Membranes

17 pages, 39717 KiB

Open AccessEditor’s ChoiceArticle

Ceramic Processing of Silicon Carbide Membranes with the Aid of Aluminum Nitrate Nonahydrate: Preparation, Characterization, and Performance

by Esra Eray, Victor Manuel Candelario and Vittorio Boffa

Membranes 2021, 11(9), 714; https://doi.org/10.3390/membranes11090714 - 17 Sep 2021

Cited by 17 | Viewed by 5817

Abstract

The development of a low-cost and environmentally-friendly procedure for the fabrication of silicon carbide (SiC) membranes while achieving good membrane performance is an important goal, but still a big challenge. To address this challenge, herein, a colloidal coating suspension of sub-micron SiC powders [...] Read more.

The development of a low-cost and environmentally-friendly procedure for the fabrication of silicon carbide (SiC) membranes while achieving good membrane performance is an important goal, but still a big challenge. To address this challenge, herein, a colloidal coating suspension of sub-micron SiC powders was prepared in aqueous media by employing aluminum nitrate nonahydrate as a sintering additive and was used for the deposition of a novel SiC membrane layer onto a SiC tubular support by dip-coating. The sintering temperature influence on the structural morphology was studied. Adding aluminum nitrate nonahydrate reduced the sintering temperature of the as-prepared membrane compared to conventional SiC membrane synthesis. Surface morphology, pore size distribution, crystalline structure, and chemical and mechanical stability of the membrane were characterized. The membrane showed excellent corrosion resistance in acidic and basic medium for 30 days with no significant changes in membrane properties. The pure water permeance of the membrane was measured as 2252 L h⁻¹ m⁻² bar⁻¹. Lastly, the final membrane with 0.35 µm mean pore size showed high removal of oil droplets (99.7%) in emulsified oil-in-water with outstanding permeability. Hence, the new SiC membrane is promising for several industrial applications in the field of wastewater treatment. Full article

(This article belongs to the Special Issue Latest Development and Application of Ceramic Membranes for Sustainability)

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14 pages, 2756 KiB

Open AccessEditor’s ChoiceArticle

Sustainable Membrane-Based Wastewater Reclamation Employing CO₂ to Impede an Ionic Precipitation and Consequent Scale Progression onto the Membrane Surfaces

by Muhammad Kashif Shahid and Younggyun Choi

Membranes 2021, 11(9), 688; https://doi.org/10.3390/membranes11090688 - 6 Sep 2021

Cited by 8 | Viewed by 3968

Abstract

CO₂ capture and utilization (CCU) is a promising approach in controlling the global discharge of greenhouse gases (GHG). This study details the experimental investigation of CO₂ utilization in membrane-based water treatment systems for lowering the potential of ionic precipitation on membrane [...] Read more.

CO₂ capture and utilization (CCU) is a promising approach in controlling the global discharge of greenhouse gases (GHG). This study details the experimental investigation of CO₂ utilization in membrane-based water treatment systems for lowering the potential of ionic precipitation on membrane surface and subsequent scale development. The CO₂ utilization in feed water reduces the water pH that enables the dissociation of salts in their respective ions, which leave the system as a concentrate. This study compares the efficiency of CO₂ and other antifouling agents (CA-1, CA-2, and CA-3) for fouling control in four different membrane-based wastewater reclamation operations. These systems include Schemes 1, 2, 3, and 4, which were operated with CA-1, CA-2, CA-3, and CO₂ as antiscalants, respectively. The flux profile and percent salt rejection achieved in Scheme 4 confirmed the higher efficiency of CO₂ utilization compared with other antifouling agents. This proficient role of CO₂ in fouling inhibition is further endorsed by the surface analysis of used membranes. The SEM, EDS, and XRD examination confirmed the higher suitability of CO₂ utilization in controlling scale deposition compared with other antiscalants. The cost estimation also supported the CO₂ utilization for environmental friendly and safe operation. Full article

(This article belongs to the Special Issue Membrane Technologies for Water and Wastewater Treatment: Advances, Challenges, and Future Avenues)

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29 pages, 2414 KiB

Open AccessEditor’s ChoiceReview

Lipid Membrane Mimetics in Functional and Structural Studies of Integral Membrane Proteins

by Saman Majeed, Akram Bani Ahmad, Ujala Sehar and Elka R. Georgieva

Membranes 2021, 11(9), 685; https://doi.org/10.3390/membranes11090685 - 3 Sep 2021

Cited by 47 | Viewed by 11239

Abstract

Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell–environment, cell–cell and virus–host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental [...] Read more.

Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell–environment, cell–cell and virus–host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental factors—resulting in damaged binding to ligands and the adoption of non-physiological conformations that prevent the protein from returning to its physiological state. Thus, elucidating IMPs’ mechanisms of function and malfunction at the molecular level is important for enhancing our understanding of cell and organism physiology. This understanding also helps pharmaceutical developments for restoring or inhibiting protein activity. To this end, in vitro studies provide invaluable information about IMPs’ structure and the relation between structural dynamics and function. Typically, these studies are conducted on transferred from native membranes to membrane-mimicking nano-platforms (membrane mimetics) purified IMPs. Here, we review the most widely used membrane mimetics in structural and functional studies of IMPs. These membrane mimetics are detergents, liposomes, bicelles, nanodiscs/Lipodisqs, amphipols, and lipidic cubic phases. We also discuss the protocols for IMPs reconstitution in membrane mimetics as well as the applicability of these membrane mimetic-IMP complexes in studies via a variety of biochemical, biophysical, and structural biology techniques. Full article

(This article belongs to the Special Issue Advanced Research on Structure–Function Relationships of Membrane Proteins)

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32 pages, 10701 KiB

Open AccessEditor’s ChoiceReview

Photocatalytic Nanofiber Membranes for the Degradation of Micropollutants and Their Antimicrobial Activity: Recent Advances and Future Prospects

by Mandla B. Chabalala, Nozipho N. Gumbi, Bhekie B. Mamba, Mohammed Z. Al-Abri and Edward N. Nxumalo

Membranes 2021, 11(9), 678; https://doi.org/10.3390/membranes11090678 - 31 Aug 2021

Cited by 38 | Viewed by 6978

Abstract

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber [...] Read more.

This review paper systematically evaluates current progress on the development and performance of photocatalytic nanofiber membranes often used in the removal of micropollutants from water systems. It is demonstrated that nanofiber membranes serve as excellent support materials for photocatalytic nanoparticles, leading to nanofiber membranes with enhanced optical properties, as well as improved recovery, recyclability, and reusability. The tremendous performance of photocatalytic membranes is attributed to the photogenerated reactive oxygen species such as hydroxyl radicals, singlet oxygen, and superoxide anion radicals introduced by catalytic nanoparticles such as TiO₂ and ZnO upon light irradiation. Hydroxyl radicals are the most reactive species responsible for most of the photodegradation processes of these unwanted pollutants. The review also demonstrates that self-cleaning and antimicrobial nanofiber membranes are useful in the removal of microbial species in water. These unique materials are also applicable in other fields such as wound dressing since the membrane allows for oxygen flow in wounds to heal while antimicrobial agents protect wounds against infections. It is demonstrated that antimicrobial activities against bacteria and photocatalytic degradation of micropollutants significantly reduce membrane fouling. Therefore, the review demonstrates that electrospun photocatalytic nanofiber membranes with antimicrobial activity form efficient cost-effective multifunctional composite materials for the removal of unwanted species in water and for use in various other applications such as filtration, adsorption and electrocatalysis. Full article

(This article belongs to the Special Issue Membrane Technology for the Removal of Organic Micropollutants and Emerging Pollutants)

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24 pages, 3729 KiB

Open AccessEditor’s ChoiceReview

Recent Progress in Mixed-Matrix Membranes for Hydrogen Separation

by Chong Yang Chuah, Xu Jiang, Kunli Goh and Rong Wang

Membranes 2021, 11(9), 666; https://doi.org/10.3390/membranes11090666 - 30 Aug 2021

Cited by 46 | Viewed by 9408

Abstract

Membrane separation is a compelling technology for hydrogen separation. Among the different types of membranes used to date, the mixed-matrix membranes (MMMs) are one of the most widely used approaches for enhancing separation performances and surpassing the Robeson upper bound limits for polymeric [...] Read more.

Membrane separation is a compelling technology for hydrogen separation. Among the different types of membranes used to date, the mixed-matrix membranes (MMMs) are one of the most widely used approaches for enhancing separation performances and surpassing the Robeson upper bound limits for polymeric membranes. In this review, we focus on the recent progress in MMMs for hydrogen separation. The discussion first starts with a background introduction of the current hydrogen generation technologies, followed by a comparison between the membrane technology and other hydrogen purification technologies. Thereafter, state-of-the-art MMMs, comprising emerging filler materials that include zeolites, metal-organic frameworks, covalent organic frameworks, and graphene-based materials, are highlighted. The binary filler strategy, which uses two filler materials to create synergistic enhancements in MMMs, is also described. A critical evaluation on the performances of the MMMs is then considered in context, before we conclude with our perspectives on how MMMs for hydrogen separation can advance moving forward. Full article

(This article belongs to the Special Issue Emerging Materials for Mixed-Matrix Membranes)

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28 pages, 2906 KiB

Open AccessFeature PaperEditor’s ChoiceReview

De Novo Ion-Exchange Membranes Based on Nanofibers

by Shaoling Zhang, Akihiko Tanioka and Hidetoshi Matsumoto

Membranes 2021, 11(9), 652; https://doi.org/10.3390/membranes11090652 - 25 Aug 2021

Cited by 8 | Viewed by 5075

Abstract

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de [...] Read more.

The unique functions of nanofibers (NFs) are based on their nanoscale cross-section, high specific surface area, and high molecular orientation, and/or their confined polymer chains inside the fibers. The introduction of ion-exchange (IEX) groups on the surface and/or inside the NFs provides de novo ion-exchangers. In particular, the combination of large surface areas and ionizable groups in the IEX-NFs improves their performance through indices such as extremely rapid ion-exchange kinetics and high ion-exchange capacities. In reality, the membranes based on ion-exchange NFs exhibit superior properties such as high catalytic efficiency, high ion-exchange and adsorption capacities, and high ionic conductivities. The present review highlights the fundamental aspects of IEX-NFs (i.e., their unique size-dependent properties), scalable production methods, and the recent advancements in their applications in catalysis, separation/adsorption processes, and fuel cells, as well as the future perspectives and endeavors of NF-based IEMs. Full article

(This article belongs to the Special Issue Novel Ion-Exchange Membranes)

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21 pages, 3192 KiB

Open AccessEditor’s ChoiceArticle

CeO₂-Blended Cellulose Triacetate Mixed-Matrix Membranes for Selective CO₂ Separation

by Chhabilal Regmi, Saeed Ashtiani, Zdeněk Sofer, Zdeněk Hrdlička, Filip Průša, Ondřej Vopička and Karel Friess

Membranes 2021, 11(8), 632; https://doi.org/10.3390/membranes11080632 - 17 Aug 2021

Cited by 19 | Viewed by 4123

Abstract

Due to the high affinity of ceria (CeO₂) towards carbon dioxide (CO₂) and the high thermal and mechanical properties of cellulose triacetate (CTA) polymer, mixed-matrix CTA-CeO₂ membranes were fabricated. A facile solution-casting method was used for the fabrication [...] Read more.

