Rational design and synthesis of ultramicroporous metal-organic frameworks for gas separation

Metal-organic frameworks (MOFs) have emerged as a new generation of porous materials that demonstrate great promise in diverse application fields, especially gas separation, due to the energy-efficient economy. One of the striking advantages of MOFs relies on their tunable pore sizes, which plays a crucial role in the separation efficiency and selectivity since smaller pore can introduce stronger host–guest interaction. Thus, fabrication of ultramicroporous (pore size < 0.7 nm) MOFs for gas separation and purification has gained increasing attention because they allow molecular-scale resolution for gas separation. In this review, we summarized several typical design strategies and synthesis methods to create ultramicroporous MOFs. We also address the latest progress for gas separation made by ultramicroporous MOFs in critical gas separation processes, especially CO2 separation, C2H4 purification, C3H6 purification, noble gas separation, and isotope separation. We anticipate that this review will provide an important guide for future research into fabricating ultramicroporous MOFs, and provide perspective on the future directions of ultramicroporous MOFs in terms of gas separation.