Polymer Mixed Matrix Membranes Research Articles

Recent advances in the interfacial engineering of MOF-based mixed matrix membranes for gas separation.

The membrane process stands as a promising and transformative technology for efficient gas separation due to its high energy efficiency, operational simplicity, low environmental impact, and easy up-and-down scaling. Metal-organic framework (MOF)-polymer mixed matrix membranes (MMMs) combine MOFs' superior gas-separation performance with polymers' processing versatility, offering the opportunity to address the limitations of pure polymer or inorganic membranes for large-scale integration. However, the incompatibility between the rigid MOFs and flexible polymer chains poses a challenge in MOF MMM fabrication, which can cause issues such as MOF agglomeration, sedimentation, and interfacial defects, substantially weakening membrane separation efficiency and mechanical properties, particularly gas separation. This review focuses on engineering MMMs' interfaces, detailing recent strategies for reducing interfacial defects, improving MOF dispersion, and enhancing MOF loading. Advanced characterisation techniques for understanding membrane properties, specifically the MOF-polymer interface, are outlined. Lastly, it explores the remaining challenges in MMM research and outlines potential future research directions.

Universal F4-Modified Strategy on Metal-Organic Framework to Chemical Stabilize PVDF-HFP as Quasi-Solid-State Electrolyte.

Solid-state electrolytes (SSEs) based on metal organic framework (MOF) and polymer mixed matrix membranes (MMMs) have shown great promotions in both lithium-ion conduction and interfacial resistance in lithium metal batteries (LMBs). However, the unwanted structural evolution and the and the obscure electrochemical reaction mechanism among two phases limit their further optimization and commercial application. Herein, fluorine-modified zirconium MOF with diverse F-quantities is synthesized, denoted as Zr-BDC-Fx (x = 0, 2, 4), to assemble high performance quais-solid-state electrolytes (QSSEs) with PVDF-HFP. The chemical complexation of F-sites in Zr-BDC-F4 stabilized PVDF-HFP chains in β-phase and disordered oscillation with enhanced charge transfer and Li transmit property. Besides, the porous confinement and electronegativity of F-groups enhanced the capture and dissociation of TFSI- anions and the homogeneous deposition of LiF solid electrolyte interphase (SEI), promoting the high-efficient transport of Li+ ions and inhibiting the growth of Li dendrites. The superb specific capacities in high-loaded Li.

MOF–Polymer Mixed Matrix Membranes as Chemical Protective Layers for Solid-Phase Detoxification of Toxic Organophosphates

Zirconium-based metal-organic frameworks (Zr-MOFs) have been demonstrated as potent catalysts for the hydrolytic detoxification of organophosphorus nerve agents and their simulants. However, the practical implementation of these Zr-MOFs is limited by the poor processability of their powdered form and the necessity of water media buffered by a volatile liquid base in the catalytic reaction. Herein, we demonstrate the efficient solid-state hydrolysis of a nerve agent simulant (dimethyl-4-nitrophenyl phosphate, DMNP) catalyzed by Zr-MOF-based mixed matrix membranes. The mixed matrix membranes were fabricated by incorporating MOF-808 into the blending matrix of poly(vinylidene fluoride) (PVDF), poly(vinylpyrrolidone) (PVP), and imidazole (Im), in which MOF-808 provides highly active catalytic sites, the hydrophilic PVP helps to retain water for promoting the hydrolytic reaction, and Im serves as a base for catalytic site regeneration. Impressively, the mixed matrix membranes displayed excellent catalytic performance for the solid-state hydrolysis of DMNP under high humidity, representing a significant step toward the practical application of Zr-MOFs in chemical protective layers against nerve agents.

Cationic Metal–Organic Framework-Based Mixed-Matrix Membranes for Fast Sensing and Removal of Cr2O72− Within Water

