggenheim, 1981), with substitution of particular atoms. In most of simulations, the structural model assumed the following composition, considered as the most common in the mixed layer illite-smectites (Środoń et al. 2009): EXCH0.4(Si3.96Al0.04)(Al1.46Fe0.17Mg0.37)O10(OH)2 Atoms of the smectites were described with CLAYFF force field (Cygan et al., 2004), while atoms of water and ethylene glycol with flexible SPC (Berendsen et al., 1981) and OPLS (Jorgensen et al., 1996) force fields, respectively. Ewald summation was used to calculate long range Coulombic interactions and the cutoff was set at 8.5 Å. Results of the simulations show that in the two-layer glycolate the content of water is relatively small: up to 0.8 H2O per half of the smectite unit cell (thereafter phuc). Clear thermodynamic preference of mono- or two-layer structure of the complex is observed for typical smectite. Based on the calculated radial distribution functions, it was confirmed that water and ethylene glycol molecules compete for the coordination sites of the calcium ions in the clay interlayers. It was also found that the differences in the smectite layer charge, charge location, and the type of the interlayer cation affect the ethylene glycol and water packing in the interlayer space and as result have strong influence on the basal spacing and on the structure of complex. Varying amounts and ratio of both ethylene glycol and water are, however, the most important factor influencing the extent of the smectite expansion. Comparison of two-layer structure obtained from molecular dynamics simulations with previous models leads to the conclusion that the arrangement of ethylene glycol molecules in the interlayers, used in simulations of X-ray diffractograms of clays, should be modified. In contrast to the Reynolds (1965) model, the main difference is that, for different location of the clay charge, interlayer ions tend to change their positions. In the case of montmorillonite, calcium ions are located in the middle of the interlayer space, while for beidellite they are located much closer to the clay surface. Water in these structures does not form distinct layers but is distributed rather broadly with a tendency to be concentrated close to the smectite surface. One-layer structure of ethylene glycol/water-smectite complex, characteristic of vermiculite was also proposed. References Berendsen, H.J.C., Postma, J.P.M., van Gunsteren, W.F., Hermans, J. (1981) Interaction models for water in relation to protein hydration. In Intermolecular Forces; Pullman, B., Ed.; D. Reidel: Amsterdam, pp 331. Cygan, R. T., Liang, J. J., and Kalinichev, A. G. (2004) Molecular models of hydroxide, oxyhydroxide, and clay phases and the development of a general force field. Journal of Physical Chemistry B, 108, 1255-1266. Jorgensen,W.L., Maxwell, D.S., Tirado-Rives, J. (1996) Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J. Am. Chem. Soc., 118, 11225-11236. Lee J.H., Guggenheim S. (1981) Single crystal X-ray refinement of pyrophyllite-1Tc. American Mineralogist, 66, 350-357 Reynolds R. C. (1965) An X-ray study of an ethylene glycol-montmorillonite complex. American Mineralogist, 50, 990-1001 Środoń J., Zeelmaekers E., Derkowski A. (2009) The charge of component layers of illite-smectite in bentonites and the nature of end-member illite. Clays and Clay Minerals, 57, 650-672

     

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    Übergeordneter Titel: 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement" ; http://hal.in2p3.fr/in2p3-00769154 ; 5th International meeting "Clays in Natural and Engineered Barriers for Radioactive Waste Confinement", Dec 2012, Montpellier, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  5. Molecular Modeling of the Swelling Properties and Interlayer Structure of Cs, and K-Montmorillonites: Effects of Charge Distribution in the Clay Layers
    Erschienen: 2012
    Verlag:  HAL CCSD

    Reliable prediction of the behaviour of radionuclides and their transport and retention in clayey formations at nuclear waste repositories requires detailed molecular scale understanding of these complex multicomponent systems. As the first step in... mehr

     

