Molecular modeling of the structure and dynamics of the interlayer and surface species of mixed-metal layered hydroxides: Chloride and water in hydrocalumite (Friedel’s salt)

Abstract The dynamical behavior of Cl- and H2O molecules in the interlayer and on the (001) surface of the Ca-aluminate hydrate hydrocalumite (Friedel’s salt) over a range of temperatures from -100 to 300 °C was studied using isothermal-isobaric molecular dynamics computer simulations. This phase is currently the best available model compound for other, typically more disordered, mixed-metal layered hydroxides. The computed crystallographic parameters and density are in good agreement with available X-ray diffraction data and the force field developed for these simulations preserves the structure and density to within less than 2% of their measured values. In contrast to the highly ordered arrangement of the interlayer water molecules interpreted from the X-ray data, the simulations reveal significant dynamic disorder in water orientations. At all simulated temperatures, the interlayer water molecules undergo rapid librations (hindered hopping rotations) around an axis essentially perpendicular to the layers. This results in breaking and reformation of hydrogen bonds with the neighboring Cl- anions and in a time-averaged nearly uniaxial symmetry at Cl-, in good agreement with recent 35Cl NMR measurements. Power spectra of translational, librational, and vibrational motions of interlayer and surface Cl- and H2O were calculated as Fourier transforms of the atomic velocity autocorrelation functions and compared with the corresponding spectra and dynamics for a bulk aqueous solution. The ordered interlayer space has significant effects on the motions. Strong electrostatic attraction between interlayer water molecules and Ca atoms in the principal layer makes the Ca···OH2 bond direction the preferred axis for interlayer water librations. The calculated diffusion coefficient of Cl- as an outer-sphere surface complex is almost three times that of inner-sphere Cl-, but is still about an order of magnitude less than that of Cl- in bulk aqueous solution at the same temperature.

[1]  R. Fischer,et al.  Hydrocalumit: Mischkristalle von “Friedelschem Salz” 3CaO Al 2 O 3 CaCl 2 10H 2 O und Tetracalciumaluminathydrat 3CaO Al 2 O 3 Ca(OH) 2 12H 2 O?. , 1980 .

[2]  D. Smith.  Molecular Computer Simulations of the Swelling Properties and Interlayer Structure of Cesium Montmorillonite , 1998 .

[3]  E. Passaglia,et al.  Hydrocalumite from Latium, Italy: its crystal structure and relationship with related synthetic phases , 1988 .

[4]  J. Perdew.  Generalized gradient approximations for exchange and correlation : a look backward and forward , 1991 .

[5]  J. Banavar,et al.  Computer Simulation of Liquids , 1988 .

[6]  Nick R. Buenfeld,et al.  Chloride Diffusion through Surface-treated Mortar Specimens , 1998 .

[7]  F. P. Glasser,et al.  Friedel’s salt, Ca2Al(OH)6(Cl,OH)·2H2O: its solid solutions and their role in chloride binding , 1998 .

[8]  B. Teppen,et al.  Molecular Dynamics Modeling of Clay Minerals. 1. Gibbsite, Kaolinite, Pyrophyllite, and Beidellite , 1997 .

[9]  B. Smit,et al.  The Swelling of Clays: Molecular Simulations of the Hydration of Montmorillonite , 1996, Science.

[10]  W. Jones,et al.  Synthesis, characterization and applications of layered double hydroxides containing organic guests , 1998 .

[11]  L. E. Chirlian,et al.  Atomic charges derived from electrostatic potentials: A detailed study , 1987 .

[12]  W. Jones,et al.  Interlayer Arrangement of Hydrated MgAl Layered Double Hydroxides Containing Guest Terephthalate Anions: Comparison of Simulation and Measurement , 1998 .

[13]  A. Delville.  Monte Carlo Simulations of Surface Hydration: An Application to Clay Wetting , 1995 .

[14]  K. Waltersson,et al.  The crystal structure of Cs[VOF3] · 12H2O , 1979 .

[15]  R. Kirkpatrick,et al.  Interlayer structure, anion dynamics, and phase transitions in mixed-metal layered hydroxides: Variable temperature 35Cl NMR spectroscopy of hydrotalcite and Ca-aluminate hydrate (hydrocalumite) , 1999 .

[16]  D. Wingate.  Surgery of the liver , 1990 .

[17]  P. Coveney,et al.  Molecular Dynamics Simulations of The Swelling of Terephthalate Containing Anionic Clays , 1999 .

[18]  P. Coveney,et al.  Simulation of layered double hydroxide intercalates , 1997 .

[19]  H. Berendsen,et al.  Interaction Models for Water in Relation to Protein Hydration , 1981 .

[20]  C. Hartnig,et al.  Water in porous glasses. A computer simulation Study , 1999 .

[21]  M. Parrinello,et al.  Polymorphic transitions in single crystals: A new molecular dynamics method , 1981 .

[22]  E. Wasserman,et al.  Molecular dynamics study of proton binding to silica surfaces , 1998 .

[23]  Bo Jönsson,et al.  A molecular dynamics simulation of a water model with intramolecular degrees of freedom , 1987 .

[24]  E. Passaglia,et al.  Hydrocalumite from Montalto di Castro, Viterbo, Italy , 1988 .

[25]  Walter Kauzmann,et al.  The Structure and Properties of Water , 1969 .

[26]  G. Sposito,et al.  Monte Carlo and Molecular Dynamics Simulations of Interfacial Structure in Lithium-Montmorillonite Hydrates , 1997 .

[27]  C. Hartzell,et al.  Molecular Modeling of the Tributyl Phosphate Complex of Europium Nitrate in the Clay Hectorite , 1998 .

[28]  K. Heinzinger,et al.  Computer Simulations of Aqueous Fluids at High Temperatures and Pressures , 1992 .

[29]  B. Delley.  An all‐electron numerical method for solving the local density functional for polyatomic molecules , 1990 .

[30]  B. Mojet,et al.  Ordering of intercalated water and carbonate anions in hydrotalcite. An NMR study , 1994 .

[31]  Robert J. Woods,et al.  Derivation of net atomic charges from molecular electrostatic potentials , 1990 .

[32]  M. C. Hermosín,et al.  Hydrotalcite-like compounds as potential sorbents of phenols from water , 1995 .