Correlation of exfoliation performance with interlayer cations of montmorillonite in the preparation of two-dimensional nanosheets

Montmorillonite (MMT) can be exfoliated into nanosheets used in a wide range of applications as two-dimensional (2D) material. The exfoliated MMT nanosheets with high diameter-thickness ratio appear to show superior properties in preparation of nanocomposites and other functional materials. In this work, the correlation of exfoliation performance with interlayer cations of MMT in the preparation of 2D nanosheets was investigated. The thickness and lateral diameter of MMT nanosheets were quantitatively measured by atomic force microscopy (AFM) technique. AFM results showed the exfoliated K-MMT had larger lateral diameter and thinner thickness than the exfoliated Ca-MMT under the same exfoliation conditions. Molecular simulation was applied to investigate the interlayer-binding energy (IBE), population analysis and density of states. K-MMT structures tend to have higher in-plane chemical bond intensity than Ca-MMT because of the impact of antibonding. The IBE of K-MMT was higher than that of Ca-MMT after the sorption of water molecules into the neighboring monolayers, indicating that thinner naonosheets tend to be easier obtained from Ca-MMT than K-MMT in liquid exfoliation. These findings might be helpful for the preparation and application of 2D MMTNS through controlling interlayer cation species and the exfoliation properties of MMT.