    Reliable prediction of the behaviour of radionuclides and their transport and retention in clayey formations at nuclear waste repositories requires detailed molecular scale understanding of these complex multicomponent systems. As the first step in our study of the effects of organic molecules on the adsorption and transport of radionuclides in hydrated clay systems we have investigated the effects of the ordering in charge distributions on the swelling behavior of montmorillonite (a smectite clay). Montmorillonite layered structure consists of aluminum-oxygen octahedral sheet sandwiched between two opposing silicon-oxygen tetrahedral sheets giving rise to a 2:1 clay mineral. Isomorphic substitutions in the tetrahedral and octahedral sheets are responsible of the negative layer charge of montmorillonite clay minerals having the chemical composition (Si8-xXx)(Al4-yYy)O20(OH)4 where X = Al3+, Y = Mg2+, Fe2+.[1]. The montmorillonite models for our study are based on a pyrophillite unit cell structure (5.16Å×8.966Å×9.347Å) obtained from the crystallographic data of Lee et al. [2]. The 4×4×2 simulation supercells were built and substitutions were made in the pyrophillite structure in order to approximate as close as possible the chemical composition of Wyoming montmorillonite [1] M24(Si248Al8)(Al112Mg16)O640(OH)128, where M is either Cs+, or K+. We have explored three different models of the substitution distributions. In the first model, the substitutions were uniformly and orderly distributed within the tetrahedral and octahedral sheets. In the second model, the substituted positions were kept ordered in the octahedral sheets but made disordered in the tetrahedral one. In the third model, the substituted positions of the octahedral sites were additionally made disordered. In order to study the swelling behavior of these montmorillonites, NPT-ensemble molecular dynamics (MD) simulations were run at T = 298 K and P = 1 bar for each of the three different substitution models and with 23 different hydration states ranging from 0 to 700 mgwater/gclay (from 0 to 42 H2O molecules per one monovalent cation). All MD runs were performed for a total of 2 ns using the CLAYFF force field [3]. After the system reached equilibrium, the last 1ns of each MD trajectory was used to compute the clay basal spacing and the swelling thermodynamic properties: hydration energy, immersion energy, isosteric heat of adsorption. These calculations indicate that in addition to the commonly observed 1-layer and 2-layer hydrates, stable hydration states corresponding to 3-layer and 4-layer hydrates can also be distinguished. These stable states (minima of hydration and immersion energies) were then selected to run further 500 ps NVT-ensemble MD simulations at the same temperature. The equilibrium parts of these NVT-simulated trajectories were then used to calculate radial distribution functions and atomic density profiles of the interlayer species in hydrated montmorillonites. References [1] Tsipursky, S.I., Drits, V.A. Clay Minerals, 19, 177-193 (1984). [2] Lee, J.H. and Guggenheim, S. American Mineralogist, 66, 350-357 (1981). [3] Cygan, R.T., Liang, J.J., Kalinichev, A.G. Journal of Physical Chemistry B, 108, 1255-1266 (2004).

     

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    Übergeordneter Titel: XIIIe journées nationale de radiochimie et de chimie nucléaire ; http://hal.in2p3.fr/in2p3-00769157 ; XIIIe journées nationale de radiochimie et de chimie nucléaire, Oct 2012, Nantes, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  6. Molecular Dynamics Simuation of Cs+ on the Hydrated Muscovite Surface: Local Structural Environment and Dynamics
    Erschienen: 2012
    Verlag:  HAL CCSD

    Adsorption of metal cations on mineral surfaces often controls their distribution in both natural and technological environments. The Callovo-Oxfordian (COx) formation, consisting largely of clay minerals like illite and smectite, is the location... mehr

     

