The rapid emergence of two-dimensional nanomaterials for high-performance separation membranes

Membrane-based nanotechnologies have gained growing attention in various separation fields due to advantages such as high energy efficiency and ecofriendliness. However, the limited and empirical design parameters of conventional membranes greatly slow down research progress on rapid and efficient molecular separations. Two-dimensional materials (2DMs) - e.g., graphene, MoS2, MXene, metal-organic frameworks, and covalent organic framework nanosheets - are rapidly emerging in the development of membranes with high selectivity and permeability. The rational tunability and precise control of interlayer distances and/or nanoporous apertures of 2DMs enable 2DM-based membranes to achieve highly specific separations. Furthermore, the ultrathin structure of 2DMs offers minimal transport resistance and thus leads to extraordinary flux rates. This review briefly outlines recent approaches in the use of various 2DMs for membrane designs. Some remarkable performances of 2DM-based membranes and their separation mechanisms are also noted. Challenges and future directions toward molecular-level designs of membranes with 2DMs are additionally discussed.