Membranes

15 pages, 2161 KiB

Open AccessEditor’s ChoiceArticle

Efficient Isolation of Outer Membrane Vesicles (OMVs) Secreted by Gram-Negative Bacteria via a Novel Gradient Filtration Method

by Ning Li, Minghui Wu, Lu Wang, Mengyu Tang, Hongbo Xin and Keyu Deng

Membranes 2024, 14(6), 135; https://doi.org/10.3390/membranes14060135 - 6 Jun 2024

Cited by 1 | Viewed by 1681

Abstract

Bacterial extracellular vesicles (bEVs) secreted by Gram-negative bacteria are referred to as outer membrane vesicles (OMVs) because they originate in the outer membrane. OMVs are membrane-coated vesicles 20–250 nm in size. They contain lipopolysaccharide (LPS), peptidoglycan, proteins, lipids, nucleic acids, and other substances [...] Read more.

Bacterial extracellular vesicles (bEVs) secreted by Gram-negative bacteria are referred to as outer membrane vesicles (OMVs) because they originate in the outer membrane. OMVs are membrane-coated vesicles 20–250 nm in size. They contain lipopolysaccharide (LPS), peptidoglycan, proteins, lipids, nucleic acids, and other substances derived from their parent bacteria and participate in the transmission of information to host cells. OMVs have broad prospects in terms of potential application in the fields of adjuvants, vaccines, and drug delivery vehicles. Currently, there remains a lack of efficient and convenient methods to isolate OMVs, which greatly limits OMV-related research. In this study, we developed a fast, convenient, and low-cost gradient filtration method to separate OMVs that can achieve industrial-scale production while maintaining the biological activity of the isolated OMVs. We compared the gradient filtration method with traditional ultracentrifugation to isolate OMVs from probiotic Escherichia coli Nissle 1917 (EcN) bacteria. Then, we used RAW264.7 macrophages as an in vitro model to study the influence on the immune function of EcN-derived OMVs obtained through the gradient filtration method. Our results indicated that EcN-derived OMVs were efficiently isolated using our gradient filtration method. The level of OMV enrichment obtained via our gradient filtration method was about twice as efficient as that achieved through traditional ultracentrifugation. The EcN-derived OMVs enriched through the gradient filtration method were successfully taken up by RAW264.7 macrophages and induced them to secrete pro-inflammatory cytokines such as tumor necrosis factor α (TNF-α) and interleukins (ILs) 6 and 1β, as well as anti-inflammatory cytokine IL-10. Furthermore, EcN-derived OMVs induced more anti-inflammatory response (i.e., IL-10) than pro-inflammatory response (i.e., TNF-α, IL-6, and IL-1β). These results were consistent with those reported in the literature. The related literature reported that EcN-derived OMVs obtained through ultracentrifugation could induce stronger anti-inflammatory responses than pro-inflammatory responses in RAW264.7 macrophages. Our simple and novel separation method may therefore have promising prospects in terms of applications involving the study of OMVs. Full article

(This article belongs to the Special Issue Design and Characterization of Membranes for Biomedical Applications)

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18 pages, 3171 KiB

Open AccessEditor’s ChoiceReview

A Short Review of Advances in MOF Glass Membranes for Gas Adsorption and Separation

by Zichen Li, Yumei Wang, Jianxin Zhang, Shiqi Cheng and Yue Sun

Membranes 2024, 14(5), 99; https://doi.org/10.3390/membranes14050099 - 25 Apr 2024

Cited by 1 | Viewed by 2392

Abstract

The phenomenon of melting in metal–organic frameworks (MOFs) has recently garnered attention. Crystalline MOF materials can be transformed into an amorphous glassy state through melt-quenching treatment. The resulting MOF glass structure eliminates grain boundaries and retains short-range order while exhibiting long-range disorder. Based [...] Read more.

The phenomenon of melting in metal–organic frameworks (MOFs) has recently garnered attention. Crystalline MOF materials can be transformed into an amorphous glassy state through melt-quenching treatment. The resulting MOF glass structure eliminates grain boundaries and retains short-range order while exhibiting long-range disorder. Based on these properties, it emerges as a promising candidate for high-performance separation membranes. MOF glass membranes exhibit permanent and accessible porosity, allowing for selective adsorption of different gas species. This review summarizes the melting mechanism of MOFs and explores the impact of ligands and metal ions on glassy MOFs. Additionally, it presents an analysis of the diverse classes of MOF glass composites, outlining their structures and properties, which are conducive to gas adsorption and separation. The absence of inter-crystalline defects in the structures, coupled with their distinctive mechanical properties, renders them highly promising for industrial gas separation applications. Furthermore, this review provides a summary of recent research on MOF glass composite membranes for gas adsorption and separation. It also addresses the challenges associated with membrane production and suggests future research directions. Full article

(This article belongs to the Special Issue Recent Advances of Metal–Organic Framework Membranes for Separation Process)

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24 pages, 2757 KiB

Open AccessEditor’s ChoiceReview

Recent Advances and Challenges in Anion Exchange Membranes Development/Application for Water Electrolysis: A Review

by Lu Liu, Hongyang Ma, Madani Khan and Benjamin S. Hsiao

Membranes 2024, 14(4), 85; https://doi.org/10.3390/membranes14040085 - 5 Apr 2024

Cited by 5 | Viewed by 4479

Abstract

In recent years, anion exchange membranes (AEMs) have aroused widespread interest in hydrogen production via water electrolysis using renewable energy sources. The two current commercial low-temperature water electrolysis technologies used are alkaline water electrolysis (AWE) and proton exchange membrane (PEM) water electrolysis. The [...] Read more.

In recent years, anion exchange membranes (AEMs) have aroused widespread interest in hydrogen production via water electrolysis using renewable energy sources. The two current commercial low-temperature water electrolysis technologies used are alkaline water electrolysis (AWE) and proton exchange membrane (PEM) water electrolysis. The AWE technology exhibited the advantages of high stability and increased cost-effectiveness with low hydrogen production efficiency. In contrast, PEM water electrolysis exhibited high hydrogen efficiency with low stability and cost-effectiveness, respectively. Unfortunately, the major challenges that AEMs, as well as the corresponding ion transportation membranes, including alkaline hydrogen separator and proton exchange membranes, still face are hydrogen production efficiency, long-term stability, and cost-effectiveness under working conditions, which exhibited critical issues that need to be addressed as a top priority. This review comprehensively presented research progress on AEMs in recent years, providing a thorough understanding of academic studies and industrial applications. It focused on analyzing the chemical structure of polymers and the performance of AEMs and established the relationship between the structure and efficiency of the membranes. This review aimed to identify approaches for improving AEM ion conductivity and alkaline stability. Additionally, future research directions for the commercialization of anion exchange membranes were discussed based on the analysis and assessment of the current applications of AEMs in patents. Full article

(This article belongs to the Collection Feature Papers in Membrane Processing and Engineering)

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17 pages, 2949 KiB

Open AccessEditor’s ChoiceArticle

Hydrophilic Modification of Dialysis Membranes Sustains Middle Molecule Removal and Filtration Characteristics

by Adam M. Zawada, Karlee Emal, Eva Förster, Saeedeh Saremi, Dirk Delinski, Lukas Theis, Florian Küng, Wenhao Xie, Joanie Werner, Manuela Stauss-Grabo, Matthias Faust, Skyler Boyington and James P. Kennedy

Membranes 2024, 14(4), 83; https://doi.org/10.3390/membranes14040083 - 3 Apr 2024

Cited by 1 | Viewed by 2223

Abstract

While efficient removal of uremic toxins and accumulated water is pivotal for the well-being of dialysis patients, protein adsorption to the dialyzer membrane reduces the performance of a dialyzer. Hydrophilic membrane modification with polyvinylpyrrolidone (PVP) has been shown to reduce protein adsorption and [...] Read more.

While efficient removal of uremic toxins and accumulated water is pivotal for the well-being of dialysis patients, protein adsorption to the dialyzer membrane reduces the performance of a dialyzer. Hydrophilic membrane modification with polyvinylpyrrolidone (PVP) has been shown to reduce protein adsorption and to stabilize membrane permeability. In this study we compared middle molecule clearance and filtration performance of nine polysulfone-, polyethersulfone-, and cellulose-based dialyzers over time. Protein adsorption was simulated in recirculation experiments, while β2-microglobulin clearance as well as transmembrane pressure (TMP) and filtrate flow were determined over time. The results of this study showed that β2-microglobulin clearance (−7.2 mL/min/m²) and filtrate flow (−54.4 mL/min) decreased strongly during the first 30 min and slowly afterwards (−0.7 mL/min/m² and −6.8 mL/min, respectively, for the next 30 min); the TMP increase (+37.2 mmHg and +8.6 mmHg, respectively) showed comparable kinetics. Across all tested dialyzers, the dialyzer with a hydrophilic modified membrane (FX CorAL) had the highest β2-microglobulin clearance after protein fouling and the most stable filtration characteristics. In conclusion, hydrophilic membrane modification with PVP stabilizes the removal capacity of middle molecules and filtration performance over time. Such dialyzers may have benefits during hemodiafiltration treatments which aim to achieve high exchange volumes. Full article

(This article belongs to the Topic Nephrology and Dialysis: From Bench to Bedside)

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20 pages, 5158 KiB

Open AccessEditor’s ChoiceArticle

Experimental Investigation on the Energy and Exergy Efficiency of the Vacuum Membrane Distillation System with Its Various Configurations

by Abdullah Najib, Turki Mana, Emad Ali, Hany Al-Ansary, Fahad Awjah Almehmadi and Mansour Alhoshan

Membranes 2024, 14(2), 54; https://doi.org/10.3390/membranes14020054 - 13 Feb 2024

Cited by 1 | Viewed by 1612

Abstract

This paper addresses a retrofitting vacuum membrane distillation (VMD) setup to reduce the accumulated pressure inside the permeated side. This modification is necessary to extend the operation of the VMD to extreme operation conditions of higher hot water temperatures. This modification, denoted as [...] Read more.

This paper addresses a retrofitting vacuum membrane distillation (VMD) setup to reduce the accumulated pressure inside the permeated side. This modification is necessary to extend the operation of the VMD to extreme operation conditions of higher hot water temperatures. This modification, denoted as a hybrid configuration, proposes the injection of a cold water stream into the VMD cell without mixing it with the permeate. Energy and exergy efficiency analyses were performed to assess the effectiveness of the hybrid configuration. The performance of the modified system indicated an improvement in terms of permeate flux (J), the gain output ratio (GOR), and the utilitarian exergetic efficiency (η_ex,u), which reach up to two and three times that of the base configuration of the VMD system. However, the exergetic efficiency (η_ex) of the hybrid system showed marginal improvement compared to the base case over the tested range of hot water temperatures. This is because the enhanced vapor production is penalized by excess energy consumption. Moreover, the highest exergy destruction percentages occurred in the operational components (e.g., heater and chillers) which fall in the range of 19.0–68.9%. The exergy destruction percentage in the original components (e.g., the VMD cell and condenser) did not exceed 8.3%. Furthermore, this study indicated that the hybrid configuration requires additional tuning and optimization to perform efficiently over wide operating conditions. Full article

(This article belongs to the Special Issue Applications of Membrane Processes in Desalination, Wastewater Treatment and Resource Recovery)

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27 pages, 7988 KiB

Open AccessEditor’s ChoiceReview

Sustainability in Membrane Technology: Membrane Recycling and Fabrication Using Recycled Waste

by Noman Khalid Khanzada, Raed A. Al-Juboori, Muzamil Khatri, Farah Ejaz Ahmed, Yazan Ibrahim and Nidal Hilal

Membranes 2024, 14(2), 52; https://doi.org/10.3390/membranes14020052 - 12 Feb 2024

Cited by 6 | Viewed by 5059

Abstract

Membrane technology has shown a promising role in combating water scarcity, a globally faced challenge. However, the disposal of end-of-life membrane modules is problematic as the current practices include incineration and landfills as their final fate. In addition, the increase in population and [...] Read more.

