New CO₂ separation membranes containing gas-selective Cu-MOFs

We examined the challenge of preparing CO₂-selective bifunctional three-dimensional Cu-metal-organic frameworks (Cu-MOFs) for use in mixed-matrix membranes (MMMs) fabricated on an asymmetric polymer support. Two different gas-selective micro-sized frameworks, [{Cu₂(Glu)₂(μ-bpa)}·(CH₃CN)]_n (Cu-MOF1) and [{Cu₂(Glu)₂(μ-bpp)}·(C₃H₆O)]_n (Cu-MOF2) (Glu=glutarate, bpa=1,2-bis(4-pyridyl)ethane, bpp=1,3-bis(4-pyridyl)propane), were synthesised and dispersed in polyoxazoline (POZ), as a matrix for the fabrication of the MMMs. SEM imaging indicated relatively good adhesion between the Cu-MOFs and POZ, without any surface treatment. The ideal selectivity of CO₂/N₂ was enhanced significantly in the Cu-MOF/POZ MMM, compared to that in a pristine POZ asymmetric membrane. Improvement in the CO₂/N₂ selectivity of the membranes was achieved via both high adsorption selectivity of CO₂ over N₂ by the Cu-MOFs, and the difference in pore sizes. The fabrication methods that use gas-selective MOFs may create new opportunities for gas-selective MOF/polymer combinations for MMMs with useful properties for large volume separations.