Surface and interface engineering in CO2-philic based UiO-66-NH2-PEI mixed matrix membranes via covalently bridging PVP for effective hydrogen purification

We report on the fabrication of the defect-free mixed-matrix membrane (MMM) based on the polyethylenimine (PEI) matrix with uniformly dispersed metal-organic framework (MOF) filler UiO-66-NH₂, covalently bonded by polyvinylpyrrolidone (PVP). The key feature of the molecular level-controlled filler deposition in prepared UiO-66-NH₂-PVP-PEI membranes was bridging the MOF particles to the PEI polymer matrix via PVP polymer chains. Such an approach improved the polymer-filler interface interactions and boosted the MOF dispersion into the polymer matrix for higher MOF loadings up to 23 wt %. The overall membrane structure and properties were characterized using FTIR, XRD, TG, DSC, SEM and 3D optical profiler techniques. Obtained results revealed the uniform dispersion of UiO-66-NH₂, the strong polymer-filler interface interactions and entanglement of PEI with UiO-66-NH₂-PVP. Furthermore, the outstanding CO₂/H₂ separation performance was determined for the UiO-66-NH₂-PVP-PEI membrane with 18 wt % of MOF loading; the average CO₂ permeability of 394 Barrer and the separation factor of 12 for circa 100 h of the membrane testing overcome the 2008 Robeson reverse upper bound limit. Such improved CO₂/H₂ separation performance was achieved due to the combination of the diffusion-solution mechanism with the preferential adsorption of the CO₂ via the reversible bicarbonate reaction with amino groups of the UiO-66-NH₂ and PEI which acts as fixed CO₂ carrier sites in MMM structure.