Pore engineering of MOFs through in-situ polymerization of dopamine into the cages to boost gas selective screening of mixed-matrix membranes

Reducing the effective pore size of MOFs is necessary to improve gas screening of mixed matrix membrane (MMMs). However, continuous and precise regulation on pore size of MOFs is still challenging. In this work, dopamine (DA) monomers are proposed to polymerize in situ into pore cages of UIO-66, achieving the tuning of effective pore size for CO 2 screening. Meanwhile, the abundant hydroxyl and amino groups in polydopamine (PDA) offer high affinity with CO 2 to improve the selective permeation of CO 2 . Furthermore, additional PDA existing outside UIO-66 at longer polymerization time can intensify the interface compatibility to promote CO 2 /N 2 selectivity. Through increasing PDA content in the cage by prolonging polymerization time, the effective pore size and total pore volume of UIO-66 are decreased by 13.2% and 59.2%, respectively, compared with pure UIO-66. Correspondingly, PDA@UIO-66/Pebax MMM presents greatly improved CO 2 separation performances, especially the CO 2 /N 2 selectivity, compared with UIO-66/Pebax MMM. Specifically, both the permeability and selectivity of CO 2 increase with the PDA content into the cages increasing, which is attributed to the synergy of reduced pore size and abundant CO 2 -philic groups in PDA. The PDA 10.3 @UIO-66/Pebax MMM shows the best CO 2 /N 2 selectivity of 70.55 and CO 2 permeability of 94.56 Barrer, 29.2% and 27.9% higher than those of UIO-66/Pebax MMM, respectively. The proposed PDA@UIO-66 based MMMs exhibit superior CO 2 separation performance, especially high CO 2 /N 2 selectivity compared with most reported UIO-66 based MMMs. Together with the good long-term stability, the proposed regulating strategy on effective pore engineering of MOFs is promising and competitive in CO 2 screening of MOFs based MMM.