The membrane also maintained stable pervaporation performance during 14 days of continuous operation, including at elevated temperatures. Reported in the Journal of Materials Science , the research investigated how membrane-fabrication conditions influenced structure, characteristics and dehydration performance. Chitosan formed the principal polymer matrix, while Fe₃O₄ nanoparticles created a mixed matrix membrane.

The nanoparticles were oriented with magnetic assistance during preparation, and STP served as the cross-linking agent. The investigators varied three main parameters: magnetic-field application, Fe₃O₄ content and STP concentration. The best reported formulation incorporated 5 wt% Fe₃O₄ in the chitosan matrix under a magnetic field and used 3 wt% STP cross-linking on a porous support.

The study therefore examined a specific membrane design as well as the effects of the selected preparation variables. The team used an extensive analytical suite to characterize the modifier and resulting membranes. Fourier-transform infrared and nuclear magnetic resonance spectroscopy, X-ray powder diffraction, dynamic light scattering and X-ray photoelectron spectroscopy were employed to examine chemical and structural characteristics.

Swelling tests, contact-angle assessments and mechanical-property evaluations characterized other aspects of membrane performance. Together, these methods were used to validate the structure and properties of the chitosan-based membranes under different preparation conditions. Computational analysis was also conducted to investigate interactions between the membrane and components of the feed, adding an interpretation of the observed separation behavior to the experimental characterization.

The transport results were reported across a broad composition range of 12–90 wt% water in the isopropanol feed. The optimized cross-linked supported membrane combined a permeation flux range of 0.13–0.65 kg/(m² h) with a separation index of at least 725 kg/(m² h) and water permeance of at least 3,577 GPU. These are material-level measurements from laboratory pervaporation experiments.

The reported evidence concerns membrane preparation, characterization and operation under the tested conditions rather than performance in a complete industrial isopropanol-production system. Continuous testing showed that the membrane retained stable pervaporation performance for 14 days, and the test included operation at elevated temperatures. The results support magnetic-field-assisted Fe₃O₄ incorporation as a way to improve the measured pervaporation characteristics of chitosan membranes for isopropanol dehydration.

The optimized combination of 5 wt% Fe₃O₄, 3 wt% STP, a porous support and magnetic assistance produced the strongest reported separation parameters while preserving performance over the reported continuous test.

Subject of Research: Magnetic Fe₃O₄ mixed matrix membranes for pervaporative dehydration of isopropanol

Article Title: Chitosan-based mixed matrix membranes with magnetically oriented Fe3O4 nanoparticles for enhanced pervaporation dehydration of isopropanol

Article References: Kuzminova, A., Dmitrenko, M., Stepanova, A., Mazur, A., Lisovenko, A., & Penkova, A. (2026). Chitosan-based mixed matrix membranes with magnetically oriented Fe3O4 nanoparticles for enhanced pervaporation dehydration of isopropanol. Journal of Materials Science, 61(40), 31358-31394. https://doi.org/10.1007/s10853-026-13626-7

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13626-7

Keywords: chitosan membranes, Fe₃O₄ nanoparticles, magnetic alignment, mixed matrix membranes, pervaporation, isopropanol dehydration, water separation, sodium tripolyphosphate, membrane transport, polymer membranes, Chitosan-based, mixed

The core challenge is one of dilution. Traditional helium recovery relies on cryogenic separation, in which the natural gas is chilled until the methane, nitrogen, and heavier hydrocarbons condense, leaving a helium-rich vapor that can be further refined to very high purity. This approach works well for feeds with substantial helium content, but it becomes progressively less economical as the helium concentration falls. When the helium content drops below roughly 0.1 mole percent, the refrigeration duty required to condense everything else around the helium becomes punishing, and the economics collapse. Because many of the remaining helium resources sit in exactly such lean streams, the industry has been searching for pre-concentration technologies that can enrich helium before it reaches the cryogenic stage, thereby shrinking the downstream load. Membranes have emerged as the leading candidate for that bulk pre-enrichment role.

The review emphasizes that dilute helium recovery is fundamentally a partial-pressure-limited problem. In a membrane separator, gases permeate through a selective barrier in response to the difference in their partial pressures across it. When helium is present at a few hundred parts per million, the partial pressure driving its transport is tiny, which caps the achievable flux and forces designers to think carefully about stage cuts, pressure ratios, and the composition of the residue stream. The authors stress that laboratory data gathered with pure gases or idealized binary mixtures can be misleading in this regime. Real natural gas carries carbon dioxide, hydrogen sulfide, water vapor, and heavy hydrocarbons that compete for permeation, plasticize polymer films, foul surfaces, and shift selectivity. The review therefore calls for mixed-gas validation under realistic impurity envelopes as a prerequisite for any credible performance claim, a point that separates rigorous membrane engineering from optimistic single-gas screening.