    Adsorption of metal cations on mineral surfaces often controls their distribution in both natural and technological environments. The Callovo-Oxfordian (COx) formation, consisting largely of clay minerals like illite and smectite, is the location investigated in France as a site for geological nuclear waste disposal and storage. The uptake of radionuclides by layered clay minerals is the principal retention process for their diffusion. Hence, detailed molecular-scale understanding of the adsorption mechanisms of radionuclides on silicate minerals is essential, because it can significantly influence their mobility under the conditions of nuclear waste repositories. Cs+ ion is one of the important components of nuclear waste that is highly soluble in water and migrates easily in surface and sub-surface environments. The atomically smooth surface of muscovite mica, KAl2(Si3Al)O10(OH)2 is often used as an accurate model of illite clay. Experimental studies suggest that Cs+ ion adsorbs directly at the muscovite surface as an "inner sphere complex" [1]. We have investigated the structure and dynamics of Cs+ (exchanged for K+) and H2O molecules at the surface of muscovite at two different hydration levels by molecular dynamics (MD) computer simulations using fully flexible CLAYFF force field [2]. At the muscovite (001) surface, water molecules can donate 2 hydrogen bonds (to other H2O and/or to the surface O atoms) and accept 2 H-bonds (from other H2O). Water molecules can also partially replace surface cations, because their hydrogens bear some positive charge. Such surface-adsorbed H2O molecules have their negatively charged oxygen atoms exposed to the fluid phase and accessible for either H-bond acceptance from other H2Os or for their coordination of surface cations in the inner-sphere or outer-sphere configuration. Atomic density profiles of the surface species evidently support the presence of Cs+ as inner sphere complexes at the muscovite interface. Angular distributions of H2O molecular orientations with respect to the muscovite surface have also been studied, as well as the dynamical behaviour of surface species in terms of their self-diffusion coefficients, H-bonding time correlation functions, and residence times. The comparison of the surface behaviour at two different hydration states and the topological details of the interfacial H-bonding network provide new insight into the structure and dynamics of hydrated Cs+ at confined geometries. The MD simulation results are compared with available experimental data and the results of previous molecular simulations [3] to provide reliable molecular view of the hydrated Cs+ ions at the surface of illite. References [1] Kim, Y., Kirkpatrick, J.R., Cygan, R.T. Geochim. Cosmochim Acta, 60, 4059-4074 (1996). [2] Cygan, R.T., Liang, J.J., Kalinichev, A.G. J. Phys. Chem. B, 108, 1255-1266 (2004). [3] Wang, J.W., Kalinichev, A.G., Kirkpatrick, R.J., Cygan, R.T. J. Phys. Chem. B, 109, 15893-15905 (2005).

     

    Export in Literaturverwaltung
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    Sprache: Englisch
    Medientyp: Konferenzveröffentlichung; Weitere
    Format: Online
    Übergeordneter Titel: XIIIe journées nationale de radiochimie et de chimie nucléaire ; http://hal.in2p3.fr/in2p3-00769158 ; XIIIe journées nationale de radiochimie et de chimie nucléaire, Oct 2012, Nantes, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  7. Slow diffusional dynamics of water in cement nanopores: Multiscale challenges for atomistic modeling (topic leader)
    Erschienen: 2012
    Verlag:  HAL CCSD

    Molecular modeling of the properties of aqueous solutions confined in the nanopores and at the interfaces of cementitious materials is complicated by the significant structural and compositional heterogeneity of these phases and also by the fact that... mehr

     