Considering that metal–organic framework (MOF)-polymer mixed-matrix membranes (MMMs) can overcome the drawbacks of intrinsic fragility and poor processability of pure-MOF membranes, we designed MOF-based MMMs for efficient removal and fast fluorescence sensing of heavily toxic ions within water systems simultaneously. In this work, a series of MOF-based MMMs are prepared by mixing a hydrolytically stable cationic [Eu7 (mtb)5(H2O)16]·NO3 8DMA·18H2O (denoted as Eu-mtb) MOF material into poly (vinylidene fluoride) with high loadings up to 70%. The free volume at the interface between the polymer and Eu-mtb particles, combined with the permanent porosity and uniform distribution of Eu-mtb particles, enables these MMMs to show fast enrichment of Cr2O7 2- from solutions and consequently have a full contact between the analyte and MOFs. The developed Eu-mtb MMM (70wt% loading) thus shows both efficient removal and exceptional fluorescence sensing of Cr2O7 2- in aqueous media. The overall adsorption capacity of the Eu-mtb MMM (70 wt% loading) for Cr2O7 2- reaches up to 33.34 mg/g, which is 3.4 times that of powder-form Eu-mtb. The detection limit of the Eu-mtb MMM (70 wt% loading) for Cr2O7 2- is around 5.73 nM, which is lower than that of the reported powder-form Eu-mtb. This work demonstrates that it is feasible to develop flexible luminescent MOF-based MMMs as a significant platform for efficient removal and sensitive sensing of pollutants from water systems simultaneously.

Magnetic field-induced improvement in O2/N2 gas separation applications of simultaneously co-casted superparamagnetic mixed matrix membranes

For industrial purposes and current challenges facing the world, the selective separation of oxygen and nitrogen gases from the air by polymer mixed matrix membranes is crucial. Due to the diamagnetic nature of water molecules used in the fabrication of the polymer membranes, the magnetic field (H) may affect the resulting separation performance. Here, using a simultaneous co-casting method, empty and superparamagnetic Fe3O4 nanoparticle-filled double-layer polyethersulfone (PES)/Pebax®1657 mixed matrix membranes are fabricated under different external magnetic field intensities in the range of H = 0–5000 Oe. The O2 and N2 permeances of the PES/Pebax® membranes are found to increase with increasing the magnetic field intensity, arising from an enhancement in the polymer chain mobility. The Fe3O4 nanoparticles form thick root-like superparamagnetic channels on the double-layer PES/Pebax® surface at a magnetic field intensity of 4000 Oe, resulting in an O2/ N2 ideal selectivity of 3.59 at a feed gas pressure of 10 bar. This indicates an improvement of 40% in the selectivity compared to a single-layer Pebax® membrane filled with Fe3O4 nanoparticles.

Polymeric mixed-matrix membranes modified with halloysite nanotubes for water and wastewater treatment: A review

Polymeric membranes are widely applied for water and wastewater treatment. However, the membranes used in the pressure driven membrane processes suffer from the undesired phenomena of fouling and biofouling. That leads to a decrease in productivity and an increase in treatment costs. The membranes used in forward osmosis, being a non – pressure driven process, are less endangered by fouling; nonetheless, due to low permeation they have limited potential in wastewater treatment. To improve the membranes performance with reference to permeability, antifouling/antibiofouling resistance and separation properties the application of various nanomaterials has been proposed. This review presents a progress in the research on the polymer mixed-matrix membranes containing pure and modified halloysite nanotubes (HNTs). The effect of HNTs on the properties and performance of membranes made of polymers such as polysulfone, polyethersulfone, polystyrene and polyvinylidene fluoride is widely discussed. Finally, the key issues to be considered in further research on the mixed-matrix membranes modified with HNTs are proposed.

Control of Physical Aging in Super-Glassy Polymer Mixed Matrix Membranes.