On the materials side, the review surveys the full spectrum of membrane platforms. Polymeric membranes, the commercial workhorses of gas separation, offer manufacturability and low cost but face the classic trade-off between permeability and selectivity, along with aging and plasticization under aggressive feeds. Carbon-based membranes, derived from the pyrolysis of polymer precursors, deliver superior molecular sieving and thermal stability but remain difficult to produce defect-free at scale. Inorganic membranes, including zeolites and other crystalline or dense ceramic systems, promise exceptional stability and selectivity yet carry high fabrication costs and brittle mechanics. Mixed-matrix membranes attempt to combine the best of both worlds by embedding selective fillers such as zeolites or metal-organic frameworks into polymer matrices, boosting transport properties while retaining processability. For each class, the review highlights the same triad of practical concerns: long-term stability in the presence of carbon dioxide, hydrogen sulfide, water, and heavy hydrocarbons; defect control during fabrication, since even rare pinholes can erode selectivity; and the leap from flat-sheet laboratory samples to industrially relevant modules.

That leap to module scale is where many promising materials have historically faltered. A membrane that performs brilliantly as a small coupon must be spun into hollow fibers or cast into spiral-wound modules with thousands of square meters of area, packed densely, and sealed reliably. Defects introduced during spinning, potting, or handling can dominate the separation behavior of the whole module, and reproducibility at manufacturing scale remains a recognized bottleneck. The review treats robust module-scale manufacturing as a key challenge standing between laboratory selectivity records and field deployment, alongside the need for standardized testing protocols that allow different materials to be compared on equal footing.

Process integration emerges from the review as the decisive lever for lean feeds. Single-stage membrane units rarely deliver both the recovery and the purity that helium markets demand, so the literature converges on multi-stage membrane cascades in which permeate streams are recompressed and passed through successive separators, with recycle loops managing the trade-off between recovery and enrichment. Even more effective, according to the assessment, are hybrid configurations that pair membranes with cryogenic distillation or with pressure swing adsorption. In a membrane-cryogenic hybrid, the membrane unit performs the bulk pre-enrichment, cutting the volumetric flow that must be refrigerated and thereby slashing the energy and capital cost of the cold box. In a membrane-adsorption hybrid, the membrane concentrates helium into a window where pressure swing adsorption units, including advanced rapid-cycle designs such as DR-PSA, can polish the stream to specification. The review identifies these hybrids as the most effective configurations for lean feeds, with advanced pressure swing adsorption concepts also emerging as competitive non-cryogenic routes for selected feed compositions.

The techno-economic analysis in the review makes clear that feasibility is not a property of the membrane alone but of the whole process context. Feed composition governs how much contaminant removal is needed upstream and how aggressively the membrane can be driven. Utility availability, particularly the access to compression, vacuum, and refrigeration capacity at a given gas processing site, shapes which hybrid architecture makes sense. The intermediate enrichment target, the helium concentration the membrane stage must deliver to the downstream unit, becomes the central design variable that ties recovery, purity, membrane area, and energy consumption together. The review highlights how these site-specific factors, rather than intrinsic membrane selectivity alone, determine whether a project pencils out economically.

The overall verdict from the literature is consistent: membranes are most advantageous as pre-enrichment steps that reduce downstream refrigeration or adsorption duty. Deployed this way, they enable cost-effective recovery at moderate helium levels and extend economic viability toward leaner feeds when embedded in optimized hybrid schemes. This positioning plays to the strengths of membrane technology, which excels at bulk removal of the dominant components but struggles to deliver final helium purity from a dilute feed in a single pass. Rather than competing head-to-head with cryogenics, membranes are best understood as a force multiplier for the existing separation infrastructure, shrinking the refrigeration load and opening helium resources that would otherwise remain stranded.

Significant hurdles remain before this vision becomes routine practice. Long-term membrane stability under sustained exposure to carbon dioxide, hydrogen sulfide, water, and heavy hydrocarbons must be demonstrated over the multi-year lifetimes that gas processing economics require. Robust, defect-free module-scale manufacturing must mature from artisanal achievement to dependable industrial process. And the review notes a subtler methodological gap: the field needs consistent integration of process, economic, and environmental metrics so that membrane hybrids, cryogenic plants, and adsorption systems can be compared fairly across studies. As helium demand from semiconductor fabrication and medical imaging continues to climb while conventional reserves tighten, the ability to scavenge trace helium from lean natural gas may shift from a research aspiration to a strategic necessity, and membrane technology, properly integrated, appears positioned to lead that transition.

Subject of Research: Membrane-based helium recovery from natural gas, covering membrane materials, hybrid process integration, and techno-economic feasibility for lean gas feeds.

Article Title: Advances in membrane-based helium recovery from natural gas: materials, process integration, and techno-economic perspectives

Article References: Gorgi, A., Yousefi, M. M., Jafari, M., & Abbasi, M. (2026). Advances in membrane-based helium recovery from natural gas: materials, process integration, and techno-economic perspectives. Frontiers in Membrane Science and Technology, 5, Article 1778324. https://doi.org/10.3389/frmst.2026.1778324

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1778324

Keywords: helium recovery, natural gas, membrane separation, gas separation membranes, mixed-matrix membranes, cryogenic hybrid processes, pressure swing adsorption, techno-economic analysis, partial-pressure-limited separation, module-scale manufacturing, membrane stability, process integration

MOFs are built from metal nodes connected by organic linkers, a modular construction that gives chemists unprecedented control over both pore structure and pore chemistry. They combine exceptionally high surface areas with tunable pore sizes, adjustable organic functionality, architectural flexibility, and thermal and physical stability. This designability sets them apart from conventional porous materials such as zeolites and activated carbons. MOFs can be deployed not only as pure crystalline films but also as fillers dispersed within polymer matrices to form mixed-matrix membranes, known as MMMs. The review, published on 6 August 2026, focuses on how three design strategies—fine-tuning of pore size, functional group engineering, and hybridization with complementary materials—can be tailored to the transport requirements of specific gas pairs, including hydrogen, carbon dioxide, olefin/paraffin mixtures, and oxygen/nitrogen separation.

