Selective Membrane Research Articles

Parallel Amperometric and Potentiometric Multianalyte Detection in a Microfluidic System

The adoption of microfluidic technologies in electrochemical biosensor development has enabled quantitative biomarker monitoring that use significantly lower volumes of reagents and samples, miniaturized electrodes, and inexpensive fabrication techniques, while presenting opportunities for multianalyte detection. We describe the fabrication of amperometric and potentiometric biosensors on a multichannel, platinum screen-printed electrode (SPE) and demonstrate their operation in parallel on a microfluidic multianalyte electrochemical sensor array (µMESA) platform.Working electrodes (WEs) of an SPE were were modified with either enzymes or ion selective membranes (ISMs) for amperometric or potentiometric measurements respectively. Oxidase enzymes were dissolved in an osmium (II) bis(2,2'-bipyridine)chloride-poly(vinylimidazole-allylamine) redox polymer and immobilized on four WEs. The use of this osmium-based electron transfer mediator has been previously reported to lower the oxidation potential of analytes and to improve overall sensor performance. The remaining four WEs were modified by electrodeposition of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), an intrinsically conductive polymer. Solid contact ISMs were prepared by combining ionophores, lipophilic ion exchangers, and a fluorosilicone polymer, and drop casting the mixtures on PEDOT:PSS-coated WEs. Plasticizer-free ISMs improve sensor lifetime by lowering the glass transition temperature and eliminating leaching of plasticizers from the ISM. By utilizing these strategies, we fabricated amperometric sensors for glucose and lactate, and potentiometric sensors for K+ and Ca2+ ions. Glucose is a primary substrate for energy metabolism while lactate is a major metabolite and signaling molecule. K+ ions maintain cell membrane physiology and homeostasis whereas Ca2+ ions serve as messengers during muscle activity and neurotransmission.Sensor characteristics like sensitivity, selectivity, linear range, and operational longevity for each biosensor were assessed using chronoamperometry or chronopotentiometry techniques on a potentiostat/potentiometer instrument. The results indicate that the sensor fabrication strategies described, in combination with our µMESA platform, can be used to measure changes in metabolite concentrations under laminar flow. Ultimately, this versatile technology may provide novel insights into complex physiological and pathological processes in biological systems.

Thin Membranes Using PFSA-Vinylon Intermediate Layer for PEM Fuel Cells

Fuel cells are attracting attention as one of the key energy devices for achieving carbon neutrality in 2050. Currently, fuel cells are being improved for versatile mobile applications. Among the components of fuel cell devices, polymer electrolyte membranes for proton exchange, in particular, are required to have high proton conductivity at high temperature, high and low humidification, and thin membranes. Proton-exchange fuel cells utilize perfluorosulfonic acid (PFSA) ionomers and membranes from Chemours and 3M and Solvay [1]. Nafion membranes with a thickness of 178-25 μm and Gore select membranes (with reinforcement) with a thickness of 20-5 μm have been commercialized [2,3]. On the other hand, thinner polymer electrolyte membranes can reduce the ohmic voltage drop in fuel cells to improve performance and lower costs. However, it is difficult to obtain thin membranes of less than 20 μm without reinforcement using PFSA ionomers.In this report, a thin PFSA electrolyte membrane (10 μm) without reinforcement was successfully developed by introducing a PFSA-vinilon composite layer as an intermediate layer of the PFSA membrane. The fuel cell evaluation revealed that it has a high current density.The ionomers used were 5% Nafion solution (DE520 CS type, EW=1100) and 6% Aquivion solution (D83-06A, EW=830). PVA (polyvinyl alcohol) was synthesized from polyvinyl acetate (PVAc, Mw=100,000). The laminated membranes (10 μm thickness) was obtained by preparing a 2 μm PFSA layer, followed by a 6 μm PFSA-PVA composite layer, then a 2 μm PFSA layer was coated. Finally, laminated membranes with PFSA-Vinylon composite layers were obtained by Formalization reaction the PFSA-PVA composite layers.FTIR evaluation of the PFSA/ PFSA-Viynylon/ PFSA multilayers confirmed the presence of an intermediate layer by observing Vinylon-derived peaks. Conductivities of about 4.5 mS/cm and 2.5 mS/cm in the thickness direction were obtained at 80°C, 90%RH and 20%RH, respectively. On the other hand, I-V evaluation was performed at 80°C, 100%RH and 35%RH using hydrogen, oxygen and air. Nafion 212 was used as a comparison membrane. The I-V characteristics of the laminated membranes showed higher current density than that of the Nafion membrane. Maximum current densities of 3 A/cm2 at 0.6 V and 3 A/cm2 at 0.4 V were obtained at 80°C, 100% RH and 35% RH with hydrogen and oxygen, respectively. Regarding the comparison of PFSA ionomers, Aquivion showed higher performance at higher current densities than Nafion [4].

