Polymer Composite Membrane with Penetrating ZIF‐7 Sheets Displays High Hydrogen Permselectivity

Oriented and penetrating molecular sieving membranes display enhanced separation performance. A polyimide (PI) solution containing highly dispersed ZIF‐7(III) sheets in CHCl₃ was deposited on a glass side and subjected to flat‐scraping with a membrane fabricator. In this way we developed a novel oriented and penetrating ZIF‐7@PI mixed matrix membrane (MMM) with 50 wt. % ZIF‐7 loading. Because the height of the ZIF‐7 sheets (5 μm) is higher than the film thickness, every ZIF‐7 sheet penetrates both surfaces of the polyimide film. Since the ZIF‐7 channels are the dominant pathway for gas permeation, the ZIF‐7@PI MMM displays a high molecular sieve performance for the separation of H₂ (0.29 nm) from larger gas molecules. At 100 °C and 2 bar, the mixture separation factors of H₂/CO₂ and H₂/CH₄ are 91.5 and 128.4, with a high H₂ permeance of about 3.0×10^?7 mol m^?2 s^?1 Pa^?1, which is promising for hydrogen separation by molecular sieving.     

A Uniformly Oriented MFI Membrane for Improved CO2 Separation

Membrane separation of CO₂ from natural gas, biogas, synthesis gas, and flu gas is a simple and energy‐efficient alternative to other separation techniques. But results for CO₂‐selective permeance have always been achieved by randomly oriented and thick zeolite membranes. Thin, oriented membranes have great potential to realize high‐flux and high‐selectivity separation of mixtures at low energy cost. We now report a facile method for preparing silica MFI membranes in fluoride media on a graded alumina support. In the resulting membrane straight channels are uniformly vertically aligned and the membrane has a thickness of 0.5 μm. The membrane showed a separation selectivity of 109 for CO₂/H₂ mixtures and a CO₂ permeance of 51×10^?7 mol m^?2 s^?1 Pa^?1 at ?35 °C, making it promising for practical CO₂ separation from mixtures.     

Elucidating Ultrafast Molecular Permeation through Well‐Defined 2D Nanochannels of Lamellar Membranes

Lamellar membranes with well‐defined 2D nanochannels show fast, selective permeation, but the underlying molecular transport mechanism is unexplored. Now, regular robust MXene Ti₃C₂T_x lamellar membranes are prepared, and the size and wettability of nanochannels are manipulated by chemically grafted hydrophilic (?NH₂) or hydrophobic (?C₆H₅, ?C₁₂H₂₅) groups. These nanochannels have a sharp difference in mass transfer behavior. Hydrophilic nanochannels, in which polar molecules form orderly aligned aggregates along channel walls, impart ultrahigh permeance (>3000 L m^?2 h^?1 bar^?1), which is more than three times higher than that in hydrophobic nanochannels with disordered molecular configuration. In contrast, nonpolar molecules with disordered configuration in both hydrophilic and hydrophobic nanochannels have comparable permeance. Two phenomenological transport models correlate the permeance with the mass transport mechanism of molecules that display ordered and disordered configuration.     

Membranes with Fast and Selective Gas‐Transport Channels of Laminar Graphene Oxide for Efficient CO2 Capture

Graphene oxide (GO) nanosheets were engineered to be assembled into laminar structures having fast and selective transport channels for gas separation. With molecular‐sieving interlayer spaces and straight diffusion pathways, the GO laminates endowed as‐prepared membranes with excellent preferential CO₂ permeation performance (CO₂ permeability: 100 Barrer, CO₂/N₂ selectivity: 91) and extraordinary operational stability (>6000 min), which are attractive for implementation of practical CO₂ capture.     