Pore size engineering is the first and perhaps most fundamental lever. Because MOF apertures can be adjusted through linker length variation, ligand composition, metal center selection, framework flexibility, defect engineering, and post-synthetic treatment, researchers can dial in molecular sieving behavior with sub-angstrom precision. The review highlights ammonia-induced treatment of ZIF-8, which alters the local framework structure and promotes a more rigid selective pathway, and defect-engineered UiO-66, which simultaneously tunes microporosity and mass transport. Strategies such as the polymer-in-cage approach, in which polymers are introduced directly into MOF pore windows, allow separation performance to be optimized for target gases while preserving the intrinsic framework. The message is clear: MOFs should be viewed not simply as porous fillers but as platforms for designing pore environments tailored to specific gas pairs.

Functional group engineering provides the second lever, and it works on two fronts at once. Polar groups such as amino (-NH2) and carboxyl (-COOH) functionalities enhance interactions with acidic gases like CO2 while simultaneously improving interfacial compatibility with polymer matrices. Amino-functionalized ZIF-8-NH2 and UiO-66-NH2 form hydrogen bonds and pi-pi interactions with polymer chains, suppressing interfacial void formation and enabling defect-free MMMs even at high filler loadings. In TEPA-functionalized MIL-101(Cr)/Pebax membranes, grafted amine groups significantly enhanced CO2/CH4 separation by increasing affinity toward CO2. COOH-functionalized MOFs go further: in UiO-66-COOH-based MMMs, thermal treatment induced a dual-crosslinked network between polymer and MOF, enhancing molecular sieving and substantially improving CO2/N2 ideal selectivity. Functional group engineering thus offers not only enhanced gas affinity but also interfacial stabilization, defect suppression, and control over polymer chain packing.

Hybridization with other materials constitutes the third strategy. Graphene oxide nanosheets have proven particularly effective additives: in GO-modified MOF-74/Pebax membranes, GO suppressed MOF aggregation and extended the gas diffusion pathway, markedly improving CO2/N2 ideal selectivity, while in GO-assisted assembly of CuBDC nanosheet membranes, GO filled the voids between rigid nanosheets to enhance continuity and mechanical stability. Ionic liquids add another dimension. In [EMIM][OAc]/CuBTC/Pebax hybrid membranes, incorporation of the IL/MOF composite improved both CO2 permeability and CO2/N2 ideal selectivity, with some membranes even surpassing the Robeson upper bound, the empirical performance ceiling for polymer membranes. Crosslinking strategies between polymers and MOFs, such as chemical crosslinking in Mg-MOF-74/PIM-1 membranes, generate interconnected microporous networks while suppressing polymer chain mobility and interfacial voids.

Hydrogen separation showcases the power of these strategies in their purest form. Because H2 has an extremely small kinetic diameter, sub-nanometer MOF pores can sieve it efficiently from larger molecules. An ammonia-treated ZIF-8 membrane achieved an H2 permeance of 376 gas permeation units (GPU) with an H2/N2 ideal selectivity of 122.4. A CuBDC-NO2 nanosheet membrane exploited controllable stacking of MOF nanosheets to regulate the effective aperture to 0.372 nanometers, delivering an H2 permeance of 1,326 GPU together with H2/CO2 and H2/CH4 selectivities of 266 and 536, respectively. Hybrid architectures pushed performance further: a GO-assisted CuBDC nanosheet membrane reached 2,867 GPU with an H2/CO2 separation factor of 95.1, a MOF-801@MXene membrane combined MOF porosity with well-defined MXene nanochannels for 2,334 GPU, and a soft-solid Zn2(Bim)4/polyamide composite delivered an exceptional H2/CO2 separation factor of 1084 by pairing straight interlayer galleries for rapid H2 transport with a polyamide layer that healed non-selective defects.

Carbon dioxide separation is the most extensively investigated application, and the review documents how defect engineering, functionalization, crosslinking, and hybridization all contribute. Defect-engineered UiO-66/PEGDA MMMs introduced additional microporosity, yielding a CO2 permeability of 470 Barrer with a CO2/N2 ideal selectivity of 41, roughly a four-fold permeability increase over the pristine polymer. A polymer-in-cage strategy using high-aspect-ratio NZIF-8 nanoplates created tortuous diffusion pathways, achieving a CO2 permeance of 333 GPU with a CO2/N2 ideal selectivity of 80. Amino-functionalized ZIF-8-NH2 in a carboxyl-containing polyimide enabled defect-free fabrication at 50 weight percent filler loading with a CO2/CH4 ideal selectivity of 89.4. Ionic-liquid-modified MOF-177/Pebax membranes achieved a remarkably high CO2/N2 ideal selectivity of 622. Perhaps most strikingly, MOF-derived glass membranes, which eliminate crystalline grain boundaries while maintaining continuous transport pathways, achieved a CO2 permeability of 19,157 Barrer in a MIL-101/coordination-polymer-glass composite and a CO2 permeance of 37,000 GPU in a topology-engineered ZIF-derived glass.

