Recent advancements in supramolecular macrocycles for two-dimensional membranes for separations

Precise and efficient separation of molecules and ions is important in many fields, including the chemical industry, textiles, and medicine. Two-dimensional (2D) materials with high specific surface areas and atomic thickness are an excellent choice for membrane building blocks. However, stacking nanosheets face-to-face usually prevents the transport of molecules or ions across such 2D membranes, thereby reducing their flux. Supramolecular macrocyclic hosts contain cucurbiturils, cyclodextrins, pillararenes, crown ethers, and calixarenes, which afford macrocyclic cavities with rigid structures that are easy to be functionalized. Thus, it is possible to construct membranes using 2D materials as “beams” and supramolecular macrocyclic compounds as “columns”. This strategy has been applied to overcome challenges related to the permeability–selectivity trade-off. Supramolecular 2D membranes have been widely used in a wide range of critical separations, including water purification, enantiomer separation, ion extraction and separation, and gas separation. This review provides a new perspective to inspire researchers to develop promising 2D supramolecular membranes with high selectivity, mild flux, and appreciable reversibility.