Selective Ion Conducting Polymers for Non-Aqueous Redox Flow Battery Applications

Providing sustainable supplies of clean energy is a critical global challenge for the future. As intermittent renewable energy sources are increasingly deployed, grid-scale energy storage solutions are increasingly needed. One approach to addressing this challenge is to use flow battery technology to store and deliver grid-scale amounts of energy. Non-aqueous redox flow batteries can be operated at higher voltages and energy densities compared to aqueous systems and, as such, may offer high volumetric energy density compared to other flow batteries. A significant challenge facing non-aqueous flow batteries, however, is the lack of selective membrane separators engineered for the unique challenges of non-aqueous electrochemical systems. Suitable membranes for non-aqueous redox flow battery applications must be stable in aggressive solvent environments, offer high conductivity, and provide selectivity to prevent cross-over of redox active molecules. Here, we report the synthesis and characterization of a series of negatively charged ion conductive polymeric membranes for non-aqueous flow battery applications. Fixed negative charges were added to a poly(phenylene oxide) backbone via a custom sulfonate group-based side chain. Lithium ion conductivity and ferrocene permeability properties were characterized to evaluate the selectivity of the membrane for ion transport relative to redox active molecule cross-over (as ferrocene is a representative redox active molecule). The polymers exhibited combinations of conductivity and selectivity that are favorable compared to other Nafion-based materials, and the materials appear to be dimensionally stable in a non-aqueous electrolyte over a period of several months. Redox active molecule cross-over was analyzed within a thermodynamic regular solution framework to highlight how thermodynamic factors contribute to cross-over properties. Ultimately, the data suggest a decoupling of ion and redox active molecule transport that could inform future efforts to develop advanced non-aqueous redox flow battery membrane separators. Altogether, this presentation discusses the transport properties and stability of these materials that show promise for non-aqueous flow battery applications.

Electrochemical Ion Separations By Recyclable Electrode Cell

Electrochemical separations using Faradaic electrodes are able to exceed the ion adsorption values as well as selectivity when compared to capacitive electrodes, which is due to the bulk reactions for the former vs. surface confined for the latter. However, the cyclability of battery/faradaic electrodes is constrained to hundreds or a few thousands of cycles. This work proposes an electrochemical ion pumping design with the unique feature of using injectable electrodes to overcome the ciclability issue and easily control the areal capacity. The idea consists on using injectable electrodes with the intention of recycling the active material once the end-of-life of the device is reached due to active material degradation. In this fashion, the active material is replaced in a straightforward deinjecting-injecting process allowing direct reuse of the inactive components of the device, thus contributing to reducing the replacement cost. This device is called Ion Pumping Injectable Cell (IPIC).Moreover, the IPIC system is a tremendously versatile technology due to the simple and easy methodology employed to replace the electrodes. In this fashion, the system was tested using different types of lithium intercalation materials (LFP and LMO), different ion capturing such as potassium (Prussian Blue Analogs, PBA´s), sodium (NMO) or more conventional activated carbon electrodes (capacitive non-selective electrode). In addition to this feature, it is important to remark that the IPIC could be used in a symmetric (e.g. LFP-LFP) or asymmetric configuration (e.g. LFP-LMO). The main difference is that the asymmetric system has the ability of storing energy while capturing ions and deliver that energy in the subsequent step. This is so due to the different electrode potential. The selectivity toward specific ions is achieved by using a chemical ion-selective separator such as an ion exchange membrane (LFP-LFP or LFP-LMO systems), or by using ion selective intercalation materials such as LFP and PBA´s without the need of selective membranes.In this work, the benefits of the injectable electrode cell architecture will be examined, the performance of different cell configurations will be discussed and the electrochemical ion separation mechanism will be analyzed for different applications. Acknowledgements : J.J. Lado and Alba Fombona-Pascual acknowledge Comunidad de Madrid for the fellowship (2020-T1/AMB-19799).