ConspectusSince the discovery of polymers of intrinsic microporosity (PIMs) in 2004, the fast size-selective interconnected pore cavities of the polymers have caused the upper bound of membrane performance to be revised, twice. Simultaneously, porous materials have meant that mixed matrix membranes (MMMs) are now a relatively simple method of enhancing transport properties. While there are now reliable routes with mixed matrices to improve the fundamental transport properties of membrane materials, many of the other properties crucial for separation applications remain largely unaddressed. Physical aging severely affects membrane performance over time, especially for those prepared from high fractional free volume polymers. Gradual densification of the glassy polymer chains causes the connected pore channels present in these materials to constrict. Studies now suggest that aging of superglassy polymer materials is a two-step process; a rapid densification occurs within the first few days, followed by a gradual rearrangement of packed chains over longer time frames toward a theoretical equilibrium state. Although advantageous in terms of size selectivity, the considerable drop in permeation over the days and weeks after manufacture greatly impacts material applicability. While often still permeating faster than traditional membrane materials, the continuous gradual collapse of cavities in these polymers are a significant challenge in the application of high free volume polymer membranes. In 2014, we discovered that the porous aromatic framework PAF-1 not only greatly improved the membrane's void space and speed of gas transport but also seemingly froze several glassy polymers in a low-density state, holding the polymer's pore channels open, a process termed as Porosity Induced Side chain Adsorption (PISA).This discovery of PISA fundamentally challenged the conventional wisdom at the time that the aging rate could only be addressed by densification of the polymer. Unlike other high-performance glassy polymers, membranes containing PAF-1 can retain their high permeability for more than a year. Several other examples of antiaging behavior have been subsequently reported by the team, where control of aging rate as a function of gas penetrant, selectivity increases, and stability at higher pressures was reported. These works also demonstrate that these mixed matrix systems had applicability for several other separations, including pervaporation, solvent nanofiltration, and as separators for energy applications. In our subsequent studies, the antiaging mechanism has been elucidated as an effect of the interaction between the polymer's accessible pendant methyl group and the aromatic pore surface of PAF-1 or other antiaging additives. In otherwise identical MMMs, where this hypothesized methyl-π interaction is either absent or interrupted, we find that the antiaging behavior expected by the fixation of the polymer chains to the pore surface and PAF-1 does not occur. As a design approach for mixed matrix membranes, targeted interfacial interactions are a promising pathway for developing other stable membranes, enabling the exciting class of PIM materials to improve industrial separation efficiency.

Metal Organic Framework Based Polymer Mixed Matrix Membranes: Review on Applications in Water Purification.

Polymeric membranes have been widely employed for water purification applications. However, the trade-off issue between the selectivity and permeability has limited its use in various applications. Mixed matrix membranes (MMMs) were introduced to overcome this limitation and to enhance the properties and performance of polymeric membranes by incorporation of fillers such as silica and zeolites. Metal-organic frameworks (MOFs) are a new class of hybrid inorganic–organic materials that are introduced as novel fillers for incorporation in polymeric matrix to form composite membranes for different applications especially water desalination. A major advantage of MOFs over other inorganic fillers is the possibility of preparing different structures with different pore sizes and functionalities, which are designed especially for a targeted application. Different MMMs fabrication techniques have also been investigated to fabricate MMMs with pronounced properties for a specific application. Synthesis techniques include blending, layer-by-layer (LBL), gelatin-assisted seed growth and in situ growth that proved to give the most homogenous dispersion of MOFs within the organic matrix. It was found that the ideal filler loading of MOFs in different polymeric matrices is 10%, increasing the filler loading beyond this value led to formation of aggregates that significantly decreased the MOFs-MMMs performance. Despite the many merits of MOFs-MMMs, the main challenge facing the upscaling and wide commercial application of MOFs-MMMs is the difficult synthesis conditions of the MOFs itself and the stability and sustainability of MOFs-MMMs performance. Investigation of new MOFs and MOFs-MMMs synthesis techniques should be carried out for further industrial applications. Among these new synthesis methods, green MOFs synthesis has been highlighted as low cost, renewable, environmentally friendly and recyclable starting materials for MOFs-MMMs. This paper will focus on the investigation of the effect of different recently introduced MOFs on the performance of MOFs-MMMs in water purification applications.

Towards High Performance Metal-Organic Framework-Microporous Polymer Mixed Matrix Membranes: Addressing Compatibility and Limiting Aging by Polymer Doping.

Membrane separation for gas purification is an energy-efficient and environment-friendly technology. However, the development of high performance membranes is still a great challenge. In principle, mixed matrix membranes (MMMs) have the potential to overcome current materials limitations, but in practice there is no straightforward method to match the properties of fillers and polymers (the main components of MMMs) in such a way that the final membrane performance reflects the high performance of the microporous filler and the processability of the continuous polymer phase. This issue is especially important when high flux polymers are utilized. In this work, we demonstrate that the use of small amounts of a glassy polymer in combination with high performance PIM-1 allow for the preparation of metal-organic framework (MOF)-based MMMs with superior separation properties and low aging rates under humid conditions, meeting the commercial target for post-combustion CO2 capture.

Flexible Metal-Organic Framework-Based Mixed-Matrix Membranes: A New Platform for H2 S Sensors.