Membrane technology has shown a promising role in combating water scarcity, a globally faced challenge. However, the disposal of end-of-life membrane modules is problematic as the current practices include incineration and landfills as their final fate. In addition, the increase in population and lifestyle advancement have significantly enhanced waste generation, thus overwhelming landfills and exacerbating environmental repercussions and resource scarcity. These practices are neither economically nor environmentally sustainable. Recycling membranes and utilizing recycled material for their manufacturing is seen as a potential approach to address the aforementioned challenges. Depending on physiochemical conditions, the end-of-life membrane could be reutilized for similar, upgraded, and downgraded operations, thus extending the membrane lifespan while mitigating the environmental impact that occurred due to their disposal and new membrane preparation for similar purposes. Likewise, using recycled waste such as polystyrene, polyethylene terephthalate, polyvinyl chloride, tire rubber, keratin, and cellulose and their derivates for fabricating the membranes can significantly enhance environmental sustainability. This study advocates for and supports the integration of sustainability concepts into membrane technology by presenting the research carried out in this area and rigorously assessing the achieved progress. The membranes’ recycling and their fabrication utilizing recycled waste materials are of special interest in this work. Furthermore, this study offers guidance for future research endeavors aimed at promoting environmental sustainability. Full article

(This article belongs to the Special Issue Sustainable Polymeric Membrane Preparation and Application)

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21 pages, 5677 KiB

Open AccessEditor’s ChoiceArticle

Field-Scale Testing of a High-Efficiency Membrane Reactor (MR)—Adsorptive Reactor (AR) Process for H₂ Generation and Pre-Combustion CO₂ Capture

by Nicholas Margull, Doug Parsley, Ibubeleye Somiari, Linghao Zhao, Mingyuan Cao, Dimitrios Koumoulis, Paul K. T. Liu, Vasilios I. Manousiouthakis and Theodore T. Tsotsis

Membranes 2024, 14(2), 51; https://doi.org/10.3390/membranes14020051 - 11 Feb 2024

Cited by 2 | Viewed by 2021

Abstract

The study objective was to field-validate the technical feasibility of a membrane- and adsorption-enhanced water gas shift reaction process employing a carbon molecular sieve membrane (CMSM)-based membrane reactor (MR) followed by an adsorptive reactor (AR) for pre-combustion CO₂ capture. The project was [...] Read more.

The study objective was to field-validate the technical feasibility of a membrane- and adsorption-enhanced water gas shift reaction process employing a carbon molecular sieve membrane (CMSM)-based membrane reactor (MR) followed by an adsorptive reactor (AR) for pre-combustion CO₂ capture. The project was carried out in two different phases. In Phase I, the field-scale experimental MR-AR system was designed and constructed, the membranes, and adsorbents were prepared, and the unit was tested with simulated syngas to validate functionality. In Phase II, the unit was installed at the test site, field-tested using real syngas, and a technoeconomic analysis (TEA) of the technology was completed. All project milestones were met. Specifically, (i) high-performance CMSMs were prepared meeting the target H₂ permeance (>1 m³/(m².hbar) and H₂/CO selectivity of >80 at temperatures of up to 300 °C and pressures of up to 25 bar with a <10% performance decline over the testing period; (ii) pelletized adsorbents were prepared for use in relevant conditions (250 °C < T < 450 °C, pressures up to 25 bar) with a working capacity of >2.5 wt.% and an attrition rate of <0.2; (iii) TEA showed that the MR-AR technology met the CO₂ capture goals of 95% CO₂ purity at a cost of electricity (COE) 30% less than baseline approaches. Full article

(This article belongs to the Special Issue Sorption and Transport Phenomena in Inorganic Membranes)

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17 pages, 13402 KiB

Open AccessEditor’s ChoiceReview

Roles of a Glycolipid MPIase in Sec-Independent Membrane Protein Insertion

by Kaoru Nomura, Shoko Mori and Keiko Shimamoto

Membranes 2024, 14(2), 48; https://doi.org/10.3390/membranes14020048 - 8 Feb 2024

Cited by 1 | Viewed by 1720

Abstract

Membrane protein integrase (MPIase), an endogenous glycolipid in Escherichia coli (E. coli) membranes, is essential for membrane protein insertion in E. coli. We have examined Sec-independent membrane protein insertion mechanisms facilitated by MPIase using physicochemical analytical techniques, namely solid-state nuclear [...] Read more.

Membrane protein integrase (MPIase), an endogenous glycolipid in Escherichia coli (E. coli) membranes, is essential for membrane protein insertion in E. coli. We have examined Sec-independent membrane protein insertion mechanisms facilitated by MPIase using physicochemical analytical techniques, namely solid-state nuclear magnetic resonance, fluorescence measurements, and surface plasmon resonance. In this review, we outline the physicochemical characteristics of membranes that may affect membrane insertion of proteins. Subsequently, we introduce our results verifying the effects of membrane lipids on insertion and estimate the impact of MPIase. Although MPIase is a minor component of E. coli membranes, it regulates insertion by altering the physicochemical properties of the membrane. In addition, MPIase promotes insertion by interacting with substrate proteins. We propose comprehensive mechanisms for the membrane insertion of proteins involving MPIase, which provide a physicochemical basis for understanding the roles of glycolipids in protein translocation. Full article

(This article belongs to the Special Issue Advanced Research on Structure-Function Relationships of Membrane Proteins, 2nd Edition)

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17 pages, 7218 KiB

Open AccessEditor’s ChoiceArticle

Identification of Membrane Fouling with Greywater Filtration by Porous Membranes: Combined Effect of Membrane Pore Size and Applied Pressure

by Hoseok Jang, Sinu Kang and Jeonghwan Kim

Membranes 2024, 14(2), 46; https://doi.org/10.3390/membranes14020046 - 7 Feb 2024

Cited by 2 | Viewed by 1926

Abstract

Membrane fouling caused by complex greywater synthesized by personal care products and detergents commercially available for household applications was investigated using dead-end microfiltration (MF) and analyzed systematically by a multistage Hermia blocking model as a first attempt. The highest flux decline was associated [...] Read more.

Membrane fouling caused by complex greywater synthesized by personal care products and detergents commercially available for household applications was investigated using dead-end microfiltration (MF) and analyzed systematically by a multistage Hermia blocking model as a first attempt. The highest flux decline was associated with the smallest pore size of the membrane (0.03 μm). This effectiveness was more pronounced at higher applied pressures to the membrane. A cake layer was formed on the membrane consisting mainly of silica particles present as ingredients in greywater. Although organic rejection was low by the porous MF membrane, the organic compound contributed to membrane fouling in the filtration stage. With a 0.03 μm pore size of the membrane, dominant fouling mechanisms were classified into three stages as applied pressure increased, such as complete pore blocking, intermediate pore blocking, and cake layer formation. Specifically, during the early stage of membrane filtration at 1.5 bar, membrane fouling was determined by complete pore blocking in the 0.10 μm pore size of the membrane. However, the later stage of membrane fouling was controlled mainly by intermediate pore blocking. Regardless of the applied pressure, pore constriction or standard blocking played an important role in the fouling rate with a 0.45 μm pore size of the membrane. Our results also support that complex formation can occur due to the concentration of organic and inorganic species present in simulated greywater. Thus, strategic approaches such as periodic, chemically enhanced backwashing need to be developed and tailored to remove both organic and inorganic fouling from MF membranes treating greywater. Full article

(This article belongs to the Special Issue Advanced Membrane Bioreactors for Wastewater Treatment 2nd Edition)

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23 pages, 9180 KiB

Open AccessEditor’s ChoiceArticle

Studying Conformational Properties of Transmembrane Domain of KCNE3 in a Lipid Bilayer Membrane Using Molecular Dynamics Simulations

by Anna Clara Miranda Moura, Isaac K. Asare, Mateo Fernandez Cruz, Antonio Javier Franco Aguado, Kaeleigh Dyan Tuck, Conner C. Campbell, Matthew W. Scheyer, Ikponwmosa Obaseki, Steve Alston, Andrea N. Kravats, Charles R. Sanders, Gary A. Lorigan and Indra D. Sahu

Membranes 2024, 14(2), 45; https://doi.org/10.3390/membranes14020045 - 4 Feb 2024

Cited by 1 | Viewed by 2094

Abstract

KCNE3 is a single-pass integral membrane protein that regulates numerous voltage-gated potassium channel functions such as KCNQ1. Previous solution NMR studies suggested a moderate degree of curved α-helical structure in the transmembrane domain (TMD) of KCNE3 in lyso-myristoylphosphatidylcholine (LMPC) micelles and isotropic bicelles [...] Read more.

KCNE3 is a single-pass integral membrane protein that regulates numerous voltage-gated potassium channel functions such as KCNQ1. Previous solution NMR studies suggested a moderate degree of curved α-helical structure in the transmembrane domain (TMD) of KCNE3 in lyso-myristoylphosphatidylcholine (LMPC) micelles and isotropic bicelles with the residues T71, S74 and G78 situated along the concave face of the curved helix. During the interaction of KCNE3 and KCNQ1, KCNE3 pushes its transmembrane domain against KCNQ1 to lock the voltage sensor in its depolarized conformation. A cryo-EM study of KCNE3 complexed with KCNQ1 in nanodiscs suggested a deviation of the KCNE3 structure from its independent structure in isotropic bicelles. Despite the biological significance of KCNE3 TMD, the conformational properties of KCNE3 are poorly understood. Here, all atom molecular dynamics (MD) simulations were utilized to investigate the conformational dynamics of the transmembrane domain of KCNE3 in a lipid bilayer containing a mixture of POPC and POPG lipids (3:1). Further, the effect of the interaction impairing mutations (V72A, I76A and F68A) on the conformational properties of the KCNE3 TMD in lipid bilayers was investigated. Our MD simulation results suggest that the KCNE3 TMD adopts a nearly linear α helical structural conformation in POPC-POPG lipid bilayers. Additionally, the results showed no significant change in the nearly linear α-helical conformation of KCNE3 TMD in the presence of interaction impairing mutations within the sampled time frame. The KCNE3 TMD is more stable with lower flexibility in comparison to the N-terminal and C-terminal of KCNE3 in lipid bilayers. The overall conformational flexibility of KCNE3 also varies in the presence of the interaction-impairing mutations. The MD simulation data further suggest that the membrane bilayer width is similar for wild-type KCNE3 and KCNE3 containing mutations. The Z-distance measurement data revealed that the TMD residue site A69 is close to the lipid bilayer center, and residue sites S57 and S82 are close to the surfaces of the lipid bilayer membrane for wild-type KCNE3 and KCNE3 containing interaction-impairing mutations. These results agree with earlier KCNE3 biophysical studies. The results of these MD simulations will provide complementary data to the experimental outcomes of KCNE3 to help understand its conformational dynamic properties in a more native lipid bilayer environment. Full article

(This article belongs to the Special Issue Analytical Sciences of/with Bio(mimetic) Membranes (Volume II))

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15 pages, 2348 KiB

Open AccessEditor’s ChoiceArticle

Impact of Concentration Polarization Phenomena on Gas Separation Processes with High-Performance Zeolite Membranes: Experiments vs. Simulations

by Omar Abdul Majid, Margarita Kuznetsova, Christophe Castel, Eric Favre and Rainier Hreiz

Membranes 2024, 14(2), 41; https://doi.org/10.3390/membranes14020041 - 1 Feb 2024

Cited by 2 | Viewed by 2169

Abstract

Polarization phenomena play a key role in membrane separation processes but remain largely unexplored for gas separations, where the mass transfer resistance is most often limited to the membrane. This assumption, which is commonly used today for the simulation of membrane gas separations, [...] Read more.

Polarization phenomena play a key role in membrane separation processes but remain largely unexplored for gas separations, where the mass transfer resistance is most often limited to the membrane. This assumption, which is commonly used today for the simulation of membrane gas separations, has to be reconsidered when high-performance materials, showing a very high permeance and/or selectivity, are used. In this study, a series of steady-state separation performances experimentally obtained on CO₂/CH₄ mixtures with a zeolite membrane are compared to the predictions of a dedicated 1D approach, recently derived and validated through CFD simulations. Polarization effects are shown to generate a significant negative impact on the separation performances, both in terms of the productivity and separation efficiency. The 1D model predictions, based on pure gas permeance data and without any adjustable parameters, are in very good agreement with the experimental data. This fast and efficient modeling approach can easily be implemented in simulation or process synthesis programs for the rigorous evaluation of membrane gas separation processes, when high-performance materials are used. Full article

(This article belongs to the Section Membrane Processing and Engineering)

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22 pages, 1495 KiB

Open AccessEditor’s ChoiceReview

Water, Protons, and the Gating of Voltage-Gated Potassium Channels

by Alisher M. Kariev and Michael E. Green

Membranes 2024, 14(2), 37; https://doi.org/10.3390/membranes14020037 - 29 Jan 2024

Cited by 1 | Viewed by 2366

Abstract

Ion channels are ubiquitous throughout all forms of life. Potassium channels are even found in viruses. Every cell must communicate with its surroundings, so all cells have them, and excitable cells, in particular, especially nerve cells, depend on the behavior of these channels. [...] Read more.