Surface implantation of ionically conductive polyhydroxyethylaniline on cation exchange membrane for efficient heavy metal ions separation

Extraction of heavy metal ions from aqueous could enable recycling of wastewater and reusing of high-value ion resources. Recently, electrodialysis (ED) technology has been applied in the removal of heavy metal ions from wastewater, however, developing high-efficient and stable heavy metal ions selective cation exchange membrane (CEM) remains an elusive challenge. Herein, we demonstrate the fabrication of high-efficient cations selective CEM with the surface implantation of ionically conductive polyhydroxyethylaniline (PANI-OH) on a commercial CEM membrane (CTG) containing sulfonic acid groups via the electrostatic attraction. Implanted hydrophilic and positively charged PANI-OH facilitates fast and selective transfer of Cu2+ over Zn2+ cations through the membrane. Meanwhile, the synergistic effect of rigid conjugate structure and hydrogen-bond interaction of PANI-OH renders the resultant membrane CTG-PANI-OH with stable structure and separation performance. As such, the Cu2+/Zn2+ permselectivity of CTG-PANI-OH membrane is ~1.70, which is about 190 % of that of the pristine CTG membrane. This work provides a facile design and strategy for the construction of high-efficient cations selective CEMs with great application prospects in the purification and extraction of heavy metal ions from wastewater.

ANALYSIS OF SCIENTIFIC RESEARCH ON CLINICAL APPLICATIONS OF L-CARNITINE IN PEDIATRIC PRACTICE

The L-carnitine molecule was discovered 115 years ago by two scientists, Prof. R. P. Krimber and Prof. V. S. Gulevich. In 1962, the role of carnitine as a carrier of long-chain fatty acids into the mitochondria through their internal, highly selective membrane was discovered. L-carnitine is a vital compound that plays a crucial role in fat metabolism and energy metabolism in the child's body. The purpose of the study is to analyze the literature data on the current features of the clinical and pharmacological substantiation of the use of L-carnitine in pediatric practice. The article discusses aspects of the use of L-carnitine in pediatric medicine. L-Carnitine, essential for fatty acid metabolism, is synthesized endogenously and obtained from dietary sources. Ninety-eight percent of it is accumulated in skeletal muscles. its critical role in primary deficiencies, such as systemic encephalomyopathies and isolated myopathies, is unequivocal. L-Carnitine modulates glucose metabolism and increases the activity of respiratory chain enzymes. In addition, it acts as an antioxidant, preventing oxidative damage and inhibiting apoptosis, a signal in response to oxidative stress. Studies show that L-carnitine may be beneficial for children with metabolic disorders, athletes, and other categories of patients. However, it is important to consider dosage, safety, and potential side effects. Thus, the accumulated clinical experience of L-carnitine use indicates various positive effects and allows us to consider it an effective preventive and therapeutic agent that can be used in the pediatric population. Its applications extend to scenarios requiring energy support during heightened mental, emotional, and physical stress, as an adjunct therapy for diverse somatic diseases, during post-illness rehabilitation, and for bolstering immune reserves.

Simultaneously promoting CO2 permeability and selectivity of polyethylene oxide membranes via introducing CO2-philic KAUST-7

To overcome the challenging trade-off between permeability and selectivity in polymer CO2 separation membranes, CO2-philic metal-organic framework (MOF) KAUST-7 was incorporated within polyethylene oxide (PEO)-type matrices to prepare mixed matrix membranes (MMMs). A cross-scale approach of quantum chemical calculations and molecular dynamics simulations was used to explore the behavior and mechanism of CO2 adsorption on KAUST-7. The strong affinity between KAUST-7 and CO2 enabled a dramatic increase in the CO2 solubility of MMMs. The 2 wt% KAUST-7 loaded MMM exhibited CO2 permeability and CO2/N2 selectivity of 608 Barrer and 75, respectively, representing 41.7% and 54% improvement compared to the neat membrane, exceeding the 2019 upper bound. Furthermore, long-term separation tests for 100 h demonstrated the stability of these membranes.