    Molecular modeling of the properties of aqueous solutions confined in the nanopores and at the interfaces of cementitious materials is complicated by the significant structural and compositional heterogeneity of these phases and also by the fact that many of the important processes span several orders of magnitude both in time and in length. Here we present an attempt to quantify the diffusional dynamics of 0.25 M KCl aqueous solution in contact with a model C-S-H binding phase (tobermorite) on the basis of molecular dynamics computer simulations. At the (001) surface of tobermorite, two types of H2O molecules can be effectively distinguished: the ones that spend most of their time within channels between the drierketten chains of silica on the tobermorite surface, and the more mobile adsorbed molecules that reside right above the interface. Within the channels, H2O molecules donate H-bonds to both the bridging and non-bridging oxygens of the Si-tetrahedra as well as to other H2O. Some of these molecules form particularly strong H-bonds persisting well over 100 ps, but many others undergo frequent librational motions and occasional diffusional jumps from one surface site to another. The average diffusion coefficients of the surface-associated H2O molecules that spend most of their time in the channels and those that lie above the nominal interface differ by about one order of magnitude (DH2O[internal]=5.0×10−11 m2/s and DH2O[external]=6.0×10−10 m2/s, respectively). The average diffusion coefficient for all surface-associated H2O molecules is about 1.0×10−10 m2/s. All of these values are significantly less than the value of 2.3×10−9 m2/s, characteristic of H2O self-diffusion in bulk liquid water. The MD simulations provided an opportunity to further quantify these relatively slow diffusional motions of H2O at the tobermorite interface on the longer time- and length- scale in terms of the Van Hove self-correlation function (VHSCF). The emerging picture is in surprisingly good agreement with available experimental data on the dynamics of surface-associated water in similar cement materials obtained by 1H NMR [1,2]. 1. Korb J.P., Monteilhet L., McDonald P.J., Mitchell J., Microstructure and texture of hydrated cement-based materials: A proton field cycling relaxometry approach. Cement and Concrete Research, 37, 2007, 295-302. 2. Korb J.P., NMR and nuclear spin relaxation of cement and concrete materialsCurrent Opinion in Colloid & Interface Science, 14, 2009, 192-202.

     

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    Übergeordneter Titel: International US-Poland Workshop "Multiscale Computational Modeling of Cementitious Materials" ; http://hal.in2p3.fr/in2p3-00769185 ; International US-Poland Workshop "Multiscale Computational Modeling of Cementitious Materials", Oct 2012, Kraków, Poland
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  8. Molecular models of natural organic matter and its colloidal aggregation in aqueous solutions: Challenges and opportunities for computer simulations
    Erschienen: 2012
    Verlag:  HAL CCSD ; De Gruyter

    Natural organic matter (NOM) is ubiquitous in soil and groundwater and its aqueous complexation with various inorganic and organic species can strongly affect the speciation, solubility and toxicity of many elements in the environment. Despite... mehr

     

    Natural organic matter (NOM) is ubiquitous in soil and groundwater and its aqueous complexation with various inorganic and organic species can strongly affect the speciation, solubility and toxicity of many elements in the environment. Despite significant geochemical, environmental and industrial interest, the molecular-scale mechanisms of the physical and chemical processes involving NOM are not yet fully understood. Recent molecular dynamics (MD) simulations using relatively simple models of NOM fragments are used here to illustrate the challenges and opportunities for the application of computational molecular modeling techniques to the structural, dynamic, and energetic characterization of metal-NOM complexation and colloidal aggregation in aqueous solutions. The predictions from large-scale MD simulations are in good qualitative agreement with available experimental observations, but also point out to the need for simulations at much larger time and length scales with more complex NOM models in order to fully capture the diversity of molecular processes involving NOM.

     

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    Übergeordneter Titel: ISSN: 0033-4545 ; EISSN: 1365-3075 ; Pure and Applied Chemistry ; http://hal.in2p3.fr/in2p3-00769189 ; Pure and Applied Chemistry, De Gruyter, 2012, &#x27E8;10.1351/PAC-CON-12-05-11&#x27E9;
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes
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  9. Metal cation complexation with natural organic matter in aqueous solutions: Molecular dynamics simulations and potentials of mean force
    Erschienen: 2010
    Verlag:  HAL CCSD ; American Chemical Society

    Natural organic matter (NOM, or humic substance) has a known tendency to form colloidal aggregates in aqueous environments, with the composition and concentration of cationic species in solution, pH, temperature, and the composition of the NOM itself... mehr

     

