Polyzwitterion-grafted UiO-66-PEI incorporating polyimide membrane for high efficiency CO₂/CH₄ separation

In this study, UiO-66-NH₂ fillers were grafted with polyethyleneimine (PEI) and poly(sulfobetaine methacrylate) (pSBMA) and subsequently incorporated into a sythesized 6FDA-ODA matrix to prepare mixed matrix membranes (MMMs). XRD, FTIR, SEM and TGA characterization techniques were used to evaluate the structure and properties of UiO-66-PEI@pSBMA and MMMs. It was found that the introduction of branched PEI and pSBMA can not only avoided the agglomeration of UiO-66-NH₂, but also improved the compatibility between the polymer matrix and filler particles. In addition, the UiO-66-PEI@PSBMA was able to bond with a noticeable amount of amino groups and water molecules, and to promote the transportation of CO₂ in the membrane. The resulting PI/UiO-66-PEI@pSBMA MMM achived remarkably enhanced gas perm-selectivity compared to pristine 6FDA-ODA membrane and exceeded the Robeson upper bound. The strategy of PEI and polyzwitterion post covalent modification for UiO-66-NH₂ provides an effective way to eliminate interface defects and enhance the gas separation of MMMs.