Due to the high affinity of ceria (CeO₂) towards carbon dioxide (CO₂) and the high thermal and mechanical properties of cellulose triacetate (CTA) polymer, mixed-matrix CTA-CeO₂ membranes were fabricated. A facile solution-casting method was used for the fabrication process. CeO₂ nanoparticles at concentrations of 0.32, 0.64 and 0.9 wt.% were incorporated into the CTA matrix. The physico-chemical properties of the membranes were evaluated by SEM-EDS, XRD, FTIR, TGA, DSC and strain-stress analysis. Gas sorption and permeation affinity were evaluated using different single gases. The CTA-CeO₂ (0.64) membrane matrix showed a high affinity towards CO₂ sorption. Almost complete saturation of CeO₂ nanoparticles with CO₂ was observed, even at low pressure. Embedding CeO₂ nanoparticles led to increased gas permeability compared to pristine CTA. The highest gas permeabilities were achieved with 0.64 wt.%, with a threefold increase in CO₂ permeability as compared to pristine CTA membranes. Unwanted aggregation of the filler nanoparticles was observed at a 0.9 wt.% concentration of CeO₂ and was reflected in decreased gas permeability compared to lower filler loadings with homogenous filler distributions. The determined gas selectivity was in the order CO₂/CH₄ > CO₂/N₂ > O₂/N₂ > H₂/CO₂ and suggests the potential of CTA-CeO₂ membranes for CO₂ separation in flue/biogas applications. Full article

(This article belongs to the Section Polymeric Membranes)

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17 pages, 2415 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Correlations between Properties of Pore-Filling Ion Exchange Membranes and Performance of a Reverse Electrodialysis Stack for High Power Density

by Hanki Kim, Jiyeon Choi, Namjo Jeong, Yeon-Gil Jung, Haeun Kim, Donghyun Kim and SeungCheol Yang

Membranes 2021, 11(8), 609; https://doi.org/10.3390/membranes11080609 - 10 Aug 2021

Cited by 15 | Viewed by 3880

Abstract

The reverse electrodialysis (RED) stack-harnessing salinity gradient power mainly consists of ion exchange membranes (IEMs). Among the various types of IEMs used in RED stacks, pore-filling ion exchange membranes (PIEMs) have been considered promising IEMs to improve the power density of RED stacks. [...] Read more.

The reverse electrodialysis (RED) stack-harnessing salinity gradient power mainly consists of ion exchange membranes (IEMs). Among the various types of IEMs used in RED stacks, pore-filling ion exchange membranes (PIEMs) have been considered promising IEMs to improve the power density of RED stacks. The compositions of PIEMs affect the electrical resistance and permselectivity of PIEMs; however, their effect on the performance of large RED stacks have not yet been considered. In this study, PIEMs of various compositions with respect to the RED stack were adopted to evaluate the performance of the RED stack according to stack size (electrode area: 5 × 5 cm² vs. 15 × 15 cm²). By increasing the stack size, the gross power per membrane area decreased despite the increase in gross power on a single RED stack. The electrical resistance of the PIEMs was the most important factor for enhancing the power production of the RED stack. Moreover, power production was less sensitive to permselectivities over 90%. By increasing the RED stack size, the contributions of non-ohmic resistances were significantly increased. Thus, we determined that reducing the salinity gradients across PIEMs by ion transport increased the non-ohmic resistance of large RED stacks. These results will aid in designing pilot-scale RED stacks. Full article

(This article belongs to the Special Issue Recent Advances in the Membranes for Reverse Electrodialysis)

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13 pages, 1492 KiB

Open AccessEditor’s ChoiceReview

Rush Hour of LATs towards Their Transport Cycle

by Adrià Nicolàs-Aragó, Joana Fort, Manuel Palacín and Ekaitz Errasti-Murugarren

Membranes 2021, 11(8), 602; https://doi.org/10.3390/membranes11080602 - 8 Aug 2021

Cited by 8 | Viewed by 3172

Abstract

The mammalian SLC7 family comprises the L-amino acid transporters (LATs) and the cationic amino acid transporters (CATs). The relevance of these transporters is highlighted by their involvement in several human pathologies, including inherited rare diseases and acquired diseases, such as cancer. In the [...] Read more.

The mammalian SLC7 family comprises the L-amino acid transporters (LATs) and the cationic amino acid transporters (CATs). The relevance of these transporters is highlighted by their involvement in several human pathologies, including inherited rare diseases and acquired diseases, such as cancer. In the last four years, several crystal or cryo-EM structures of LATs and CATs have been solved. These structures have started to fill our knowledge gap that previously was based on the structural biology of remote homologs of the amino acid–polyamine–organocation (APC) transporters. This review recovers this structural and functional information to start generating the molecular bases of the transport cycle of LATs. Special attention is given to the known transporter conformations within the transport cycle and the molecular bases for substrate interaction and translocation, including the asymmetric interaction of substrates at both sides of the plasma membrane. Full article

(This article belongs to the Collection Membrane Protein Structure and Functions)

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19 pages, 8262 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Titanium Dioxide Hollow Nanofiber for Photocatalytic Degradation of Methylene Blue Dye

by Nurul Natasha Mohammad Jafri, Juhana Jaafar, Nur Hashimah Alias, Sadaki Samitsu, Farhana Aziz, Wan Norharyati Wan Salleh, Mohd Zamri Mohd Yusop, Mohd Hafiz Dzarfan Othman, Mukhlis A Rahman, Ahmad Fauzi Ismail, Takeshi Matsuura and Arun M. Isloor

Membranes 2021, 11(8), 581; https://doi.org/10.3390/membranes11080581 - 30 Jul 2021

Cited by 26 | Viewed by 4343

Abstract

Environmental crisis and water contamination have led to worldwide exploration for advanced technologies for wastewater treatment, and one of them is photocatalytic degradation. A one-dimensional hollow nanofiber with enhanced photocatalytic properties is considered a promising material to be applied in the field. Therefore, [...] Read more.

Environmental crisis and water contamination have led to worldwide exploration for advanced technologies for wastewater treatment, and one of them is photocatalytic degradation. A one-dimensional hollow nanofiber with enhanced photocatalytic properties is considered a promising material to be applied in the field. Therefore, we synthesized titanium dioxide hollow nanofibers (THNF) with extended surface area, light-harvesting properties and an anatase–rutile heterojunction via a template synthesis method and followed by a calcination process. The effect of calcination temperature on the formation and properties of THNF were determined and the possible mechanism of THNF formation was proposed. THNF nanofibers produced at 600 °C consisted of a mixture of 24.2% anatase and 75.8% rutile, with a specific surface area of 81.2776 m²/g. The hollow nanofibers also outperformed the other catalysts in terms of photocatalytic degradation of MB dye, at 85.5%. The optimum catalyst loading, dye concentration, pH, and H₂O₂ concentration were determined at 0.75 g/L, 10 ppm, pH 11, and 10 mM, respectively. The highest degradation of methylene blue dye achieved was 95.2% after 4 h of UV irradiation. Full article

(This article belongs to the Section Membrane Chemistry)

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29 pages, 4366 KiB

Open AccessEditor’s ChoiceArticle

Application and Analysis of Bipolar Membrane Electrodialysis for LiOH Production at High Electrolyte Concentrations: Current Scope and Challenges

by Alonso González, Mario Grágeda, Adrián Quispe, Svetlana Ushak, Philippe Sistat and Marc Cretin

Membranes 2021, 11(8), 575; https://doi.org/10.3390/membranes11080575 - 29 Jul 2021

Cited by 24 | Viewed by 7709

Abstract

The objective of this work was to evaluate obtaining LiOH directly from brines with high LiCl concentrations using bipolar membrane electrodialysis by the analysis of Li⁺ ion transport phenomena. For this purpose, Neosepta BP and Fumasep FBM bipolar membranes were characterized by [...] Read more.

The objective of this work was to evaluate obtaining LiOH directly from brines with high LiCl concentrations using bipolar membrane electrodialysis by the analysis of Li⁺ ion transport phenomena. For this purpose, Neosepta BP and Fumasep FBM bipolar membranes were characterized by linear sweep voltammetry, and the Li⁺ transport number in cation-exchange membranes was determined. In addition, a laboratory-scale reactor was designed, constructed, and tested to develop experimental LiOH production tests. The selected LiCl concentration range, based on productive process concentrations for Salar de Atacama (Chile), was between 14 and 34 wt%. Concentration and current density effects on LiOH production, current efficiency, and specific electricity consumption were evaluated. The highest current efficiency obtained was 0.77 at initial concentrations of LiOH 0.5 wt% and LiCl 14 wt%. On the other hand, a concentrated LiOH solution (between 3.34 wt% and 4.35 wt%, with a solution purity between 96.0% and 95.4%, respectively) was obtained. The results of this work show the feasibility of LiOH production from concentrated brines by means of bipolar membrane electrodialysis, bringing the implementation of this technology closer to LiOH production on a larger scale. Moreover, being an electrochemical process, this could be driven by Solar PV, taking advantage of the high solar radiation conditions in the Atacama Desert in Chile. Full article

(This article belongs to the Topic Electromaterials for Environment & Energy)

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18 pages, 2900 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Dimeric Vanadium Uptake and Species in Nafion™ and Novel Membranes from Vanadium Redox Flow Batteries Electrolytes

by Christian Lutz, Michael Breuckmann, Sven Hampel, Martin Kreyenschmidt, Xi Ke, Sabine Beuermann, Katharina Schafner, Thomas Turek, Ulrich Kunz, Ana Guilherme Buzanich, Martin Radtke and Ursula E. A. Fittschen

Membranes 2021, 11(8), 576; https://doi.org/10.3390/membranes11080576 - 29 Jul 2021

Cited by 4 | Viewed by 4268

Abstract

A core component of energy storage systems like vanadium redox flow batteries (VRFB) is the polymer electrolyte membrane (PEM). In this work, the frequently used perfluorosulfonic-acid (PFSA) membrane Nafion™ 117 and a novel poly (vinylidene difluoride) (PVDF)-based membrane are investigated. A well-known problem [...] Read more.

A core component of energy storage systems like vanadium redox flow batteries (VRFB) is the polymer electrolyte membrane (PEM). In this work, the frequently used perfluorosulfonic-acid (PFSA) membrane Nafion™ 117 and a novel poly (vinylidene difluoride) (PVDF)-based membrane are investigated. A well-known problem in VRFBs is the vanadium permeation through the membrane. The consequence of this so-called vanadium crossover is a severe loss of capacity. For a better understanding of vanadium transport in membranes, the uptake of vanadium ions from electrolytes containing V_dimer(IV–V) and for comparison also V(II), V(III), V(IV), and V(V) by both membranes was studied. UV/VIS spectroscopy, X-ray absorption near edge structure spectroscopy (XANES), total reflection X-ray fluorescence spectroscopy (TXRF), inductively coupled plasma optical emission spectrometry (ICP-OES), and micro X-ray fluorescence spectroscopy (microXRF) were used to determine the vanadium concentrations and the species inside the membrane. The results strongly support that V_dimer(IV–V), a dimer formed from V(IV) and V(V), enters the nanoscopic water-body of Nafion™ 117 as such. This is interesting, because as of now, only the individual ions V(IV) and V(V) were considered to be transported through the membrane. Additionally, it was found that the V_dimer(IV–V) dimer partly dissociates to the individual ions in the novel PVDF-based membrane. The V_dimer(IV–V) dimer concentration in Nafion™ was determined and compared to those of the other species. After three days of equilibration time, the concentration of the dimer is the lowest compared to the monomeric vanadium species. The concentration of vanadium in terms of the relative uptake λ = n(V)/n(SO₃) are as follows: V(II) [λ = 0.155] > V(III) [λ = 0.137] > V(IV) [λ = 0.124] > V(V) [λ = 0.053] > V_dimer(IV–V) [λ = 0.039]. The results show that the V_dimer(IV–V) dimer needs to be considered in addition to the other monomeric species to properly describe the transport of vanadium through Nafion™ in VRFBs. Full article

(This article belongs to the Special Issue Advanced Membranes for Energy and Environment: Synthesis and Characterization)

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20 pages, 3323 KiB

Open AccessEditor’s ChoiceArticle

Recovery of Valuable Solutes from Organic Solvent/Water Mixtures via Direct Contact Membrane Distillation (DCMD) as a Non-Heated Process

by Yuki Suga, Ryosuke Takagi and Hideto Matsuyama

Membranes 2021, 11(8), 559; https://doi.org/10.3390/membranes11080559 - 23 Jul 2021

Cited by 4 | Viewed by 4937

Abstract

Recently, the demand for the recovery of valuable solutes from organic solvents/water mixtures has increased in various fields. Furthermore, due to the abundance of heat-sensitive valuable solutes, the demand for non-heated concentration technologies has increased. In this study, the direct contact membrane distillation [...] Read more.