    Natural organic matter (NOM, or humic substance) has a known tendency to form colloidal aggregates in aqueous environments, with the composition and concentration of cationic species in solution, pH, temperature, and the composition of the NOM itself playing important roles. Strong interaction of carboxylic groups of NOM with dissolved metal cations is thought to be the leading chemical interaction in NOM supramolecular aggregation. Computational molecular dynamics (MD) study of the interactions of Na+, Mg2+, and Ca2+ with the carboxylic groups of a model NOM fragment and acetate anions in aqueous solutions provides new quantitative insight into the structure, energetics, and dynamics of the interactions of carboxylic groups with metal cations, their association, and the effects of cations on the colloidal aggregation of NOM molecules. Potentials of mean force and the equilibrium constants describing overall ion association and the distribution of metal cations between contact ion pairs and solvent-separated ions pairs were computed from free MD simulations and restrained umbrella sampling calculations. The results provide insight into the local structural environments of metalâˆ'carboxylate association and the dynamics of exchange among these sites. All three cations prefer contact ion pair to solvent-separated ion pair coordination, and Na+ and Ca2+ show a strong preference for bidentate contact ion pair formation. The average residence time of a Ca2+ ion in a contact ion pair with the carboxylic groups is of the order of 0.5 ns, whereas the corresponding residence time of a Na+ ion is only between 0.02 and 0.05 ns. The average residence times of a Ca2+ ion in a bidentate coordinated contact ion pair vs a monodentate coordinated contact ion pair are about 0.5 and 0.08 ns, respectively. On the 10 ns time scale of our simulations, aggregation of the NOM molecules occurs in the presence of Ca2+ but not Na+ or Mg2+. These results agree with previous experimental observations and are explained by both Ca2+ ion bridging between NOM molecules and decreased repulsion between the NOM molecules due to the reduced net charge of the NOMâˆ'metal complexes. Simulations on a larger scale are needed to further explore the relative importance of the different aggregation mechanisms and the stability of NOM aggregates.

     

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    Übergeordneter Titel: ISSN: 0743-7463 ; EISSN: 1520-5827 ; Langmuir ; http://hal.in2p3.fr/in2p3-00769191 ; Langmuir, American Chemical Society, 2010, 26, pp.15909-15919. &#x27E8;10.1021/la102535n&#x27E9;
    Schlagworte: Natural organic matter; Supramolecular aggregation; Molecular dynamics simulations; potential of mean force; [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes
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  10. Structure and Energetics of Smectite Interlayer Hydration: Molecular Dynamics Investigations of Na- and Ca Hectorite

    Molecular-scale interactions present at mineral-water interfaces and in clay interlayer galleries control numerous environmental processes, including chemical interactions in soils and transport of nutrients and pollutants through them.[1-4]... mehr

     

    Molecular-scale interactions present at mineral-water interfaces and in clay interlayer galleries control numerous environmental processes, including chemical interactions in soils and transport of nutrients and pollutants through them.[1-4] Understanding these processes requires accurate knowledge of the structure, energetics, and dynamics of the interaction among the mineral substrate, ions, and water molecules.[5, 6] Challenges to this objective include experimental difficulties in probing these interfaces and interlayers at the molecular scale; fully characterizing the mineral substrate; and identifying how the mineral surface, ions, and water molecules each contribute to the overall structure, energetics, and dynamics of these systems.[6] Linked computational molecular dynamics (MD) simulations and experimental nuclear magnetic resonance (NMR) studies are particularly effective in addressing these issues.[7-9] Here we focus on MD studies of Na- and Ca-smectite (hectorite) interlayer galleries to provide a molecular-scale picture of the structure and dynamics of their hydration[9, 10] and to complement our earlier NMR investigations of these systems.[7-9] Classical MD simulations were undertaken in the NPT and NVT ensembles to determine the structural and energetic changes with increasing hydration with focus on the single- and double-layer hydrates. The results show substantial changes in the hydration of the interlayer cations, the orientations of the water molecules, the hydrogen bond network involving the water molecules and basal oxygen atoms, and the resulting potential energies as the interlayer gallery expands. [1] Scheidegger et al. (1996) Soil Science 161 813-831. [2] Stumm (1997) Colloids and Surfaces A-Physicochemical and Engineering Aspects 120 143-166. [3] O'Day (1999) Reviews of Geophysics 37 249-274. [4] Koretsky (2000) Journal of Hydrology 230 127-171. [5] Wang et al. (2001) Chemistry of Materials 13 145-150. [6] Wang et al. (2006) Geochimica et Cosmochimica Acta 70 562-582. [7] Bowers et al. (2008) Journal of Physical Chemistry C 112 6430-6438. [8] Bowers et al. (2011) Journal of Physical Chemistry C 115 23395-23407. [9] Bowers et al. (2012), unpublished. [10] Morrow et al. (2012) Journal of Physical Chemistry C, submitted.