Fabrication of Crystalline Microporous Membrane from 2D MOF Nanosheets for Gas Separation

Metal‐organic frameworks (MOFs)‐based membranes have shown great potentials as applications in gas separation. In this work, a uniform membrane based on 2D MOF Ni₃(HITP)₂ (HITP=2,3,6,7,10,11‐hexaaminotriphenylene) was fabricated on ordered macroporous AAO via the filtration method. To fabricate the membrane, we obtained the Ni₃(HITP)₂ nanosheets as building blocks via a soft‐physical exfoliation method successfully that were confirmed by AFM and TEM. We also studied the H₂, CO₂ and N₂ adsorption isotherms of Ni₃(HITP)₂ powder at room temperature, which shows Ni₃(HITP)₂ has high heats of adsorption for CO₂ and high selectivity of CO₂ over N₂. Gas permeation tests indicate that the Ni₃(HITP)₂ membrane shows high permeance and selectivity of CO₂ over N₂, as well as good selectivity of H₂ over N₂. The ideal separation factors of CO₂/N₂ and H₂/N₂ from sing‐gas permeances are 13.6 and 7.8 respectively, with CO₂ permeance of 3.15×10^?6 mol?m^?2?s^?1?Pa^?1. The membrane also showed good stability, durability and reproducibility, which are of potential interest for practical applications in the CO₂ separations.     

Oppositely Charged Ti3C2Tx MXene Membranes with 2D Nanofluidic Channels for Osmotic Energy Harvesting

Membrane‐based reverse electrodialysis (RED) is considered as the most promising technique to harvest osmotic energy. However, the traditional membranes are limited by high internal resistance and low efficiency, resulting in undesirable power densities. Herein, we report the combination of oppositely charged Ti₃C₂T_x MXene membranes (MXMs) with confined 2D nanofluidic channels as high‐performance osmotic power generators. The negatively or positively charged 2D MXene nanochannels exhibit typical surface‐charge‐governed ion transport and show excellent cation or anion selectivity. By mixing the artificial sea water (0.5 m NaCl) and river water (0.01 m NaCl), we obtain a maximum power density of ca. 4.6 Wm^?2, higher than most of the state‐of‐the‐art membrane‐based osmotic power generators, and very close to the commercialization benchmark (5 Wm^?2). Through connecting ten tandem MXM‐RED stacks, the output voltage can reach up 1.66 V, which can directly power the electronic devices.     

Uniformly Oriented Zeolite ZSM‐5 Membranes with Tunable Wettability on a Porous Ceramic

Facile fabrication of well‐intergrown, oriented zeolite membranes with tunable chemical properties on commercially proven substrates is crucial to broadening their applications for separation and catalysis. Rationally determined electrostatic adsorption can enable the direct attachment of a b‐oriented silicalite‐1 monolayer on a commercial porous ceramic substrate. Homoepitaxially oriented, well‐intergrown zeolite ZSM‐5 membranes with a tunable composition of Si/Al=25–∞ were obtained by secondary growth of the monolayer. Intercrystallite defects can be eliminated by using Na⁺ as the mineralizer to promote lateral crystal growth and suppress surface nucleation in the direction of the straight channels, as evidenced by atomic force microscopy measurements. Water permeation testing shows tunable wettability from hydrophobic to highly hydrophilic, giving the potential for a wide range of applications.     

Formation of Ultrathin,Continuous Metal–Organic Framework Membranes on Flexible Polymer Substrates

Metal–organic framework (MOF) materials have an enormous potential in separation applications, but to realize their potential as semipermeable membranes they need to be assembled into thin continuous macroscopic films for fabrication into devices. By using a facile immersion technique, we prepared ultrathin, continuous zeolitic imidazolate framework (ZIF‐8) membranes on titania‐functionalized porous polymeric supports. The coherent ZIF‐8 layer was surprisingly flexible and adhered well to the support, and the composite membrane could sustain bending and elongation. The membranes exhibited molecular sieving behavior, close to the theoretical permeability of ZIF‐8, with hydrogen permeance up to 201×10^?7 mol m^?2 s^?1 Pa^?1 and an ideal H₂/CO₂ selectivity of 7:1. This approach offers significant opportunities to exploit the unique properties of MOFs in the fabrication of separation and sensing devices.     

