Anion Substitution in Porous Aromatic Frameworks: Boosting Molecular Permeability and Selectivity for Membrane Acetylene Separation

Abstract Precise tailoring of pore chemistry is indispensable for efficient membrane gas separation, particularly for the challenging acetylene system. Here, a strategy called “anion substitution” is reported, to strengthen the interaction between anions and acetylene within the pores, for radically improving gas selectivity and permeability. The anions F⁻ and OH⁻ are infixed in iPAF‐1 to replace the original Cl⁻ ion. Their small anionic radii allow retention of the original high porosity of iPAF‐1‐Cl in iPAF‐1‐F and iPAF‐1‐OH. Highly basic F⁻ and OH⁻ confined in the pores attract acidic acetylene strongly and preferentially. Nanoparticles of iPAF‐1 are processed to form mixed matrix membranes, represented by iPAF‐1‐OH/6FDA‐ODA. The prepared membranes exhibit remarkable performance in separating acetylene from ethylene and ethane. Transplantation of porous and functional iPAF‐1‐OH into 6FDA‐ODA significantly enhances both acetylene permeability (sevenfold) and permselectivity (fivefold) for acetylene over ethylene and ethane, which is crucial for membrane acetylene gas separation.