Enantioseparation processes and mechanisms in functionalized graphene membranes: Facilitated or retarded transport?

Up to date, functionalized graphene-based membranes have exhibited a promising potential in the enantioseparation. However, since precisely controlling the interlayer distance of two-dimensional materials is a great challenge in practical experiments, the transport mechanism of chiral guests in such membranes, together with various critical parameters that play a controlling role in the transport behaviors of the preferentially binding enantiomer in narrow channels, remains to be explored. The molecular dynamics (MD) simulation, especially using the steered MD (SMD) method, might be an alternative way to investigate the enantioseparation processes and mechanisms of layered membranes with different interlayer distances. In this work, D-alanine modified graphene sheets with different interlayer distances were built as membrane models, whereas D- and L-phenylalanine were selected as chiral probes. The effect of the interlayer distance and the applied external force on the enantioseparation performance was examined. Results show that such two parameters exert a significant influence on the enantioseparation performance: (a) Increasing the interlayer distance would result in a conversion from the retarded to the facilitated mechanism at a proper external force (medium); (b) both the large and small driving forces would only lead to the appearance of the retarded transport for the preferential enantiomer, unlike the moderate force; (c) the interaction energy of L-phenylalanine with D-isomer selector decreases with the rising interlayer distances studied in this work, regardless of what the external force is. Our findings can provide guidance on the practical applications in the membrane-based chiral separation.