Ion channels are ubiquitous throughout all forms of life. Potassium channels are even found in viruses. Every cell must communicate with its surroundings, so all cells have them, and excitable cells, in particular, especially nerve cells, depend on the behavior of these channels. Every channel must be open at the appropriate time, and only then, so that each channel opens in response to the stimulus that tells that channel to open. One set of channels, including those in nerve cells, responds to voltage. There is a standard model for the gating of these channels that has a section of the protein moving in response to the voltage. However, there is evidence that protons are moving, rather than protein. Water is critical as part of the gating process, although it is hard to see how this works in the standard model. Here, we review the extensive evidence of the importance of the role of water and protons in gating these channels. Our principal example, but by no means the only example, will be the K_v1.2 channel. Evidence comes from the effects of D₂O, from mutations in the voltage sensing domain, as well as in the linker between that domain and the gate, and at the gate itself. There is additional evidence from computations, especially quantum calculations. Structural evidence comes from X-ray studies. The hydration of ions is critical in the transfer of ions in constricted spaces, such as the gate region and the pore of a channel; we will see how the structure of the hydrated ion fits with the structure of the channel. In addition, there is macroscopic evidence from osmotic experiments and streaming current measurements. The combined evidence is discussed in the context of a model that emphasizes the role of protons and water in gating these channels. Full article

(This article belongs to the Special Issue Function and Malfunction of Ion Channels in Biological Cell Membrane)

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12 pages, 1393 KiB

Open AccessEditor’s ChoiceArticle

Ultra-Stable Inorganic Mesoporous Membranes for Water Purification

by Ralph A. Bauer, Minghui Qiu, Melissa C. Schillo-Armstrong, Matthew T. Snider, Zi Yang, Yi Zhou and Hendrik Verweij

Membranes 2024, 14(2), 34; https://doi.org/10.3390/membranes14020034 - 27 Jan 2024

Cited by 1 | Viewed by 1943

Abstract

Thin, supported inorganic mesoporous membranes are used for the removal of salts, small molecules (PFAS, dyes, and polyanions) and particulate species (oil droplets) from aqueous sources with high flux and selectivity. Nanofiltration membranes can reject simple salts with 80–100% selectivity through a space [...] Read more.

Thin, supported inorganic mesoporous membranes are used for the removal of salts, small molecules (PFAS, dyes, and polyanions) and particulate species (oil droplets) from aqueous sources with high flux and selectivity. Nanofiltration membranes can reject simple salts with 80–100% selectivity through a space charge mechanism. Rejection by size selectivity can be near 100% since the membranes can have a very narrow size distribution. Mesoporous membranes have received particular interest due to their (potential) stability under operational conditions and during defouling operations. More recently, membranes with extreme stability became interesting with the advent of in situ fouling mitigation by means of ultrasound emitted from within the membrane structure. For this reason, we explored the stability of available and new membranes with accelerated lifetime tests in aqueous solutions at various temperatures and pH values. Of the available ceria, titania, and magnetite membranes, none were actually stable under all test conditions. In earlier work, it was established that mesoporous alumina membranes have very poor stability. A new nanofiltration membrane was made of cubic zirconia membranes that exhibited near-perfect stability. A new ultrafiltration membrane was made of amorphous silica that was fully stable in ultrapure water at 80 °C. This work provides details of membrane synthesis, stability characterization and data and their interpretation. Full article

(This article belongs to the Special Issue Latest Research on Pollutants Removal from Aqueous Media by Membrane Processes)

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17 pages, 3101 KiB

Open AccessEditor’s ChoiceArticle

Development of a New Affinity Gold Polymer Membrane with Immobilized Protein A

by Tobias Steegmüller, Tim Kratky, Lena Gollwitzer, Sebastian Patrick Schwaminger and Sonja Berensmeier

Membranes 2024, 14(2), 31; https://doi.org/10.3390/membranes14020031 - 24 Jan 2024

Cited by 1 | Viewed by 1971

Abstract

New and highly selective stationary phases for affinity membrane chromatography have the potential to significantly enhance the efficiency and specificity of therapeutic protein purification by reduced mass transfer limitations. This work developed and compared different immobilization strategies for recombinant Protein A ligands to [...] Read more.

New and highly selective stationary phases for affinity membrane chromatography have the potential to significantly enhance the efficiency and specificity of therapeutic protein purification by reduced mass transfer limitations. This work developed and compared different immobilization strategies for recombinant Protein A ligands to a gold-sputtered polymer membrane for antibody separation in terms of functionalization and immobilization success, protein load, and stability. Successful, functionalization was validated via X-ray photoelectron spectroscopy (XPS). Here, a recombinant Protein A ligand was coupled by N-hydroxysuccinimide (NHS)/N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) chemistry to carboxy-functionalized, gold-sputtered membranes. We achieved a binding capacity of up to 104 ± 17 mg of the protein ligand per gram of the gold-sputtered membrane. The developed membranes were able to successfully capture and release the monoclonal antibody (mAb) Trastuzumab, as well as antibodies from fresh frozen human blood plasma in both static and dynamic setups. Therefore, they demonstrated successful functionalization and immobilization strategies. The antibody load was tested using bicinchoninic acid (BCA), ultraviolet-visible spectroscopy (UV-vis) measurements, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The outcome is a fully functional affinity membrane that can be implemented in a variety of different antibody purification processes, eliminating the need for creating individualized strategies for modifying the surface to suit different substrates or conditions. Full article

(This article belongs to the Special Issue Application of Advanced Membrane Materials in Bioseparation)

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14 pages, 4224 KiB

Open AccessEditor’s ChoiceArticle

Facilitating Water Permeation in Graphene Oxide Membranes via Incorporating Sulfonato Calix[n]arenes

by Yufan Ji, Shurui Dong, Yiping Huang, Changhai Yue, Hao Zhu, Dan Wu and Jing Zhao

Membranes 2024, 14(2), 32; https://doi.org/10.3390/membranes14020032 - 24 Jan 2024

Cited by 1 | Viewed by 1688

Abstract

Graphene oxide (GO) with its atomic thickness and abundant functional groups holds great potential in molecular-scale membrane separation. However, constructing high-speed and highly selective water transport channels within GO membranes remains a key challenge. Herein, sulfonato calix[n]arenes (SCn) molecules with a cavity structure, [...] Read more.

Graphene oxide (GO) with its atomic thickness and abundant functional groups holds great potential in molecular-scale membrane separation. However, constructing high-speed and highly selective water transport channels within GO membranes remains a key challenge. Herein, sulfonato calix[n]arenes (SCn) molecules with a cavity structure, hydrophilic entrance, and hydrophobic wall were incorporated into GO interlayer channels through a layer-by-layer assembly approach to facilitate water permeation in a water/ethanol separation process. The hydrophilic entrance enables preferential access of water molecules to the cavity over ethanol molecules, while the high hydrophobicity of the cavity wall confers low resistance for water diffusion. After incorporating SCn molecules, the membrane shows a remarkable increase in the water/ethanol separation factor from 732 to 1260, while the permeate flux also increases by about 50%. In addition, the strong electrostatic interactions between the building blocks endow the membrane with excellent swelling resistance even under a high water content. This work provides an effective strategy of constructing high-efficiency water transport channels in membrane. Full article

(This article belongs to the Special Issue Graphene Oxide Membrane for Sustainable Energy and Environmental Applications)

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25 pages, 3235 KiB

Open AccessEditor’s ChoiceReview

Membrane Separation Technology in Direct Air Capture

by Pavlo Ignatusha, Haiqing Lin, Noe Kapuscinsky, Ludmila Scoles, Weiguo Ma, Bussaraporn Patarachao and Naiying Du

Membranes 2024, 14(2), 30; https://doi.org/10.3390/membranes14020030 - 24 Jan 2024

Cited by 3 | Viewed by 4502

Abstract

Direct air capture (DAC) is an emerging negative CO₂ emission technology that aims to introduce a feasible method for CO₂ capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO₂ concentrations, carbon [...] Read more.

Direct air capture (DAC) is an emerging negative CO₂ emission technology that aims to introduce a feasible method for CO₂ capture from the atmosphere. Unlike carbon capture from point sources, which deals with flue gas at high CO₂ concentrations, carbon capture directly from the atmosphere has proved difficult due to the low CO₂ concentration in ambient air. Current DAC technologies mainly consider sorbent-based systems; however, membrane technology can be considered a promising DAC approach since it provides several advantages, e.g., lower energy and operational costs, less environmental footprint, and more potential for small-scale ubiquitous installations. Several recent advancements in validating the feasibility of highly permeable gas separation membrane fabrication and system design show that membrane-based direct air capture (m-DAC) could be a complementary approach to sorbent-based DAC, e.g., as part of a hybrid system design that incorporates other DAC technologies (e.g., solvent or sorbent-based DAC). In this article, the ongoing research and DAC application attempts via membrane separation have been reviewed. The reported membrane materials that could potentially be used for m-DAC are summarized. In addition, the future direction of m-DAC development is discussed, which could provide perspective and encourage new researchers’ further work in the field of m-DAC. Full article

(This article belongs to the Special Issue Advanced Membrane Materials for CO₂ Capture and Separation)

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21 pages, 1633 KiB

Open AccessEditor’s ChoiceReview

Simultaneous Wastewater Treatment and Resources Recovery by Forward Osmosis Coupled with Microbial Fuel Cell: A Review

by Hengliang Zhang, Liang Duan, Shilong Li, Qiusheng Gao, Mingyue Li, Fei Xing and Yang Zhao

Membranes 2024, 14(2), 29; https://doi.org/10.3390/membranes14020029 - 23 Jan 2024

Cited by 4 | Viewed by 2364

Abstract

Osmotic microbial fuel cells (OsMFCs) with the abilities to simultaneously treat wastewater, produce clean water, and electricity provided a novel approach for the application of microbial fuel cell (MFC) and forward osmosis (FO). This synergistic merging of functions significantly improved the performances of [...] Read more.

Osmotic microbial fuel cells (OsMFCs) with the abilities to simultaneously treat wastewater, produce clean water, and electricity provided a novel approach for the application of microbial fuel cell (MFC) and forward osmosis (FO). This synergistic merging of functions significantly improved the performances of OsMFCs. Nonetheless, despite their promising potential, OsMFCs currently receive inadequate attention in wastewater treatment, water reclamation, and energy recovery. In this review, we delved into the cooperation mechanisms between the MFC and the FO. MFC facilitates the FO process by promoting water flux, reducing reverse solute flux (RSF), and degrading contaminants in the feed solution (FS). Moreover, the water flux based on the FO principle contributed to MFC’s electricity generation capability. Furthermore, we summarized the potential roles of OsMFCs in resource recovery, including nutrient, energy, and water recovery, and identified the key factors, such as configurations, FO membranes, and draw solutions (DS). We prospected the practical applications of OsMFCs in the future, including their capabilities to remove emerging pollutants. Finally, we also highlighted the existing challenges in membrane fouling, system expansion, and RSF. We hope this review serves as a useful guide for the practical implementation of OsMFCs. Full article

(This article belongs to the Special Issue Advances in Modeling, Control, and Optimization of Membrane Distillation and Membrane Separation Processes)

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14 pages, 1804 KiB

Open AccessEditor’s ChoiceReview

The Application of Membrane Separation Technology in the Pharmaceutical Industry

by Ruirui Ma, Juan Li, Ping Zeng, Liang Duan, Jimin Dong, Yunxia Ma and Lingkong Yang

Membranes 2024, 14(1), 24; https://doi.org/10.3390/membranes14010024 - 17 Jan 2024

Cited by 4 | Viewed by 4455

Abstract

With the advancement in membrane technology, membrane separation technology has been found increasingly widespread applications in the pharmaceutical industry. It is utilized in drug separation and purification, wastewater treatment, and the recycling of wastewater resources. This study summarizes the application history of membrane [...] Read more.

With the advancement in membrane technology, membrane separation technology has been found increasingly widespread applications in the pharmaceutical industry. It is utilized in drug separation and purification, wastewater treatment, and the recycling of wastewater resources. This study summarizes the application history of membrane technology in the pharmaceutical industry, presents practical engineering examples of its applications, analyzes the various types of membrane technologies employed in the pharmaceutical sector, and finally, highlights the application cases of renowned international and Chinese membrane technology companies in the pharmaceutical field. Full article

(This article belongs to the Special Issue Sustainable Membrane Technologies for Wastewater Treatment)

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28 pages, 2689 KiB

Open AccessEditor’s ChoiceReview

Green Synthesis of Cation Exchange Membranes: A Review

by Stef Depuydt and Bart Van der Bruggen

Membranes 2024, 14(1), 23; https://doi.org/10.3390/membranes14010023 - 17 Jan 2024

Cited by 2 | Viewed by 3737

Abstract

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health [...] Read more.