Recently, the demand for the recovery of valuable solutes from organic solvents/water mixtures has increased in various fields. Furthermore, due to the abundance of heat-sensitive valuable solutes, the demand for non-heated concentration technologies has increased. In this study, the direct contact membrane distillation (DCMD) using hydrophobic polyvinylidene difluoride (PVDF) hollow fiber membranes was investigated to confirm the possibility of recovering valuable solutes from organic solvents/water mixtures as a non-heated process. The DCMD with 1000 ppm NaCl aqueous solution achieved 0.8 kg/m²·h of vapor flux and >99.9% of NaCl retention, even at feed and coolant temperatures of 25 and 10 °C, respectively. Furthermore, when DCMD was conducted under various conditions, including feed temperatures of 25, 35 and 45 °C, and organic solvent concentration of 15, 30 and 50 wt%, using ethanol/water and acetonitrile/water mixtures containing 1000 ppm NaCl. A surfactant was also used as a valuable solute, in addition to NaCl. As a result, it was found that the total vapor flux increased with increasing temperature and concentration of organic solvents, as the partial vapor pressure of the organic solvents increased. Additionally, no solute leaked under any condition, even when the surfactant was used as a valuable solute. Full article

(This article belongs to the Special Issue Novel Materials for the Preparation and Application of Desalination Membranes)

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15 pages, 6949 KiB

Open AccessEditor’s ChoiceArticle

Membrane Fouling Controlled by Adjustment of Biological Treatment Parameters in Step-Aerating MBR

by Dimitra C. Banti, Manassis Mitrakas and Petros Samaras

Membranes 2021, 11(8), 553; https://doi.org/10.3390/membranes11080553 - 22 Jul 2021

Cited by 18 | Viewed by 3981

Abstract

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the [...] Read more.

A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT₁) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5–3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤ 2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial products (SMP), were also maintained at low concentrations, contributing additionally to the reduction of ΤΜP. Finally, the step-aerating MBR process and the selected imposed operating conditions of HRT, F/M and DO improved the MBR performance in terms of fouling control, facilitating its future wider application. Full article

(This article belongs to the Special Issue Advanced Research on Membrane Bioreactors 2021–2022)

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16 pages, 3546 KiB

Open AccessEditor’s ChoiceArticle

Electron Microscopic Confirmation of Anisotropic Pore Characteristics for ECMO Membranes Theoretically Validating the Risk of SARS-CoV-2 Permeation

by Makoto Fukuda, Tomoya Furuya, Kazunori Sadano, Asako Tokumine, Tomohiro Mori, Hitoshi Saomoto and Kiyotaka Sakai

Membranes 2021, 11(7), 529; https://doi.org/10.3390/membranes11070529 - 14 Jul 2021

Cited by 10 | Viewed by 5577

Abstract

The objective of this study is to clarify the pore structure of ECMO membranes by using our approach and theoretically validate the risk of SARS-CoV-2 permeation. There has not been any direct evidence for SARS-CoV-2 leakage through the membrane in ECMO support for [...] Read more.

The objective of this study is to clarify the pore structure of ECMO membranes by using our approach and theoretically validate the risk of SARS-CoV-2 permeation. There has not been any direct evidence for SARS-CoV-2 leakage through the membrane in ECMO support for critically ill COVID-19 patients. The precise pore structure of recent membranes was elucidated by direct microscopic observation for the first time. The three types of membranes, polypropylene, polypropylene coated with thin silicone layer, and polymethylpentene (PMP), have unique pore structures, and the pore structures on the inner and outer surfaces of the membranes are completely different anisotropic structures. From these data, the partition coefficients and intramembrane diffusion coefficients of SARS-CoV-2 were quantified using the membrane transport model. Therefore, SARS-CoV-2 may permeate the membrane wall with the plasma filtration flow or wet lung. The risk of SARS-CoV-2 permeation is completely different due to each anisotropic pore structure. We theoretically demonstrate that SARS-CoV-2 is highly likely to permeate the membrane transporting from the patient’s blood to the gas side, and may diffuse from the gas side outlet port of ECMO leading to the extra-circulatory spread of the SARS-CoV-2 (ECMO infection). Development of a new generation of nanoscale membrane confirmation is proposed for next-generation extracorporeal membrane oxygenator and system with long-term durability is envisaged. Full article

(This article belongs to the Special Issue Advances in Extracorporeal Membrane Oxygenation)

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11 pages, 2712 KiB

Open AccessEditor’s ChoiceArticle

Simulation on Pore Formation from Polymer Solution at Surface in Contact with Solid Substrate via Thermally Induced Phase Separation

by Yasushi Mino, Naruki Fukukawa and Hideto Matsuyama

Membranes 2021, 11(7), 527; https://doi.org/10.3390/membranes11070527 - 13 Jul 2021

Cited by 9 | Viewed by 3975

Abstract

The formation of porous structures from polymer solutions at the surface in contact with various solid surfaces via a thermally-induced phase separation (TIPS) process is investigated. The pore formation process at the bulk and the surface of the poly(methyl methacrylate)/cyclohexanol solution is simulated [...] Read more.

The formation of porous structures from polymer solutions at the surface in contact with various solid surfaces via a thermally-induced phase separation (TIPS) process is investigated. The pore formation process at the bulk and the surface of the poly(methyl methacrylate)/cyclohexanol solution is simulated with a model based on the phase field method. When the compatibilities between the polymer-rich phase formed by the phase separation and the solid surface are high or low, surface porosity decreases. In contrast, for the solid surface having similar compatibilities with the polymer and solvent, high surface porosity is achieved. This indicates that the compatibility between the solid surface and polymer solution is important, and that optimal compatibility results in high surface porosity. The knowledge obtained in this work is useful to design the coagulation bath component in the membrane preparation process by TIPS for achieving high surface porosity. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in Japan 2021, 2022)

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25 pages, 3687 KiB

Open AccessEditor’s ChoicePerspective

Emerging Materials to Prepare Mixed Matrix Membranes for Pollutant Removal in Water

by Yu Jie Lim, So Min Lee, Rong Wang and Jaewoo Lee

Membranes 2021, 11(7), 508; https://doi.org/10.3390/membranes11070508 - 5 Jul 2021

Cited by 53 | Viewed by 6084

Abstract

Various pollutants of different sizes are directly (e.g., water-borne diseases) and indirectly (e.g., accumulation via trophic transfer) threatening our water health and safety. To cope with this matter, multifaceted approaches are required for advanced wastewater treatment more efficiently. Wastewater treatment using mixed matrix [...] Read more.

Various pollutants of different sizes are directly (e.g., water-borne diseases) and indirectly (e.g., accumulation via trophic transfer) threatening our water health and safety. To cope with this matter, multifaceted approaches are required for advanced wastewater treatment more efficiently. Wastewater treatment using mixed matrix membranes (MMMs) could provide an excellent alternative since it could play two roles in pollutant removal by covering adsorption and size exclusion of water contaminants simultaneously. This paper provides an overview of the research progresses and trends on the emerging materials used to prepare MMMs for pollutant removal from water in the recent five years. The transition of the research trend was investigated, and the most preferred materials to prepare MMMs were weighed up based on the research trend. Various application examples where each emerging material was used have been introduced along with specific mechanisms underlying how the better performance was realized. Lastly, the perspective section addresses how to further improve the removal efficiency of pollutants in an aqueous phase, where we could find a niche to spot new materials to develop environmentally friendly MMMs, and where we could further apply MMMs. Full article

(This article belongs to the Special Issue Emerging Materials for Mixed-Matrix Membranes)

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14 pages, 2251 KiB

Open AccessEditor’s ChoiceArticle

Enhanced Performance of Carbon Molecular Sieve Membranes Incorporating Zeolite Nanocrystals for Air Separation

by Chong Yang Chuah, Kunli Goh and Tae-Hyun Bae

Membranes 2021, 11(7), 489; https://doi.org/10.3390/membranes11070489 - 29 Jun 2021

Cited by 23 | Viewed by 4172

Abstract

Three different zeolite nanocrystals (SAPO-34, PS-MFI and ETS-10) were incorporated into the polymer matrix (Matrimid^® 5218) as polymer precursors, with the aim of fabricating mixed-matrix carbon molecular sieve membranes (CMSMs). These membranes are investigated for their potential for air separation process. Based [...] Read more.

Three different zeolite nanocrystals (SAPO-34, PS-MFI and ETS-10) were incorporated into the polymer matrix (Matrimid^® 5218) as polymer precursors, with the aim of fabricating mixed-matrix carbon molecular sieve membranes (CMSMs). These membranes are investigated for their potential for air separation process. Based on our gas permeation results, incorporating porous materials is feasible to improve O₂ permeability, owing to the creation of additional porosities in the resulting mixed-matrix CMSMs. Owing to this, the performance of the CMSM with 30 wt% PS-MFI loading is able to surpass the upper bound limit. This study demonstrates the feasibility of zeolite nanocrystals in improving O₂/N₂ separation performance in CMSMs. Full article

(This article belongs to the Special Issue Emerging Materials for Mixed-Matrix Membranes)

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16 pages, 3565 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesized of Ag/Ag₂O Nanoparticles Using Aqueous Leaves Extracts of Phoenix dactylifera L. and Their Azo Dye Photodegradation

by Salah Eddine Laouini, Abderrhmane Bouafia, Alexander V. Soldatov, Hamed Algarni, Mohammed Laid Tedjani, Gomaa A. M. Ali and Ahmed Barhoum

Membranes 2021, 11(7), 468; https://doi.org/10.3390/membranes11070468 - 25 Jun 2021

Cited by 111 | Viewed by 7265

Abstract

In this study, silver/silver oxide nanoparticles (Ag/Ag₂O NPs) were successfully biosynthesized using Phoenix dactylifera L. aqueous leaves extract. The effect of different plant extract/precursor contractions (volume ratio, v/v%) on Ag/Ag₂O NP formation, their optical properties, and [...] Read more.

In this study, silver/silver oxide nanoparticles (Ag/Ag₂O NPs) were successfully biosynthesized using Phoenix dactylifera L. aqueous leaves extract. The effect of different plant extract/precursor contractions (volume ratio, v/v%) on Ag/Ag₂O NP formation, their optical properties, and photocatalytic activity towards azo dye degradation, i.e., Congo red (CR) and methylene blue (MB), were investigated. X-ray diffraction confirmed the crystalline nature of Ag/Ag₂O NPs with a crystallite size range from 28 to 39 nm. Scanning electron microscope images showed that the Ag/Ag₂O NPs have an oval and spherical shape. UV–vis spectroscopy showed that Ag/Ag₂O NPs have a direct bandgap of 2.07–2.86 eV and an indirect bandgap of 1.60–1.76 eV. Fourier transform infrared analysis suggests that the synthesized Ag/Ag₂O NPs might be stabilized through the interactions of -OH and C=O groups in the carbohydrates, flavonoids, tannins, and phenolic acids present in Phoenix dactylifera L. Interestingly, the prepared Ag/Ag₂O NPs showed high catalytic degradation activity for CR dye. The photocatalytic degradation of the azo dye was monitored spectrophotometrically in a wavelength range of 250–900 nm, and a high decolorization efficiency (84.50%) was obtained after 50 min of reaction. As a result, the use of Phoenix dactylifera L. aqueous leaves extract offers a cost-effective and eco-friendly method. Full article

(This article belongs to the Collection Polymeric Membranes: Science, Materials and Applications)

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20 pages, 4935 KiB

Open AccessEditor’s ChoiceReview

Structures and Dynamics of Native-State Transmembrane Protein Targets and Bound Lipids

by Michael Overduin, Catharine Trieber, R. Scott Prosser, Louis-Philippe Picard and Joey G. Sheff

Membranes 2021, 11(6), 451; https://doi.org/10.3390/membranes11060451 - 17 Jun 2021

Cited by 13 | Viewed by 5497

Abstract

Membrane proteins work within asymmetric bilayers of lipid molecules that are critical for their biological structures, dynamics and interactions. These properties are lost when detergents dislodge lipids, ligands and subunits, but are maintained in native nanodiscs formed using styrene maleic acid (SMA) and [...] Read more.

