A review on anion-pillared metal–organic frameworks (APMOFs) and their composites with the balance of adsorption capacity and separation selectivity for efficient gas separation

Anion-pillared MOFs with customized pore size/shape and chemistry have broken the trade-off between adsorption capacity and separation selectivity, which have been used for high efficient separation of gas mixtures, including CO 2 separation, C 2 H 4 purification, C 3 H 6 purification, C 4 isomers separation, C 5 olefins separation, xylene isomers separation, and Xe/Kr separation. • The first review of anion-pillared MOFs (APMOFs) and their composites are proposed. • The types and uniqueness of APMOFs are discussed. • The reasons for breaking the trade-off of gas mixtures separation on APMOFs are analyzed in details. • The synergistic effects between pore size/shape and chemistry are emphasized. • The challenges and future outlooks of APMOFs are also highlighted. Metal-organic frameworks (MOFs) have gained widespread attention in many fields, especially in gas adsorption and separation. However, traditional MOFs always suffer from a trade-off (i.e., the coordination of adsorption capacity and separation selectivity) effect when separating some challenging and similar gas mixtures. As one type of promising MOFs, anion-pillared MOFs (APMOFs) are designed by introducing another member of anion pillar with abundant hydrogen-bonding acceptors (e.g., F, O, and H), which are capable of overcoming the technical bottleneck of the trade-off owing to novel synergistic effects by the coordination of pore size/shape and chemistry. With the dramatic increase in the number of reported APMOFs, a comprehensive review of their structures and properties is necessary to better cater to this hot topic. In this review, various type of APMOFs with diverse topologies and building blocks are categorised by anions, such as MFSIX (MF 6 2- , M = Metal), FOXF (MO x F 6-x 2- ), DICRO (CrO 7 2- ), BSF (B 12 H 12 2- ), MOFOUR (MO 4 2- ), and the like. In addition, recent progresses for gas separation by APMOFs and their composites are also comprehensively focused on, including CO 2 separation, C 2 H 4 purification, C 3 H 6 purification, C 4 isomers separation, C 5 olefins separation, xylene isomers separation, and Xe/Kr separation. Furthermore, some important issues concerning the design strategies and corresponding applications are emphasized, which should attract more and more attentions in the future.