Cation exchange membranes (CEMs) play a significant role in the transition to a more sustainable/green society. They are important components for applications such as water electrolysis, artificial photosynthesis, electrodialysis and fuel cells. Their synthesis, however, is far from being sustainable, affecting safety, health and the environment. This review discusses and evaluates the possibilities of synthesizing CEMs that are more sustainable and green. First, the concepts of green and sustainable chemistry are discussed. Subsequently, this review discusses the fabrication of conventional perfluorinated CEMs and how they violate the green/sustainability principles, eventually leading to environmental and health incidents. Furthermore, the synthesis of green CEMs is presented by dividing the synthesis into three parts: sulfonation, material selection and solvent selection. Innovations in using gaseous SO3 or gas–liquid interfacial plasma technology can make the sulfonation process more sustainable. Regarding the selection of polymers, chitosan, cellulose, polylactic acid, alginate, carrageenan and cellulose are promising alternatives to fossil fuel-based polymers. Finally, water is the most sustainable solvent and many biopolymers are soluble in it. For other polymers, there are a limited number of studies using green solvents. Promising solvents are found back in other membrane, such as dimethyl sulfoxide, Cyrene™, Rhodiasolv^® PolarClean, TamiSolve NxG and γ-valerolactone. Full article

(This article belongs to the Special Issue Electrochemical Membranes: Materials, Characterization, Testing, and Cleaning)

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13 pages, 6584 KiB

Open AccessEditor’s ChoiceArticle

Effect of Long-Term Sodium Hypochlorite Cleaning on Silicon Carbide Ultrafiltration Membranes Prepared via Low-Pressure Chemical Vapor Deposition

by Asif Jan, Mingliang Chen, Michiel Nijboer, Mieke W. J. Luiten-Olieman, Luuk C. Rietveld and Sebastiaan G. J. Heijman

Membranes 2024, 14(1), 22; https://doi.org/10.3390/membranes14010022 - 15 Jan 2024

Viewed by 2658

Abstract

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. [...] Read more.

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. However, the effect of NaClO cleaning on ceramic membranes, particularly the number of cleaning cycles they can undergo to alleviate irreversible fouling, remains poorly understood. Silicon carbide (SiC) membranes have garnered widespread attention for water and wastewater treatment, but their chemical stability in NaClO has not been studied. Low-pressure chemical vapor deposition (LP-CVD) provides a simple and economical route to prepare/modify ceramic membranes. As such, LP-CVD facilitates the preparation of SiC membranes: (a) in a single step; and (b) at much lower temperatures (700–900 °C) in comparison with sol-gel methods (ca. 2000 °C). In this work, SiC ultrafiltration (UF) membranes were prepared via LP-CVD at two different deposition temperatures and pressures. Subsequently, their chemical stability in NaClO was investigated over 200 h of aging. Afterward, the properties and performance of as-prepared SiC UF membranes were evaluated before and after aging to determine the optimal deposition conditions. Our results indicate that the SiC UF membrane prepared via LP-CVD at 860 °C and 100 mTorr exhibited excellent resistance to NaClO aging, while the membrane prepared at 750 °C and 600 mTorr significantly deteriorated. These findings not only highlight a novel preparation route for SiC membranes in a single step via LP-CVD, but also provide new insights about the careful selection of LP-CVD conditions for SiC membranes to ensure their long-term performance and robustness under harsh chemical cleaning conditions. Full article

(This article belongs to the Special Issue Inorganic Membranes for Energy and Environmental Applications)

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17 pages, 14440 KiB

Open AccessEditor’s ChoiceArticle

Inducing Deep Sweeps and Vortex Ejections on Patterned Membrane Surfaces to Mitigate Surface Fouling

by August H. Young, Nico Hotz, Brian T. Hawkins and Zbigniew J. Kabala

Membranes 2024, 14(1), 21; https://doi.org/10.3390/membranes14010021 - 13 Jan 2024

Cited by 1 | Viewed by 1902

Abstract

Patterned membrane surfaces offer a hydrodynamic approach to mitigating concentration polarization and subsequent surface fouling. However, when subjected to steady crossflow conditions, surface patterns promote particle accumulation in the recirculation zones of cavity-like spaces. In order to resolve this issue, we numerically subject [...] Read more.

Patterned membrane surfaces offer a hydrodynamic approach to mitigating concentration polarization and subsequent surface fouling. However, when subjected to steady crossflow conditions, surface patterns promote particle accumulation in the recirculation zones of cavity-like spaces. In order to resolve this issue, we numerically subject a two-dimensional, patterned membrane surface to a rapidly pulsed crossflow. When combined with cavity-like spaces, such as the valleys of membrane surface patterns, a rapidly pulsed flow generates mixing mechanisms (i.e., the deep sweep and the vortex ejection) and disrupts recirculation zones. In only four pulses, we demonstrate the ability of these mechanisms to remove over half of the particles trapped in recirculation zones via massless particle tracking studies (i.e., numerical integration of the simulated velocity field). The results of this work suggest that when combined with a rapidly pulsed inlet flow, patterned membrane surfaces can not only alleviate concentration polarization and the surface fouling that follows but also reduce the need for traditional cleaning methods that require operational downtime and often involve the use of abrasive chemical agents. Full article

(This article belongs to the Special Issue Theoretical Study of Membrane Processes)

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13 pages, 2453 KiB

Open AccessEditor’s ChoiceArticle

Cannabidiol Strengthening of Gastric Tight Junction Complexes Analyzed in an Improved Xenopus Oocyte Assay

by Laura Stein, Marie-Luise Vollstaedt and Salah Amasheh

Membranes 2024, 14(1), 18; https://doi.org/10.3390/membranes14010018 - 8 Jan 2024

Cited by 1 | Viewed by 2104

Abstract

Cannabidiol (CBD), the non-psychoactive compound derived from the cannabis plant, has gained attention in recent years as a remedy against gastrointestinal disorders ranging from nausea and inflammation to abdominal pain. Recent advances demonstrated an effect on inflammatory pathways and barrier proteins. However, information [...] Read more.

Cannabidiol (CBD), the non-psychoactive compound derived from the cannabis plant, has gained attention in recent years as a remedy against gastrointestinal disorders ranging from nausea and inflammation to abdominal pain. Recent advances demonstrated an effect on inflammatory pathways and barrier proteins. However, information on possible direct effects is scarce and needs to be addressed, as applications are currently increasing in popularity. To accomplish this, we have employed Xenopus laevis oocytes as a heterologous expression system for analysis of the direct effects on stomach-specific claudins and further developed tight junction (TJ) protein interaction assays. Human claudin-4, claudin-5, and claudin-18.2 were expressed in Xenopus oocytes, clustered in pairs to form contact areas, and analyzed in a two-cell model approach, including measurement of the contact area and contact strength. CLDN4/5/18 + CLDN4/5/18 oocyte pairs were incubated with 20 µM CBD or with 40 µM CBD and were compared to cells without CBD treatment (ctrl). For interaction analysis, the contact area was measured after 24 h and 48 h. Whereas CBD did not affect the size of the protein interaction area, Double Orbital Challenge experiments revealed an increased contact strength after 24 h incubation with CBD. In addition, the Xenopus oocyte experiments were accompanied by an analysis of claudin-4, -5, and -18 expression in gastric epithelium by immunoblotting and immunohistochemistry. Claudin-4, -5, and -18 were strongly expressed, indicating a major role for gastric epithelial barrier function. In summary, our study shows direct effects of 40 µM CBD on Xenopus oocytes heterologously expressing a stomach-specific claudin combination, indicating a supportive and beneficial effect of CBD on gastric TJ proteins. Full article

(This article belongs to the Special Issue The Xenopus Oocyte: A Tool for Membrane Biology, Second Edition)

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16 pages, 5171 KiB

Open AccessEditor’s ChoiceArticle

Promising Fluorine-Free Ion Exchange Membranes Based on a Poly(ether-block-amide) Copolymer and Sulfonated Montmorillonite: Influence of Different Copolymer Segment Ratios

by Manhal H. Ibrahim Al-Mashhadani, Khirdakhanim Salmanzade, András Tompos and Asmaa Selim

Membranes 2024, 14(1), 17; https://doi.org/10.3390/membranes14010017 - 6 Jan 2024

Cited by 1 | Viewed by 2280

Abstract

Novel composite membranes employing a poly(ether-block-amide) (PEBAX) copolymer and sulfonated montmorillonite (S-MMT) as a filler were developed. The ratio of polyether to polyamide blocks was investigated using PEBAX 2533 and PEBAX 4533 based on the membrane properties and performance. Additionally, the effect of [...] Read more.

Novel composite membranes employing a poly(ether-block-amide) (PEBAX) copolymer and sulfonated montmorillonite (S-MMT) as a filler were developed. The ratio of polyether to polyamide blocks was investigated using PEBAX 2533 and PEBAX 4533 based on the membrane properties and performance. Additionally, the effect of the changing filler ratio was monitored. The interaction between the S-MMT as nanofiller and the polymer matrix of PEBAX2533 and PEBAX4533 as well as the crystalline nature and thermal and mechanical stability of the composite membranes were evaluated using Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and tensile test. The composite membrane with 7 wt.% S-MMT showed the highest water uptake of 21% and 16% and an acceptable swelling degree of 16% and 9% for PEBAX 2533 and PEBAX 4533 composite membranes, respectively. In terms of water uptake and ion exchange capacity at room temperature, the new un-protonated membranes are superior to un-protonated Nafion. Meanwhile, with the same S-MMT content, the ion conductivity of PEBAX 2533 and PEBAX 4533 composite membranes is 2 and 1.6 mS/cm, and their ion exchange capacity is 0.9 and 1.10 meq/g. Full article

(This article belongs to the Special Issue Advanced Polymeric Membranes for Fuel Cell Applications)

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13 pages, 4179 KiB

Open AccessEditor’s ChoiceArticle

High-Degree Concentration Organic Solvent Forward Osmosis for Pharmaceutical Pre-Concentration

by Ryoichi Takada, Ryosuke Takagi and Hideto Matsuyama

Membranes 2024, 14(1), 14; https://doi.org/10.3390/membranes14010014 - 4 Jan 2024

Cited by 2 | Viewed by 1910

Abstract

Over half of the pharmaceutical industry’s capital investments are related to the purification of active pharmaceutical ingredients (APIs). Thus, a cost-effective purification process with a highly concentrated solution is urgently required. In addition, the purification process should be nonthermal because most APIs and [...] Read more.

Over half of the pharmaceutical industry’s capital investments are related to the purification of active pharmaceutical ingredients (APIs). Thus, a cost-effective purification process with a highly concentrated solution is urgently required. In addition, the purification process should be nonthermal because most APIs and their intermediates are temperature-sensitive. This study investigated a high-degree concentration organic solvent forward osmosis (OSFO) membrane process. A polyketone-based thin-film composite hollow fiber membrane with a polyamide selective layer on the bore surface was used as the OSFO membrane to achieve a high tolerance for organic solvents and an effective concentration. MeOH, sucrose octaacetate (SoA), and 2M polyethylene glycol 400 (PEG-400)/MeOH solution were used as the solvent, model API, and a draw solution (DS), respectively. OSFO was performed at room temperature (23 ± 3 °C). Consequently, the 11 wt% SoA/MeOH solution was concentrated to 52 wt% without any SoA leakage into the DS. To our knowledge, there are no studies in which up to a 5 wt% concentration by OSFO has been demonstrated. However, the final feed solution contained 17 wt% PEG-400. This study demonstrates the promising potential of OSFO for pharmaceutical pre-concentration and the technical problems that need to be solved for social implementation. Full article

(This article belongs to the Special Issue Development and Application of Membrane Separation Processes, 2nd Edition)

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15 pages, 2946 KiB

Open AccessEditor’s ChoiceArticle

Antibacterial Activity Assessment of Chitosan/Alginate Lavender Essential Oil Membranes for Biomedical Applications

by Encarnación Cruz Sánchez, María Teresa García, Ignacio Gracia, Soledad Illescas Fernández-Bermejo, Juan Francisco Rodríguez, Jesús Manuel García-Vargas and Dolors Vidal Roig

Membranes 2024, 14(1), 12; https://doi.org/10.3390/membranes14010012 - 1 Jan 2024

Cited by 2 | Viewed by 2536

Abstract

The demand for natural products in the treatment of dermatological pathologies has boosted the use of bioactive substances such as lavender essential oil (LEO), which stands out for its anti-inflammatory and antioxidant properties and its antimicrobial potential. Biopolymers such as chitosan (CHT) and [...] Read more.