Beyond hydrogen and carbon dioxide, MOF membranes are tackling separations once considered nearly impossible for polymers. Olefin/paraffin separation is industrially vital but difficult because the gas pairs share very similar molecular sizes and physicochemical properties. Defect-engineered AZIF-8 nanoparticles enhanced framework rigidity and molecular sieving precision while improving polymer compatibility, allowing 6FDA-DAM/AZIF-8 MMMs to reach a propylene permeability of 79.4 Barrer with a propylene/propane ideal selectivity of 39.8. Layered MOF membranes modified with an ionic liquid/AgBF4 composite exploited silver-mediated facilitated transport, transforming an intrinsically non-selective membrane into an olefin-selective one with mixed-gas separation factors of 28.8 for propylene/propane and 12.0 for ethylene/ethane. Gallate-based MOFs also emerged as promising fillers: a Co-gallate/PIM-1 MMM with a three-dimensionally interconnected porous framework achieved a propylene permeability of 3,552 Barrer with a selectivity of 8.8, improvements of 106.5 and 131.6 percent over pristine PIM-1. For air separation, an o-carborane-modified ZIF-8/PIM-1 membrane combined molecular sieving with preferential nitrogen adsorption inhibition, achieving an O2 permeability of 796.5 Barrer and an O2/N2 separation factor of 8.9, surpassing the 2015 Robeson upper bound.

The review is careful to note that reported performance values from different studies were obtained under different temperatures, pressures, feed compositions, and membrane thicknesses, and should not be interpreted as direct quantitative comparisons. It also acknowledges that practical deployment still faces significant hurdles: scale-up fabrication, substrate adhesion, defect formation during growth or activation, and stability under humidity, pressure, and gas impurities. Pure MOF films suffer from grain-boundary defects and mechanical fragility, while MMMs are limited by filler agglomeration, interfacial voids, plasticization, and physical aging, especially under mixed-gas and high-pressure conditions. Future progress, the authors argue, will depend on more robust interface-engineering strategies, more scalable fabrication routes, and more realistic testing protocols that reflect industrial operating environments.

Even with these caveats, the trajectory is unmistakable. The modular combination of metal nodes and organic linkers gives MOFs a degree of structural diversity and chemical tunability that no other membrane material class currently matches. By linking pore architecture, pore chemistry, and interfacial design to the transport behavior of target gas systems, MOF-based membranes are converging on solutions to the permeability-selectivity trade-off that has constrained polymer membranes for decades. As materials design and process integration mature, these crystalline frameworks are expected to play an increasingly central role in energy-efficient separations, from hydrogen purification for the emerging hydrogen economy to carbon capture at industrial scale, positioning MOFs as a foundational platform for next-generation membrane technology.

Subject of Research: Metal-organic framework membranes for gas separation

Article Title: Designable features of metal-organic frameworks for diverse gas separation membranes

Article References: Son, H. J., & Lee, C. S. (2026). Designable features of metal-organic frameworks for diverse gas separation membranes. Frontiers in Membrane Science and Technology, 5, Article 1909558. https://doi.org/10.3389/frmst.2026.1909558

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1909558

Keywords: metal-organic frameworks, gas separation, membranes, hydrogen purification, carbon dioxide capture, mixed-matrix membranes, pore size engineering, functional group engineering, graphene oxide, ionic liquids, olefin paraffin separation, Robeson upper bound

The choice of base polymer is deliberate. Polyvinylidene fluoride, or PVDF, is a semi-crystalline fluoropolymer prized for its thermal stability, chemical resistance, mechanical strength, and ease of processing, properties that stem from strong dipole interactions between fluorine and carbon atoms along its backbone. It is also piezoelectric and ferroelectric, which has made it popular in sensors and energy devices as well as membranes. But in water treatment, PVDF carries a stubborn flaw: it is intrinsically hydrophobic. Water molecules do not spread readily across its surface, so permeability suffers, fouling takes hold more easily, and operating costs climb as pumps work harder to push water through reluctant pores.

Forward osmosis offers a way around the energy penalty of pressure-driven desalination. Instead of forcing water through a membrane with hydraulic pressure, as reverse osmosis does, FO exploits the natural tendency of water to diffuse from a solution of low osmotic pressure to one of high osmotic pressure. A concentrated draw solution, in this study a 2 molar sodium chloride brine, pulls water across a semipermeable membrane from the feed side. The process runs under mild conditions, achieves high water recovery, and fouls less than pressure-driven systems, but its efficiency hinges on the membrane itself, and hydrophobic PVDF has long been a limiting factor.

Enter hydroxyapatite, the calcium phosphate mineral that gives bones and teeth their strength. The team synthesized ultralong hydroxyapatite nanowires, abbreviated UHA, using a solvothermal method in which calcium chloride, sodium hydroxide, sodium dihydrogen phosphate, oleic acid, water, and methanol were sealed in a Teflon-lined stainless-steel autoclave and heated at 180 degrees Celsius for 24 hours. Oleic acid plays a key role, guiding the mineral to grow into exceptionally long, high-aspect-ratio wires rather than bulky particles. These nanowires are hydrophilic, chemically stable, and biocompatible, and their hydroxyl and phosphate surface groups form strong hydrogen bonds with water and with the surrounding polymer, making them ideal candidates for membrane modification.