Biomimetic Nanocones that Enable High Ion Permselectivity

Artificial counterparts of conical‐shaped transmembrane protein channels are of interest in biomedical sciences for biomolecule detection and selective ion permeation based on ionic size and/or charge differences. However, industrial‐scale applications such as seawater desalination, separation of mono‐ from divalent cations, and treatment of highly‐saline industrial waste effluents are still big challenges for such biomimetic channels. A simple monomer seeding experimental approach is used to grow ionically conductive biomimetic charged nanocone pores at the surface of an acid‐functionalized membrane. These readily scalable nanocone membranes enable ultra‐fast cation permeation (Na⁺=8.4× vs. Mg²⁺=1.4×) and high ion charge selectivity (Na⁺/Mg²⁺=6×) compared to the commercial state‐of‐the‐art permselective membrane (CSO, Selemion, Japan) owing to negligible surface resistance and positively charged conical pore walls.     

Evolution of the precipitation kinetics,morphologies, permeation performances,and crystallization behaviors of polyvinylidenefluoride (PVDF) hollow fiber membrane by adding different molecular weight polyvinylpyrrolidone (PVP)

Polyvinylidenefluoride (PVDF) hollow fiber membranes were fabricated by wet spinning (wet/wet) and dry‐jet wet spinning (dry/wet; 3 cm air gap) processes with four types of polyvinylpyrrolidone (PVP) of different molecular weight as additives. Evolution of the precipitation kinetics, morphologies, permeation performances, and crystallization behaviors of the as‐spun PVDF membranes were investigated. The PVDF membranes were well characterized by numerous state‐of‐the‐art analytical techniques: scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and attenuated total reflectance fourier Transform Infrared (FTIR‐ATR) and elucidated accompanying with its precipitation kinetics obtained by light transmittance measurements. The precipitation kinetics results confirm that four PVDF/PVP/NMP dopes experience instantaneous demixing mechanism and the precipitation rate decreases as PVP molecular weight increases. Little peaks are found in the precipitation curves of the PVDF dopes containing PVP of low molecular weight. The SEM images indicate that the middle sponge‐like layer sandwiched by double finger‐like layers becomes thinner for the special precipitation behaviors. Visible large pores exist in the internal surfaces of the PVDF membranes spun by both wet/wet and dry/wet spinning processes. The increase in PVP molecular weight restricts the formation of large pores in the internal surfaces of the PVDF membranes for the increase in dope viscosity. The pure water permeability (PWP) of the as‐spun PVDF membranes increases initially and then decreases as PVP molecular weight increases. The largest PWP flux of 316.7 L m^?2 h^?1 bar^?1 is obtained for the PVDF membrane containing PVP K25 by wet/wet spinning process. The rejections for bovine serum albumin (BSA) by the as‐spun PVDF membranes range from 35.4 to 82.9%. It illustrates that typical PVDF ultrafiltration membranes were obtained in this research. The melting temperature(T_m) of the PVDF hollow fiber membranes decreases with the increase in the PVP molecular weight as a whole. IR spectra and XRD patterns verify the exclusive formation of β crystalline phase structure in the as‐spun PVDF membranes. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrogen Production by Water Dissociation in Surface‐Modified BaCoxFeyZr1−x−yO3−δ Hollow‐Fiber Membrane Reactor with Improved Oxygen Permeation

A porous perovskite BaCo_xFe_yZr_0.9?x?yPd_0.1O_3?δ (BCFZ‐Pd) coating was deposited onto the outer surface of a BaCo_xFe_yZr_1?x?yO_3?δ (BCFZ) perovskite hollow‐fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ‐Pd porous layer on the outer surface of a dense BCFZ hollow‐fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ‐Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH₄ onto the permeation side of the membrane. The blank BCFZ membrane and surface‐modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H₂ min^?1 cm^?2 at 950 °C after depositing a BCFZ‐Pd porous layer onto the BCFZ membrane.     