The demand for natural products in the treatment of dermatological pathologies has boosted the use of bioactive substances such as lavender essential oil (LEO), which stands out for its anti-inflammatory and antioxidant properties and its antimicrobial potential. Biopolymers such as chitosan (CHT) and alginate (ALG) are biodegradable and biocompatible and have proven their viability in biomedical applications such as skin regeneration. The inhibitory effect of LEO on the growth of skin-related bacterial species Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa and the fungus Candida albicans was studied by incorporating 1% v/v LEO encapsulated in CHT, ALG, and CHT/ALG membranes. Despite the verification of the antimicrobial effect of all type of membranes, no synergistic effect was observed following the addition of LEO. S. aureus and P. aeruginosa showed the most growth on the different substrates and C. albicans demonstrated the highest inhibition. This is a first approach using microorganisms isolated from clinical samples or skin microbiota. Further investigation would be advisable using more clinical strains for each microorganism to validate their biomedical applicability. Full article

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27 pages, 5353 KiB

Open AccessEditor’s ChoiceReview

Membrane-Based Technologies for Post-Combustion CO₂ Capture from Flue Gases: Recent Progress in Commonly Employed Membrane Materials

by Petros Gkotsis, Efrosini Peleka and Anastasios Zouboulis

Membranes 2023, 13(12), 898; https://doi.org/10.3390/membranes13120898 - 2 Dec 2023

Cited by 11 | Viewed by 9237

Abstract

Carbon dioxide (CO₂), which results from fossil fuel combustion and industrial processes, accounts for a substantial part of the total anthropogenic greenhouse gases (GHGs). As a result, several carbon capture, utilization and storage (CCUS) technologies have been developed during the last [...] Read more.

Carbon dioxide (CO₂), which results from fossil fuel combustion and industrial processes, accounts for a substantial part of the total anthropogenic greenhouse gases (GHGs). As a result, several carbon capture, utilization and storage (CCUS) technologies have been developed during the last decade. Chemical absorption, adsorption, cryogenic separation and membrane separation are the most widely used post-combustion CO₂ capture technologies. This study reviews post-combustion CO₂ capture technologies and the latest progress in membrane processes for CO₂ separation. More specifically, the objective of the present work is to present the state of the art of membrane-based technologies for CO₂ capture from flue gases and focuses mainly on recent advancements in commonly employed membrane materials. These materials are utilized for the fabrication and application of novel composite membranes or mixed-matrix membranes (MMMs), which present improved intrinsic and surface characteristics and, thus, can achieve high selectivity and permeability. Recent progress is described regarding the utilization of metal–organic frameworks (MOFs), carbon molecular sieves (CMSs), nanocomposite membranes, ionic liquid (IL)-based membranes and facilitated transport membranes (FTMs), which comprise MMMs. The most significant challenges and future prospects of implementing membrane technologies for CO₂ capture are also presented. Full article

(This article belongs to the Special Issue Advances in Modeling, Control, and Optimization of Membrane Distillation and Membrane Separation Processes)

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20 pages, 8184 KiB

Open AccessEditor’s ChoiceArticle

Surface-Modified Pore-Filled Anion-Exchange Membranes for Efficient Energy Harvesting via Reverse Electrodialysis

by Ji-Hyeon Lee, Do-Hyeong Kim and Moon-Sung Kang

Membranes 2023, 13(12), 894; https://doi.org/10.3390/membranes13120894 - 30 Nov 2023

Cited by 3 | Viewed by 2001

Abstract

In this study, novel pore-filled anion-exchange membranes (PFAEMs) modified with polypyrrole (PPy) and reduced graphene oxide (rGO) were developed to improve the energy harvesting performance of reverse electrodialysis (RED). The surface-modified PFAEMs were fabricated by varying the contents of PPy and rGO through [...] Read more.

In this study, novel pore-filled anion-exchange membranes (PFAEMs) modified with polypyrrole (PPy) and reduced graphene oxide (rGO) were developed to improve the energy harvesting performance of reverse electrodialysis (RED). The surface-modified PFAEMs were fabricated by varying the contents of PPy and rGO through simple spin coating and chemical/thermal treatments. It was confirmed that the PPy and PPy/rGO layers introduced on the membrane surface did not significantly increase the electrical resistance of the membrane and could effectively control surface characteristics, such as structural tightness, hydrophilicity, and electrostatic repulsion. The PPy/rGO-modified PFAEM showed excellent monovalent ion selectivity, more than four times higher than that of the commercial membrane (AMX, Astom Corp., Tokyo, Japan). This means that the PPy/rGO layer can effectively reduce the permeation of multivalent ions with a high charge intensity and a relatively large hydration radius compared to monovalent ions. The results of evaluating the performance of the surface-modified PFAEMs by applying them to a RED cell revealed that the decrease in potential difference occurring in the membrane was reduced by effectively suppressing the uphill transport of multivalent ions. Consequently, the PPy/rGO-modified membrane exhibited a 5.43% higher power density than the AMX membrane. Full article

(This article belongs to the Special Issue Surface Modification of Ion Exchange Membranes)

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17 pages, 8117 KiB

Open AccessEditor’s ChoiceArticle

Heterogeneous Anion-Exchange Membranes with Enhanced Ion Conductivity for Continuous Electrodeionization

by Ji-Min Lee and Moon-Sung Kang

Membranes 2023, 13(12), 888; https://doi.org/10.3390/membranes13120888 - 27 Nov 2023

Cited by 2 | Viewed by 2907

Abstract

In this study, the optimal fabrication parameters of a heterogeneous anion-exchange membrane (AEM) using an ionomer binder are investigated to improve the performance of continuous electrodeionization (CEDI) for producing ultrapure water. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is selected as the base material for preparing the [...] Read more.

In this study, the optimal fabrication parameters of a heterogeneous anion-exchange membrane (AEM) using an ionomer binder are investigated to improve the performance of continuous electrodeionization (CEDI) for producing ultrapure water. Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is selected as the base material for preparing the ionomer binder and quaternized to have various ion exchange capacities (IECs). The optimal content of ion-exchange resin (IER) powder according to the IEC of the ionomer binder is then determined through systematic analyses. In conclusion, it is revealed that a heterogeneous AEM with optimal performance can be fabricated when the IEC of the ionomer binder is lowered and the content of IER powder is also lower than that of conventional heterogeneous membranes. Moreover, crosslinked quaternized PPO (QPPO) nanofiber powder is used as an additive to improve ion conductivity without deteriorating the mechanical properties of the membrane. The membrane fabricated under optimal conditions exhibits significantly lower electrical resistance (4.6 Ω cm²) despite a low IER content (30 wt%) compared to the commercial membrane (IONAC MA-3475, 13.6 Ω cm²) while also demonstrating moderate tensile strength (9.7 MPa) and a high transport number (ca. 0.97). Furthermore, it is proven that the prepared membrane exhibits a superior ion removal rate (99.86%) and lower energy consumption (0.35 kWh) compared to the commercial membrane (99.76% and 0.4 kWh, respectively) in CEDI experiments. Full article

(This article belongs to the Section Polymeric Membranes)

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18 pages, 2604 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Calcium Ions on hIAPP Channel Activity: Possible Implications in T2DM

by Daniela Meleleo, Giuseppe Cibelli, Anna Valenzano, Maria Mastrodonato and Rosanna Mallamaci

Membranes 2023, 13(11), 878; https://doi.org/10.3390/membranes13110878 - 9 Nov 2023

Cited by 1 | Viewed by 1897

Abstract

The calcium ion (Ca²⁺) has been linked to type 2 diabetes mellitus (T2DM), although the role of Ca²⁺ in this disorder is the subject of intense investigation. Serum Ca²⁺ dyshomeostasis is associated with the development of insulin resistance, reduced [...] Read more.

The calcium ion (Ca²⁺) has been linked to type 2 diabetes mellitus (T2DM), although the role of Ca²⁺ in this disorder is the subject of intense investigation. Serum Ca²⁺ dyshomeostasis is associated with the development of insulin resistance, reduced insulin sensitivity, and impaired glucose tolerance. However, the molecular mechanisms involving Ca²⁺ ions in pancreatic β-cell loss and subsequently in T2DM remain poorly understood. Implicated in the decline in β-cell functions are aggregates of human islet amyloid polypeptide (hIAPP), a small peptide secreted by β-cells that shows a strong tendency to self-aggregate into β-sheet-rich aggregates that evolve toward the formation of amyloid deposits and mature fibrils. The soluble oligomers of hIAPP can permeabilize the cell membrane by interacting with bilayer lipids. Our study aimed to evaluate the effect of Ca²⁺ on the ability of the peptide to incorporate and form ion channels in zwitterionic planar lipid membranes (PLMs) composed of palmitoyl-oleoyl-phosphatidylcholine (POPC) and on the aggregation process of hIAPP molecules in solution. Our results may help to clarify the link between Ca²⁺ ions, hIAPP peptide, and consequently the pathophysiology of T2DM. Full article

(This article belongs to the Special Issue Structure-Function Relationships and Biological Processes of Membrane Proteins)

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22 pages, 1869 KiB

Open AccessEditor’s ChoiceReview

Adsorptive Membranes Incorporating Ionic Liquids (ILs), Deep Eutectic Solvents (DESs) or Graphene Oxide (GO) for Metal Salts Extraction from Aqueous Feed

by Liyan Qalyoubi, Ioannis Zuburtikudis, Hadil Abu Khalifeh and Enas Nashef

Membranes 2023, 13(11), 874; https://doi.org/10.3390/membranes13110874 - 3 Nov 2023

Cited by 4 | Viewed by 2231

Abstract

Water scarcity is a significant concern, particularly in arid regions, due to the rapid growth in population, industrialization, and climate change. Seawater desalination has emerged as a conventional and reliable solution for obtaining potable water. However, conventional membrane-based seawater desalination has drawbacks, such [...] Read more.

Water scarcity is a significant concern, particularly in arid regions, due to the rapid growth in population, industrialization, and climate change. Seawater desalination has emerged as a conventional and reliable solution for obtaining potable water. However, conventional membrane-based seawater desalination has drawbacks, such as high energy consumption resulting from a high-pressure requirement, as well as operational challenges like membrane fouling and high costs. To overcome these limitations, it is crucial to enhance the performance of membranes by increasing their efficiency, selectivity, and reducing energy consumption and footprint. Adsorptive membranes, which integrate adsorption and membrane technologies, offer a promising approach to address the drawbacks of standalone membranes. By incorporating specific materials into the membrane matrix, composite membranes have demonstrated improved permeability, selectivity, and reduced pressure requirements, all while maintaining effective pollutant rejection. Researchers have explored different adsorbents, including emerging materials such as ionic liquids (ILs), deep eutectic solvents (DESs), and graphene oxide (GO), for embedding into membranes and utilizing them in various applications. This paper aims to discuss the existing challenges in the desalination process and focus on how these materials can help overcome these challenges. It will also provide a comprehensive review of studies that have reported the successful incorporation of ILs, DESs, and GO into membranes to fabricate adsorptive membranes for desalination. Additionally, the paper will highlight both the current and anticipated challenges in this field, as well as present prospects, and provide recommendations for further advancements. Full article

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16 pages, 6238 KiB

Open AccessEditor’s ChoiceArticle

High-Performance FAU Zeolite Membranes Derived from Nano-Seeds for Gas Separation

by Qing Wang, Huiyuan Chen, Feiyang He, Qiao Liu, Nong Xu, Long Fan, Chuyan Wang, Lingyun Zhang and Rongfei Zhou

Membranes 2023, 13(11), 858; https://doi.org/10.3390/membranes13110858 - 26 Oct 2023

Cited by 4 | Viewed by 3062

Abstract

In this study, high-performance FAU (NaY type) zeolite membranes were successfully synthesized using small-sized seeds of 50 nm, and their gas separation performance was systematically evaluated. Employing nano-sized NaY seeds and an ultra-dilute reaction solution with a molar composition of 80 Na₂ [...] Read more.

In this study, high-performance FAU (NaY type) zeolite membranes were successfully synthesized using small-sized seeds of 50 nm, and their gas separation performance was systematically evaluated. Employing nano-sized NaY seeds and an ultra-dilute reaction solution with a molar composition of 80 Na₂O: 1Al₂O₃: 19 SiO₂: 5000H₂O, the effects of synthesis temperature, crystallization time, and porous support (α-Al₂O₃ or mullite) on the formation of FAU membranes were investigated. The results illustrated that further extending the crystallization time or increasing the synthesis temperature led to the formation of a NaP impurity phase on the FAU membrane layer. The most promising FAU membrane with a thickness of 2.7 µm was synthesized on an α-Al₂O₃ support at 368 K for 8 h and had good reproducibility. The H₂ permeance of the membrane was as high as 5.34 × 10⁻⁷ mol/(m² s Pa), and the H₂/C₃H₈ and H₂/i-C₄H₁₀ selectivities were 183 and 315, respectively. The C₃H₆/C₃H₈ selectivity of the membrane was as high as 46, with a remarkably high C₃H₆ permeance of 1.35 × 10⁻⁷ mol/(m² s Pa). The excellent separation performance of the membrane is mainly attributed to the thin, defect-free membrane layer and the relatively wide pore size (0.74 nm). Full article

(This article belongs to the Section Membrane Applications)

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18 pages, 1327 KiB

Open AccessEditor’s ChoiceReview

The Latest Achievements of Liquid Membranes for Rare Earth Elements Recovery from Aqueous Solutions—A Mini Review

by Małgorzata A. Kaczorowska

Membranes 2023, 13(10), 839; https://doi.org/10.3390/membranes13100839 - 21 Oct 2023

Cited by 5 | Viewed by 2565

Abstract

The systematic increase in the use of rare earth elements (REEs) in various technologically advanced products around the world (e.g., in electronic devices), the growing amount of waste generated by the use of high-tech materials, and the limited resources of naturally occurring REE [...] Read more.