Fabrication followed the workhorse route of membrane science: non-solvent-induced phase inversion. The researchers dispersed UHA nanowires in dimethylformamide by stirring and ultrasonication, dissolved PVDF at about 70 degrees Celsius to form a transparent casting solution, and let it rest overnight to release trapped air. The solution was then cast onto glass with a knife set to 200 micrometers and plunged into a water bath, where phase inversion locked in the membrane’s asymmetric structure. Six compositions were prepared, containing 0, 0.1, 0.3, 0.5, 0.7, and 1.0 weight percent UHA relative to PVDF, allowing the team to trace exactly how filler loading reshaped the material.

Characterization told a consistent story across three techniques. X-ray diffraction showed the characteristic PVDF crystalline peak near 2θ of 20 degrees alongside new hydroxyapatite peaks between 25 and 35 degrees, whose intensity grew steadily with loading while the polymer peaks stayed put, evidence that PVDF and UHA interact physically without forming new chemical phases. Infrared spectroscopy confirmed the same picture: hydroxyl bands between 3,200 and 3,500 wavenumbers strengthened with UHA content, phosphate vibrations appeared in the 875 to 1,030 and 560 to 600 regions, and the polymer’s own carbon-hydrogen and carbon-fluorine signatures remained essentially unchanged. Scanning electron microscopy revealed the morphological payoff, with pristine membranes showing semi-dense, poorly defined surfaces while the composites developed homogeneous, interconnected pores and, at 1.0 percent loading, a tangled, carpet-like fibrous network resembling nacre in cross-section.

Wettability measurements tied the chemistry directly to performance. The mean flow pore size rose from about 0.14 micrometers in the pristine membrane to roughly 0.26 micrometers at moderate filler loading, and the water contact angle fell as nanowires accumulated, confirming that the hydroxyl and phosphate groups raised surface energy and eased the membrane’s embrace of water. More hydrophilic surfaces mean less resistance to water transport and fewer opportunities for contaminants to stick. The improvements were not without cost, however. Tensile testing showed Young’s modulus dropping from about 70 to 25 megapascals and elongation at break falling from 600 to 250 percent as UHA content increased, a shift from ductile toward more brittle behavior caused by rigid particles restricting polymer chain movement and creating stress concentration sites.

In forward osmosis tests with distilled water as feed and 2 molar sodium chloride as draw, run for over three hours with mass logged every minute, the membranes delivered water fluxes between 2.1 and 3.6 LMH and reverse salt fluxes between 13 and 66 grams per square meter per hour. The best water flux came at the highest UHA loading, but the selectivity picture was more nuanced. The membrane containing 0.5 percent nanowires, designated M3, showed a notably lower reverse salt flux than the trend, suggesting an optimal balance where improved structural homogeneity suppresses salt transport while preserving water permeability. At higher loadings, additional interfacial pathways appear to open, letting salt slip back toward the feed and eroding the driving force. The authors note that precise control of the additive ratio is therefore essential to reconcile permeability, selectivity, and long-term stability.

The composite membranes also held their performance over time, with no decline in water flux during extended operation, a sign of improved fouling resistance and reduced salt accumulation on the surface. Compared with previously published PVDF-based forward osmosis membranes tested under similar conditions, the PVDF/UHA results fall squarely within the range reported for thin-film composite and modified PVDF systems, validating the fabrication method while pointing to room for further gains. Beyond desalination, the researchers see applications in wastewater treatment and even in separating and concentrating precious metals and dyes from solution, where hydrophilic, fouling-resistant membranes are equally valuable.

What makes the work compelling is its economy of means. Rather than designing an entirely new polymer or resorting to exotic nanomaterials, the team combined two robust, well-understood substances, a durable fluoropolymer and a bone-like calcium phosphate, and let their complementary properties do the work. The nanowires’ extraordinary length allows them to interpenetrate and reinforce the polymer matrix, building interconnected water channels that blunt internal concentration polarization, the hidden enemy of forward osmosis efficiency. The trade-off in mechanical flexibility is real, and the salt selectivity at high loadings still needs tuning, but the study demonstrates that a 70 percent jump in water flux can be achieved with a straightforward blending step. As freshwater demand rises and desalination plants multiply worldwide, such incremental but meaningful improvements in membrane design may prove to be exactly the kind of practical innovation the water sector needs.