Self‐Assembled Columnar Triazole Quartets: An Example of Synergistic Hydrogen‐Bonding/Anion–π Interactions

The self‐assembly of triazole amphiphiles was examined in solution, the solid state, and in bilayer membranes. Single‐crystal X‐ray diffraction experiments show that stacked protonated triazole quartets (T₄) are stabilized by multiple strong interactions with two anions. Hydrogen bonding/ion pairing of the anions are combined with anion–π recognition to produce columnar architectures. In bilayer membranes, low transport activity is observed when the T₄ channels are operated as H⁺/X^? translocators, but higher transport activity is observed for X^? in the presence of the K⁺‐carrier valinomycin. These self‐assembled superstructures, presenting intriguing structural behaviors such as directionality, and strong anion encapsulation by hydrogen bonding supported by vicinal anion–π interactions can serve as artificial supramolecular channels for transporting anions across lipid bilayer membranes.     

L‐Tryptophan‐Induced Electron Transport across Supported Lipid Bilayers: an Alkyl‐Chain Tilt‐Angle,and Bilayer‐Symmetry Dependence

Molecular orientation‐dependent electron transport across supported 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine (DPPC) lipid bilayers (SLBs) on semiconducting indium tin oxide (ITO) is reported with an aim towards potential nanobiotechnological applications. A bifunctional strategy is adopted to form symmetric and asymmetric bilayers of DPPC that interact with L ‐tryptophan, and are analyzed by surface manometry and atomic force microscopy. Polarization‐dependent real‐time Fourier transform infrared reflection absorption spectroscopy (FT‐IRRAS) analysis of these SLBs reveals electrostatic, hydrogen‐bonding, and cation–π interactions between the polar head groups of the lipid and the indole side chains. Consequently, a molecular tilt arises from the effective interface dipole, facilitating electron transport across the ITO‐anchored SLBs in the presence of an internal Fe(CN)₆^4?/3? redox probe. The incorporation of tryptophan enhances the voltammetric features of the SLBs. The estimated electron‐transfer rate constants for symmetric and asymmetric bilayers (k_s=2.0×10^?2 and 2.8×10^?2 s^?1) across the two‐dimensional (2D) ordered DPPC/tryptophan SLBs are higher compared to pure DPPC SLBs (k_s=3.2×10^?3 and 3.9×10^?3 s^?1). In addition, they are molecular tilt‐dependent, as it is the case with the standard apparent rate constants ${k_{{\rm{app}}}^0 }$ , estimated from electrochemical impedance spectroscopy and bipotentiostatic experiments with a Pt ultramicroelectrode. Lower magnitudes of k_s and ${k_{{\rm{app}}}^0 }$ imply that electrochemical reactions across the ITO–SLB electrodes are kinetically limited and consequently governed by electron tunneling across the SLBs. Standard theoretical rate constants ${\left( {k_{{\rm{th}}}^0 } \right)}$ accrued upon electron tunneling comply with the potential‐independent electron‐tunneling coefficient β=0.15 Å^?1. Insulator–semiconductor transitions moving from a liquid‐expanded to a condensed 2D‐phase state of the SLBs are noted, adding a new dimension to their transport behavior. These results highlight the role of tryptophan in expediting electron transfer across lipid bilayer membranes in a cellular environment and can provide potential clues towards patterned lipid nanocomposites and devices.     

Synthesis and Characterization of Phenolphthalein‐Containing Sulfonated Poly(arylene ether phosphine oxide)s by Direct Polycondensation for Proton Exchange Membrane