Metal-organic framework (MOF)-polymer mixed-matrix membranes (MMMs) have shown great potential and superior performance in gas separations. However, their sensing application has not been fully established yet. Herein, a rare example of using flexible MOF-based MMMs as a fluorescent turn-on sensor for the detection of hydrogen sulfide (H2 S) is reported. These MOF-based MMMs are readily prepared by mixing a highly stable aluminum-based nano-MOF (Al-MIL-53-NO2 ) into poly(vinylidene fluoride) with high loadings up to 70%. Unlike the intrinsic fragility and poor processability of pure-MOF membranes, these MMMs exhibit desirable flexibility and processability that are more suitable for practical sensing applications. The uniform distribution of Al-MIL-53-NO2 particles combined with the permanent pores of MOFs enable these MMMs to show good water permeation flux and consequently have a full contact between the analyte and MOFs. The developed MMM sensor (70% MOF loading) thus shows a highly remarkable detection selectivity and sensitivity for H2 S with an exceptionally low detection limit around 92.31 × 10-9 m, three orders of magnitude lower than the reported powder-form MOFs. This work demonstrates that it is feasible to develop flexible luminescent MOF-based MMMs as a novel platform for chemical sensing applications.

Zirconium-Based Nanoscale Metal-Organic Framework/Poly(ε-caprolactone) Mixed-Matrix Membranes as Effective Antimicrobials.

Metal-organic framework (MOF)-polymer mixed-matrix membranes (MMMs) have shown their superior performance in gas separation. However, their biological application has not been well-explored yet. Herein, a series of zirconium-based MOF MMMs with high MOF loading and homogeneous composition have been prepared through a facile drawdown coating process. Poly(ε-caprolactone) (PCL) has been selected as a binder for its good biocompatibility and biodegradability. Zr-MOF nanoparticles, UiO-66, and MOF-525, have been utilized as "filler" because of their superior chemical stability, good biological safety, and versatile functions. Both UiO-66/PCL MMMs and MOF-525/PCL MMMs have a uniform appearance even at the highest loading of 50 wt % for UiO-66 and 30 wt % for MOF-525, respectively. The integrity of pore structures of UiO-66 within MMMs maintains well, which is evidenced by dye separation. All obtained MMMs possess good biocompatibility and mechanical property. Upon irradiation, MOF-525/PCL MMMs generate reactive oxygen species and serve as effective antibacterial photodynamic agents against Escherichia coli. This study offers an alternative system for forming homogeneous MOF/polymer MMMs and represents the first example of exploiting hybrid MMMs for biological applications.

Separation of proteins and antifouling properties of polyphenylsulfone based mixed matrix hollow fiber membranes

Abstract Polymer mixed matrix membranes are the state-of-the-art materials for membrane based pharmaceuticals and bio-macromolecule separation applications. The present work demonstrates the fabrication of PPSu (polyphenylsulfone) and SPPSu (Sulfonated polyphenylsulfone)/nanoparticle titanium oxide (TiO2) hollow fiber membranes by phase inversion technique. SPPSu/TiO2 hollow fiber membranes resulted on higher flux about 25.5% compare to neat membrane, and with improved thermal and mechanical properties. The tethered of nanoparticle TiO2 and sulfonation on polymer matrix tailors the surface chemistry of the composite hollow fiber membrane by altering the morphology and water permeability. Cross section morphology was analyzed using a scanning electron microscopy (SEM). Surface topography were scanned using atomic force microscope (AFM) and nanocomposite membrane resulted with smooth surfaces. The pH-dependent surface charge properties of the prepared hollow fibers were determined through electro kinetic analyzer, demonstrating that the sulfonated PPSu blend membrane surface was negatively charged. The prepared membranes were also subjected to rejection ability of varying molecular weights of proteins and assigned the molecular weight cut-off of the membranes. SPPSu/TiO2 mixed matrix membranes resulted in improved (Rt ≈ 22%) antifouling properties.

Computational Methods for MOF/Polymer Membranes.

