Mixed-Matrix Membranes Formed from Imide-Functionalized UiO-66-NH₂ for Improved Interfacial Compatibility

Abstract

Mixed-matrix membranes (MMMs) formed by dispersing metal–organic framework (MOF) particles in polymers have attracted significant attention because these composite systems can potentially surpass the separation performance of pure polymers alone. However, performance improvements are often unrealized because of poor interfacial compatibility between the MOF and the polymer, which results in interfacial defects. From a practical perspective, strategies are needed to address these defects so that MMMs can be deployed in real-world separation processes. From a fundamental perspective, strategies are needed to reliably form defect-free MMMs so that transport models can be applied to estimate pure MOF property sets, thereby enabling the development of robust structure–property relationships. To address these interfacial challenges, we have developed a method to surface-functionalize a UiO-66-NH 2 MOF with a nanoscopic shell of covalently tethered 4,4′-(hexafluoroisopropylidene)diphthalic anhydride–Durene oligomers. When combined with a high-molecular-weight polymer of identical chemical structure to that of the imide-functional MOF surface, defect-free MMMs with uniform particle dispersions can be formed. With this technique, both permeabilities and selectivities of select gases in the MMMs were improved at loadings ranging from 5 to 40 wt %. At a 40 wt % loading, CO 2 permeability and CO 2 /CH 4 selectivity were enhanced by 48 and 15%, respectively. Additionally, pure MOF permeabilities for H 2 , N 2 , O 2 , CH 4 , and CO 2 were predicted by the Maxwell model.

Enhancing the Separation Performance of Glassy PPO with the Addition of a Molecular Sieve (ZIF-8): Gas Transport at Various Temperatures

“…MOFs have been proven to have a higher affinity with organic polymer matrices with respect to zeolites, given the organic nature of the linkers that connect the metal clusters to one another [30]. Nevertheless, different strategies have been developed to further increase the interfacial compatibility between the components of MOF-based MMMs [31][32][33].…”

A Physical Entangling Strategy for Simultaneous Interior and Exterior Modification of Metal–Organic Framework with Polymers

“…For instance, to improve the interfacial compatibility in MOF‐based mixed matrix membranes (MMMs), the most pursued approach is to covalently anchor functional moieties to a reactive group such as ‐NH 2 , ‐OH, ‐N 3 , or ‐COOH native to the MOF structure [20, 27–31] . The strong linkage between the polymer and the MOF reduces the possibility of interfacial separation thereby avoiding defect formation in the membrane [20, 32–35] . Nevertheless, many MOFs do not possess suitable reactive functional groups for grafting thus limiting the extended application of this method.…”

Effects of different porous fillers on interfacial properties of poly (vinyl alcohol) hybrid films

“…At present, the hybridization method seems to be the most attractive to many researchers since respective superior features of both polymer matrix and filler materials can be well retained, including the easy processability and mechanical integrity of PVA and the flexible selection of the type and loading of porous fillers 16–18 . Furthermore, the addition of porous fillers can not only alter the bulky matrix microstructure of PVA but also influences the hydrophilic feature of PVA hybrids, subsequently affecting the film separation performance 16,18,19 . For example, Deng et al 20 have reported a non‐drying, water‐based method to fabricate a high‐quality ZIF‐8 (39 wt%)/PVA hybrid film for the dehydration of an ethanol/water mixture (90:10 in wt%) at 25°C and they found that compared to the permeability of 5.64 × 10 −5 cm 3 ·cm/(cm 2 ·s·kPa) and separation factor of 543 for the neat PVA film, the hybridization has greatly promoted both values, respectively, to 1.56 × 10 −4 cm 3 ·cm/(cm 2 ·s·kPa) and 4725.…”

“…In our earlier works, 10,11 the embedded zeolites of ZSM‐5 and Hβ into PVA have greatly boosted pervaporation separation selectivity and retained permeance for the isopropanol dehydration, probably due to the favorable hydrophilic and rigid porous features of zeolite as verified by the results of swelling and water contact angle tests. All these works tend to suggest, the embedded porous fillers must maintain a proper balance between hydrophilicity and hydrophobicity for successful dehydration performances 19,21 . Therefore, it is of great significance to explore the interfacial properties of the hybrid films so as to better understand the resultant separation performance.…”