A series of novel phenolphthalein‐containing sulfonated poly(arylene ether phosphine oxide)s (sPAEPP) with various sulfonation degrees were synthesized by direct polycondensation. The structure of sPAEPP was confirmed by ¹H‐NMR, ¹³C‐NMR, and IR spectroscopy. The high‐molecular weight of these polymers was determined by gel permeation chromatography (GPC). The transparent, tough, and flexible membranes could be achieved by solution casting. The macroscopic properties and microstructure of the obtained membranes were investigated in detail. The results showed that these sPAEPP membranes displayed excellent properties in terms of swelling, proton conductivity, and methanol permeability. For example, sPAEPP‐100 membrane exhibited an appropriate water uptake of 33.1%, a swelling ratio of only 11.7% (lower than 20.1% of Nafion 117), a proton conductivity of 0.11 S cm^?1 (similar to that of Nafion 117) at 80 °C, and a methanol permeability of 4.82 × 10^?7 cm² s^?1. Meanwhile, it also presented outstanding oxidative stability. Atomic force microscope (AFM) micrographs showed that the hydrophilic domains of the sPAEPP‐100 membrane formed connected and narrow ionic channels, which contributed to its high proton conductivity and good dimensional stability. As a result, sPAEPP‐100 membrane displays excellent application prospect for fuel cells. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1097–1104     

Novel proton-conductive nanochannel membranes with modified SiO2 nanospheres for direct methanol fuel cells

A novel approach is proposed to prepare a proton-conductive nanochannel membrane based on polyvinylidene difluoride (PVDF) porous membrane with modified SiO₂ nanospheres. The hydrophilic PVDF porous membrane with a 450-nm inner pore size was chosen as the supporting structure. Pristine SiO₂ with a uniform particle size of 95–110 nm was synthesized and functionalized with –NH₂ and –COOH, respectively. Through-plane channels of porous membrane and arranged functional nanoparticles in pores could contribute to constituting efficient proton transfer channels. The characteristics such as morphology, thermal stability, water uptake, dimensional swelling, proton conductivity and methanol permeability as proton exchange membranes, of the SiO₂ nanospheres, and the composite membrane were investigated. The formation of ionic channels in membrane enhanced the water uptakes and proton conduction abilities of the composite membranes. PVDF/Nafion/SiO₂–NH₂ exhibited superior proton conductivities (0.21 S cm^?1) over other samples due to several proton sites and the acid–base pairs formed between –NH₂ and –SO₃H. Furthermore, all the composite membranes exhibited improved methanol resistance compared with Nafion. Therefore, such a design based on porous membrane provided feasibility for high-performance proton exchange membrane in fuel cell applications.     

Ultrathin pH‐Sensitive Nanoporous Membranes for Superfast Size‐Selective Separation

Stimuli‐responsive nanoporous membranes have attracted increasing interest in various fields due to their abrupt changes of permeation/separation in response to the external environment. Here we report ultrathin pH‐sensitive nanoporous membranes that are easily fabricated by the self‐assembly of poly(acrylic acid) (PAA) in a metal hydroxide nanostrand solution. PAA‐adsorbed nanostrands (2.5–5.0 nm) and PAA‐Cu^II nanogels (2.0–2.5 nm) grow competitively during self‐assembly. The PAA‐adsorbed nanostrands are deposited on a porous support to fabricate ultrathin PAA membranes. The membranes display ultrafast water permeation and good rejection as well as significant pH‐sensitivity. The 28 nm‐thick membrane has a water flux decrease from 3740 to 1350 L m^?1 h^?1 bar^?1 (pH 2.0 to 7.0) with a sharp decrease at pH 5.0. This newly developed pH‐sensitive nanoporous membranes may find a wide range of applications such as controlled release and size‐ and charge‐selective separation.     

Permeation of oxygen dissolved in water through substituted polyacetylene membranes

The permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficients P in the range 10^?9?10^?8 cm³ (STP) cm cm^?2s^?1 cmHg^?1. The resistance r of the boundary layer and the permeability P_∞, at infinite membrane thickness were determined from the dependence of P on membrane thickness. The r values of Si-containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. The P_∞, values of Si-containing and aliphatic polyacetylenes agreed closely with the permeability coefficients P_g for gaseous oxygen. In contrast, P_∞ values for aromatic polyacetylenes were larger than P_g values.     

