Preparation And Performance Syudy Of Gas Separation Membranes Based On Polymer Of Intrinsic Microporosity (PIM-1)

Greenhouse gas separation,storage,and utilization are extremely urgent due to the growing climate problems and resource shortages.Polymer-based membrane separation as one of the most promising technologies for large-scale and high-efficient gas separation has been studied extensively for decades in virtue of its low-cost and energy saving process.The emergence of ultra-permeable polymers of intrinsic microporosity（PIMs）,particularly the PIM-1 with excellent solubility in common solvents,has attracted a lot of research interests towards next generation high-performance membrane fabrication for CO₂ separations.However,despite the high gas permeability and excellent workability,PIM-1 exhibits relative low gas selectivity and suffers from significant physical aging,therefore the researches focused on improving the permselectivity and long-term stability of PIM-1 based membranes have been developed rapidly in recent years.Herein,in this study,PIM-1 membranes were improved based on the design and modification of the molecular structure of PIM-1 and the preparation of hybrid matrix film by combining PIM-1with metal-organic framework nanomaterials（MOFs）.The physicochemical properties and gas separation performance of the resultant membranes were studied,and the structure-properties relationship was analyzed.The molecular structure of PIM-1 was modified by thermal treatment.An intermediate temperature range was deliberately utilized to tune PIM-1 membrane microstructure in nitrogen atmosphere to enhance gas separation performance.During intermediate thermal manipulation,the synergistic effects of thermal-induced cross-linking and decomposition on PIM-1 membranes have optimized the micropores for significantly increasing membrane molecular-sieving ability with the boosted selectivity of 350（H₂/N₂）,1472（H₂/CH₄）,3774（H₂/C₃H₈）and 197（CO₂/CH₄）respectively,with the H₂ permeability of 234 Barrer,correspondingly,surpassing the“Robeson’s Upper Bound”.Although the gas selectivity was significantly improved by the simple and easy operation of thermal-induced crosslinking and decomposition,it was accompanied by a significant reduction in gas permeability and high energy consumption of heat treatment,which is not suitable for industrial application and large-scale development.A simple and low energy consumption method was used to modify PIM-1membrane,by constructing mixed matrix membrane combined with MOFs.We developed an in-situ method to synthesize monodispersed ZIF-8 nanocrystals with unique dopamine（DA）surface decoration layer（ZIF-8-DA）in aqueous solution at room temperature.Interestingly,the in-situ formation of the monodispersed ZIF-8-DA nanocrystals experiences a triple-stage crystallization process,resulting in a rhombic dodecahedron architecture,which is greatly different from the synthesis of conventional ZIF-8.The crystallinity and abundant microporosity of ZIF-8-DA nanocrystals is well maintained even with the DA surface decoration.ZIF-8-DA was combined with PIM-1 and Matrimid polymer,respectively,to construct mixed matrix membranes.ZIF-8-DA existed good interface with both PIM-1 and Matrimid polymer.Owing to the interaction between ZIF-8-DA and the groups on Matrimid and pore properties of ZIF-8-DA,ZIF-8-DA/Matrimid mixed matrix membranes exhibit both higher gas permeability and selectivity than the pristine Matrimid polyimide membrane,which breaks out the traditional“trade-off”phenomena between permeability and selectivity.To solve the problems that poor filler-polymer interfacial compatibility,filler agglomeration,and upper limit of loading in conventional MMM synthesis methods,we designed a universal bottom-up method for in situ nanosized MOFs assembly within polymer matrices.Consequently,our method eliminating the traditional post-synthetic step significantly enhanced MOF dispersion,interfacial compatibility,and loading to an unprecedented 67.2 wt.%in synthesized MMMs.Utilizing experimental techniques and complementary density functional theory（DFT）simulation,we validated that these enhancements synergistically ameliorated CO₂ solubility,which was significantly different from other works where MOF typically promoted gas diffusion.Our approach simultaneously improves CO₂ permeability and selectivity and superior carbon-capture performance is maintained even during long-term tests;the mechanical strength is retained even with ultrahigh MOF loadings.This symbiosis-inspired de novo strategy can potentially pave the way for next-generation MMMs that can fully exploit the unique characteristics of both MOFs and matrices.