In situ conversion of ZnO to ZIF-8 in polyimide for ultra-high permeance organic solvent nanofiltration mixed matrix membranes

Mixed matrix membranes (MMMs) incorporating ZIF-8 nanoparticles through non-solvent induced phase separation (NIPS) hold great potential in the organic solvent nanofiltration (OSN) field, but their advancement and application have been significantly hindered by ZIF-8’s instability of ZIF-8 in aqueous conditions and major interfacial incompatibilities with polymers. This study presents an approach to overcome these obstacles by initially forming crosslinked ZnO/polyimide (PI) MMMs via NIPS and crosslinking processes, followed by in-situ conversion of ZnO to ZIF-8 within the membrane structure. This method prevents direct contact of ZIF-8 with water, optimizes the interface between ZIF-8 and the polymer, and modulates the pore structure of the membranes. The resulting crosslinked ZIF-8/PI membranes exhibit an ultra-high ethanol permeance of 42.7 L m⁻ 2  h⁻ 1  bar⁻ 1 and a 99.5 % rejection of Rose Bengal dye, surpassing the performance of all state-of-the-art OSN MMMs to our knowledge. Additionally, these membranes also demonstrate excellent separation performance in harsh solvents such as DMF and NMP. The findings of this study not only significantly advance the development of OSN membranes but also offer insights into the optimization of membrane fabrication techniques, setting a new benchmark for the design of high-performance OSN membranes.