Metal-organic framework (MOF)/polymer mixed matrix membranes (MMMs) have received significant interest in the last decade. MOFs are incorporated into polymers to make MMMs that exhibit improved gas permeability and selectivity compared with pure polymer membranes. The fundamental challenge in this area is to choose the appropriate MOF/polymer combinations for a gas separation of interest. Even if a single polymer is considered, there are thousands of MOFs that could potentially be used as fillers in MMMs. As a result, there has been a large demand for computational studies that can accurately predict the gas separation performance of MOF/polymer MMMs prior to experiments. We have developed computational approaches to assess gas separation potentials of MOF/polymer MMMs and used them to identify the most promising MOF/polymer pairs. In this Personal Account, we aim to provide a critical overview of current computational methods for modeling MOF/polymer MMMs. We give our perspective on the background, successes, and failures that led to developments in this area and discuss the opportunities and challenges of using computational methods for MOF/polymer MMMs.

Recent Progress in Zeolite/Zeotype Membranes

This is a comprehensive review of the recent progresses made in the field of zeolite membranes. It describes zeolitic materials and methods of membrane fabrication, followed by a summary of applications for gas separation, pervaporation and separation of liquid mixtures. Special attention is called to polymer mixed matrix membranes (MMMs) and membranes based on metal organic frame works (MOFs). In this comprehensive survey, the following trends were observed during the past 5 – 10 years. New zeolitic materials and new synthesis methods, such as hydrothermal synthesis, seeding and microwave heating, have been continuously reported in the literature. Many efforts have been devoted to the synthesis of hybrid or mixed matrix membranes (MMMs) since MMMs clearly outperformed polymeric membranes. MOFs also showed improved performance in gas separation. Many attempts have been made to develop thin (1µm) supported zeolite layers on a variety of carriers such as capillaries, fibers, tubes, etc. The assembly of nanozeolite building blocks and nanosheets is the starting point for the synthesis of thin defect free zeolite membranes. The present review presents the recent progresses made in the field of zeolite/zeotype membranes. Different types of zeolite membranes, methods of preparation and application aspects especially for separation of gases have been focused on, including the individual zeolites which are in use or are to be used as inorganic fillers in mixed matrix membranes (MMMs). Despite the enormous efforts of researchers, the commercialization of zeolite membranes has been achieved only in a limited area. The future works necessary to change the current situation are hence suggested.

Zeolitic imidazolate framework composite membranes and thin films: synthesis and applications

Zeolitic imidazolate frameworks (ZIFs), a subclass of metal organic frameworks, are built of tetrahedral metal ions bridged by imidazolates. They have permanent porosity and relatively high thermal and chemical stability, which make them attractive candidates for many industrial applications. In recent years, significant progress has been made in developing ZIFs into membranes and thin films for gas separation, liquid separation (pervaporation) and functional devices. Various techniques, such as direct synthesis, secondary synthesis, reactive seeding and functional chemicals as linkers, and contra-diffusion synthesis, have been reported for the fabrication of ZIF membranes and films. As ZIFs have good compatibility with polymers, they have been incorporated into polymers with high loadings to form mixed matrix membranes. The resulting symmetric dense or asymmetric composite membranes exhibit good performance in gas separation and liquid separation via pervaporation. The recent developments of ZIF membranes/films, ZIF-polymer mixed matrix membranes and their applications are reviewed in this article.

Power-law scaling behavior of membranes

The variation of the permeation properties of membranes with respect to the effective sizes of the molecules employed is investigated. Data reported in the literature corresponding to ceramic and metal-supported silicalite membranes, polymeric Teflon membranes and silicalite filled PDMS mixed matrix membranes are employed in the calculations. Additionally, experiments are performed to obtain the permeabilities of the polymeric mixed matrix membranes filled with various ion-exchanged forms of the ZSM-5 zeolite. In general, quite linear relationships are obtained between the log (permeability) and the log (size) values. This implies that the membranes investigated in this study exhibit significant size scaling behavior. For such membranes, a relatively higher degree of the size sensitivity signifies a relatively higher ability for discriminating between molecules of different sizes. This provides a unique opportunity for enhancing the selectivity values since selectivity for one component in a mixture of gas molecules of different effective sizes is related to the degree of the size sensitivity of membranes. Modification methods, such as ion-exchange, seem to have the potential of creating differences in the scaling properties of zeolite samples and thus providing higher selectivities. Increasing the loading of the zeolite in the zeolite–polymer mixed matrix membranes may also lead to a similar result in case the size sensitivity of the zeolite is relatively higher than that of the polymer. When the size scaling information is to be derived and applied for the purpose of monitoring the selectivities, attention should also be paid to the temperature and pressure ranges of applicability.