A Glutathione Activatable Ion Channel Induces Apoptosis in Cancer Cells by Depleting Intracellular Glutathione Levels

Cancer cells use elevated glutathione (GSH) levels as an inner line of defense to evade apoptosis and develop drug resistance. In this study, we describe a novel 2,4‐nitrobenzenesulfonyl (DNS) protected 2‐hydroxyisophthalamide system that exploits GSH for its activation into free 2‐hydroxyisophthalamide forming supramolecular M⁺/Cl^? channels. Better permeation of the DNS protected compound into MCF‐7 cells compared to the free 2‐hydroxyisophthalamide and GSH‐activatable ion transport resulted in higher cytotoxicity, which was associated with increased oxidative stress that further reduced the intracellular GSH levels and altered mitochondrial membrane permeability leading to the induction of the intrinsic apoptosis pathway. The GSH‐activatable transport‐mediated cell death was further validated in rat insulinoma cells (INS‐1E); wherein the intracellular GSH levels showed a direct correlation to the resulting cytotoxicity. Lastly, the active compound was found to restrict the growth and proliferation of 3D spheroids of MCF‐7 cells with efficiency similar to that of the anticancer drug doxorubicin.     

Selective and Efficient Removal of Fluoride from Water: In Situ Engineered Amyloid Fibril/ZrO2 Hybrid Membranes

We report a new strategy for efficient removal of F^? from contaminated water streams, and it relies on carbon hybrid membranes made of amyloid fibril/ZrO₂ nanoparticles (<10 nm). These membranes exhibit superior selectivity for F^? against various competitive ions, with a distribution coefficient (K_d) as high as 6820 mL g^?1, exceeding commercial ion‐exchange resins (IRA‐900) by 180 times and outdoing the performance of most commercial carbon‐activated aluminum membranes. At both low and high (ca. 200 mg L^?1) F^? concentrations, the membrane efficiency exceeds 99.5 % removal. For real untreated municipal tap water (ca. 2.8 mg L^?1) under continuous operating mode, data indicates that about 1750 kg water m^?2 membrane can be treated while maintaining drinking water quality, and the saturated membranes can be regenerated and reused several times without decrease in performance. This technology is promising for mitigating the problem of fluoride water contamination worldwide.     

Synthesis and characterization of anhydrous conducting polyimide/ionic liquid complex membranes via a new route for high‐temperature fuel cells

The paper deals with the synthesis and characterization of a new series of anhydrous conducting acid‐doped complex membranes based on polyimide (PI) and ionic liquid (IL) for high‐temperature fuel cells via a new route. For this purpose, three imidazolium‐based ILs (RIm⁺BF₄^?) with different alkyl chain lengths (R=methyl, ethyl, and butyl) are added into polyamic acid (PAA) intermediate prepared from the reaction of benzophenonetetracarboxylic dianhydride and diaminodiphenylsulfone in different –COOH/imidazolium molar ratios (n = 0.5, 1, and 2). Then, the thermally imidized complex membrane was doped with H₂SO₄. The conductivities of acid‐doped PI/IL complex membranes prepared by taking n of 1 are found to be in the range of 10^?4?10^?5 S cm^?1 at 180°C, whereas the acid‐free PI/IL complex membranes show the conductivity at around 10^?9?10^?10 S cm^?1. Thermogravimetric analysis results reveal that the acid‐doped PI/IL complex membranes are thermally stable up to 250°C. Dynamic mechanical analysis results of the acid‐doped ionically interacted complex membrane show that the mechanical strengths of the PI/IL complex membranes including 1‐methyl imidazolium tetrafluoroborate (MeIm‐BF₄) and 1‐ethyl 3‐methyl imidazolium tetrafluoroborate (EtIm‐BF₄) are comparable with those of pristine PI until 200°C. Furthermore, it can be clearly emphasized that the ionic interaction between carboxylic acid groups of PAA's and IL's cations offers a positive role in long‐term conductivity stability by preventing the IL migration at high temperatures. On the other hand, preliminary methanol permeability tests of the acid‐doped membranes show that they can also be considered as an alternative for direct methanol fuel cells. Copyright © 2011 John Wiley & Sons, Ltd.