The systematic increase in the use of rare earth elements (REEs) in various technologically advanced products around the world (e.g., in electronic devices), the growing amount of waste generated by the use of high-tech materials, and the limited resources of naturally occurring REE ores resulted in an intensive search for effective and environmentally safe methods for recovering these elements. Among these methods, techniques based on the application of various types of liquid membranes (LMs) play an important role, primarily due to their high efficiency, the simplicity of membrane formation and use, the utilization of only small amounts of environmentally hazardous reagents, and the possibility of simultaneous extraction and back-extraction and reusing the membranes after regeneration. However, because both primary and secondary sources (e.g., waste) of REEs are usually complex and contain a wide variety of components, and the selectivity and efficiency of LMs depend on many factors (e.g., the composition and form of the membrane, nature of the recovered ions, composition of the feed and stripping phases, etc.), new membranes are being developed that are “tailored” to the properties of the recovered rare earth elements and to the character of the solution in which they occur. This review describes the latest achievements (since 2019) related to the recovery of a range of REEs with the use of various liquid membranes (supported liquid membranes (SLMs), emulsion liquid membranes (ELMs), and polymer inclusion membranes (PIMs)), with particular emphasis on methods that fall within the trend of eco-friendly solutions. Full article

(This article belongs to the Special Issue Membrane Systems for Metal Ion Extraction)

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15 pages, 2596 KiB

Open AccessEditor’s ChoiceReview

A Comprehensive Analysis of the Impact of Inorganic Matter on Membrane Organic Fouling: A Mini Review

by Qiusheng Gao, Liang Duan, Yanyan Jia, Hengliang Zhang, Jianing Liu and Wei Yang

Membranes 2023, 13(10), 837; https://doi.org/10.3390/membranes13100837 - 20 Oct 2023

Cited by 5 | Viewed by 2192

Abstract

Membrane fouling is a non-negligible issue affecting the performance of membrane systems. Particularly, organic fouling is the most persistent and severe form of fouling. The complexation between inorganic and organic matter may exacerbate membrane organic fouling. This mini review systematically analyzes the role [...] Read more.

Membrane fouling is a non-negligible issue affecting the performance of membrane systems. Particularly, organic fouling is the most persistent and severe form of fouling. The complexation between inorganic and organic matter may exacerbate membrane organic fouling. This mini review systematically analyzes the role of inorganic matter in membrane organic fouling. Inorganic substances, such as metal ions and silica, can interact with organic foulants like humic acids, polysaccharides, and proteins through ionic bonding, hydrogen bonding, coordination, and van der Waals interactions. These interactions facilitate the formation of larger aggregates that exacerbate fouling, especially for reverse osmosis membranes. Molecular simulations using molecular dynamics (MD) and density functional theory (DFT) provide valuable mechanistic insights complementing fouling experiments. Polysaccharide fouling is mainly governed by transparent exopolymer particle (TEP) formations induced by inorganic ion bridging. Inorganic coagulants like aluminum and iron salts mitigate fouling for ultrafiltration but not reverse osmosis membranes. This review summarizes the effects of critical inorganic constituents on fouling by major organic foulants, providing an important reference for membrane fouling modeling and fouling control strategies. Full article

(This article belongs to the Special Issue Membrane Separation Systems: Design and Applications)

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25 pages, 5593 KiB

Open AccessEditor’s ChoiceReview

A Recent Review of Electrospun Porous Carbon Nanofiber Mats for Energy Storage and Generation Applications

by Al Mamun, Mohamed Kiari and Lilia Sabantina

Membranes 2023, 13(10), 830; https://doi.org/10.3390/membranes13100830 - 13 Oct 2023

Cited by 7 | Viewed by 2905

Abstract

Electrospun porous carbon nanofiber mats have excellent properties, such as a large surface area, tunable porosity, and excellent electrical conductivity, and have attracted great attention in energy storage and power generation applications. Moreover, due to their exceptional properties, they can be used in [...] Read more.

Electrospun porous carbon nanofiber mats have excellent properties, such as a large surface area, tunable porosity, and excellent electrical conductivity, and have attracted great attention in energy storage and power generation applications. Moreover, due to their exceptional properties, they can be used in dye-sensitized solar cells (DSSCs), membrane electrodes for fuel cells, catalytic applications such as oxygen reduction reactions (ORRs), hydrogen evolution reactions (HERs), and oxygen evolution reactions (OERs), and sensing applications such as biosensors, electrochemical sensors, and chemical sensors, providing a comprehensive insight into energy storage development and applications. This study focuses on the role of electrospun porous carbon nanofiber mats in improving energy storage and generation and contributes to a better understanding of the fabrication process of electrospun porous carbon nanofiber mats. In addition, a comprehensive review of various alternative preparation methods covering a wide range from natural polymers to synthetic carbon-rich materials is provided, along with insights into the current literature. Full article

(This article belongs to the Special Issue Nanofibrous Membrane for Biomedical, Environmental and Energy Application)

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15 pages, 8704 KiB

Open AccessEditor’s ChoiceArticle

Differences in the Effect of Mn²⁺ on the Reverse Osmosis Membrane Fouling Caused by Different Types of Organic Matter: Experimental and Density Functional Theory Evidence

by Qiusheng Gao, Liang Duan, Yanyan Jia, Hengliang Zhang, Jianing Liu and Wei Yang

Membranes 2023, 13(10), 823; https://doi.org/10.3390/membranes13100823 - 5 Oct 2023

Cited by 3 | Viewed by 1879

Abstract

Landfill leachate from some sites contains a high concentration of Mn²⁺, which may cause reverse osmosis (RO) membrane fouling during RO treatment. In this study, the effect of Mn²⁺ on RO membrane fouling caused by typical organic pollutants (humic acid [...] Read more.

Landfill leachate from some sites contains a high concentration of Mn²⁺, which may cause reverse osmosis (RO) membrane fouling during RO treatment. In this study, the effect of Mn²⁺ on RO membrane fouling caused by typical organic pollutants (humic acid (HA), protein (BSA), and sodium alginate (SA)) was systematically investigated, and it was found that Mn²⁺ exacerbates RO membrane fouling caused by HA, SA, and HBS (mixture of HA + BSA + SA). When the Mn²⁺ concentration was 0.5 mM and 0.05 mM separately, the membrane fouling caused by HA and SA began to become significant. On the other hand, with for HBS fouling only, the water flux decreased significantly by about 21.7% and further decreased with an increasing Mn²⁺ concentration. However, Mn²⁺ has no direct effect on BSA. The effect degrees to which Mn²⁺ affected RO membrane fouling can be expressed as follows: HBS > SA > HA > BSA. The density functional theory (DFT) calculations also gave the same results. In modeling the reaction of the complexation of Mn²⁺ with the carboxyl group in these four types of organic matter, BSA has the highest energy (−55.7 kJ/mol), which predicts that BSA binding to Mn²⁺ is the most unstable compared to other organic matter. The BSA carboxylate group also has the largest bond length (2.538–2.574 Å) with Mn²⁺ and the weakest interaction force, which provides a theoretical basis for controlling RO membrane fouling exacerbated by Mn²⁺. Full article

(This article belongs to the Special Issue Membrane Separation Systems: Design and Applications)

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18 pages, 2146 KiB

Open AccessEditor’s ChoiceArticle

Polymeric Inclusion Membranes Based on Ionic Liquids for Selective Separation of Metal Ions

by Adrián Hernández-Fernández, Eduardo Iniesta-López, Anahí Ginestá-Anzola, Yolanda Garrido, Antonia Pérez de los Ríos, Joaquín Quesada-Medina and Francisco José Hernández-Fernández

Membranes 2023, 13(9), 795; https://doi.org/10.3390/membranes13090795 - 13 Sep 2023

Cited by 2 | Viewed by 1861

Abstract

In this work, poly(vinyl chloride)-based polymeric ionic liquid inclusion membranes were used in the selective separation of Fe(III), Zn(II), Cd(II), and Cu(II) from hydrochloride aqueous solutions. The ionic liquids under study were 1-octyl-3-methylimidazolium hexafluorophosphate, [omim⁺][PF₆⁻] and methyl trioctyl [...] Read more.

In this work, poly(vinyl chloride)-based polymeric ionic liquid inclusion membranes were used in the selective separation of Fe(III), Zn(II), Cd(II), and Cu(II) from hydrochloride aqueous solutions. The ionic liquids under study were 1-octyl-3-methylimidazolium hexafluorophosphate, [omim⁺][PF₆⁻] and methyl trioctyl ammonium chloride, [MTOA⁺][Cl⁻]. For this purpose, stability studies of different IL/base polymer compositions against aqueous phases were carried out. Among all polymer inclusion membranes studied, [omim⁺][PF₆⁻]/PVC membranes at a ratio of 30/70 and [MTOA⁺][Cl⁻]/PVC membranes at a ratio of 70/30 were able to retain up to 82% and 48% of the weight of the initial ionic liquid, respectively, after being exposed to a solution of metal ions in 1 M HCl for 2048 h (85 days). It was found that polymer inclusion membranes based on the ionic liquid methyl trioctyl ammonium chloride allowed the selective separation of Zn(II)/Cu(II) and Zn(II)/Fe(III) mixtures with separation factors of 1996, 606 and, to a lesser extent but also satisfactorily, Cd(II)/Cu(II) mixtures, with a separation factor of 112. Therefore, selecting the appropriate ionic liquid/base polymer mixture makes it possible to create polymeric inclusion membranes capable of selectively separating target metal ions. Full article

(This article belongs to the Special Issue Advances in Modeling, Control, and Optimization of Membrane Distillation and Membrane Separation Processes)

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16 pages, 1640 KiB

Open AccessEditor’s ChoiceArticle

Ultrafiltration and Nanofiltration for the Removal of Pharmaceutically Active Compounds from Water: The Effect of Operating Pressure on Electrostatic Solute—Membrane Interactions

by Alexandre Giacobbo, Isabella Franco Pasqualotto, Rafael Cabeleira de Coronel Machado Filho, Miguel Minhalma, Andréa Moura Bernardes and Maria Norberta de Pinho

Membranes 2023, 13(8), 743; https://doi.org/10.3390/membranes13080743 - 19 Aug 2023

Cited by 7 | Viewed by 1998

Abstract

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were [...] Read more.

The present work investigates nanofiltration (NF) and ultrafiltration (UF) for the removal of three widely used pharmaceutically active compounds (PhACs), namely atenolol, sulfamethoxazole, and rosuvastatin. Four membranes, two polyamide NF membranes (NF90 and NF270) and two polyethersulfone UF membranes (XT and ST), were evaluated in terms of productivity (permeate flux) and selectivity (rejection of PhACs) at pressures from 2 to 8 bar. Although the UF membranes have a much higher molecular weight cut-off (1000 and 10,000 Da), when compared to the molecular weight of the PhACs (253–482 Da), moderate rejections were observed. For UF, rejections were dependent on the molecular weight and charge of the PhACs, membrane molecular weight cut-off (MWCO), and operating pressure, demonstrating that electrostatic interactions play an important role in the removal of PhACs, especially at low operating pressures. On the other hand, both NF membranes displayed high rejections for all PhACs studied (75–98%). Hence, considering the optimal operating conditions, the NF270 membrane (MWCO = 400 Da) presented the best performance, achieving permeate fluxes of about 100 kg h⁻¹ m⁻² and rejections above 80% at a pressure of 8 bar, that is, a productivity of about twice that of the NF90 membrane (MWCO = 200 Da). Therefore, NF270 was the most suitable membrane for this application, although the tight UF membranes under low operating pressures displayed satisfactory results. Full article

(This article belongs to the Special Issue Honorary Issue for Prof João G. Crespo)

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21 pages, 2447 KiB

Open AccessEditor’s ChoiceArticle

MID-FTIR-PLS Chemometric Analysis of Cr(VI) from Aqueous Solutions Using a Polymer Inclusion Membrane-Based Sensor

by Armando Martínez de la Peña, Eduardo Rodríguez de San Miguel and Josefina de Gyves

Membranes 2023, 13(8), 740; https://doi.org/10.3390/membranes13080740 - 18 Aug 2023

Cited by 2 | Viewed by 1418

Abstract

A partial least squares (PLS) quantitative chemometric method based on the analysis of the mid-Fourier transform infrared spectroscopy (MID-FTIR) spectrum of polymer inclusion membranes (PIMs) used for the extraction of Cr(VI) from aqueous media is developed. The system previously optimized considering the variables [...] Read more.