Membrane proteins work within asymmetric bilayers of lipid molecules that are critical for their biological structures, dynamics and interactions. These properties are lost when detergents dislodge lipids, ligands and subunits, but are maintained in native nanodiscs formed using styrene maleic acid (SMA) and diisobutylene maleic acid (DIBMA) copolymers. These amphipathic polymers allow extraction of multicomponent complexes of post-translationally modified membrane-bound proteins directly from organ homogenates or membranes from diverse types of cells and organelles. Here, we review the structures and mechanisms of transmembrane targets and their interactions with lipids including phosphoinositides (PIs), as resolved using nanodisc systems and methods including cryo-electron microscopy (cryo-EM) and X-ray diffraction (XRD). We focus on therapeutic targets including several G protein-coupled receptors (GPCRs), as well as ion channels and transporters that are driving the development of next-generation native nanodiscs. The design of new synthetic polymers and complementary biophysical tools bodes well for the future of drug discovery and structural biology of native membrane:protein assemblies (memteins). Full article

(This article belongs to the Special Issue Analytical Sciences Of / With Bio(mimetic) Membranes)

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12 pages, 9321 KiB

Open AccessEditor’s ChoiceArticle

Rapid Production and Purification of Dye-Loaded Liposomes by Electrodialysis-Driven Depletion

by Gamid Abatchev, Andrew Bogard, Zoe Hutchinson, Jason Ward and Daniel Fologea

Membranes 2021, 11(6), 417; https://doi.org/10.3390/membranes11060417 - 31 May 2021

Cited by 3 | Viewed by 5919

Abstract

Liposomes are spherical-shaped vesicles that enclose an aqueous milieu surrounded by bilayer or multilayer membranes formed by self-assembly of lipid molecules. They are intensively exploited as either model membranes for fundamental studies or as vehicles for delivery of active substances in vivo and [...] Read more.

Liposomes are spherical-shaped vesicles that enclose an aqueous milieu surrounded by bilayer or multilayer membranes formed by self-assembly of lipid molecules. They are intensively exploited as either model membranes for fundamental studies or as vehicles for delivery of active substances in vivo and in vitro. Irrespective of the method adopted for production of loaded liposomes, obtaining the final purified product is often achieved by employing multiple, time consuming steps. To alleviate this problem, we propose a simplified approach for concomitant production and purification of loaded liposomes by exploiting the Electrodialysis-Driven Depletion of charged molecules from solutions. Our investigations show that electrically-driven migration of charged detergent and dye molecules from solutions that include natural or synthetic lipid mixtures leads to rapid self-assembly of loaded, purified liposomes, as inferred from microscopy and fluorescence spectroscopy assessments. In addition, the same procedure was successfully applied for incorporating PEGylated lipids into the membranes for the purpose of enabling long-circulation times needed for potential in vivo applications. Dynamic Light Scattering analyses and comparison of electrically-formed liposomes with liposomes produced by sonication or extrusion suggest potential use for numerous in vitro and in vivo applications. Full article

(This article belongs to the Collection Feature Papers in Membranes in Life Sciences)

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35 pages, 7848 KiB

Open AccessEditor’s ChoiceArticle

Silica Fouling in Reverse Osmosis Systems–Operando Small-Angle Neutron Scattering Studies

by Vitaliy Pipich, Thomas Starc, Johan Buitenhuis, Roni Kasher, Winfried Petry, Yoram Oren and Dietmar Schwahn

Membranes 2021, 11(6), 413; https://doi.org/10.3390/membranes11060413 - 30 May 2021

Cited by 5 | Viewed by 3459

Abstract

We present operando small-angle neutron scattering (SANS) experiments on silica fouling at two reverse osmose (RO) membranes under almost realistic conditions of practiced RO desalination technique. To its realization, two cells were designed for pressure fields and tangential feed cross-flows up to 50 [...] Read more.

We present operando small-angle neutron scattering (SANS) experiments on silica fouling at two reverse osmose (RO) membranes under almost realistic conditions of practiced RO desalination technique. To its realization, two cells were designed for pressure fields and tangential feed cross-flows up to 50 bar and 36 L/h, one cell equipped with the membrane and the other one as an empty cell to measure the feed solution in parallel far from the membrane. We studied several aqueous silica dispersions combining the parameters of colloidal radius, volume fraction, and ionic strength. A relevant result is the observation of Bragg diffraction as part of the SANS scattering pattern, representing a crystalline cake layer of simple cubic lattice structure. Other relevant parameters are silica colloidal size and volume fraction far from and above the membrane, as well as the lattice parameter of the silica cake layer, its volume fraction, thickness, and porosity in comparison with the corresponding permeate flux. The experiments show that the formation of cake layer depends to a large extent on colloidal size, ionic strength and cross-flow. Cake layer formation proved to be a reversible process, which could be dissolved at larger cross-flow. Only in one case we observed an irreversible cake layer formation showing the characteristics of an unstable phase transition. We likewise observed enhanced silica concentration and/or cake formation above the membrane, giving indication of a first order liquid–solid phase transformation. Full article

(This article belongs to the Special Issue Theoretical and Experimental Investigation of the Mass and Heat Transfers in Membrane Separation Processes)

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13 pages, 3390 KiB

Open AccessEditor’s ChoiceArticle

Carbon Dioxide Enrichment PEBAX/MOF Composite Membrane for CO₂ Separation

by Po-Hsiang Tang, Pamela Berilyn So, Wa-Hua Li, Zi-You Hui, Chien-Chieh Hu and Chia-Her Lin

Membranes 2021, 11(6), 404; https://doi.org/10.3390/membranes11060404 - 28 May 2021

Cited by 37 | Viewed by 6404

Abstract

Zeolitic imidazole framework (ZIF-8) was incorporated into poly(ether-block-amide) (Pebax-1657) in differing ratios to prepare mixed matrix membranes (MMMs) for gas separation. As ZIF-8 loading is increased, gas separation selectivity also gradually increases. For economic considerations, the proportion of the increase in selectivity to [...] Read more.

Zeolitic imidazole framework (ZIF-8) was incorporated into poly(ether-block-amide) (Pebax-1657) in differing ratios to prepare mixed matrix membranes (MMMs) for gas separation. As ZIF-8 loading is increased, gas separation selectivity also gradually increases. For economic considerations, the proportion of the increase in selectivity to the amount of MOF loaded per unit was calculated. The results show that mixing 5% MOF gives the best unit performance. With this, a variety of MOFs (UiO-66, UiO-66-NH₂, A520, MIL-68(Al) and MIL-100(Fe)) were mixed with PEBAX at 5 loading to prepare MMMs. In this work, metal-organic frameworks (MOFs) were processed using the dry-free method, where in the synthesized MOF was not dried prior to incorporation. The gas separation performance test carried out shows the highest separation performance was exhibited by P-UiO-66, wherein the CO₂/N₂ gas selectivity was 85.94, and the permeability was 189.77 (Barrer), which was higher than Robeson’s Upper bound in 2008, and obtained a high permeability and selectivity among mixed matrix membranes. In the preparation of high quality MMMs for gas separation, details regarding the interface phenomenon were assessed. Full article

(This article belongs to the Special Issue Advances in MOF-Based Membranes)

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22 pages, 3356 KiB

Open AccessEditor’s ChoiceArticle

Use of the Microheterogeneous Model to Assess the Applicability of Ion-Exchange Membranes in the Process of Generating Electricity from a Concentration Gradient

by Denis Davydov, Elena Nosova, Sergey Loza, Aslan Achoh, Alexander Korzhov, Mikhail Sharafan and Stanislav Melnikov

Membranes 2021, 11(6), 406; https://doi.org/10.3390/membranes11060406 - 28 May 2021

Cited by 11 | Viewed by 3371

Abstract

The paper shows the possibility of using a microheterogeneous model to estimate the transport numbers of counterions through ion-exchange membranes. It is possible to calculate the open-circuit potential and power density of the reverse electrodialyzer using the data obtained. Eight samples of heterogeneous [...] Read more.

The paper shows the possibility of using a microheterogeneous model to estimate the transport numbers of counterions through ion-exchange membranes. It is possible to calculate the open-circuit potential and power density of the reverse electrodialyzer using the data obtained. Eight samples of heterogeneous ion-exchange membranes were studied, two samples for each of the following types of membranes: Ralex CM, Ralex AMH, MK-40, and MA-41. Samples in each pair differed in the year of production and storage conditions. In the work, these samples were named “batch 1” and “batch 2”. According to the microheterogeneous model, to calculate the transport numbers of counterions, it is necessary to use the concentration dependence of the electrical conductivity and diffusion permeability. The electrolyte used was a sodium chloride solution with a concentration range corresponding to the conditional composition of river water and the salinity of the Black Sea. During the research, it was found that samples of Ralex membranes of different batches have similar characteristics over the entire range of investigated concentrations. The calculated values of the transfer numbers for membranes of different batches differ insignificantly: ±0.01 for Ralex AMH in 1 M NaCl. For MK-40 and MA-41 membranes, a significant scatter of characteristics was found, especially in concentrated solutions. As a result, in 1 M NaCl, the transport numbers differ by ±0.05 for MK-40 and ±0.1 for MA-41. The value of the open circuit potential for the Ralex membrane pair showed that the experimental values of the potential are slightly lower than the theoretical ones. At the same time, the maximum calculated power density is higher than the experimental values. The maximum power density achieved in the experiment on reverse electrodialysis was 0.22 W/m², which is in good agreement with the known literature data for heterogeneous membranes. The discrepancy between the experimental and theoretical data may be the difference in the characteristics of the membranes used in the reverse electrodialysis process from the tested samples and does not consider the shadow effect of the spacer in the channels of the electrodialyzer. Full article

(This article belongs to the Special Issue Membrane-based Technologies for Water and Energy Sustainability)

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14 pages, 2243 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhanced Performance of Polymer Electrolyte Membranes via Modification with Ionic Liquids for Fuel Cell Applications

by Jonathan Teik Ean Goh, Ainul Rasyidah Abdul Rahim, Mohd Shahbudin Masdar and Loh Kee Shyuan

Membranes 2021, 11(6), 395; https://doi.org/10.3390/membranes11060395 - 27 May 2021

Cited by 27 | Viewed by 4218

Abstract

The polymer electrolyte membrane (PEM) is a key component in the PEM fuel cell (PEMFC) system. This study highlights the latest development of PEM technology by combining Nafion^® and ionic liquids, namely 2–Hydroxyethylammonium Formate (2–HEAF) and Propylammonium Nitrate (PAN). Test membranes were [...] Read more.

The polymer electrolyte membrane (PEM) is a key component in the PEM fuel cell (PEMFC) system. This study highlights the latest development of PEM technology by combining Nafion^® and ionic liquids, namely 2–Hydroxyethylammonium Formate (2–HEAF) and Propylammonium Nitrate (PAN). Test membranes were prepared using the casting technique. The impact of functional groups in grafting, morphology, thermal stability, ion exchange capacity, water absorption, swelling and proton conductivity for the prepared membranes is discussed. Both hybrid membranes showed higher values in ion exchange capacity, water uptake and swelling rate as compared to the recast pure Nafion^® membrane. The results also show that the proton conductivity of Nafion^®/2–HEAF and Nafion^®/PAN membranes increased with increasing ionic liquid concentrations. The maximum values of proton conductivity for Nafion^®/2–HEAF and Nafion^®/PAN membranes were 2.87 and 4.55 mScm⁻¹, respectively, equivalent to 2.2 and 3.5 times that of the pure recast Nafion^® membrane. Full article

(This article belongs to the Special Issue Development of Novel Materials for Proton Exchange Membrane Fuel Cells)

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15 pages, 865 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in the Prediction of Fouling in Membrane Bioreactors

by Yaoke Shi, Zhiwen Wang, Xianjun Du, Bin Gong, Veeriah Jegatheesan and Izaz Ul Haq

Membranes 2021, 11(6), 381; https://doi.org/10.3390/membranes11060381 - 24 May 2021

Cited by 38 | Viewed by 5723

Abstract

Compared to the traditional activated sludge process, the membrane bioreactor (MBR) has several advantages such as the production of high-quality effluent, generation of low excess sludge, smaller footprint requirements, and ease of automatic control of processes. The MBR has a broader prospect of [...] Read more.