Subject of Research: Mixed-matrix PVDF membranes reinforced with ultralong hydroxyapatite nanowires for enhanced forward osmosis desalination

Article Title: Ultralong hydroxyapatite nanowire-incorporated PVDF mixed-matrix membranes for enhanced forward osmosis performance

Article References: Gomaa, M. G., Abdel-Aal, E.-S. A., Russo, F., Galiano, F., Figoli, A., & Abdel-Ghafar, H. M. (2026). Ultralong hydroxyapatite nanowire-incorporated PVDF mixed-matrix membranes for enhanced forward osmosis performance. Frontiers in Membrane Science and Technology, 5, Article 1894848. https://doi.org/10.3389/frmst.2026.1894848

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1894848

Keywords: forward osmosis, desalination, PVDF, hydroxyapatite nanowires, mixed-matrix membranes, water flux, membrane fouling, hydrophilicity, water treatment, phase inversion, reverse salt flux, nanocomposites

The target application is alkaline water electrolysis, one of the most mature and cost-effective routes to green hydrogen because it relies on non-precious-metal electrodes and concentrated potassium hydroxide electrolyte. Conventional alkaline electrolyzers use porous diaphragms, such as the commercial Zirfon 500 separator, whose electrolyte-filled pores conduct hydroxide ions. This design carries an intrinsic trade-off: increasing porosity lowers ionic resistance but raises the risk of hydrogen and oxygen gas crossover, which threatens product gas purity and can create hazardous gas mixtures. Anion exchange membranes avoid this problem by conducting hydroxide ions through fixed cationic groups, but those groups degrade under concentrated KOH at elevated temperatures. Ion-solvating membranes offer a third path: they are dense films that transport potassium and hydroxide ions through an absorbed KOH/water phase, without any fixed ionic groups that could be chemically attacked.

The challenge for ion-solvating membranes is that their conductivity depends entirely on how much electrolyte the polymer retains. The team chose poly [2,2′-(1,4-naphthalene)-5,5′-bibenzimidazole], or NPBI, as the matrix because its rigid aromatic backbone and bulky naphthalene units preserve dimensional stability in hot concentrated alkali. However, dense NPBI still limits ion transport because conduction is governed by the amount and distribution of the retained KOH/water phase. The researchers therefore synthesized NPBI by polycondensing 3,3′-diaminobenzidine with 1,4-naphthalenedicarboxylic acid in Eaton’s reagent, achieving a yield above 78 percent, and then dispersed BDC-ZIF-8 filler at loadings of 10 to 50 weight percent relative to the polymer mass. The membranes were cast from DMAc solutions and dried to an average thickness of 23 ± 2 micrometers, roughly twenty times thinner than the 500-micrometer Zirfon reference separator.

The upcycling chemistry itself is elegant. Transparent PET bottles were washed, dried, and cut into flakes, then depolymerized in an ethanol/water mixture with sodium hydroxide at 80 °C for 12 hours under ambient pressure. Acidification with hydrochloric acid to a pH below 3 precipitated the recovered BDC with a yield exceeding 98 percent. Elemental analysis confirmed the recovered linker contained 57.53 weight percent carbon and 3.71 weight percent hydrogen with no detectable nitrogen or sulfur impurities, matching commercial BDC. The team then combined zinc nitrate hexahydrate, 2-methylimidazole, and the recovered BDC in a molar ratio of approximately 11.1:10.0:1.0 and heated the mixture solvothermally at 140 °C for 24 hours. The resulting BDC-ZIF-8 retained the main diffraction peaks of the ZIF-8 framework at 7.3, 10.4, and 12.7 degrees, while developing additional weak peaks at 8.3 and 9.1 degrees that reflect secondary coordination environments introduced by the dicarboxylate linker.

Porosity measurements revealed why this filler is so effective at retaining electrolyte. Nitrogen adsorption isotherms showed type I behavior with a hysteresis loop, indicating coexisting micropores and mesopores. The Brunauer–Emmett–Teller specific surface area reached 1488 square meters per gram, with a micropore volume of 0.56 cubic centimeters per gram and a total pore volume of 1.45 cubic centimeters per gram. Fourier-transform infrared spectroscopy confirmed that the free carboxylic acid C=O stretching peak near 1670 wavenumbers disappeared after framework formation, replaced by asymmetric and symmetric carboxylate stretching peaks at approximately 1558 and 1378 wavenumbers, alongside Zn–N stretching near 422 wavenumbers. These spectral features demonstrate that the carboxylate groups of the upcycled linker coordinated directly with zinc ions, creating polar interaction sites that can hydrogen-bond with water molecules and hydrated potassium ions inside the membrane.

After three days of immersion in 6 M KOH at 80 °C, the electrolyte uptake data told a clear story. The polymer/filler solid fraction decreased from 49 percent in pristine NPBI to 40 percent in the 40 weight percent membrane, while the water fraction rose from 34 to 37 percent and the KOH fraction climbed from 17 to 23 percent. Contact angle measurements reinforced this picture: the DI water contact angle of dry membranes fell from 71.46 to 55.67 degrees as filler loading increased, and after KOH doping all membranes became extremely wettable, with KOH contact angles below 10 degrees. Crucially, the rigid BDC-ZIF-8 domains acted as physical reinforcing phases that suppressed excessive swelling. Pristine NPBI showed relatively large thickness and volume changes after electrolyte uptake, whereas the mixed-matrix membranes exhibited more stabilized dimensional changes despite their higher electrolyte fractions, preserving lateral dimensional stability.

