Direct-through channels of ZIF-8 composite membranes via in-situ PolyBMA sealing: Radical-induced phase transformation and dye removal efficiency

Metal-organic frameworks (MOFs)-based hybrid composite membranes are promising candidates for achieving highly efficient water purification. In this study, a facile, novel pressure-induced filtration method involving in-situ polymerization of butyl methacrylate (BMA) was proposed for sealing ZIF-8 nanoparticles on top of polyethersulfone (PES) ultrafiltration membrane support. The developed (ZIF-8+polyBMA)/PES composite membranes with thin toplayers of <1 μm present attractive water permeance (up to 31 LMH/bar) and good rejection of Congo red (99.2 %) and Methylene blue (99.1 %). The ZIF-8 particles served as direct-through channels with superior separation performance due to their high porosity and tunable pore structure, while the interstices were successfully sealed with polyBMA by in-situ polymerization, as demonstrated by SEM and dye removal experiments. It was found that the morphology of ZIF-8 transformed from a rhombic dodecahedron to two-dimensional hexagonal nanosheets during the fabrication process. We hypothesize that this surprising phenomenon is caused by the reaction of the initiators (Na₂S₂O₅ and K₂S₂O₈) that generate the hydroxyl and sulfate radicals attacking and transforming the Zn-MIM bond network of ZIF-8. However, insights into the structural changes need to be further investigated to understand the mechanism involved.