Fast prepare exfoliated montmorillonite water suspension with assistance of melamine cyanurate and the superlattice obtained by self-assembly

To explore the exfoliation mechanism of montmorillonite (MMT) layers assisted by melamine cyanurate (MCA), the MCA crystal structures based on the concentration of raw materials and the preparation of MMT-MCA superlattice are investigated. Here, the correlation between MCA crystal growth and concentration of cyanuric acid (CA) and melamine (MA) water solutions on glass substrate are analyzed using XRD and SEM. With the increasing of concentration of CA and MA water solutions, the stacking of MCA layers along [202] axis is enhanced gradually compared with the growth of single MCA layer along (202) plane, resulting in the transform of MCA morphology from sheet to column. The exfoliated MMT monolayers with sizes of hundreds on nanometer can be obtained and well dispersed in the supernatant of MMT-MCA superlattice. After removing the solvent of the supernatant, the formed coating show that the MCA crystal with columnar structure is well inserted into MMT galleries, which is the main driving force that increases basal spacing (d-space) of MMT layers. And, the sandwich-like superlattice is formed by the restacking of MMT and MCA in the coating of MMT-MCA suspension, where the MMT is single or few layers, and the d-space of MMT can even be increased to micron-scale.