A TIFSIX pillared MOF with unprecedented zsd topology for efficient separation of acetylene from quaternary mixtures

The separation of acetylene (C2H2) from carbon dioxide (CO2) and other C1-C2 light hydrocarbons is important to produce C2H2 in high purity as well as recover other gases. However, it is challenged by the trade-off between the adsorption capacity and selectivity due to the similar physical properties. In this work, we reported a new TiF62− anion (TIFSIX) pillared porous metal organic framework ZNU-4 (ZNU = Zhejiang Normal University) with unprecedented zsd topology for selective C2H2 capture. The utilization of 1,4-di(1H-imidazol-1-yl)benzene (DIB) as the organic linker in ZNU-4 generates a highly twisted framework, resulting in a distinctive topological net with unique narrow 1D channels suitable for C2H2 trap. ZNU-4 features robust-flexible isotherms for C2H2 adsorption and the capacity under 1 bar and 298 K is as high as 85 cm3/g, 1.9, 2.1 and 7.1 folds of CO2, C2H4 and CH4 uptake. The IAST selectivity of C2H2 over CO2, C2H4, CH4 is 9, 12, and 300, respectively, higher than those of most popular porous materials. Modelling study indicated that C2H2 is trapped by cooperative Ti-F···HC≡CH···N(DIB) hydrogen bonding along with other weak Van der Waals interactions. Such cooperative bonding interactions have never been disclosed in other fluorinated anions pillared MOFs due to the absence of second binding site from organic linkers. The breakthrough experiments further confirmed the highly selective C2H2 separation performance from binary C2H2/CO2 mixtures, ternary C2H2/CO2/CH4 mixtures and quaternary C2H2/CO2/CH4/C2H4 mixtures. The separation factor of ZNU-4 for equimolar C2H2/CO2 mixture is 5.4, superior to those of many other benchmark materials.