A partial least squares (PLS) quantitative chemometric method based on the analysis of the mid-Fourier transform infrared spectroscopy (MID-FTIR) spectrum of polymer inclusion membranes (PIMs) used for the extraction of Cr(VI) from aqueous media is developed. The system previously optimized considering the variables membrane composition, extraction time, and pH, is characterized in terms of its adsorption isotherm, distribution coefficient, extraction percent, and enrichment factor. A Langmuir-type adsorption behavior with K_L = 2199 cm³/mmol, q_max = 0.188 mmol/g, and 0 < R_L < 1 indicates that metal adsorption is favorable. The characterization of the extraction reaction is performed as well, showing a 1:1 Cr(VI):Aliquat 336 ratio, in agreement with solvent extraction data. The principal component analysis (PCA) of the PIMs reveals a complex pattern, which is satisfactorily simplified and related to Cr(VI) concentrations through the use of a variable selection method (iPLS) in which the bands in the ranges 3451–3500 cm⁻¹ and 3751–3800 cm⁻¹ are chosen. The final PLS model, including the 100 wavelengths selected by iPLS and 10 latent variables, shows excellent parameter values with root mean square error of calibration (RMSEC) of 3.73115, root mean square error of cross-validation (RMSECV) of 6.82685, bias of −1.91847 × 10⁻¹³, cross-validation (CV) bias of 0.185947, R² Cal of 0.98145, R² CV of 0.940902, recovery% of 104.02 ± 4.12 (α = 0.05), sensitivity% of 0.001547 ppb, analytical sensitivity (γ) of 3.8 ppb, γ⁻¹: 0.6 ppb⁻¹, selectivity of 0.0155, linear range of 5.8–100 ppb, limit of detection (LD) of 1.9 ppb, and limit of quantitation (LQ) of 5.8 ppb. The developed PIM sensor is easy to implement as it requires few manipulations and a reduced number of chemical compounds in comparison to other similar reported systems. Full article

(This article belongs to the Special Issue New Trends in Polymer Inclusion Membranes 2.0)

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41 pages, 4959 KiB

Open AccessEditor’s ChoiceReview

Large-Scale Synthesis of Covalent Organic Frameworks: Challenges and Opportunities

by Harsh Vardhan, Grace Rummer, Angela Deng and Shengqian Ma

Membranes 2023, 13(8), 696; https://doi.org/10.3390/membranes13080696 - 27 Jul 2023

Cited by 10 | Viewed by 4355

Abstract

Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the [...] Read more.

Connecting organic building blocks by covalent bonds to design porous crystalline networks has led to covalent organic frameworks (COFs), consequently transferring the flexibility of dynamic linkages from discrete architectures to extended structures. By virtue of the library of organic building blocks and the diversity of dynamic linkages and topologies, COFs have emerged as a novel field of organic materials that propose a platform for tailor-made complex structural design. Progress over the past two decades in the design, synthesis, and functional exploration of COFs in diverse applications successively established these frameworks in materials chemistry. The large-scale synthesis of COFs with uniform structures and properties is of profound importance for commercialization and industrial applications; however, this is in its infancy at present. An innovative designing and synthetic approaches have paved novel ways to address future hurdles. This review article highlights the fundamental of COFs, including designing principles, coupling reactions, topologies, structural diversity, synthetic strategies, characterization, growth mechanism, and activation aspects of COFs. Finally, the major challenges and future trends for large-scale COF fabrication are outlined. Full article

(This article belongs to the Special Issue Porous MOF/COF for Membrane Applications)

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16 pages, 11361 KiB

Open AccessEditor’s ChoiceArticle

In Situ Formation of Silver Nanoparticles Induced by Cl-Doped Carbon Quantum Dots for Enhanced Separation and Antibacterial Performance of Nanofiltration Membrane

by Yi-Fang Mi, Jia-Li Liu, Wen Xia, Shu-Heng He and Bao-Qing Shentu

Membranes 2023, 13(8), 693; https://doi.org/10.3390/membranes13080693 - 25 Jul 2023

Cited by 4 | Viewed by 1298

Abstract

Polyamide (PA) nanofiltration (NF) membranes suffer from biofouling, which will deteriorate their separation performance. In this study, we proposed a strategy to incorporate silver nanoparticles (Ag NPs) into PA NF membranes in situ, in order to simultaneously enhance water permeability and antibacterial performance. [...] Read more.

Polyamide (PA) nanofiltration (NF) membranes suffer from biofouling, which will deteriorate their separation performance. In this study, we proposed a strategy to incorporate silver nanoparticles (Ag NPs) into PA NF membranes in situ, in order to simultaneously enhance water permeability and antibacterial performance. The chloride-doped carbon quantum dots (Cl-CQDs) with photocatalytic performance were pre-embedded in the PA selective layer. Under visible light irradiation, the photogenerated charge carriers generated by Cl-CQDs rapidly transported to silver ions (Ag⁺ ions), resulting in the in situ formation of Ag NPs. The proposed strategy avoided the problem of aggregating Ag NPs, and the amount of Ag NPs on the membrane surfaces could be easily tuned by changing silver nitrate (AgNO₃) concentrations and immersion times. These uniformly dispersed Ag NPs increased membrane hydrophilicity. Thus, the obtained thin film nanocomposite Ag NPs (TFN-Ag) membrane exhibited an improved water flux (31.74 L m⁻² h⁻¹), which was ~2.98 times that of the pristine PA membrane; meanwhile, the sodium sulfate (Na₂SO₄) rejection rate was 96.11%. The sterilization rates of the TFN-Ag membrane against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were 99.55% and 99.52%, respectively. Thus, this facile strategy simultaneously improved the permeability and antibacterial property of PA NF membranes. Full article

(This article belongs to the Special Issue Mixed-Matrix Membranes and Polymeric Membranes 2.0)

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16 pages, 3052 KiB

Open AccessEditor’s ChoiceReview

Current and Potential Applications of Green Membranes with Nanocellulose

by Stefanos (Steve) Nitodas, Meredith Skehan, Henry Liu and Raj Shah

Membranes 2023, 13(8), 694; https://doi.org/10.3390/membranes13080694 - 25 Jul 2023

Cited by 5 | Viewed by 1776

Abstract

Large-scale applications of nanotechnology have been extensively studied within the last decade. By exploiting certain advantageous properties of nanomaterials, multifunctional products can be manufactured that can contribute to the improvement of everyday life. In recent years, one such material has been nanocellulose. Nanocellulose [...] Read more.

Large-scale applications of nanotechnology have been extensively studied within the last decade. By exploiting certain advantageous properties of nanomaterials, multifunctional products can be manufactured that can contribute to the improvement of everyday life. In recent years, one such material has been nanocellulose. Nanocellulose (NC) is a naturally occurring nanomaterial and a high-performance additive extracted from plant fibers. This sustainable material is characterized by a unique combination of exceptional properties, including high tensile strength, biocompatibility, and electrical conductivity. In recent studies, these unique properties of nanocellulose have been analyzed and applied to processes related to membrane technology. This article provides a review of recent synthesis methods and characterization of nanocellulose-based membranes, followed by a study of their applications on a larger scale. The article reviews successful case studies of the incorporation of nanocellulose in different types of membrane materials, as well as their utilization in water purification, desalination, gas separations/gas barriers, and antimicrobial applications, in an effort to provide an enhanced comprehension of their capabilities in commercial products. Full article

(This article belongs to the Special Issue Preparation and Application of Advanced Functional Membranes)

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29 pages, 2156 KiB

Open AccessEditor’s ChoiceReview

A Review on Membrane Fouling Prediction Using Artificial Neural Networks (ANNs)

by Waad H. Abuwatfa, Nour AlSawaftah, Naif Darwish, William G. Pitt and Ghaleb A. Husseini

Membranes 2023, 13(7), 685; https://doi.org/10.3390/membranes13070685 - 24 Jul 2023

Cited by 12 | Viewed by 4338

Abstract

Membrane fouling is a major hurdle to effective pressure-driven membrane processes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Fouling refers to the accumulation of particles, organic and inorganic matter, and microbial cells on the membrane’s external and internal [...] Read more.

Membrane fouling is a major hurdle to effective pressure-driven membrane processes, such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Fouling refers to the accumulation of particles, organic and inorganic matter, and microbial cells on the membrane’s external and internal surface, which reduces the permeate flux and increases the needed transmembrane pressure. Various factors affect membrane fouling, including feed water quality, membrane characteristics, operating conditions, and cleaning protocols. Several models have been developed to predict membrane fouling in pressure-driven processes. These models can be divided into traditional empirical, mechanistic, and artificial intelligence (AI)-based models. Artificial neural networks (ANNs) are powerful tools for nonlinear mapping and prediction, and they can capture complex relationships between input and output variables. In membrane fouling prediction, ANNs can be trained using historical data to predict the fouling rate or other fouling-related parameters based on the process parameters. This review addresses the pertinent literature about using ANNs for membrane fouling prediction. Specifically, complementing other existing reviews that focus on mathematical models or broad AI-based simulations, the present review focuses on the use of AI-based fouling prediction models, namely, artificial neural networks (ANNs) and their derivatives, to provide deeper insights into the strengths, weaknesses, potential, and areas of improvement associated with such models for membrane fouling prediction. Full article

(This article belongs to the Special Issue Membrane Fouling in Water/Wastewater Treatment: Characterization, Modeling and Control)

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21 pages, 13797 KiB

Open AccessEditor’s ChoiceArticle

Investigation of Photocatalytic PVDF Membranes Containing Inorganic Nanoparticles for Model Dairy Wastewater Treatment

by Elias Jigar Sisay, Ákos Ferenc Fazekas, Tamás Gyulavári, Judit Kopniczky, Béla Hopp, Gábor Veréb and Zsuzsanna László

Membranes 2023, 13(7), 656; https://doi.org/10.3390/membranes13070656 - 10 Jul 2023

Cited by 5 | Viewed by 1667

Abstract

Membrane separation processes are promising methods for wastewater treatment. Membrane fouling limits their wider use; however, this may be mitigated using photocatalytic composite materials for membrane preparation. This study aimed to investigate photocatalytic polyvinylidene fluoride (PVDF)-based nanocomposite membranes for treating model dairy wastewater [...] Read more.

Membrane separation processes are promising methods for wastewater treatment. Membrane fouling limits their wider use; however, this may be mitigated using photocatalytic composite materials for membrane preparation. This study aimed to investigate photocatalytic polyvinylidene fluoride (PVDF)-based nanocomposite membranes for treating model dairy wastewater containing bovine serum albumin (BSA). Membranes were fabricated via physical coating (with TiO₂, and/or carbon nanotubes, and/or BiVO₄) and blending (with TiO₂). Another objective of this study was to compare membranes of identical compositions fabricated using different techniques, and to examine how various TiO₂ concentrations affect the antifouling and cleaning performances of the blended membranes. Filtration experiments were performed using a dead-end cell. Filtration resistances, BSA rejection, and photocatalytic cleanability (characterized by flux recovery ratio (FRR)) were measured. The surface characteristics (SEM, EDX), roughness (measured by atomic force microscopy, AFM), wettability (contact angle measurements), and zeta potential of the membranes were also examined. Coated PVDF membranes showed higher hydrophilicity than the pristine PVDF membrane, as evidenced by a decreased contact angle, but the higher hydrophilicity did not result in higher fluxes, unlike the case of blended membranes. The increased surface roughness resulted in increased reversible fouling, but decreased BSA retention. Furthermore, the TiO₂-coated membranes had a better flux recovery ratio (FRR, 97%) than the TiO₂-blended membranes (35%). However, the TiO₂-coated membrane had larger total filtration resistances and a lower water flux than the commercial pristine PVDF membrane and TiO₂-blended membrane, which may be due to pore blockage or an additional coating layer formed by the nanoparticles. The BSA rejection of the TiO₂-coated membrane was lower than that of the commercial pristine PVDF membrane. In contrast, the TiO₂-blended membranes showed lower resistance than the pristine PVDF membrane, and exhibited better antifouling performance, superior flux, and comparable BSA rejection. Increasing the TiO₂ content of the TiO₂-blended membranes (from 1 to 2.5%) resulted in increased antifouling and comparable BSA rejection (more than 95%). However, the effect of TiO₂ concentration on flux recovery was negligible. Full article

(This article belongs to the Special Issue Modeling and Simulation of Industrial and Environmental Membrane Technologies)

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25 pages, 2438 KiB

Open AccessEditor’s ChoiceReview

Forward Osmosis Application for the Removal of Emerging Contaminants from Municipal Wastewater: A Review

by Mónica Salamanca, Mar Peña, Antonio Hernandez, Pedro Prádanos and Laura Palacio

Membranes 2023, 13(7), 655; https://doi.org/10.3390/membranes13070655 - 10 Jul 2023

Cited by 5 | Viewed by 2705

Abstract

Forward osmosis (FO) has attracted special attention in water and wastewater treatment due to its role in addressing the challenges of water scarcity and contamination. The presence of emerging contaminants in water sources raises concerns regarding their environmental and public health impacts. Conventional [...] Read more.

