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

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.