NaCl solution crystallization progress on graphene surface induced by cation-π interaction

By using molecular dynamics simulations, we researched the NaCl solution crystallization progress with different concentrations on the graphene surface and found that the ions will quickly be adsorbed to the graphene surface due to the cation-π interaction between Na⁺ and graphene, accompanied by ion dehydration and electrostatic interaction between positive and negative ions, the small cluster formed. Gradually the smaller clusters gather to form the bigger two-dimensional crystal on the graphene surface, rather than forming the three-dimensional bulk-like NaCl crystal without the cation-π interaction. As the increase of concentration, the size of clusters increases, but the morphology remains the same. Moreover, the abnormal NaCl stoichiometric ratio crystal appears during the crystallization progress in the two-dimensional clusters, especially at lower concentrations. The number of abnormal NaCl clusters increases significantly as the concentration decreases from 2.7 M to 1.0 M. The normal Na-Cl ratio is predominant when the concentration approaches saturation levels. This work is beneficial to understanding the crystallization process from the molecular level and helps design new material development and valuable resource recovery and utilization.