Compared to the traditional activated sludge process, the membrane bioreactor (MBR) has several advantages such as the production of high-quality effluent, generation of low excess sludge, smaller footprint requirements, and ease of automatic control of processes. The MBR has a broader prospect of its applications in wastewater treatment and reuse. However, membrane fouling is the biggest obstacle for its wider application. This paper reviews the techniques available to predict fouling in MBR, discusses the problems associated with predicting fouling status using artificial neural networks and mathematical models, summarizes the current state of fouling prediction techniques, and looks into the trends in their development. Full article

(This article belongs to the Special Issue CESE-2019: Applications of Membranes for Sustainability)

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21 pages, 5063 KiB

Open AccessEditor’s ChoiceArticle

Study of Anion Exchange Membrane Properties Incorporating N-spirocyclic Quaternary Ammonium Cations and Aqueous Organic Redox Flow Battery Performance

by Misgina Tilahun Tsehaye, Xian Yang, Tobias Janoschka, Martin D. Hager, Ulrich S. Schubert, Fannie Alloin and Cristina Iojoiu

Membranes 2021, 11(5), 367; https://doi.org/10.3390/membranes11050367 - 18 May 2021

Cited by 17 | Viewed by 6004

Abstract

Flexible cross-linked anion exchange membranes (AEMs) based on poly (p-phenylene oxide) grafted with N-spirocyclic quaternary ammonium cations were synthesized via UV-induced free-radical polymerization by using diallylpiperidinium chloride as an ionic monomer. Five membranes with ion exchange capacity (IEC) varying between [...] Read more.

Flexible cross-linked anion exchange membranes (AEMs) based on poly (p-phenylene oxide) grafted with N-spirocyclic quaternary ammonium cations were synthesized via UV-induced free-radical polymerization by using diallylpiperidinium chloride as an ionic monomer. Five membranes with ion exchange capacity (IEC) varying between 1.5 to 2.8 mmol Cl⁻·g⁻¹ polymer were obtained and the correlation between IEC, water uptake, state of water in the membrane and ionic conductivity was studied. In the second part of this study, the influence of properties of four of these membranes on cell cycling stability and performance was investigated in an aqueous organic redox flow battery (AORFB) employing dimethyl viologen (MV) and N,N,N-2,2,6,6-heptamethylpiperidinyl oxy-4-ammonium chloride (TMA-TEMPO). The influence of membrane properties on cell cycling stability and performance was studied. At low-current density (20 mA·cm⁻²), the best capacity retention was obtained with lower IEC membranes for which the water uptake, freezable water and TMA-TEMPO and MV crossover are low. However, at a high current density (80 mA·cm⁻²), membrane resistance plays an important role and a membrane with moderate IEC, more precisely, moderate ion conductivity and water uptake was found to maintain the best overall cell performance. The results in this work contribute to the basic understanding of the relationship between membrane properties and cell performance, providing insights guiding the development of advanced membranes to improve the efficiency and power capability for AORFB systems. Full article

(This article belongs to the Section Membrane Analysis and Characterization)

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37 pages, 2405 KiB

Open AccessEditor’s ChoiceReview

Prediction of Permeate Flux in Ultrafiltration Processes: A Review of Modeling Approaches

by Carolina Quezada, Humberto Estay, Alfredo Cassano, Elizabeth Troncoso and René Ruby-Figueroa

Membranes 2021, 11(5), 368; https://doi.org/10.3390/membranes11050368 - 18 May 2021

Cited by 38 | Viewed by 9873

Abstract

In any membrane filtration, the prediction of permeate flux is critical to calculate the membrane surface required, which is an essential parameter for scaling-up, equipment sizing, and cost determination. For this reason, several models based on phenomenological or theoretical derivation (such as gel-polarization, [...] Read more.

In any membrane filtration, the prediction of permeate flux is critical to calculate the membrane surface required, which is an essential parameter for scaling-up, equipment sizing, and cost determination. For this reason, several models based on phenomenological or theoretical derivation (such as gel-polarization, osmotic pressure, resistance-in-series, and fouling models) and non-phenomenological models have been developed and widely used to describe the limiting phenomena as well as to predict the permeate flux. In general, the development of models or their modifications is done for a particular synthetic model solution and membrane system that shows a good capacity of prediction. However, in more complex matrices, such as fruit juices, those models might not have the same performance. In this context, the present work shows a review of different phenomenological and non-phenomenological models for permeate flux prediction in UF, and a comparison, between selected models, of the permeate flux predictive capacity. Selected models were tested with data from our previous work reported for three fruit juices (bergamot, kiwi, and pomegranate) processed in a cross-flow system for 10 h. The validation of each selected model’s capacity of prediction was performed through a robust statistical examination, including a residual analysis. The results obtained, within the statistically validated models, showed that phenomenological models present a high variability of prediction (values of R-square in the range of 75.91–99.78%), Mean Absolute Percentage Error (MAPE) in the range of 3.14–51.69, and Root Mean Square Error (RMSE) in the range of 0.22–2.01 among the investigated juices. The non-phenomenological models showed a great capacity to predict permeate flux with R-squares higher than 97% and lower MAPE (0.25–2.03) and RMSE (3.74–28.91). Even though the estimated parameters have no physical meaning and do not shed light into the fundamental mechanistic principles that govern these processes, these results suggest that non-phenomenological models are a useful tool from a practical point of view to predict the permeate flux, under defined operating conditions, in membrane separation processes. However, the phenomenological models are still a proper tool for scaling-up and for an understanding the UF process. Full article

(This article belongs to the Special Issue Numerical Modelling in Membrane Processes)

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21 pages, 3980 KiB

Open AccessEditor’s ChoiceReview

Peripheral Membrane Proteins: Promising Therapeutic Targets across Domains of Life

by Deborah M. Boes, Albert Godoy-Hernandez and Duncan G. G. McMillan

Membranes 2021, 11(5), 346; https://doi.org/10.3390/membranes11050346 - 8 May 2021

Cited by 40 | Viewed by 9965

Abstract

Membrane proteins can be classified into two main categories—integral and peripheral membrane proteins—depending on the nature of their membrane interaction. Peripheral membrane proteins are highly unique amphipathic proteins that interact with the membrane indirectly, using electrostatic or hydrophobic interactions, or directly, using hydrophobic [...] Read more.

Membrane proteins can be classified into two main categories—integral and peripheral membrane proteins—depending on the nature of their membrane interaction. Peripheral membrane proteins are highly unique amphipathic proteins that interact with the membrane indirectly, using electrostatic or hydrophobic interactions, or directly, using hydrophobic tails or GPI-anchors. The nature of this interaction not only influences the location of the protein in the cell, but also the function. In addition to their unique relationship with the cell membrane, peripheral membrane proteins often play a key role in the development of human diseases such as African sleeping sickness, cancer, and atherosclerosis. This review will discuss the membrane interaction and role of periplasmic nitrate reductase, CymA, cytochrome c, alkaline phosphatase, ecto-5’-nucleotidase, acetylcholinesterase, alternative oxidase, type-II NADH dehydrogenase, and dihydroorotate dehydrogenase in certain diseases. The study of these proteins will give new insights into their function and structure, and may ultimately lead to ground-breaking advances in the treatment of severe diseases. Full article

(This article belongs to the Collection Feature Papers in Membranes in Life Sciences)

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12 pages, 3661 KiB

Open AccessEditor’s ChoiceArticle

Physical Properties and Reactivity of Microdomains in Phosphatidylinositol-Containing Supported Lipid Bilayer

by Toshinori Motegi, Kingo Takiguchi, Yohko Tanaka-Takiguchi, Toshiki Itoh and Ryugo Tero

Membranes 2021, 11(5), 339; https://doi.org/10.3390/membranes11050339 - 3 May 2021

Cited by 8 | Viewed by 3817

Abstract

We characterized the size, distribution, and fluidity of microdomains in a lipid bilayer containing phosphatidylinositol (PI) and revealed their roles during the two-dimensional assembly of a membrane deformation protein (FBP17). The morphology of the supported lipid bilayer (SLB) consisting of PI and phosphatidylcholine [...] Read more.

We characterized the size, distribution, and fluidity of microdomains in a lipid bilayer containing phosphatidylinositol (PI) and revealed their roles during the two-dimensional assembly of a membrane deformation protein (FBP17). The morphology of the supported lipid bilayer (SLB) consisting of PI and phosphatidylcholine (PC) on a mica substrate was observed with atomic force microscope (AFM). Single particle tracking (SPT) was performed for the PI+PC-SLB on the mica substrate by using the diagonal illumination setup. The AFM topography showed that PI-derived submicron domains existed in the PI+PC-SLB. The spatiotemporal dependence of the lateral lipid diffusion obtained by SPT showed that the microdomain had lower fluidity than the surrounding region and worked as the obstacles for the lipid diffusion. We observed the two-dimensional assembly of FBP17, which is one of F-BAR family proteins included in endocytosis processes and has the function generating lipid bilayer tubules in vitro. At the initial stage of the FBP17 assembly, the PI-derived microdomain worked as a scaffold for the FBP17 adsorption, and the fluid surrounding region supplied FBP17 to grow the FBP17 domain via the lateral molecular diffusion. This study demonstrated an example clearly revealing the roles of two lipid microregions during the protein reaction on a lipid bilayer. Full article

(This article belongs to the Special Issue Interaction of Proteins with Biomembrane)

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30 pages, 3899 KiB

Open AccessEditor’s ChoiceReview

Characterizing the Structure and Interactions of Model Lipid Membranes Using Electrophysiology

by Joyce El-Beyrouthy and Eric Freeman

Membranes 2021, 11(5), 319; https://doi.org/10.3390/membranes11050319 - 27 Apr 2021

Cited by 15 | Viewed by 6493

Abstract

The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often [...] Read more.

The cell membrane is a protective barrier whose configuration determines the exchange both between intracellular and extracellular regions and within the cell itself. Consequently, characterizing membrane properties and interactions is essential for advancements in topics such as limiting nanoparticle cytotoxicity. Characterization is often accomplished by recreating model membranes that approximate the structure of cellular membranes in a controlled environment, formed using self-assembly principles. The selected method for membrane creation influences the properties of the membrane assembly, including their response to electric fields used for characterizing transmembrane exchanges. When these self-assembled model membranes are combined with electrophysiology, it is possible to exploit their non-physiological mechanics to enable additional measurements of membrane interactions and phenomena. This review describes several common model membranes including liposomes, pore-spanning membranes, solid supported membranes, and emulsion-based membranes, emphasizing their varying structure due to the selected mode of production. Next, electrophysiology techniques that exploit these structures are discussed, including conductance measurements, electrowetting and electrocompression analysis, and electroimpedance spectroscopy. The focus of this review is linking each membrane assembly technique to the properties of the resulting membrane, discussing how these properties enable alternative electrophysiological approaches to measuring membrane characteristics and interactions. Full article

(This article belongs to the Section Biological Membrane Composition and Structures)

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25 pages, 5652 KiB

Open AccessEditor’s ChoiceReview

Polymers and Solvents Used in Membrane Fabrication: A Review Focusing on Sustainable Membrane Development

by Xiaobo Dong, David Lu, Tequila A. L. Harris and Isabel C. Escobar

Membranes 2021, 11(5), 309; https://doi.org/10.3390/membranes11050309 - 23 Apr 2021

Cited by 169 | Viewed by 27056

Abstract

(1) Different methods have been applied to fabricate polymeric membranes with non-solvent induced phase separation (NIPS) being one of the mostly widely used. In NIPS, a solvent or solvent blend is required to dissolve a polymer or polymer blend. N-methyl-2-pyrrolidone (NMP), dimethylacetamide [...] Read more.

