Effect of interlayer counterions on the structures of dry montmorillonites with Si4+/Al3+ substitution

Density functional theory calculations were performed to study the intercalating behaviors of positively charged counterions in montmorillonites (MMTs) with Si4+/Al3+ substitution in their first internal layer. The substitution has great influence on the interaction between the counterions and the internal surface as well as on the MMT lattice structures. The intercalated counterions are characterized by their strong bonding with the six-oxygen-ring (SOR) on the substituted layer and with the O atoms on the opposite surface. The cations with smaller radii or higher charge have stronger interaction with the surface atoms. The inclusion of dispersion correction in the calculations leads to small changes to the lattice structures.

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• Si4+/Al3+ substitution enriches negative charge on internal surface.
• Counterion adsorption leads to considerable distortion to MMT structures.
• Counterions are trapped by six-oxygen-ring and bond with the O atoms.
• Strong bonding is formed for small-sized and/or highly charged cations.