     

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    Sprache: Englisch
    Medientyp: Konferenzveröffentlichung; Weitere
    Format: Online
    Übergeordneter Titel: Symposium 8g: Structure and dynamics of ions and water at mineral-water interfaces: insights from experimental and computational studies, 2012 Goldschmidt Conference ; http://hal.in2p3.fr/in2p3-00769208 ; Symposium 8g: Structure and dynamics of ions and water at mineral-water interfaces: insights from experimental and computational studies, 2012 Goldschmidt Conference, Jun 2012, Montreal, Canada
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  11. Molecular structure and dynamics of nano-confined aqueous solutions: Computer simulations of clay, cement, and polymer membranes
    Erschienen: 2012
    Verlag:  HAL CCSD

    Molecular-scale knowledge of the thermodynamic, structural, and transport properties of water confined by interfaces and nano-pores of various materials is crucial for quantitative understanding and prediction of many natural and technological... mehr

     

    Molecular-scale knowledge of the thermodynamic, structural, and transport properties of water confined by interfaces and nano-pores of various materials is crucial for quantitative understanding and prediction of many natural and technological processes, including carbon sequestration, water desalination, nuclear waste storage, cement chemistry, fuel cell technology, etc. Experimental nanoscale studies of such systems are not always feasible, and their results often require considerable interpretation in the efforts to extract surface- and confinement-specific quantitative information from the measurements. Computational molecular modeling significantly complements such efforts and provides invaluable molecular-scale background for better understanding of the specific effects of the substrate structure and composition on the structure, dynamics and reactivity of interfacial and nano-confined aqueous solutions. Based on the successful development and implementation of the CLAYFF force field (Cygan et al., 2004), we have recently performed a series of molecular dynamics simulations of aqueous interfaces with several representative inorganic and organic nanoporous materials (Ahn et al., 2008; Kalinichev et al., 2007, 2010; Wang et al., 2006, 2009) in order to better understand and quantify the effects of the substrate composition and structure on the properties of interfacial and nano-confined aqueous solutions. Individual H2O molecules and hydrated ions at interfaces simultaneously participate in several dynamic processes, which can be characterized by different, but equally important time- and length- scales. The first molecular layer of interfacial water at all substrates is often highly ordered, indicating reduced translational and orientational mobility of the H2O molecules. However, this ordering can not be simply described as "ice-like", but rather resembles the behavior of supercooled water or amorphous ice, although with significant substrate-specific variations. These results help to interpret experimental NMR, IR, X-ray, and neutron scattering measurements performed for the same systems. Ahn, W.-Y., Kalinichev, A.G., Clark, M.M. (2008) Effects of background cations on the fouling of polyethersulfone membranes by natural organic matter: Experimental and molecular modeling study. J.Membr.Sci., 309,128-140. Cygan R.T., Liang J.-J., Kalinichev A.G. (2004) Molecular models of hydroxide, oxyhydroxide, and clay phases and the development of a general force field. Journal of Physical Chemistry B, 108, 1255-1266. Kalinichev A.G., Wang, J., Kirkpatrick R. J. (2007) Molecular dynamics modeling of the structure, dynamics and energetics of mineral-water interfaces: Application to cement materials. Cement and Concrete Res., 37, 337-347. Kalinichev, A.G., Kumar, P., Kirkpatrick, R.J. (2010) Effects of hydrogen bonding on the properties of layered double hydroxides intercalated with organic acids: MDF computer simulations. Philos. Mag., 90, 2475-2488. Wang J., Kalinichev A.G., Kirkpatrick R.J. (2006) Effects of substrate structure and composition on the structure, dynamics and energetics of water on mineral surfaces: MD modeling study. Geochim. Cosmochim. Acta, 70, 562-582. Wang J., Kalinichev A.G., Kirkpatrick R.J. (2009) Asymmetric hydrogen bonding and orientational ordering of water at hydrophobic and hydrophilic surfaces: A comparison of water/vapor, water/talc, and water/mica interfaces. J.Phys.Chem.C, 113, 11077-11085.

