Synthesis of Cuprous Organic Frameworks with Adjustable Pores as Membrane Materials for C3H6/C3H8 Separation

Abstract

Metal–covalent organic frameworks (MCOFs) combining the advantages of open metal sites of metal–organic frameworks and covalent connections of COFs are potential platform for gas separation. Herein, three 2D cuprous-based MCOFs (Cu-COFs, named Cu-TABA, Cu-TFBA, and Cu-TP) are designed and synthesized through Schiff base condensation using two trinuclear cuprous complexes and three organic building blocks with different sizes. These Cu-COFs possess high crystallinity, good stability, and microporous structure with gradually decreasing pore size. The 1D columnar channels facilitate the rapid transport of gas molecules along the layer-by-layer stacking direction. The open cuprous ions serve as adsorption sites and interact strongly with propylene (C₃H₆) through π-complexation. The mixed matrix membranes (MMMs) fabricated by Cu-COFs and polymer (6FDA-DAM) exhibit superior propylene/propane (C₃H₆/C₃H₈) separation performance; shown by C₃H₆ permeability as high as 85.5 Barrer and C₃H₆/C₃H₈ selectivity reaching 36.6, much higher than those of pure 6FDA-DAM membrane. The performance beyond most reported MMMs demonstrates that Cu-COFs are candidate membrane materials for C₃H₆/C₃H₈ separation.