Ab initio molecular dynamics study of the hydration of Li+, Na+ and K+ in a montmorillonite model. Influence of isomorphic substitution

Abstract

The present work reports ab initio molecular dynamics simulations, based on density functional theory using the PBE functional, of Li(+)- Na(+)- and K(+)-montmorillonites, considering three types of isomorphic substitutions in the montmorillonite layer: tetrahedral (T(sub)), octahedral (O(sub)) and both (OT(sub)). These simulations allow us to evaluate the effect of each type of substitution on the inner- outer-sphere complex formation of the alkali cations. It is observed that, for the three kinds of substituted montmorillonites, K(+) remains bound to the surface confirming its role as swelling inhibitor. In contrast, Li(+) tends to hydrate and coordinate to 4 water molecules in all cases, except for OT(sub), for which one of the two Li(+) cations remains bound to the oxygens close to the substituted tetrahedral site. Finally, Na(+) presents an intermediate behaviour, binding to the surface in T(sub) montmorillonite but being hydrated in O(sub). These simulations show that the hydration/adsorption behaviour of alkali cations in the swelling process of montmorillonite depends on the affinity of the cation for water and the surface, as well as on the type of substitution that controls the negative charge on surface oxygen atoms.

A periodic DFT study of adsorption of water on sodium-montmorillonite (001) basal and (010) edge surface

“…It could be observed that there were alternate potential states in MMT layer where the O atoms in MMT were located at the potential valley due to their negative mulliken charge while the Al, Mg, Si atoms were located close to the potential peak due to their positive Mulliken charge. The similar behavior was reported by several studies [51,52]. A closer look at Fig.7 indicated that there were valleys around z= 0.42 and 0.47 in M(001)W-1 and M(010)W-1, respectively, corresponding to the location of both the adsorbed water molecules with negative Mulliken charge of -0.03 e. These valleys above surface were able to provide adsorption active sites for new species, such as water molecules.…”

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

“…321,412,413 ). Moreover, accounting for dispersion interactions appears to be important to describe the structure and dynamics of liquid water, 414 which otherwise becomes overstructured, 415,416 especially when using GGA functionals.…”

Optimal Location of Vanadium in Muscovite and Its Geometrical and Electronic Properties by DFT Calculation

“…Especially, surfaces and interlayers of phyllosilicate were studied by DFT calculations [13][14][15]. The quantum chemical calculations can identify the most steady state by comparing the total energies of different structures, and analyzing the interaction between V and oxygen in the lattice, which further affects the related physical and chemical properties of muscovite.…”