Enhancing Acetylene/Ethylene Separation through Cation Exchange in an Anion-Pillared Hybrid Ultramicroporous MOF

The purification of ethylene (C2H4) from a mixture of acetylene/ethylene (C2H2/C2H4) gases is of great importance for manufacturing various downstream commodities; however, it is highly challenging due to their similar physicochemical properties. Herein, two hybrid ultramicroporous materials, LIFM-107(Cu/Ni), featuring functionalized hexafluorosilicate (SiF62–) anions and a small pore size, are successfully constructed through a cation-exchange protocol for efficient C2H2/C2H4 separation. Compared with the prototypical LIFM-107(Zn), the resultant LIFM-107(Cu/Ni), especially for LIFM-107(Cu), showcases improved C2H2/C2H4 separation performance demonstrated by the transient breakthrough experiments. Additionally, the underlying gas adsorption mechanism has been well established by in situ infrared spectroscopy experiments and molecular modeling, in which a strong C2H2-nanotrap stemming from the strong C–H···F hydrogen bonds interactions and C≡C···H/C–H···π forces plays a pivotal role in the preferential C2H2 adsorption process.