Greener synthesis of thin-film nanocomposite membranes with varied nanofillers for enhanced organic micropollutant removal

Nowadays, the green process in membrane science is essential for industrial applications. The nanofiltration (NF) membrane developed by a green approach with effective separation of micropollutant from aqueous media makes it possible. Here, we designed a series of thin-film nanocomposite membranes prepared with structurally and morphologically different nanofillers, such as graphene oxide (GO)–NH2, arginine (Arg)-MMT and cloisite (C) MMT-NH2. The vapour-phase interfacial polymerisation (VP-IP) process is used to prepare highly selective and permeable thin-film nanocomposite (TFN) membranes. The polymerization reaction was done on the surface of the polysulfone (PSf) support membrane between an aqueous phase solution of 3,5-diaminobenzoic acid (DABA) and vapours of trimesoyl chloride (TMC). The nanomaterials' and prepared membranes' chemical and physical properties were determined using different characterization techniques. The TFN membranes (TFN-1, TFN-2 and TFN-3) prepared using three different nanomaterials (GO-NH2, Arg-MMT, CMMT-NH2) were compared for their separation against pharmaceutical compounds sulfamethoxazole (SMZ), triclosan (TRI), diclofenac (DIC) and cephalexin (CEP). The membranes demonstrated good hydrophilicity and antibacterial activity, resulting in a reasonable permeate flux rate. The fabricated membranes showed excellent selectivity for pharmaceutical compounds. Still, the TFN-3 membrane embedded with CMMT-NH2 nanomaterial recorded the highest rejection rate (> 99%) compared to the TFN-2 (Arg-MMT) and TFN-1 (GO-NH2) membranes. In contrast, the permeate flux rates for the individual TFN membranes showed slight variation. The developed TFN membranes via green and sustainable vapour-phase interfacial polymerization process demonstrated the possibility of being utilized for removing organic micropollutants from water to prevent the terrible devastation of our environment and aquatic systems.

Ion-pairing design of covalent organic framework membranes for separation and controlled release of pharmaceuticals

Intrinsically charged covalent organic frameworks (COFs) afford specific ionic nanochannels for mass transport, and thus become promising platforms to design membranes with unique selectivity. However, internal electrostatic repulsion and large-pore frameworks cause significant barriers that greatly limit membrane performances. Herein, we report a novel strategy to synchronously crystallize and upgrade cationic COF membranes by ion-pairing design. Ion-paired guest molecules are involved in electric-driven interfacial crystallization to offset the charges of the ionic monomers and host frameworks. This host-guest neutralization promotes the crystallization of compact COF membranes. Lateral dimension and charge nature of guest molecules fundamentally affect the ion-pairing efficiency. Tight encapsulation of the large-sized electronegative molecules effectually narrows the molecular sieving channels, yielding a significant elevation in membrane selectivity. The membrane rejection of organic ions with a size larger than 1.2 nm thus can be improved from below 50 % to above 85 % with a water permeance of ∼10 L m−2 h−1 bar−1. Prominently, our membranes demonstrate efficient recovery and pH-dependent release of bioactive pharmaceuticals, with a release rate that is 12 times higher in an acidic solution compared to a neutral environment. This work provides an ion-pairing strategy to regulate COF membranes for pharmaceutical industries and beyond.

