Insights into the influence mechanism of different interlayer cations on the hydration activity of montmorillonite surface: A DFT calculation

Abstract

Montmorillonite is one of the main components of mudstones. Physical changes in the microstructure of montmorillonite after water absorption are the root cause of softening and disintegration of mudstone and the deterioration of bearing properties. In this study, the adsorption behavior and hydration mechanism of water molecules on the surface of four cationic forms of montmorillonites (Li–Mt, Na–Mt, K–Mt, and Ca–Mt) were investigated by density functional theory (DFT). The results indicated that water molecules were adsorbed mainly through electrostatic attractive force with interlayer cations. The electrostatic attraction decreased in the following order: Ca-Mt > Li-Mt > Na-Mt > K-Mt; and Ca–Mt demonstrated the strongest adsorption capacity. When adsorption occurred, there was a large charge transfer between the atom of a water molecule (Ow) and interlayer cations, and the hybridization of Ow 2p orbitals with Li 1 s, Na 3 s, K 4 s, and Ca 4 s orbitals formed bonds with certain ionic characteristic. This work directly explained the interaction mechanism of water molecules with montmorillonite at the atomic and electronic levels, which provided a new perspective to understand the adsorption process of water molecules on clay mineral surfaces.