(1) Different methods have been applied to fabricate polymeric membranes with non-solvent induced phase separation (NIPS) being one of the mostly widely used. In NIPS, a solvent or solvent blend is required to dissolve a polymer or polymer blend. N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMAc), dimethylformamide (DMF) and other petroleum-derived solvents are commonly used to dissolve some petroleum-based polymers. However, these components may have negative impacts on the environment and human health. Therefore, using greener and less toxic components is of great interest for increasing membrane fabrication sustainability. The chemical structure of membranes is not affected by the use of different solvents, polymers, or by the differences in fabrication scale. On the other hand, membrane pore structures and surface roughness can change due to differences in diffusion rates associated with different solvents/co-solvents diffusing into the non-solvent and with differences in evaporation time. (2) Therefore, in this review, solvents and polymers involved in the manufacturing process of membranes are proposed to be replaced by greener/less toxic alternatives. The methods and feasibility of scaling up green polymeric membrane manufacturing are also examined. Full article

(This article belongs to the Collection Polymeric Membranes: Science, Materials and Applications)

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24 pages, 42226 KiB

Open AccessEditor’s ChoiceReview

State-of-the-Art and Opportunities for Forward Osmosis in Sewage Concentration and Wastewater Treatment

by Xing Wu, Cher Hon Lau, Biplob Kumar Pramanik, Jianhua Zhang and Zongli Xie

Membranes 2021, 11(5), 305; https://doi.org/10.3390/membranes11050305 - 21 Apr 2021

Cited by 22 | Viewed by 5030

Abstract

The application of membrane technologies for wastewater treatment to recover water and nutrients from different types of wastewater can be an effective strategy to mitigate the water shortage and provide resource recovery for sustainable development of industrialisation and urbanisation. Forward osmosis (FO), driven [...] Read more.

The application of membrane technologies for wastewater treatment to recover water and nutrients from different types of wastewater can be an effective strategy to mitigate the water shortage and provide resource recovery for sustainable development of industrialisation and urbanisation. Forward osmosis (FO), driven by the osmotic pressure difference between solutions divided by a semi-permeable membrane, has been recognised as a potential energy-efficient filtration process with a low tendency for fouling and a strong ability to filtrate highly polluted wastewater. The application of FO for wastewater treatment has received significant attention in research and attracted technological effort in recent years. In this review, we review the state-of-the-art application of FO technology for sewage concentration and wastewater treatment both as an independent treatment process and in combination with other treatment processes. We also provide an outlook of the future prospects and recommendations for the improvement of membrane performance, fouling control and system optimisation from the perspectives of membrane materials, operating condition optimisation, draw solution selection, and multiple technologies combination. Full article

(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in Australasia)

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19 pages, 19670 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Calixresorcin[4]arene-Mediated Transport of Pb(II) Ions through Polymer Inclusion Membrane

by Joanna Konczyk and Wojciech Ciesielski

Membranes 2021, 11(4), 285; https://doi.org/10.3390/membranes11040285 - 13 Apr 2021

Cited by 12 | Viewed by 2909

Abstract

A facilitated transport of Pb(II) through polymer inclusion membrane (PIM) containing 1,8,15,22-tetra(1-heptyl)-calixresorcin[4]arene and its tetra- and octasubstituted derivatives containing phosphoryl, thiophosphoryl or ester groups as an ion carrier was investigated. The efficiency of Pb(II) removal from aqueous nitrate solutions was considered as a [...] Read more.

A facilitated transport of Pb(II) through polymer inclusion membrane (PIM) containing 1,8,15,22-tetra(1-heptyl)-calixresorcin[4]arene and its tetra- and octasubstituted derivatives containing phosphoryl, thiophosphoryl or ester groups as an ion carrier was investigated. The efficiency of Pb(II) removal from aqueous nitrate solutions was considered as a function of the composition of membrane (effect of polymer, plasticizer, and carrier), feed (effect of initial metal concentration and presence of other metal ions) and stripping phases, and temperature of the process conducting. Two kinetic models were applied for the transport description. The highest Pb(II) ions removal efficiency was obtained for the membrane with tetrathiophosphorylated heptyl-calixresorcin[4]arene as an ion carrier. The activation energy value, found from Eyring plot to be equal 38.7 ± 1.3 kJ/mol, suggests that the transport process is controllable both by diffusion and chemical reaction. The competitive transport of Pb(II) over Zn(II), Cd(II), and Cr(III) ions across PIMs under the optimal conditions was also performed. It was found that the Cr(III) ions’ presence in the feed phase disturb effective re-extraction of Pb(II) ions from membrane to stripping phase. Better stability of PIM-type than SLM-type membrane was found. Full article

(This article belongs to the Special Issue Polymer Membranes in Separation Process)

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16 pages, 10154 KiB

Open AccessEditor’s ChoiceReview

S-Layer Ultrafiltration Membranes

by Bernhard Schuster and Uwe B. Sleytr

Membranes 2021, 11(4), 275; https://doi.org/10.3390/membranes11040275 - 8 Apr 2021

Cited by 15 | Viewed by 4418

Abstract

Monomolecular arrays of protein subunits forming surface layers (S-layers) are the most common outermost cell envelope components of prokaryotic organisms (bacteria and archaea). Since S-layers are periodic structures, they exhibit identical physicochemical properties for each constituent molecular unit down to the sub-nanometer level. [...] Read more.

Monomolecular arrays of protein subunits forming surface layers (S-layers) are the most common outermost cell envelope components of prokaryotic organisms (bacteria and archaea). Since S-layers are periodic structures, they exhibit identical physicochemical properties for each constituent molecular unit down to the sub-nanometer level. Pores passing through S-layers show identical size and morphology and are in the range of ultrafiltration membranes. The functional groups on the surface and in the pores of the S-layer protein lattice are accessible for chemical modifications and for binding functional molecules in very precise fashion. S-layer ultrafiltration membranes (SUMs) can be produced by depositing S-layer fragments as a coherent (multi)layer on microfiltration membranes. After inter- and intramolecular crosslinking of the composite structure, the chemical and thermal resistance of these membranes was shown to be comparable to polyamide membranes. Chemical modification and/or specific binding of differently sized molecules allow the tuning of the surface properties and molecular sieving characteristics of SUMs. SUMs can be utilized as matrices for the controlled immobilization of functional biomolecules (e.g., ligands, enzymes, antibodies, and antigens) as required for many applications (e.g., biosensors, diagnostics, enzyme- and affinity-membranes). Finally, SUM represent unique supporting structures for stabilizing functional lipid membranes at meso- and macroscopic scale. Full article

(This article belongs to the Special Issue Biological and Biomimetic Membranes: New Materials and Emerging Processes 2021)

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14 pages, 1909 KiB

Open AccessEditor’s ChoiceArticle

The C-Terminus of Perilipin 3 Shows Distinct Lipid Binding at Phospholipid-Oil-Aqueous Interfaces

by Amber R. Titus, Ellyse N. Ridgway, Rebecca Douglas, Elena Sánchez Brenes, Elizabeth K. Mann and Edgar E. Kooijman

Membranes 2021, 11(4), 265; https://doi.org/10.3390/membranes11040265 - 6 Apr 2021

Cited by 9 | Viewed by 4090

Abstract

Lipid droplets (LDs) are ubiquitously expressed organelles; the only intracellular organelles that contain a lipid monolayer rather than a bilayer. Proteins localize and bind to this monolayer as they do to intracellular lipid bilayers. The mechanism by which cytosolic LD binding proteins recognize, [...] Read more.

Lipid droplets (LDs) are ubiquitously expressed organelles; the only intracellular organelles that contain a lipid monolayer rather than a bilayer. Proteins localize and bind to this monolayer as they do to intracellular lipid bilayers. The mechanism by which cytosolic LD binding proteins recognize, and bind, to this lipid interface remains poorly understood. Amphipathic α-helix bundles form a common motif that is shared between cytosolic LD binding proteins (e.g., perilipins 2, 3, and 5) and apolipoproteins, such as apoE and apoLp-III, found on lipoprotein particles. Here, we use pendant drop tensiometry to expand our previous work on the C-terminal α-helix bundle of perilipin 3 and the full-length protein. We measure the recruitment and insertion of perilipin 3 at mixed lipid monolayers at an aqueous-phospholipid-oil interface. We find that, compared to its C-terminus alone, the full-length perilipin 3 has a higher affinity for both a neat oil/aqueous interface and a phosphatidylcholine (PC) coated oil/aqueous interface. Both the full-length protein and the C-terminus show significantly more insertion into a fully unsaturated PC monolayer, contrary to our previous results at the air-aqueous interface. Additionally, the C-terminus shows a preference for lipid monolayers containing phosphatidylethanolamine (PE), whereas the full-length protein does not. These results strongly support a model whereby both the N-terminal 11-mer repeat region and C-terminal amphipathic α-helix bundle domains of perilipin 3 have distinct lipid binding, and potentially biological roles. Full article

(This article belongs to the Special Issue Protein-Lipid Interactions as Key Regulators of Cell Function)

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23 pages, 1949 KiB

Open AccessEditor’s ChoiceReview

Aerobic Granular Sludge–Membrane BioReactor (AGS–MBR) as a Novel Configuration for Wastewater Treatment and Fouling Mitigation: A Mini-Review

by Riccardo Campo, Claudio Lubello, Tommaso Lotti and Gaetano Di Bella

Membranes 2021, 11(4), 261; https://doi.org/10.3390/membranes11040261 - 4 Apr 2021

Cited by 25 | Viewed by 6900

Abstract

This mini-review reports the effect of aerobic granular sludge (AGS) on performance and membrane-fouling in combined aerobic granular sludge–membrane bioreactor (AGS–MBR) systems. Membrane-fouling represents a major drawback hampering the wider application of membrane bioreactor (MBR) technology. Fouling can be mitigated by applying aerobic [...] Read more.

This mini-review reports the effect of aerobic granular sludge (AGS) on performance and membrane-fouling in combined aerobic granular sludge–membrane bioreactor (AGS–MBR) systems. Membrane-fouling represents a major drawback hampering the wider application of membrane bioreactor (MBR) technology. Fouling can be mitigated by applying aerobic granular sludge technology, a novel kind of biofilm technology characterized by high settleability, strong microbial structure, high resilience to toxic/recalcitrant compounds of industrial wastewater, and the possibility to simultaneously remove organic matter and nutrients. Different schemes can be foreseen for the AGS–MBR process. However, an updated literature review reveals that in the AGS–MBR process, granule breakage represents a critical problem in all configurations, which often causes an increase of pore-blocking. Therefore, to date, the objective of research in this sector has been to develop a stable AGS–MBR through multiple operational strategies, including the cultivation of AGS directly in an AGS–MBR reactor, the occurrence of an anaerobic-feast/aerobic-famine regime in continuous-flow reactors, maintenance of average granule dimensions far from critical values, and proper management of AGS scouring, which has been recently recognized as a crucial factor in membrane-fouling mitigation. Full article

(This article belongs to the Collection Featured Reviews in Membrane Science)

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15 pages, 785 KiB

Open AccessEditor’s ChoiceReview

The Nanoscopic Organization of Synapse Structures: A Common Basis for Cell Communication

by Xiaojuan Yang and Wim Annaert

Membranes 2021, 11(4), 248; https://doi.org/10.3390/membranes11040248 - 30 Mar 2021

Cited by 14 | Viewed by 6409

Abstract

Synapse structures, including neuronal and immunological synapses, can be seen as the plasma membrane contact sites between two individual cells where information is transmitted from one cell to the other. The distance between the two plasma membranes is only a few tens of [...] Read more.