Enhancing nanofiltration membrane selectivity between mineral salts and organic pollutants by sulfonic acid functionalization for drinking water treatment

Efficient removal of natural organic matter (NOM) and organic micropollutants (OMPs) while preserving essential mineral salts is a critical goal of high-quality drinking water production, which has not been satisfyingly achieved by available nanofiltration (NF) membranes. In this study, a facile modification strategy was developed to enhance membrane salt/organics selectivity, purposely utilizing the advantages of sulfonic acid groups including high hydrophilicity, strong acidity and low complexation propensity for divalent cations. The post-treatment using a heated alkaline solution of taurine endowed the membrane with reduced active layer thickness, properly enlarged pore size and more favorable surface characteristics inheriting from grafted sulfonic acid groups. Compared to the control one, the optimal modified membrane exhibited a more than doubled water permeance and significantly reduced rejections of Ca2+ and Mg2+, while maintaining a high removal capacity for OMPs. The membrane superiority in the rejection selectivity between mineral salts and NOM was further demonstrated for natural surface water treatment, which outperformed a variety of commercial NF membranes. Improved dual resistance to Ca2+-involved organic fouling and scaling was also achieved by the sulfonic acid functionalized membrane with a higher passage of Ca2+. This study provides insights on the fit-for-purpose enhancement of membrane performance for more efficient water treatment.

Resonances for a Solvable Model of Ultrasound Scattering by a Cell Membrane

We study the resonances for scattering of acoustic waves by cell membrane. Due to the fact that we deal with this phenomenon only, we use the simplest model of the membrane as a potential supported by a surface. The asymptotics of the Green’s function with the singularity at the surface is obtained. The influence of the surface curvature on the resonances is investigated. An application of the result to explanation of selective cancer cell membrane destruction in ultrasonic field is discussed.

NeuM: A Neuron‐Selective Probe Incorporates into Live Neuronal Membranes via Enhanced Clathrin‐Mediated Endocytosis in Primary Neurons

AbstractThe development of a small‐molecule probe designed to selectively target neurons would enhance the exploration of intricate neuronal structures and functions. Among such probes, NeuO stands out as the pioneer and has gained significant traction in the field of research. Nevertheless, neither the mechanism behind neuron‐selectivity nor the cellular localization has been determined. Here, we introduce NeuM, a derivative of NeuO, designed to target neuronal cell membranes. Furthermore, we elucidate the mechanism behind the selective neuronal membrane trafficking that distinguishes neurons. In an aqueous buffer, NeuM autonomously assembles into micellar structures, leading to the quenching of its fluorescence (Φ=0.001). Upon exposure to neurons, NeuM micelles were selectively internalized into neuronal endosomes via clathrin‐mediated endocytosis. Through the endocytic recycling pathway, NeuM micelles integrate into neuronal membrane, dispersing fluorescent NeuM molecules in the membrane (Φ=0.61). Molecular dynamics simulations demonstrated that NeuM, in comparison to NeuO, possesses optimal lipophilicity and molecular length, facilitating its stable incorporation into phospholipid layers. The stable integration of NeuM within neuronal membrane allows the prolonged monitoring of neurons, as well as the visualization of intricate neuronal structures.

NeuM: A Neuron-Selective Probe Incorporates into Live Neuronal Membranes via Enhanced Clathrin-Mediated Endocytosis in Primary Neurons.

The development of a small-molecule probe designed to selectively target neurons would enhance the exploration of intricate neuronal structures and functions. Among such probes, NeuO stands out as the pioneer and has gained significant traction in the field of research. Nevertheless, neither the mechanism behind neuron-selectivity nor the cellular localization has been determined. Here, we introduce NeuM, a derivative of NeuO, designed to target neuronal cell membranes. Furthermore, we elucidate the mechanism behind the selective neuronal membrane trafficking that distinguishes neurons. In an aqueous buffer, NeuM autonomously assembles into micellar structures, leading to the quenching of its fluorescence (Φ=0.001). Upon exposure to neurons, NeuM micelles were selectively internalized into neuronal endosomes via clathrin-mediated endocytosis. Through the endocytic recycling pathway, NeuM micelles integrate into neuronal membrane, dispersing fluorescent NeuM molecules in the membrane (Φ=0.61). Molecular dynamics simulations demonstrated that NeuM, in comparison to NeuO, possesses optimal lipophilicity and molecular length, facilitating its stable incorporation into phospholipid layers. The stable integration of NeuM within neuronal membrane allows the prolonged monitoring of neurons, as well as the visualization of intricate neuronal structures.

