Enhancement of molecular-sieving properties by constructing surface nano-metric layer via vapor cross-linking

Polyamide-based vapor cross-linked layer has been identified to enhance molecular-sieving properties of tris(2-aminoethyl) amine (TAEA) treated 6FDA-Durene membranes. The resultant membranes, with a nano-metric thickness of cross-linked layer, have tunable H₂/CO₂ separation properties from CO₂-selective to H₂-selective. Incorporation of less than 100nm ZIF-71 nano-particles boosted the molecular-sieving characteristics of TAEA-treated mixed matrix membranes (MMMs). Not only does the 60-min treated MMM containing 10wt% ZIF-71 show a 34% increment in ideal H₂/CO₂ selectivity as compared to the membrane without ZIF-71 (62.5 vs. 46.8), but also exhibits a 1.8-fold higher H₂ permeability (540 vs. 300Barrer). X-ray Photoelectron Spectroscopy (XPS) revealed new N-Zn bonds in TAEA-treated MMMs, owing to the linkage between TAEA and ZIF-71, which may mitigate non-selective interfacial voids in MMMs. As a conclusion, the proposed vapor cross-linking method is approved to solve the most challenging issue (i.e., non-selective interfacial voids) in MMM fabrication.