Synapse structures, including neuronal and immunological synapses, can be seen as the plasma membrane contact sites between two individual cells where information is transmitted from one cell to the other. The distance between the two plasma membranes is only a few tens of nanometers, but these areas are densely populated with functionally different proteins, including adhesion proteins, receptors, and transporters. The narrow space between the two plasma membranes has been a barrier for resolving the synaptic architecture due to the diffraction limit in conventional microscopy (~250 nm). Various advanced super-resolution microscopy techniques, such as stimulated emission depletion (STED), structured illumination microscopy (SIM), and single-molecule localization microscopy (SMLM), bypass the diffraction limit and provide a sub-diffraction-limit resolving power, ranging from 10 to 100 nm. The studies using super-resolution microscopy have revealed unprecedented details of the nanoscopic organization and dynamics of synaptic molecules. In general, most synaptic proteins appear to be heterogeneously distributed and form nanodomains at the membranes. These nanodomains are dynamic functional units, playing important roles in mediating signal transmission through synapses. Herein, we discuss our current knowledge on the super-resolution nanoscopic architecture of synapses and their functional implications, with a particular focus on the neuronal synapses and immune synapses. Full article

(This article belongs to the Special Issue Dynamics and Nano-Organization in Plasma Membranes)

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52 pages, 5630 KiB

Open AccessEditor’s ChoiceReview

Frontiers of Membrane Desalination Processes for Brackish Water Treatment: A Review

by Soraya Honarparvar, Xin Zhang, Tianyu Chen, Ashkan Alborzi, Khurshida Afroz and Danny Reible

Membranes 2021, 11(4), 246; https://doi.org/10.3390/membranes11040246 - 29 Mar 2021

Cited by 69 | Viewed by 10168

Abstract

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, [...] Read more.

Climate change, population growth, and increased industrial activities are exacerbating freshwater scarcity and leading to increased interest in desalination of saline water. Brackish water is an attractive alternative to freshwater due to its low salinity and widespread availability in many water-scarce areas. However, partial or total desalination of brackish water is essential to reach the water quality requirements for a variety of applications. Selection of appropriate technology requires knowledge and understanding of the operational principles, capabilities, and limitations of the available desalination processes. Proper combination of feedwater technology improves the energy efficiency of desalination. In this article, we focus on pressure-driven and electro-driven membrane desalination processes. We review the principles, as well as challenges and recent improvements for reverse osmosis (RO), nanofiltration (NF), electrodialysis (ED), and membrane capacitive deionization (MCDI). RO is the dominant membrane process for large-scale desalination of brackish water with higher salinity, while ED and MCDI are energy-efficient for lower salinity ranges. Selective removal of multivalent components makes NF an excellent option for water softening. Brackish water desalination with membrane processes faces a series of challenges. Membrane fouling and scaling are the common issues associated with these processes, resulting in a reduction in their water recovery and energy efficiency. To overcome such adverse effects, many efforts have been dedicated toward development of pre-treatment steps, surface modification of membranes, use of anti-scalant, and modification of operational conditions. However, the effectiveness of these approaches depends on the fouling propensity of the feed water. In addition to the fouling and scaling, each process may face other challenges depending on their state of development and maturity. This review provides recent advances in the material, architecture, and operation of these processes that can assist in the selection and design of technologies for particular applications. The active research directions to improve the performance of these processes are also identified. The review shows that technologies that are tunable and particularly efficient for partial desalination such as ED and MCDI are increasingly competitive with traditional RO processes. Development of cost-effective ion exchange membranes with high chemical and mechanical stability can further improve the economy of desalination with electro-membrane processes and advance their future applications. Full article

(This article belongs to the Special Issue Ion-Exchange Membranes and Related Processes)

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33 pages, 8587 KiB

Open AccessEditor’s ChoiceReview

The Roles of Membrane Technology in Artificial Organs: Current Challenges and Perspectives

by Bao Tran Duy Nguyen, Hai Yen Nguyen Thi, Bich Phuong Nguyen Thi, Dong-Ku Kang and Jeong F. Kim

Membranes 2021, 11(4), 239; https://doi.org/10.3390/membranes11040239 - 28 Mar 2021

Cited by 47 | Viewed by 11589

Abstract

The recent outbreak of the COVID-19 pandemic in 2020 reasserted the necessity of artificial lung membrane technology to treat patients with acute lung failure. In addition, the aging world population inevitably leads to higher demand for better artificial organ (AO) devices. Membrane technology [...] Read more.

The recent outbreak of the COVID-19 pandemic in 2020 reasserted the necessity of artificial lung membrane technology to treat patients with acute lung failure. In addition, the aging world population inevitably leads to higher demand for better artificial organ (AO) devices. Membrane technology is the central component in many of the AO devices including lung, kidney, liver and pancreas. Although AO technology has improved significantly in the past few decades, the quality of life of organ failure patients is still poor and the technology must be improved further. Most of the current AO literature focuses on the treatment and the clinical use of AO, while the research on the membrane development aspect of AO is relatively scarce. One of the speculated reasons is the wide interdisciplinary spectrum of AO technology, ranging from biotechnology to polymer chemistry and process engineering. In this review, in order to facilitate the membrane aspects of the AO research, the roles of membrane technology in the AO devices, along with the current challenges, are summarized. This review shows that there is a clear need for better membranes in terms of biocompatibility, permselectivity, module design, and process configuration. Full article

(This article belongs to the Special Issue Polymer Membranes and beyond for Sustainable Separations: From Synthesis, Characterization to Applications)

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35 pages, 29822 KiB

Open AccessEditor’s ChoiceReview

Green Approaches for Sustainable Development of Liquid Separation Membrane

by Wei Jie Lee, Pei Sean Goh, Woei Jye Lau, Ahmad Fauzi Ismail and Nidal Hilal

Membranes 2021, 11(4), 235; https://doi.org/10.3390/membranes11040235 - 25 Mar 2021

Cited by 30 | Viewed by 7850

Abstract

Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat [...] Read more.

Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat to all living things on Earth. Seawater, as a natural resource abundantly available all around the world, is a potential water source to fulfil the increasing water demand. Climate-independent seawater desalination has been touted as a crucial alternative to provide fresh water. While the membrane-based desalination process continues to dominate the global desalination market, the currently employed membrane fabrication materials and processes inevitably bring adverse impacts to the environment. This review aims to elucidate and provide a comprehensive outlook of the recent efforts based on greener approaches used for desalination membrane fabrication, which paves the way towards achieving sustainable and eco-friendly processes. Membrane fabrication using green chemistry effectively minimizes the generation of hazardous compounds during membrane preparation. The future trends and recommendations which could potentially be beneficial for researchers in this field are also highlighted. Full article

(This article belongs to the Collection New Challenges in Membranes for Water and Wastewater Application)

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17 pages, 1838 KiB

Open AccessEditor’s ChoiceReview

Physiological Basis of Extracorporeal Membrane Oxygenation and Extracorporeal Carbon Dioxide Removal in Respiratory Failure

by Barbara Ficial, Francesco Vasques, Joe Zhang, Stephen Whebell, Michael Slattery, Tomas Lamas, Kathleen Daly, Nicola Agnew and Luigi Camporota

Membranes 2021, 11(3), 225; https://doi.org/10.3390/membranes11030225 - 22 Mar 2021

Cited by 30 | Viewed by 12930

Abstract

Extracorporeal life support (ECLS) for severe respiratory failure has seen an exponential growth in recent years. Extracorporeal membrane oxygenation (ECMO) and extracorporeal CO₂ removal (ECCO₂R) represent two modalities that can provide full or partial support of the native lung function, [...] Read more.

Extracorporeal life support (ECLS) for severe respiratory failure has seen an exponential growth in recent years. Extracorporeal membrane oxygenation (ECMO) and extracorporeal CO₂ removal (ECCO₂R) represent two modalities that can provide full or partial support of the native lung function, when mechanical ventilation is either unable to achieve sufficient gas exchange to meet metabolic demands, or when its intensity is considered injurious. While the use of ECMO has defined indications in clinical practice, ECCO₂R remains a promising technique, whose safety and efficacy are still being investigated. Understanding the physiological principles of gas exchange during respiratory ECLS and the interactions with native gas exchange and haemodynamics are essential for the safe applications of these techniques in clinical practice. In this review, we will present the physiological basis of gas exchange in ECMO and ECCO₂R, and the implications of their interaction with native lung function. We will also discuss the rationale for their use in clinical practice, their current advances, and future directions. Full article

(This article belongs to the Special Issue Advances in Extracorporeal Membrane Oxygenation)

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54 pages, 12920 KiB

Open AccessEditor’s ChoiceReview

Polymer Membranes for All-Vanadium Redox Flow Batteries: A Review

by Dennis Düerkop, Hartmut Widdecke, Carsten Schilde, Ulrich Kunz and Achim Schmiemann

Membranes 2021, 11(3), 214; https://doi.org/10.3390/membranes11030214 - 18 Mar 2021

Cited by 58 | Viewed by 13370

Abstract

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research [...] Read more.

Redox flow batteries such as the all-vanadium redox flow battery (VRFB) are a technical solution for storing fluctuating renewable energies on a large scale. The optimization of cells regarding performance, cycle stability as well as cost reduction are the main areas of research which aim to enable more environmentally friendly energy conversion, especially for stationary applications. As a critical component of the electrochemical cell, the membrane influences battery performance, cycle stability, initial investment and maintenance costs. This review provides an overview about flow-battery targeted membranes in the past years (1995–2020). More than 200 membrane samples are sorted into fluoro-carbons, hydro-carbons or N-heterocycles according to the basic polymer used. Furthermore, the common description in membrane technology regarding the membrane structure is applied, whereby the samples are categorized as dense homogeneous, dense heterogeneous, symmetrical or asymmetrically porous. Moreover, these properties as well as the efficiencies achieved from VRFB cycling tests are discussed, e.g., membrane samples of fluoro-carbons, hydro-carbons and N-heterocycles as a function of current density. Membrane properties taken into consideration include membrane thickness, ion-exchange capacity, water uptake and vanadium-ion diffusion. The data on cycle stability and costs of commercial membranes, as well as membrane developments, are compared. Overall, this investigation shows that dense anion-exchange membranes (AEM) and N-heterocycle-based membranes, especially poly(benzimidazole) (PBI) membranes, are suitable for VRFB requiring low self-discharge. Symmetric and asymmetric porous membranes, as well as cation-exchange membranes (CEM) enable VRFB operation at high current densities. Amphoteric ion-exchange membranes (AIEM) and dense heterogeneous CEM are the choice for operation mode with the highest energy efficiency. Full article

(This article belongs to the Special Issue Membrane Surface Modification and Functionalization)

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13 pages, 9126 KiB

Open AccessEditor’s ChoiceArticle

Substrate-Independent, Regenerable Anti-Biofouling Coating for Polymeric Membranes

by Juan Zhang, Guang Wang, Jianhua Zhang, Zhiguang Xu, Yan Zhao, Yichao Wang, Fenghua She, Stephen Gray and Lingxue Kong

Membranes 2021, 11(3), 205; https://doi.org/10.3390/membranes11030205 - 13 Mar 2021

Cited by 8 | Viewed by 3213

Abstract

Biofouling is a common but significant issue in the membrane process as it reduces permeate flux, increases energy costs, and shortens the life span of membranes. As an effective antibacterial agent, a small amount of silver nanoparticles (AgNPs) immobilized on membrane surfaces will [...] Read more.