     

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    Übergeordneter Titel: NATO Advanced Research Workshop on the Physical Chemistry of Capillary and Bound/Confined Liquids ; http://hal.in2p3.fr/in2p3-00769209 ; NATO Advanced Research Workshop on the Physical Chemistry of Capillary and Bound/Confined Liquids, May 2012, Ein Bokek, Israel
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  12. Computational molecular modeling for nuclear waste management and other radiochemical applications (invited talk)
    Erschienen: 2012
    Verlag:  HAL CCSD

    Safe and sustainable management of nuclear energy poses major scientific and engineering challenges, one of which is the necessity to make the environmental impacts of the long-term nuclear waste storage as small as possible. This requires... mehr

     

    Safe and sustainable management of nuclear energy poses major scientific and engineering challenges, one of which is the necessity to make the environmental impacts of the long-term nuclear waste storage as small as possible. This requires significant improvements in our understanding of the behaviour of radionuclides and their retention mechanisms in geological formations of nuclear waste repositories over the ranges of time and distance spanning many orders of magnitude. Detailed molecular scale knowledge of the complex chemical and physical processes controlling the interaction of radionuclides with clay and cementitious materials is crucial for building better predictive models of their adsorption and mobility in natural and engineered barriers of the nuclear waste repositories. The presence of natural organic matter (NOM) in clayey formations and its complexation with metal ions in aqueous solutions has significant effect on the transport properties of the radionuclides. In this presentation, we will overview our current efforts to apply computational molecular modeling techniques to address these problems on the fundamental molecular level. We use classical molecular dynamics (MD) simulations for detailed quantitative studies of the structural, energetic and dynamic aspects of interactions between radionuclides, organic matter and clay particles. Structural and thermodynamic parameters are obtained by studying different processes such as hydration, adsorption, complexation, and intercalation. The complexation mechanisms of organic molecules with aqueous metal ions will then be presented using the free energy calculations. Metal cations can strongly associate with negatively charged functional groups of organic molecules and with negatively charged clay surfaces. This allows us to predict that cationic bridging could be the most probable mechanism responsible for the controlling effects of organics on the behaviour of radionuclides is clays and other repository materials. Our most recent results demonstrating how the nature of the adsorbed cations affects the structural and dynamic properties of the mineral-water interface and also the effect of disordered substitution in on the adsorption and swelling behaviour of clay minerals will then be discussed briefly.

     

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    Übergeordneter Titel: Journée GRIM3 2012, Groupe de Recherche Interdisciplinaire sur les Matériaux, les Molécules et la Matière ; http://hal.in2p3.fr/in2p3-00769210 ; Journée GRIM3 2012, Groupe de Recherche Interdisciplinaire sur les Matériaux, les Molécules et la Matière, Mar 2012, Nantes, France
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDE.IE]Environmental Sciences/Environmental Engineering; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  13. Molecular dynamics simulations on the structure and dynamics of H2O, K+, NH4+ on hydrated muscovite surface
    Erschienen: 2011
    Verlag:  HAL CCSD

    The investigation of water-mineral interfaces plays a pivotal role in the study of various environmental and geochemical problems. The prime reason for exploring the ion-water-mineral interactions lies in the fact that it determines several phenomena... mehr

     

