Structurally ordered core-shell MOFs in mixed matrix membrane as magnetic sieves for O2/N2 separation

Membrane separation technology has broad application prospects in O2/N2 separation, and improving the permselectivity of membranes remains a key problem to be solved. O2 and N2 have different magnetic properties and can be separated by magnetism. In addition, coupling magnetic separation with the use of a molecular sieve supported by metal-organic frameworks (MOFs) could further enhance the separation ability. In this work, a magnetic core-shell MOF (Fe3O4@ZIF-8) was prepared as a filler, and the impacts of the Fe3O4@ZIF-8 morphology, loading, channel magnetic properties and ordered arrangement on membrane O2/N2 selectivity were evaluated. To establish a magnetic-sieving O2 permeation channel, the preparation process was carried out in a magnetic field so that the fillers in the membrane were arranged orderly. Due to the synergistic impact of the structurally ordered MOF channel and magnetism, the gas transport performance of the resulting magnetic mixed matrix membranes (MMMs) was substantially improved. Therefore, the O2 permeability and O2/N2 selectivity of the 15 wt%Fe3O4@ZIF-8-8/Pebax MMMs reached 194 Barrer and 11.97, respectively. This study not only presents a novel approach for creating high-performance O2/N2 membranes but also plays a leading role in the development of magnetism-controlled multiscale (magnetic core-shell and filler-ordered) membrane structural engineering.