Gas-blocking integrity survived the filler incorporation. Bubble point pressures of the KOH-doped membranes ranged from 6.2 to 6.5 bar, comparable to the 6.1 ± 0.4 bar of pristine NPBI and far exceeding the 2 ± 1 bar of commercial Zirfon 500. Ex situ hydrogen permeability of the wet membranes measured between 0.395 and 0.418 Barrer, essentially unchanged from the 0.571 Barrer of pristine NPBI and roughly 160 times lower than the 89.6 Barrer of Zirfon 500. Mechanical testing showed that moderate filler loadings strengthened the membranes: dry tensile stress increased from 70.20 MPa in pristine NPBI to 78.17 and 79.35 MPa at 20 and 30 weight percent filler, respectively, and after KOH doping the 20 weight percent membrane reached 55.97 MPa, a 47.87 percent increase over doped pristine NPBI. However, the 40 weight percent membrane weakened dramatically to 38.74 MPa dry and 24.57 MPa doped, reflecting filler aggregation and interfacial heterogeneity that concentrate stress during deformation.

The ion transport improvements translated directly into cell performance. Area resistance measured in 6 M KOH at 80 °C fell from 0.067 Ω cm² in pristine NPBI to 0.062, 0.046, 0.040, and 0.037 Ω cm² at 10, 20, 30, and 40 weight percent filler, respectively, all below the 0.079 Ω cm² of Zirfon 500. In zero-gap single cells with bare nickel felt electrodes, the current density at 1.8 V rose from 0.291 A cm⁻² for pristine NPBI to 0.704 A cm⁻² for the 40 weight percent membrane, and at 2.0 V the same membrane delivered 1.809 A cm⁻² compared with 0.913 A cm⁻² for pristine NPBI. Electrochemical impedance spectroscopy confirmed the trend: high-frequency resistance dropped from 0.290 Ω cm² for pristine NPBI to 0.166 Ω cm² for the 40 weight percent cell. The loading-dependent trade-off became apparent in long-term testing, however. During 500 hours of ex situ alkaline exposure, the 10 and 20 weight percent membranes maintained low area resistance stably, while the 30 and 40 weight percent membranes, despite their lower initial resistance, showed gradually increasing resistance over time.

The alkaline stability analysis of the filler itself explains this behavior. When BDC-ZIF-8 powder was aged in 6 M KOH at 80 °C for up to 21 days, the imidazolate C=N vibration peak and the coordinated carboxylate stretching peaks gradually weakened, indicating partial modification of the BDC–Zn coordination environment. Yet the Zn–N vibration near 422 wavenumbers remained detectable after 21 days, and scanning electron microscopy showed the powders retained their overall particle morphology with only surface roughening. After three months of alkaline exposure, all membranes maintained continuous structures without macroscopic cracks, confirming that the resistance increase at high filler loading arose from morphological heterogeneity rather than membrane collapse. Based on its balanced mechanical properties, low cell resistance, and stable long-term behavior, the 20 weight percent membrane was selected for continuous operation, sustaining 100 hours at 0.3 A cm⁻² in 6 M KOH at 80 °C with an average cell voltage of 1.798 V and a maximum of 1.804 V.

This study demonstrates that waste PET can be upcycled into a functional electrolyte-retaining metal–organic framework filler for next-generation alkaline electrolyzers, closing a loop between plastic recycling and green hydrogen production. The findings also carry a clear design lesson: filler loading must be optimized to balance electrolyte retention, ion transport, membrane morphology, and alkaline stability, because the lowest initial resistance does not necessarily correspond to the most stable long-term performance. As hydrogen economies scale up and plastic waste streams continue to grow, strategies that convert one problem into the solution for another could prove decisive. The researchers note that further studies under practical operating conditions are needed to evaluate the applicability of these membranes in larger alkaline water electrolysis systems, but the demonstration that a discarded beverage bottle can help split water into hydrogen marks a compelling step toward circular clean-energy materials.

Subject of Research: Materials Science

Article Title: Waste PET-derived BDC-ZIF-8 as an electrolyte-retaining filler for NPBI-based ion-solvating mixed-matrix membranes in alkaline water electrolysis

Article References: Park, S. J., Seo, J., Lee, Y.-R., Choi, Y.-W., Choi, J., & Lee, J. H. (2026). Waste PET-derived BDC-ZIF-8 as an electrolyte-retaining filler for NPBI-based ion-solvating mixed-matrix membranes in alkaline water electrolysis. Frontiers in Membrane Science and Technology, 5, Article 1892925. https://doi.org/10.3389/frmst.2026.1892925

Image Credits: AI Generated

DOI: 10.3389/frmst.2026.1892925

Keywords: alkaline water electrolysis, BDC-ZIF-8, ion-solvating membranes, metal–organic framework, NPBI, waste PET, green hydrogen, mixed-matrix membranes, Waste, PET-derived, electrolyte-retaining, filler

The central obstacle the team set out to solve is a familiar one in membrane science. Mixed-matrix membranes combine the easy processing of polymers with the precisely engineered pores of crystalline materials, but the recipe has a built-in ceiling. When the fraction of porous filler climbs beyond a modest threshold, the particles aggregate, defects appear at the polymer–filler interface, and the membrane’s performance collapses rather than improves. Most strategies have therefore kept filler loadings low, which means the polymer dominates transport and the carefully designed pores of the filler contribute little. The intrinsic transport properties of the crystalline material are effectively wasted.

The Tianjin-led group overturned the conventional design philosophy. Rather than maximizing strong interactions between polymer and filler to glue the two phases together, they pursued what they call a weak-interaction inlaying strategy. By balancing the interaction energies between polymer and filler on one hand and between filler particles themselves on the other, they found that the single-crystal COFs could be dispersed uniformly at loadings reaching 75.5 percent by volume, an extraordinary fraction for a mixed-matrix membrane. At such loadings the filler no longer acts as a minor additive; it becomes the dominant, continuous transport network through which gas molecules travel.

