Interlayer Porosity in Montmorillonite Intercalated with Keggin-like Cation Studied by Molecular Mechanics Simulation

Molecular mechanics simulation using Cerius(2) modeling environment have been used to investigate the structure of montmorillonite, intercalated with Keggin-like cation(7+). Present work is focused to the strategy of modelling in case of intercalated layered structures and to investigation of structure parameters characterizing the interlayer porosity, that means: the interlayer distance, the position, orientation and distribution of Keggin cations in the interlayer space and the stacking of layers. Molecular simulations revealed the structure of the interlayer and led to the following conclusions: In the most stable configuration the 3-fold axis of Keggin cation is perpendicular to the silicate layer. This orientation of Keggin cations leads to the basal spacing 19.51 (10(-10) m). Energy minimization during the translation of Keggin cation along the silicate layer gives only small fluctuations of basal spacing and no correlation has been found between the shift of cation along the layers and the value of basal spacing. No systematic relationship has been found between the shift of cation and crystal energy and no systematic relationship exists between the mutual shift of two successive layers and the values of basal spacing and crystal energy. Consequently, no two-dimensional ordering of Keggin cations in the interlayer and no regular stacking of layers can be expected. X-ray diffraction diagrams obtained for montmorillonites, intercalated with Keggin cation, confirm present conclusions

Modelling of intercalated clay minerals

Molecular mechanics simulations in Cerius(2) modelling environment have been used to investigate the structure of montmorillonites, intercalated with aluminium complex cations. Two different intercalating species have been investigated: 1. Keggin cation (ideal and hydrolyzed) and 2. gibbsite-like polymers, arranged in two layers in the interlayer of montmorillonites. The results of molecular simulations showed that the position, orientation, and concentration of Keggin cations in the interlayer space depends on the degree of hydrolysis. The average values of basal spacings for different degree of hydrolysis are within the range of 19.51--20.05 10(-10) m. in the case of gibbsite-like polymers, arranged in two layers in the interlayer of montmorillonites, basal spacing depends on the mutual position of Al-OH polymers. Average basal spacings for different arrangements of Al(OH)(3) fragments are in the range of 19.58-20.06 10(-10) m. Molecular simulations also showed that for both intercalating species no two-dimensional ordering of complex cations can occur in the interlayer of montmorillonites

Molecular simulations of montmorillonite intercalated with aluminum complex cations. Part I: Intercalation with [Al13O4(OH)(24+x)(H2O)(12−x)]((7−x)+)

The structure of montmorillonite intercalated with [Al1304(OH)(24+x)(H20)(l2- x)] (7-x)+ cations (Al-13((7-x)+) for short), where x = 0, 2 and 4, has been studied using the Cerius z modeling environment. The Crystal Packer module used in the present study takes into account only the nonbonded interactions between the silicate layer and the Keggin cations. Minimization of the total sublimation energy led to the following conclusions: the structure of the interlayer (that is, the orientation of Keggin cations and the basal spacing) depends on the charge of cations (that is, on the degree of hydrolysis, x). The values of basal spacings in the range 19.38-20.27 Å have been obtained, depending on the charge and arrangement of cations in the interlayer. The dominating contribution to the total sublimation energy comes from the electrostatic interactions. Translations of Al-13((7-x)+) cations along the 2:1 layers give only small fluctuations of the total sublimation energy and basal spacings. No preference for the position of Al-13((7-x)+) cations in the interlayer of montmorillonite was found during translation along the 2:1 layers. This result confirmed the inhomogeneous distribution of cations in the interlayer and turbostratic stacking of layers

Molecular Simulations of Montmorillonite Intercalated with Aluminum Complex Cations. Part II: Intercalation with Al(OH)3-Fragment Polymers

The Crystal Packer module in the Cerius 2 modeling environment has been used to study the structure of montmorillonite intercalated with Al(OH)3-fragment (gibbsite-like) polymers. Basal spacings in gibbsite-like polymers arranged in 2 layers in the interlayer of montmorillonite varied in the range 19.54-20.13 Å, depending on the type and arrangement of AI(OH)3 fragments. The inhomogeneous distribution of intercalating species in the interlayer and, consequently, the turbostratic stacking of layers has been found for gibbsite-like polymers as well as in the case of Keggin cations (Capková et al. 1998). The dominating contribution to the total sublimation energy comes from electrostatic interactions for both intercalating species, gibbsite-like polymers and Keggin cations

Structure analysis of intercalated clays using combination of molecular simulations, powder diffraction and IR spectroscopy

Combination of molecular simulations with x-ray powder diffraction and TR spectroscopy has been used to study the structure of montmorillonites, intercalated with aluminium complex cations. Two different intercalating species have been investigated: (1) Keggin cation - ideal and hydrolysed and (2) gibbsite-like polymers, arranged in two layers in the interlayer of montmorillonites. The results of molecular simulations showed, that for Keggin cations, the crystal packing depends on the degree of hydrolysis, exhibiting the basal spacings within the range 19.38 - 20.27 (10(-10)m). I, case of gibbite-like polymers, arranged in two layers in the interlayer, basal spacings within the range 19.58 - 20.06 (10(-10)m) have been found, in dependence on the mutual position of Al-OH polymers. Results of molecular simulations showed, that no two-dimensional ordering of complex cations and no reggular stacking of layers can occure in the interlayer of montmorillonites. All the conclusions of modelling were in agreement with the results of XRD analysis