Prediction of a natural clay membrane selectivity towards heavy metal cations removal from wastewater: An electrochemical study

Prediction of a natural clay membrane selectivity towards heavy metal cations removal from wastewater: An electrochemical study

A high selective and permeable C7N6 monolayer membrane for H2 purification: First-principles and molecular dynamics simulations

Designing efficient membranes for hydrogen purification and separation is highly desired because of the development of the hydrogen economy. Using the combination methods of density functional theory (DFT) calculations and molecular dynamics (MD) simulations, we theoretically investigated the performance of the C7N6 monolayer for H2 purification and separation. Our DFT calculations indicate that H2 molecules would permeate through the C7N6 monolayer with a relatively low energy barrier (0.689 eV), and the C7N6 monolayer has an ultra-high selectivity of 7.47 × 106, 5.71 × 109, 1.19 × 1011, and 1.08 × 1012 for H2/O2, H2/CO2, H2/CO, and H2/N2 at even high temperature of 500 K, respectively. The MD simulations confirmed that the high selectivity and permeability of the H2 gas above 500 K. Even at higher temperatures of 800 to 1000 K, almost all of H2 gas can be separated by the C7N6 membrane without any other foreign gases passing through the membrane, indicating that the C7N6 monolayer can be used as an ultra-high performance H2 purification and separation membrane on the practical conditions as the C7N6 monolayers are dynamically, thermodynamically, and mechanically stable.

Coion exclusion properties of cation exchange membranes in 2:1 divalent salt solutions

The selectivity of ion exchange membranes hinges on their capacity to exclude coions. Yet, understanding how they reject coions in multivalent salt solutions remains challenging. This study presents a new molecular theory to understand coion exclusion. It examines counterion and coion condensation, including electrosteric effects. Supported by experimental data [Gokturk et al., Nat. Commun., 13 (2022)], we analyze cation exchange membrane potential in a 2:1 salt solution, revealing insights into coion selectivity and exclusion mechanisms. Notably, our theory deviates from earlier research by accommodating condensed divalent counterions that bind to one or two fixed-charged monomers. Additionally, we account for many-body electrostatic interactions, allowing the former to bind to sorbed coions. Our findings highlight the importance of coion condensation, especially in low-concentration salt conditions where coions are mainly condensed. This effect becomes less significant as the external solution concentration rises. These findings clarify the suitability of the ideal Donnan model in high-concentration salts, but its accuracy decreases in low-concentration situations. To summarize, our study emphasizes the need to account for counterion and coion condensation to understand membrane selectivity in low-concentration multivalent salt solutions.

Molecular insights into the differential membrane targeting of maximin 1 in prokaryotic and eukaryotic cells

Antimicrobial resistance is a pressing global health concern, underscoring the need for alternative treatments. Antimicrobial peptides (AMPs) have shown promise in this regard, with maximin 1 being a cationic, amphipathic AMP possessing antibacterial, antifungal, and antiviral activities with low hemolytic activity. In this study, we used molecular dynamics simulation to investigate the molecular basis for membrane selectivity of Maximin 1. By studying interactions between maximin 1 and different models of prokaryotic (anionic) and eukaryotic (zwitterionic) membranes, we found that Maximin 1 interacts more strongly with the prokaryotic membrane due to electrostatic attraction, while it weakly interacts with the zwitterionic eukaryotic membrane. Our simulations also revealed that Gly-1, Lys-5, Lys-11, Lys-15, and Lys-19 were identified to play a crucial role in the adsorption of maximin unto the prokaryotic membrane surface. The alpha-helical nature of the peptide, in addition to its amphipathic nature, was necessary for the adsorption of the peptide onto the surface of the prokaryotic membrane. Interestingly, the later transition of the alpha helix into a random coil was crucial in penetrating the prokaryotic membrane while hindering interactions with the eukaryotic membrane. Residues in the middle region of the peptide (residues 9–16) were also responsible for permeating the prokaryotic membrane over the eukaryotic membrane. These findings shed light on the peptide’s selective targeting of bacterial membranes over human cell membranes and could inform the design of more effective AMPs. Communicated by Ramaswamy H. Sarma

Mixed matrix membranes incorporating amino-functionalized ZIF-8-NH2 in a carboxylic polyimide for molecularly selective gas separation