The choice of filler matters as much as the loading. Covalent organic frameworks are a class of porous crystalline polymers built from light elements such as carbon, nitrogen, oxygen and hydrogen, linked by strong covalent bonds into periodic lattices with regularly sized pores. Unlike metal–organic frameworks, they contain no metal nodes, making them fully organic and compatible with an organic polymer matrix. The team used single-crystal COFs, whose well-defined, defect-minimized lattices preserve the exact pore geometry designed into the material. When these crystals are embedded intact, the membrane inherits their intrinsic transport channels rather than a degraded approximation of them.

The resulting membranes create what the authors describe as filler-dominated pathways for fast carbon dioxide transport. Gas molecules moving through the membrane encounter a continuous network of COF pores whose size and chemistry favor carbon dioxide over nitrogen, while the surrounding polymer simply holds the architecture together. Because the interfaces remain clean and compatible even at very high filler content, there are no leaky voids that would undermine selectivity and no dense polymer regions that would choke off flow. The combination of high permeability and maintained selectivity pushes the materials well beyond the conventional upper-bound trade-off line that has long constrained polymer membranes for carbon dioxide–nitrogen separations.

The numbers are striking in context. A permeability of 74,800 Barrer is orders of magnitude above typical commercial polymer membranes for post-combustion capture, which often sit in the tens to low hundreds of Barrer. High permeability translates directly into smaller membrane areas and lower driving pressures for a given capture duty, which in turn reduces the capital cost and energy consumption of a capture plant. Previous life-cycle assessments have suggested that membrane separation can compete with the amine-based chemical absorption processes used today, but only if membrane materials reach the permeability–selectivity combination that makes module sizes practical. This work moves that target substantially closer.

Performance on day one means little if a membrane degrades, and polymer membranes are notorious for physical ageing, the gradual collapse of free volume that throttles transport over months and years. The team addressed this concern directly with long-term tests. Membranes based on polyimide retained approximately 85 percent of their initial permeability after six months of ageing at room temperature, a result that suggests the rigid crystalline COF network helps stabilize the membrane structure against the densification that normally erodes polymer performance. For a material operating at such extreme filler loadings, this stability is itself a notable finding.

The work also carries a broader methodological lesson for materials chemistry. The weak-interaction inlaying strategy reframes the interface problem: instead of fighting aggregation with ever-stronger polymer–filler bonding, the researchers tuned the relative strengths of competing interactions so that dispersion remains thermodynamically comfortable. That principle, balancing polymer–filler against filler–filler interaction energies, could plausibly extend beyond COFs to other crystalline fillers and beyond carbon capture to other molecular separations, from hydrogen purification to hydrocarbon cracking. The study’s authors, including co-first authors Hanze Ma and Shilin Guo, with Guangwei He and Zhongyi Jiang as corresponding authors, frame the approach as a general route to exploiting the intrinsic properties of porous crystals inside processable membranes.

Scalability remains the decisive question for any laboratory membrane advance. The team emphasizes solution processability as a design requirement, and the fact that the membranes are all-organic, formulated from polymer and COF in solution, aligns with existing membrane fabrication methods rather than requiring exotic deposition techniques. Still, translating a laboratory coupon into square meters of defect-free membrane module, and validating performance on real flue gas with its humidity, sulfur impurities and temperature swings, will demand further engineering. The six-month ageing data and the robust interfacial design are encouraging early signals, but industrial pilots will be the true test.

Even with those caveats, the study represents one of the most compelling demonstrations yet that the long-standing permeability–selectivity trade-off can be beaten by design rather than merely nudged. By making the crystalline filler the membrane rather than a garnish on it, the researchers have effectively built a processable, polymer-locked single-crystal separation device. If the approach survives scale-up, membranes of this kind could shrink the footprint and energy bill of post-combustion carbon capture, a technology the Intergovernmental Panel on Climate Change and the International Energy Agency both identify as essential to limiting warming. In a field where incremental gains are the norm, a seventy-thousand-Barrer membrane with intact selectivity is the kind of result that redraws the map.

Subject of Research: All-organic mixed-matrix membranes with single-crystal covalent organic frameworks for energy-efficient carbon capture

Article Title: All-organic mixed-matrix membranes with single-crystal covalent organic frameworks for carbon capture

Article References: Ma, H., Guo, S., Su, P., Zhao, Q., Wang, S., Ren, Y., Fu, J., Zhang, H., Zhang, T., Yuan, S., Pan, Q., Villalobos, L. F., Li, Y., Ma, X., Agrawal, K. V., He, G., & Jiang, Z. (2026). All-organic mixed-matrix membranes with single-crystal covalent organic frameworks for carbon capture. Nature Energy. https://doi.org/10.1038/s41560-026-02149-9

Image Credits: AI Generated

DOI: 10.1038/s41560-026-02149-9

Keywords: carbon capture, covalent organic frameworks, mixed-matrix membranes, gas separation, CO2 permeability, polyimide, membrane technology, porous materials, post-combustion capture, polymer membranes, Nature Energy, materials science