MOF ligand engineering boosts molecular-sieving property of mixed-matrix membrane for methanol/methyl acetate azeotropic separation

Pervaporation membrane process is promising for separation of organic-organic azeotropic systems, while a trade-off relationship restricts the performance of widely-studied polymeric membranes. In this work, we proposed a MOF ligand engineering strategy to boost the molecular-sieving property of mixed-matrix membrane (MMM) by synergistically manipulating the channel size, affinity and interfacial morphology. Specially, we designed UiO-66-(NH₂)₂/polyvinyl alcohol (PVA) mixed-matrix membranes to separate methanol (MeOH)/methyl acetate (MeOAc) azeotropic mixture via pervaporation process. By comparing the incorporation of UiO-66-(NH₂)₂, UiO-66 and p-phenylenediamine (PPD), the MOF pore size and chemistry were systematically investigated on the influence of microstructures and separation performance of the MMMs. The results demonstrated that the rationally introduced para-position –NH₂ groups on the terephthalic acid (BDC) ligands not only finely reduce the MOF pore size of UiO-66 filler, but also improve the interfacial compatibility via hydrogen bonding between UiO-66 and PVA chain, as well as enhance the MeOH affinity in the MMM. The optimized 7.5 wt% UiO-66-(NH₂)₂/PVA MMM exhibited a total flux of 1554.6 g/m²h and a separation factor of 70.9 in 20 wt% MeOH/MeOAc azeotropic mixture at 30 °C, which is superior to the state-of-the-art membranes. The ligand engineering strategy offers a route for regulating the morphology and molecular transport property of mixed-matrix membranes.