Mixed matrix membranes (MMMs) combine the advantages of polymers and inorganic materials and demonstrate higher gas permeability than polymeric membranes, which, however, face the challenge of incompatible interface ascribed to the intrinsically different nature of the polymer and inorganic phase. To overcome this hurdle, herein, co-polyimide (6FBDA) was designed with carboxylic side groups to enhance the interfacial compatibility with amino-functionalized MOF(ZIF-8-NH2) via intensive π-π stacking and hydrogen bonds. The imidazole units in 6FBDA resemble ZIF-8-NH2 ligands and promote π-π stacking of polymer and MOF while the carboxylic moieties establish hydrogen bonds with the amino ligands of ZIF-8-NH2, significantly improving the interfacial compatibility of polymer and MOF. The defect-free MMMs with 50 wt% MOF loading demonstrate a CO2 and H2 permeability of 80.8 Barrer and 127.5 Barrer, respectively, with a CO2/CH4 and H2/CH4 selectivity of 89.4 and 141.7, respectively, exceeding 2008 Robeson upper bounds. The experimental concept of this work opens a door for fabricating molecularly selective gas separation membranes with prospects for energy-efficient CO2 capture and hydrogen separations.

Constructing hierarchically elongated porous structure in ultrathin ultrahigh molecular weight polyethylene membrane: Achieving high selectivity with remained permeability

Anisotropic pores with a high aspect ratio exhibit higher permeability as well as selectivity than circular pores. Herein, highly selective porous membranes exhibiting elongated slit-like pores and disk-like interlayer large pores are fabricated successfully by biaxial stretching and further constrained uniaxial stretching of ultrahigh molecular weight polyethylene gel films. The thickness and the surface roughness of the porous membrane decrease, and the pore size distribution become narrow during biaxial stretching, while the porous structure become elongated during constrained uniaxial stretching. The thickness decreases from 173.23 μm to 2.33 μm, which reduces the resistance to water passage and then increases the water permeability from approximately 540 L/ (m2 h bar) to 780 L/ (m2 h bar). Due to the presence of mineral oil, the porosity is maintained and even high ratios of constrained uniaxial stretching do not close the pores. The elongation of the porous structure resulted in a significant reduction of the membrane pore size. At a total stretching ratio of 144 times, the pore size of the porous membrane with only biaxial stretching is 0.098 μm, while that of the porous membrane with biaxial stretching and further constrained uniaxial stretching is 0.048 μm. The separation accuracy and stability of the porous membrane improve distinctly, ascribing that the small pore size can reject small particles and prevent the particles from entering the membrane. This study provides one novel strategy to regulate the porous structure of porous polymer membranes for improving the separation efficiency.

Thin selective layered mixed matrix membranes (MMMs) with defective UiO-66 induced interface engineering toward highly enhanced pervaporation performance

The thin selective layer in mixed matrix membranes (MMMs) with high pervaporation performance is in high demand because of their high productivity. However, it has been limited because of the defective interface of sieving fillers in MMMs and the instability to permeate molecules, resulting in instability and degradation in the membrane state and pervaporation performance. Herein, we synthesized defective UiO-66 (DUiO66) by controlling the concentration of the reactants and then analyzed the characteristics of the defects. We confirmed that defects of the missing linker are induced in its structure, and DUiO66 (1.324) has a higher defect density than conventional UiO66 (1.064). Those led to the highly enhanced interface of DUiO66 with polyvinyl alcohol (PVA) matrix and water solvent, resulting in mechanical stability and a uniformed thin selective layer. Crosslinked thin-layered PVA MMMs with DUiO66 (XPDUiO66) were applied to the flat-sheet type and hollow fiber type membranes and then examined for the pervaporation performance to separate IPA/water solution (mainly 80/20 and 90/10 (w/w)). The thin-layered flat type and hollow fiber type XPDUiO66 revealed a dramatic increase in flux by 5.6 and 5.0 times compared to the free-standing type MMM while almost maintaining selectivity. Notably, the flat-sheet type XPDUiO66-2 increased around 606% and 1,664% in PSI relative to XPVA at a feed solution of 80/20 and 90/10 (w/w) IPA/water, respectively. The current work offers significant findings on the relationship between defective MOF-applied MMMs and pervaporation performance.