Forward osmosis (FO) has attracted special attention in water and wastewater treatment due to its role in addressing the challenges of water scarcity and contamination. The presence of emerging contaminants in water sources raises concerns regarding their environmental and public health impacts. Conventional wastewater treatment methods cannot effectively remove these contaminants; thus, innovative approaches are required. FO membranes offer a promising solution for wastewater treatment and removal of the contaminants in wastewater. Several factors influence the performance of FO processes, including concentration polarization, membrane fouling, draw solute selection, and reverse salt flux. Therefore, understanding and optimizing these factors are crucial aspects for improving the efficiency and sustainability of the FO process. This review stresses the need for research to explore the potential and challenges of FO membranes to meet municipal wastewater treatment requirements, to optimize the process, to reduce energy consumption, and to promote scalability for potential industrial applications. In conclusion, FO shows promising performance for wastewater treatment, dealing with emerging pollutants and contributing to sustainable practices. By improving the FO process and addressing its challenges, we could contribute to improve the availability of water resources amid the global water scarcity concerns, as well as contribute to the circular economy. Full article

(This article belongs to the Collection Feature Papers in Membrane Engineering and Applications)

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18 pages, 3338 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in Membranes Used for Nanofiltration to Remove Heavy Metals from Wastewater: A Review

by Cristina Ileana Covaliu-Mierlă, Oana Păunescu and Horia Iovu

Membranes 2023, 13(7), 643; https://doi.org/10.3390/membranes13070643 - 4 Jul 2023

Cited by 11 | Viewed by 4142

Abstract

The presence of heavy metal ions in polluted wastewater represents a serious threat to human health, making proper disposal extremely important. The utilization of nanofiltration (NF) membranes has emerged as one of the most effective methods of heavy metal ion removal from wastewater [...] Read more.

The presence of heavy metal ions in polluted wastewater represents a serious threat to human health, making proper disposal extremely important. The utilization of nanofiltration (NF) membranes has emerged as one of the most effective methods of heavy metal ion removal from wastewater due to their efficient operation, adaptable design, and affordability. NF membranes created from advanced materials are becoming increasingly popular due to their ability to depollute wastewater in a variety of circumstances. Tailoring the NF membrane’s properties to efficiently remove heavy metal ions from wastewater, interfacial polymerization, and grafting techniques, along with the addition of nano-fillers, have proven to be the most effective modification methods. This paper presents a review of the modification processes and NF membrane performances for the removal of heavy metals from wastewater, as well as the application of these membranes for heavy metal ion wastewater treatment. Very high treatment efficiencies, such as 99.90%, have been achieved using membranes composed of polyvinyl amine (PVAM) and glutaraldehyde (GA) for Cr³⁺ removal from wastewater. However, nanofiltration membranes have certain drawbacks, such as fouling of the NF membrane. Repeated cleaning of the membrane influences its lifetime. Full article

(This article belongs to the Special Issue Preparation and Application of Novel Polymer Membranes)

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24 pages, 1200 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Challenges and Solutions for Global Water Scarcity

by Hilla Shemer, Shlomo Wald and Raphael Semiat

Membranes 2023, 13(6), 612; https://doi.org/10.3390/membranes13060612 - 20 Jun 2023

Cited by 31 | Viewed by 11965

Abstract

Climate change, global population growth, and rising standards of living have put immense strain on natural resources, resulting in the unsecured availability of water as an existential resource. Access to high-quality drinking water is crucial for daily life, food production, industry, and nature. [...] Read more.

Climate change, global population growth, and rising standards of living have put immense strain on natural resources, resulting in the unsecured availability of water as an existential resource. Access to high-quality drinking water is crucial for daily life, food production, industry, and nature. However, the demand for freshwater resources exceeds the available supply, making it essential to utilize all alternative water resources such as the desalination of brackish water, seawater, and wastewater. Reverse osmosis desalination is a highly efficient method to increase water supplies and make clean, affordable water accessible to millions of people. However, to ensure universal access to water, various measures need to be implemented, including centralized governance, educational campaigns, improvements in water catchment and harvesting technologies, infrastructure development, irrigation and agricultural practices, pollution control, investments in novel water technologies, and transboundary water cooperation. This paper provides a comprehensive overview of measures for utilizing alternative water sources, with particular emphasis on seawater desalination and wastewater reclamation techniques. In particular, membrane-based technologies are critically reviewed, with a focus on their energy consumption, costs, and environmental impacts. Full article

(This article belongs to the Section Membrane Applications)

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23 pages, 3410 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Advanced Hybrid System for Ammonium Valorization as Liquid Fertilizer from Treated Urban Wastewaters: Validation of Natural Zeolites Pretreatment and Liquid-Liquid Membrane Contactors at Pilot Plant Scale

by Álvaro Mayor, Mònica Reig, Xanel Vecino, José Luis Cortina and César Valderrama

Membranes 2023, 13(6), 580; https://doi.org/10.3390/membranes13060580 - 2 Jun 2023

Cited by 9 | Viewed by 1633

Abstract

This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH₃) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before [...] Read more.

This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH₃) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before the HFMC. The system was tested with wastewater treatment plant (WWTP) effluent (mainstream, 50 mg N-NH₄/L) and anaerobic digestion centrates (sidestream, 600–800 mg N-NH₄/L) from another WWTP. Natural zeolite, primarily clinoptilolite, demonstrated effective desorption of retained ammonium using a 2% NaOH solution in a closed-loop configuration, resulting in an ammonia-rich brine that enabled over 95% NH₃ recovery using polypropylene HFMCs. A 1 m³/h demonstration plant processed both urban wastewaters, which were pretreated by ultrafiltration, removing over 90% of suspended solids and 60–65% of COD. The 2% NaOH regeneration brines (2.4–5.6 g N-NH₄/L) were treated in a closed-loop HFMC pilot system, producing 10–15% N streams with potential use as liquid fertilizers. The resulting ammonium nitrate was free of heavy metals and organic micropollutants, making it suitable for use as liquid fertilizer. This comprehensive N management solution for urban wastewater applications can contribute to local economies while achieving reduced N discharge and circularity goals. Full article

(This article belongs to the Special Issue Applications of Membrane Processes in Desalination, Wastewater Treatment and Resource Recovery)

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37 pages, 6260 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Cation Exchange Membranes and Process Optimizations in Electrodialysis for Selective Metal Separation: A Review

by Önder Tekinalp, Pauline Zimmermann, Steven Holdcroft, Odne Stokke Burheim and Liyuan Deng

Membranes 2023, 13(6), 566; https://doi.org/10.3390/membranes13060566 - 30 May 2023

Cited by 31 | Viewed by 6239

Abstract

The selective separation of metal species from various sources is highly desirable in applications such as hydrometallurgy, water treatment, and energy production but also challenging. Monovalent cation exchange membranes (CEMs) show a great potential to selectively separate one metal ion over others of [...] Read more.

The selective separation of metal species from various sources is highly desirable in applications such as hydrometallurgy, water treatment, and energy production but also challenging. Monovalent cation exchange membranes (CEMs) show a great potential to selectively separate one metal ion over others of the same or different valences from various effluents in electrodialysis. Selectivity among metal cations is influenced by both the inherent properties of membranes and the design and operating conditions of the electrodialysis process. The research progress and recent advances in membrane development and the implication of the electrodialysis systems on counter-ion selectivity are extensively reviewed in this work, focusing on both structure–property relationships of CEM materials and influences of process conditions and mass transport characteristics of target ions. Key membrane properties, such as charge density, water uptake, and polymer morphology, and strategies for enhancing ion selectivity are discussed. The implications of the boundary layer at the membrane surface are elucidated, where differences in the mass transport of ions at interfaces can be exploited to manipulate the transport ratio of competing counter-ions. Based on the progress, possible future R&D directions are also proposed. Full article

(This article belongs to the Special Issue Membrane Systems for Metal Ion Extraction)

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37 pages, 4819 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Developing Enzyme Immobilization with Fibrous Membranes: Longevity and Characterization Considerations

by Yue Yuan, Jialong Shen and Sonja Salmon

Membranes 2023, 13(5), 532; https://doi.org/10.3390/membranes13050532 - 20 May 2023

Cited by 9 | Viewed by 3358

Abstract

Fibrous membranes offer broad opportunities to deploy immobilized enzymes in new reactor and application designs, including multiphase continuous flow-through reactions. Enzyme immobilization is a technology strategy that simplifies the separation of otherwise soluble catalytic proteins from liquid reaction media and imparts stabilization and [...] Read more.

Fibrous membranes offer broad opportunities to deploy immobilized enzymes in new reactor and application designs, including multiphase continuous flow-through reactions. Enzyme immobilization is a technology strategy that simplifies the separation of otherwise soluble catalytic proteins from liquid reaction media and imparts stabilization and performance enhancement. Flexible immobilization matrices made from fibers have versatile physical attributes, such as high surface area, light weight, and controllable porosity, which give them membrane-like characteristics, while simultaneously providing good mechanical properties for creating functional filters, sensors, scaffolds, and other interface-active biocatalytic materials. This review examines immobilization strategies for enzymes on fibrous membrane-like polymeric supports involving all three fundamental mechanisms of post-immobilization, incorporation, and coating. Post-immobilization offers an infinite selection of matrix materials, but may encounter loading and durability issues, while incorporation offers longevity but has more limited material options and may present mass transfer obstacles. Coating techniques on fibrous materials at different geometric scales are a growing trend in making membranes that integrate biocatalytic functionality with versatile physical supports. Biocatalytic performance parameters and characterization techniques for immobilized enzymes are described, including several emerging techniques of special relevance for fibrous immobilized enzymes. Diverse application examples from the literature, focusing on fibrous matrices, are summarized, and biocatalyst longevity is emphasized as a critical performance parameter that needs increased attention to advance concepts from lab scale to broader utilization. This consolidation of fabrication, performance measurement, and characterization techniques, with guiding examples highlighted, is intended to inspire future innovations in enzyme immobilization with fibrous membranes and expand their uses in novel reactors and processes. Full article

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13 pages, 4627 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydration and Mobility of Alkaline Metal Cations in Sulfonic Cation Exchange Membranes

by Vitaly I. Volkov, Nikita A. Slesarenko, Alexander V. Chernyak, Irina A. Avilova and Victor P. Tarasov

Membranes 2023, 13(5), 518; https://doi.org/10.3390/membranes13050518 - 16 May 2023

Cited by 5 | Viewed by 1400

Abstract

The interconnection of ionogenic channel structure, cation hydration, water and ionic translational mobility was revealed in Nafion and MSC membranes based on polyethylene and grafted sulfonated polystyrene. A local mobility of Li⁺, Na⁺ and Cs⁺ cations and water molecules [...] Read more.

The interconnection of ionogenic channel structure, cation hydration, water and ionic translational mobility was revealed in Nafion and MSC membranes based on polyethylene and grafted sulfonated polystyrene. A local mobility of Li⁺, Na⁺ and Cs⁺ cations and water molecules was estimated via the ¹H, ⁷Li, ²³Na and ¹³³Cs spin relaxation technique. The calculated cation and water molecule self-diffusion coefficients were compared with experimental values measured using pulsed field gradient NMR. It was shown that macroscopic mass transfer is controlled by molecule and ion motion near sulfonate groups. Lithium and sodium cations whose hydrated energy is higher than water hydrogen bond energy move together with water molecules. Cesium cations in possession of low hydrated energy are directly jumping between neighboring sulfonate groups. Cation Li⁺, Na⁺ and Cs⁺ hydration numbers (h) in membranes were calculated from ¹H chemical shift water molecule temperature dependences. The values calculated from the Nernst–Einstein equation and the experimental conductivity values were close to each other in Nafion membranes. In MSC membranes, calculated conductivities were one order of magnitude more compared to the experimental ones, which is explained by the heterogeneity of the membrane pore and channel system. Full article

(This article belongs to the Section Membrane Physics and Theory)

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