Mixed-matrix membranes (MMMs) with an ideal polymer−filler interface and high gas separation performance are very challenging to fabricate because of incompatibility between the fillers and the polymer matrix. This work provides a simple technique to prepare a series of cross-linked MMMs (xMMM@n) by covalently attaching UiO-66-NB metal−organic frameworks (MOFs) within the PEG/PPG−PDMS copolymer matrix via ringopening metathesis polymerization and in situ membrane casting. The norbornene-modified MOF (UiO-66-NB) is successfully copolymerized and dispersed homogeneously into a PEG/PPG− PDMS matrix because of very fast polymer formation and strong covalent interaction between MOFs and the rubbery polymer. A significant improvement in gas permeability is achieved in membranes up to a 5 wt % MOF loading compared to the pristine polymer membrane without affecting selectivity. The CO 2 /N 2 separation performance of xMMM@1, xMMM@3, and xMMM@5 with 1, 3, and 5 wt % MOF loading, respectively, surpassed Robeson's 2008 upper bound. In addition, the best performing membrane, xMMM@3 (P CO 2 = 585 Barrer and CO 2 /N 2 ∼53), approaches the 2019 upper bound, indicating that the cross-linked MMMs (xMMM@n) are very promising for CO 2 separation from flue gas. The experimental results of our study were evaluated and are supported by theoretical data obtained using the Maxwell model for MMMs. Moreover, the developed MMMs, xMMM@ns, displayed outstanding antiplasticization performance at pressures of up to 25 atm and very stable antiaging performance for up to 11 months with good temperature switching behaviors.
Polymer membranes with excellent thermomechanical properties and good gas separation performance are desirable for efficient CO2 separation. A series of copolyimide membranes are prepared for the first time using PIM-PI-1, a hard segment with high CO2 permeability, and poly(ethylene glycol)/poly(propylene glycol) (PEG/PPG), a soft segment with high CO2 selectivity. Two different unit polymers are combined to compensate the limitations of each polymer (e.g., the fast aging and moderate selectivity of PIM-PI-1 and the poor mechanical properties and lower permeability of PEG/PPG). The corresponding PIM-(durene–PEG/PPG) membranes exhibit an excellent combination of mechanical properties and gas separation performance compared to the typical PI-PEG-based copolymer membrane. The improved mechanical property is attributed to the unique chain threading and the reinforcement between the spiro unit of PIM and the flexible PEG/PPG at the molecular level, which has not previously been exploited for membranes. The PIM-(durene–PEG/PPG) membranes show a high CO2 permeability of 350–669 Barrer and a high CO2/N2 selectivity of 33.5–40.3. The experimental results are further evaluated with theoretical results obtained from molecular simulation studies, and a very good agreement between the experimental results and simulation results is found. Moreover, the PIM-(durene–PEG/PPG) copolymer membranes display excellent anti-aging performance for up to 1 year.
Metal–organic framework (MOF) incorporated mixed–matrix membranes (MMMs) attract great interest for gas separation applications because they overcome limitations faced by typical polymer membranes, including permeability–selectivity trade‐off, aging effect, and plasticization phenomenon. However, optimal MOF–polymer interface compatibility is the key challenge in fabricating defect‐free high‐performance gas‐separation MMMs. Here, a surface modification strategy of the UiO‐66‐NH2 MOF using a covalently bound PIM‐PI‐oligomer is developed to engineer interface compatibility with the polymer that has an identical chemical structure (PIM‐PI‐1) in the MMMs. A series of MMMs are prepared with different loadings of homogeneously distributed PIM‐PI‐functionalized MOFs (PPM). Significant improvements in CO2/N2 and CO2/CH4 selectivity and permeability are achieved with these MMMs, ranging from 5 to 10 wt% of the PPM loadings. The MMM with 10 wt% loading (PPM‐10@MMM) shows a CO2 permeability of 3827.3 Barrer and a CO2/N2 and CO2/CH4 selectivity of 24 and 13.4, respectively. This surpasses the 2008 Robeson upper bound for CO2/N2 and is very close to the 2008 upper bound for CO2/CH4. The experimental results are further compared using Maxwell's equation for MMMs. The resulting MMMs show a plasticization resistance against CO2 up to 25 atm pressure and anti‐aging performance for 180 h.
Mixed matrix membranes (MMMs) have attracted significant attention for overcoming the limitations of traditional polymeric membranes for gas separation through the improvement of both permeability and selectivity. However, the development of defect-free MMMs remains challenging due to the poor compatibility of the metal–organic framework (MOF) with the polymer matrix. Thus, we report a surface-modification strategy for a MOF through grafting of a polymer with intrinsic microporosity onto the surface of UiO-66-NH2. This method allows us to engineer the MOF–polymer interface in the MMMs using Pebax as a support. The insertion of a PIM structure onto the surface of UiO-66-NH2 provides additional molecular transport channels and enhances the CO2 transport by increasing the compatibility between the polymer and fillers for efficient gas separation. As a result, MMM with 1 wt% loading of PIM-grafted-MOF (PIM-g-MOF) exhibited very promising separation performance, with CO2 permeability of 247 Barrer and CO2/N2 selectivity of 56.1, which lies on the 2008 Robeson upper bound. Moreover, this MMM has excellent anti-aging properties for up to 240 days and improved mechanical properties (yield stress of 16.08 MPa, Young’s modulus of 1.61 GPa, and 596.5% elongation at break).
In this study, we report a series of ether bond-free (i.e., full carbon backbone) copolymers, prepared for the first time by a simple one-step Friedel−Crafts (F−C) polycondensation reaction using biphenyl-isatin (BP-Isa), a torsion-resistant rigid segment with high CO 2 selectivity, and biphenyl-trifluoroacetophenone (BP-TFAPh), a highly permeable ladder-type segment. The copolymer exhibits a high molecular weight, moderate BET surface area, and excellent thermophysical properties. (BP-Isa) x -(BP-TFAPh) y copolymers containing over 50% TFAPh loading show a perfect combination of mechanical properties and gas separation properties, outperforming most commercial gas separation polymers, most F-C polymers, and high-performance PIM-PI-1 polymer membranes. (BP-Isa) x -(BP-TFAPh) y copolymer membranes with loadings over 50% also exhibited a good CO 2 permeability of 394−526 Barrer and good CO 2 /N 2 and CO 2 /CH 4 selectivities of 24.4−29.0 and 19−25, respectively. Also, the 50:50 composition of the copolymer films exhibited excellent antiaging properties for up to one month, with good resistance to plasticization at pressures of up to 15 atm.
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