Effect of interlayer cations on exfoliating 2D montmorillonite nanosheets with high aspect ratio: From experiment to molecular calculation

Abstract

Abstract In this work, the montmorillonite (MMT) with different interlayer ions (Na+ and Ca2+) were exfoliated to prepare high aspect ratio 2D montmorillonite nanosheets (MMTNS). The effect of interlayer cations was experimentally and theoretically studied through the atomic force microscope (AFM) and molecular simulation. Na-MMT could be more easily exfoliated to monolayer with the thickness of 0–1 nm compared to Ca-MMT, and the exfoliated Na-MMTNS have higher lateral diameter than Ca-MMTNS under the same condition, leading to that the Na-MMTNS with high aspect ratio can be more readily obtained. This observation was sufficiently interpreted by molecular dynamic simulation and first principles calculations including band structure, density of states, electron density difference and electron localization function. It is indicated that the interlayer binding energy of Na-MMT was weaker while its in-plane structure was stronger compared with Ca-MMT. The strong interacting force between interlayer Ca atoms and the in-plane atoms will cause structural failure after exfoliating Ca-MMT off to 2D nanosheets. It is suggested that the interaction between the extranuclear electrons of atoms in MMT layer and interlayer cations will affect the overall intensity and apparent exfoliation properties.