    The investigation of water-mineral interfaces plays a pivotal role in the study of various environmental and geochemical problems. The prime reason for exploring the ion-water-mineral interactions lies in the fact that it determines several phenomena ranging from transport of elements, swelling, dispersion, and mineral alteration and so on. These interactions would be different for different surface cations and at different degrees of hydration. Recent experimental studies support the notion that the K+ ions on the hydrated muscovite surface can be exchanged for the hydronium ions. Similarly, surface K+ ions can also be exchanged for ammonium in the aqueous solution (e.g., in tobelite). We have investigated the structure and dynamics of these ionic species at the hydrated surface of muscovite by molecular dynamics (MD) computer simulations using CLAYFF force field. In addition to replacing the interlayer cations, a series of MD simulations have been performed with varying amounts of water on the muscovite surface at ambient conditions for each of the exchanged cations. Atomic density profiles as functions of the distance from the muscovite surface were calculated for all atoms types present in the simulation. The comparison of hydration states and the topological details of the H-bonding network around the three ions on the surface help to interpret the structure and dynamics of the ions in the confined geometries. The angular distributions of the H2O, H3O+, and NH4+ molecules with respect to the muscovite surface have been studied. The dynamics of water molecules were further examined by self-diffusion coefficients calculated from the mean square displacement of oxygen (or nitrogen) atoms and by exchange/reorientation time correlation functions of the surface molecules. Results obtained from the simulations are compared with the available experimental data and other previous simulations and provide reliable molecular-scale view of the structure and dynamics of ions and water on the muscovite surface.

     

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    Übergeordneter Titel: Clay Minerals Society - 48th Annual Meeting ; https://hal.in2p3.fr/in2p3-00769211 ; Clay Minerals Society - 48th Annual Meeting, Sep 2011, Lake Tahoe, United States
    Schlagworte: [CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry; [CHIM.MATE]Chemical Sciences/Material chemistry; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; [SDE.MCG]Environmental Sciences/Global Changes; [SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
  14. Structure, Energetics, and Dynamics of Smectite Clay Interlayer Hydration: Molecular Dynamics and Metadynamics Investigation of Na-Hectorite
    Erschienen: 2013
    Verlag:  HAL CCSD ; American Chemical Society

    This paper presents a classical molecular dynamics (MD) and metadynamics investigation of the relationships between the structure, energetics, and dynamics of Na-hydroxyhectorite and serves to provide additional, molecular-scale insight into the... mehr

     

    This paper presents a classical molecular dynamics (MD) and metadynamics investigation of the relationships between the structure, energetics, and dynamics of Na-hydroxyhectorite and serves to provide additional, molecular-scale insight into the interlayer hydration of this mineral. The computational results support a model for interlayer H2O structure and dynamics based on 2H NMR spectroscopy and indicate that H2O molecules undergo simultaneous fast librational motions about the H2O C2 symmetry axis and site hopping with C3 symmetry with respect to the surface normal. Hydration energy minima occur at one-, one-and-one-half-, and two-water-layer hydrates, which for the composition modeled correspond to 3, 5.5, and 10 H2O/Na+, respectively. Na+ ions are coordinated by basal O atoms (OMIN) at the lowest hydration levels and by H2O molecules (OH2O) in the two-layer hydrate, and H2O molecules have an average of three H-bonds at the greatest hydration levels. The metadynamics calculations yield activation energies for site hopping of H2O molecules of 6.0 kJ/mol for the one-layer structure and 3.3 kJ/mol for hopping between layers in the two-layer structure. Computed diffusion coefficients for water and Na+ are substantially less than in bulk liquid water, as expected in a nanoconfined environment, and are in good agreement with previous results.

     

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    Übergeordneter Titel: ISSN: 1932-7447 ; EISSN: 1932-7455 ; Journal of Physical Chemistry C ; https://hal.in2p3.fr/in2p3-00870391 ; Journal of Physical Chemistry C, 2013, 117, pp.5172-5187. &#x27E8;10.1021/jp312286g&#x27E9;
    Schlagworte: [CHIM.RADIO]Chemical Sciences/Radiochemistry
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