Biofouling is a common but significant issue in the membrane process as it reduces permeate flux, increases energy costs, and shortens the life span of membranes. As an effective antibacterial agent, a small amount of silver nanoparticles (AgNPs) immobilized on membrane surfaces will alleviate the membrane from biofouling. However, loading AgNPs on the membrane surface remains a challenge due to the low loading efficiency or the lack of bonding stability between AgNPs and the membrane surface. In this study, a substrate-independent method is reported to immobilize silver nanoparticles on polymeric membrane surfaces by firstly modifying the membrane surface with functional groups and then forming silver nanoparticles in situ. The obtained membranes had good anti-biofouling properties as demonstrated from disk diffusion and anti-biofouling tests. The silver nanoparticles were stably immobilized on the membrane surfaces and easily regenerated. This method is applicable to various polymeric micro-, ultra-, nano-filtration and reverse osmosis (RO) membranes. Full article

(This article belongs to the Special Issue Nanostructured Membranes II)

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12 pages, 4619 KiB

Open AccessEditor’s ChoiceArticle

Trastuzumab Modulates the Protein Cargo of Extracellular Vesicles Released by ERBB2⁺ Breast Cancer Cells

by Silvia Marconi, Sara Santamaria, Martina Bartolucci, Sara Stigliani, Cinzia Aiello, Maria Cristina Gagliani, Grazia Bellese, Andrea Petretto, Katia Cortese and Patrizio Castagnola

Membranes 2021, 11(3), 199; https://doi.org/10.3390/membranes11030199 - 12 Mar 2021

Cited by 9 | Viewed by 3484

Abstract

Cancers overexpressing the ERBB2 oncogene are aggressive and associated with a poor prognosis. Trastuzumab is an ERBB2 specific recombinant antibody employed for the treatment of these diseases since it blocks ERBB2 signaling causing growth arrest and survival inhibition. While the effects of Trastuzumab [...] Read more.

Cancers overexpressing the ERBB2 oncogene are aggressive and associated with a poor prognosis. Trastuzumab is an ERBB2 specific recombinant antibody employed for the treatment of these diseases since it blocks ERBB2 signaling causing growth arrest and survival inhibition. While the effects of Trastuzumab on ERBB2 cancer cells are well known, those on the extracellular vesicles (EVs) released from these cells are scarce. This study focused on ERBB2⁺ breast cancer cells and aimed to establish what type of EVs they release and whether Trastuzumab affects their morphology and molecular composition. To these aims, we performed immunoelectron microscopy, immunoblot, and high-resolution mass spectrometry analyses on EVs purified by differential centrifugation of culture supernatant. Here, we show that EVs released from ERBB2⁺ breast cancer cells are polymorphic in size and appearance and that ERBB2 is preferentially associated with large (120 nm) EVs. Moreover, we report that Trastuzumab (Tz) induces the expression of a specific glycosylated 50 kDa isoform of the CD63 tetraspanin and modulates the expression of 51 EVs proteins, including TOP1. Because these proteins are functionally associated with organelle organization, cytokinesis, and response to lipids, we suggest that Tz may influence these cellular processes in target cells at distant sites via modified EVs. Full article

(This article belongs to the Collection Feature Papers in Membranes in Life Sciences)

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16 pages, 12788 KiB

Open AccessEditor’s ChoiceArticle

Interactions of Linear Analogues of Battacin with Negatively Charged Lipid Membranes

by Kinga Burdach, Dagmara Tymecka, Aneta Urban, Robert Lasek, Dariusz Bartosik and Slawomir Sek

Membranes 2021, 11(3), 192; https://doi.org/10.3390/membranes11030192 - 10 Mar 2021

Cited by 7 | Viewed by 3003

Abstract

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this [...] Read more.

The increasing resistance of bacteria to available antibiotics has stimulated the search for new antimicrobial compounds with less specific mechanisms of action. These include the ability to disrupt the structure of the cell membrane, which in turn leads to its damage. In this context, amphiphilic lipopeptides belong to the class of the compounds which may fulfill this requirement. In this paper, we describe two linear analogues of battacin with modified acyl chains to tune the balance between the hydrophilic and hydrophobic portion of lipopeptides. We demonstrate that both compounds display antimicrobial activity with the lowest values of minimum inhibitory concentrations found for Gram-positive pathogens. Therefore, their mechanism of action was evaluated on a molecular level using model lipid films mimicking the membrane of Gram-positive bacteria. The surface pressure measurements revealed that both lipopeptides show ability to bind and incorporate into the lipid monolayers, resulting in decreased ordering of lipids and membrane fluidization. Atomic force microscopy (AFM) imaging demonstrated that the exposure of the model bilayers to lipopeptides leads to a transition from the ordered gel phase to disordered liquid crystalline phase. This observation was confirmed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) results, which revealed that lipopeptide action causes a substantial increase in the average tilt angle of lipid acyl chains with respect to the surface normal to compensate for lipopeptide insertion into the membrane. Moreover, the peptide moieties in both molecules do not adopt any well-defined secondary structure upon binding with the lipid membrane. It was also observed that a small difference in the structure of a lipophilic chain, altering the balance between hydrophobic and hydrophilic portion of the molecules, results in different insertion depth of the active compounds. Full article

(This article belongs to the Special Issue Dynamics of Drug Delivery to Model and Cell Membranes)

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16 pages, 6074 KiB

Open AccessEditor’s ChoiceReview

Thin-Film Composite Nanofiltration Membranes for Non-Polar Solvents

by Seungmin Lee, Taewon Kang, Jong Young Lee, Jiyu Park, Seoung Ho Choi, Jin-Yeong Yu, Serin Ok and Sang-Hee Park

Membranes 2021, 11(3), 184; https://doi.org/10.3390/membranes11030184 - 9 Mar 2021

Cited by 24 | Viewed by 6468

Abstract

Organic solvent nanofiltration (OSN) has been recognized as an eco-friendly separation system owing to its excellent cost and energy saving efficiency, easy scale-up in the narrow area and mild operation conditions. Membrane properties are the key part in terms of determining the separation [...] Read more.

Organic solvent nanofiltration (OSN) has been recognized as an eco-friendly separation system owing to its excellent cost and energy saving efficiency, easy scale-up in the narrow area and mild operation conditions. Membrane properties are the key part in terms of determining the separation efficiency in the OSN system. In this review paper, the recently reported OSN thin-film composite (TFC) membranes were investigated to understand insight of membrane materials and performance. Especially, we highlighted the representative study concepts and materials of the selective layer of OSN TFC membranes for non-polar solvents. The proper choice of monomers and additives for the selective layer forms much more interconnected voids and the enhanced microporosity, which can improve membrane performance of the OSN TFC membrane with reducing the transport resistance. Therefore, this review paper could be an important bridge to connect with the next-generation OSN TFC membranes for non-polar solvents. Full article

(This article belongs to the Special Issue Polymer Membranes and beyond for Sustainable Separations: From Synthesis, Characterization to Applications)

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20 pages, 5392 KiB

Open AccessEditor’s ChoiceArticle

Batch Reverse Osmosis Desalination Modeling under a Time-Dependent Pressure Profile

by Abdeljalil Chougradi, François Zaviska, Ahmed Abed, Jérôme Harmand, Jamal-Eddine Jellal and Marc Heran

Membranes 2021, 11(3), 173; https://doi.org/10.3390/membranes11030173 - 28 Feb 2021

Cited by 20 | Viewed by 4918

Abstract

As world demand for clean water increases, reverse osmosis (RO) desalination has emerged as an attractive solution. Continuous RO is the most used desalination technology today. However, a new generation of configurations, working in unsteady-state feed concentration and pressure, have gained more attention [...] Read more.

As world demand for clean water increases, reverse osmosis (RO) desalination has emerged as an attractive solution. Continuous RO is the most used desalination technology today. However, a new generation of configurations, working in unsteady-state feed concentration and pressure, have gained more attention recently, including the batch RO process. Our work presents a mathematical modeling for batch RO that offers the possibility of monitoring all variables of the process, including specific energy consumption, as a function of time and the recovery ratio. Validation is achieved by comparison with data from the experimental set-up and an existing model in the literature. Energetic comparison with continuous RO processes confirms that batch RO can be more energy efficient than can continuous RO, especially at a higher recovery ratio. It used, at recovery, 31% less energy for seawater and 19% less energy for brackish water. Modeling also proves that the batch RO process does not have to function under constant flux to deliver good energetic performance. In fact, under a linear pressure profile, batch RO can still deliver better energetic performance than can a continuous configuration. The parameters analysis shows that salinity, pump and energy recovery devices efficiencies are directly linked to the energy demand. While increasing feed volume has a limited effect after a certain volume due to dilution, it also shows, interestingly, a recovery ratio interval in which feed volume does not affect specific energy consumption. Full article

(This article belongs to the Special Issue Composite Conducting Membranes: Preparation, Properties, and Applications)

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13 pages, 5504 KiB

Open AccessEditor’s ChoiceArticle

Effect of ZnO Nanoparticle Content on the Structural and Ionic Transport Parameters of Polyvinyl Alcohol Based Proton-Conducting Polymer Electrolyte Membranes

by Omed Gh. Abdullah, Yahya A. K. Salman, Dana A. Tahir, Gelas M. Jamal, Hawzhin T. Ahmed, Azhin H. Mohamad and Auday K. Azawy

Membranes 2021, 11(3), 163; https://doi.org/10.3390/membranes11030163 - 26 Feb 2021

Cited by 32 | Viewed by 3518

Abstract

Proton conducting nanocomposite solid polymer electrolytes (NSPEs) based on polyvinyl alcohol/ammonium nitrate (PVA/NH₄NO₃) and different contents of zinc oxide nanoparticles (ZnO-NPs) have been prepared using the casting solution method. The XRD analysis revealed that the sample with 2 wt.% [...] Read more.

Proton conducting nanocomposite solid polymer electrolytes (NSPEs) based on polyvinyl alcohol/ammonium nitrate (PVA/NH₄NO₃) and different contents of zinc oxide nanoparticles (ZnO-NPs) have been prepared using the casting solution method. The XRD analysis revealed that the sample with 2 wt.% ZnO-NPs has a high amorphous content. The ionic conductivity analysis for the prepared membranes has been carried out over a wide range of frequencies at varying temperatures. Impedance analysis shows that sample with 2 wt.% ZnO-NPs has a smaller bulk resistance compared to that of undoped polymer electrolyte. A small amount of ZnO-NPs was found to enhance the proton-conduction significantly; the highest obtainable room-temperature ionic conductivity was 4.71 × 10⁻⁴ S/cm. The effect of ZnO-NP content on the transport parameters of the prepared proton-conducting NSPEs was investigated using the Rice–Roth model; the results reveal that the increase in ionic conductivity is due to an increment in the number of proton ions and their mobility. Full article

(This article belongs to the Section Polymeric Membranes)

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17 pages, 1498 KiB

Open AccessEditor’s ChoiceReview

Membrane Protein Stabilization Strategies for Structural and Functional Studies

by Ekaitz Errasti-Murugarren, Paola Bartoccioni and Manuel Palacín

Membranes 2021, 11(2), 155; https://doi.org/10.3390/membranes11020155 - 22 Feb 2021

Cited by 27 | Viewed by 7307

Abstract

Accounting for nearly two-thirds of known druggable targets, membrane proteins are highly relevant for cell physiology and pharmacology. In this regard, the structural determination of pharmacologically relevant targets would facilitate the intelligent design of new drugs. The structural biology of membrane proteins is [...] Read more.

Accounting for nearly two-thirds of known druggable targets, membrane proteins are highly relevant for cell physiology and pharmacology. In this regard, the structural determination of pharmacologically relevant targets would facilitate the intelligent design of new drugs. The structural biology of membrane proteins is a field experiencing significant growth as a result of the development of new strategies for structure determination. However, membrane protein preparation for structural studies continues to be a limiting step in many cases due to the inherent instability of these molecules in non-native membrane environments. This review describes the approaches that have been developed to improve membrane protein stability. Membrane protein mutagenesis, detergent selection, lipid membrane mimics, antibodies, and ligands are described in this review as approaches to facilitate the production of purified and stable membrane proteins of interest for structural and functional studies. Full article

(This article belongs to the Special Issue Experimental and Computational Methods for Membrane Protein Design)

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