Improving the permselectivity of asymmetric isoporous membranes by blending the micro-sized metal-organic frameworks(MOFs) crystals with block copolymer

Nanomaterials are widely used to improve the separation performance for asymmetric isoporous membranes. Different from those prevalent researches, MOFs crystals with particle sizes of 0.52–0.75 μm which were an order magnitude larger than the molecular size of block copolymers (BCPs) were loaded to casting solution, and their tailoring on membrane formation and permselectivity of isoporous membranes prepared via the SNIPS were carefully investigated. As far as we know, 3D particles with such big size have never been added to isoporous membranes before. Results from small angle X-ray scattering indicated that the microphase separation in solutions had been increased obviously although MOFs crystals were too large to co-assemble with BCPs. This interesting finding was assigned to the breathing effect from MOFs crystals that increased the effective concentrations of BCPs. Morphology observation indicated that MOFs crystals located on surface were fully covered by a thin layer of BCPs which also assembled into defect-free, isoporous structures. This result was observed even though the contents of MOFs in membranes reached 40 wt%. It was measured that the permeability and selectivity to protein mixtures improved obviously by the MOFs crystals blended to membranes. Finally, with the removal of MOFs from membranes by acid etching, the permselectivity of membranes improved further. Considering the easy synthesis and good dispersibility, micro-sized MOFs crystals can be used as more effective additives to improve the separation performances for isoporous membranes than that of nanomaterials. This finding will pave the ways for preparing the high-performance isoporous membranes by using MOFs crystals as the additives for block copolymers.