Membranes

21 pages, 4718 KiB

Open AccessEditor’s ChoiceArticle

Novel Cellulose Acetate-Based Monophasic Hybrid Membranes for Improved Blood Purification Devices: Characterization under Dynamic Conditions

by Adriana Janeca, Flávia S. C. Rodrigues, Maria Clara Gonçalves and Mónica Faria

Membranes 2021, 11(11), 825; https://doi.org/10.3390/membranes11110825 - 27 Oct 2021

Cited by 12 | Viewed by 3816

Abstract

A novel cellulose acetate-based monophasic hybrid skinned amine-functionalized CA-SiO₂-(CH₂)₃NH₂ membrane was synthesized using an innovative method which combines the phase inversion and sol-gel techniques. Morphological characterization was performed by scanning electron microscopy (SEM), and the chemical [...] Read more.

A novel cellulose acetate-based monophasic hybrid skinned amine-functionalized CA-SiO₂-(CH₂)₃NH₂ membrane was synthesized using an innovative method which combines the phase inversion and sol-gel techniques. Morphological characterization was performed by scanning electron microscopy (SEM), and the chemical composition was analyzed by Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). The characterization of the monophasic hybrid CA-SiO₂-(CH₂)₃NH₂ membrane in terms of permeation properties was carried out in an in-house-built single hemodialysis membrane module (SHDMM) under dynamic conditions. Permeation experiments were performed to determine the hydraulic permeability (Lp), molecular weight cut-off (MWCO) and the rejection coefficients to urea, creatinine, uric acid, and albumin. SEM confirmed the existence of a very thin (<1 µm) top dense layer and a much thicker bottom porous surface, and ATR-FTIR showed the main bands belonging to the CA-based membranes. Permeation studies revealed that the Lp and MWCO of the CA-SiO₂-(CH₂)₃NH₂ membrane were 66.61 kg·h⁻¹·m⁻²·bar⁻¹ and 24.5 kDa, respectively, and that the Lp was 1.8 times higher compared to a pure CA membrane. Furthermore, the CA-SiO₂-(CH₂)₃NH₂ membrane fully permeated urea, creatinine, and uric acid while completely retaining albumin. Long-term filtration studies of albumin solutions indicated that fouling does not occur at the surface of the CA-SiO₂-(CH₂)₃NH₂ membrane. Full article

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

► Show Figures

Graphical abstract

30 pages, 5108 KiB

Open AccessEditor’s ChoiceReview

A Review on Ion-Exchange Membranes Fouling during Electrodialysis Process in Food Industry, Part 2: Influence on Transport Properties and Electrochemical Characteristics, Cleaning and Its Consequences

by Natalia Pismenskaya, Myriam Bdiri, Veronika Sarapulova, Anton Kozmai, Julie Fouilloux, Lassaad Baklouti, Christian Larchet, Estelle Renard and Lasâad Dammak

Membranes 2021, 11(11), 811; https://doi.org/10.3390/membranes11110811 - 25 Oct 2021

Cited by 24 | Viewed by 4995

Abstract

Ion-exchange membranes (IEMs) are increasingly used in dialysis and electrodialysis processes for the extraction, fractionation and concentration of valuable components, as well as reagent-free control of liquid media pH in the food industry. Fouling of IEMs is specific compared to that observed in [...] Read more.

Ion-exchange membranes (IEMs) are increasingly used in dialysis and electrodialysis processes for the extraction, fractionation and concentration of valuable components, as well as reagent-free control of liquid media pH in the food industry. Fouling of IEMs is specific compared to that observed in the case of reverse or direct osmosis, ultrafiltration, microfiltration, and other membrane processes. This specificity is determined by the high concentration of fixed groups in IEMs, as well as by the phenomena inherent only in electromembrane processes, i.e., induced by an electric field. This review analyzes modern scientific publications on the effect of foulants (mainly typical for the dairy, wine and fruit juice industries) on the structural, transport, mass transfer, and electrochemical characteristics of cation-exchange and anion-exchange membranes. The relationship between the nature of the foulant and the structure, physicochemical, transport properties and behavior of ion-exchange membranes in an electric field is analyzed using experimental data (ion exchange capacity, water content, conductivity, diffusion permeability, limiting current density, water splitting, electroconvection, etc.) and modern mathematical models. The implications of traditional chemical cleaning are taken into account in this analysis and modern non-destructive membrane cleaning methods are discussed. Finally, challenges for the near future were identified. Full article

(This article belongs to the Special Issue In-Depth on the Fouling and Antifouling of Ion-Exchange Membranes)

► Show Figures

Graphical abstract

17 pages, 5790 KiB

Open AccessEditor’s ChoiceArticle

A Facile Method to Control Pore Structure of PVDF/SiO₂ Composite Membranes for Efficient Oil/Water Purification

by Qianqian Xu, Yuchao Chen, Tonghu Xiao and Xing Yang

Membranes 2021, 11(11), 803; https://doi.org/10.3390/membranes11110803 - 22 Oct 2021

Cited by 16 | Viewed by 2801

Abstract

The use of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes to purify oily water has received much attention. However, it is challenging to obtain high-performance PVDF microfiltration membranes due to severe surface fouling and rapid decline of permeability. This study explored a new approach [...] Read more.

The use of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes to purify oily water has received much attention. However, it is challenging to obtain high-performance PVDF microfiltration membranes due to severe surface fouling and rapid decline of permeability. This study explored a new approach to fabricate high-performance PVDF/silica (SiO₂) composite membrane via the use of a polymer solution featuring lower critical solution temperature (LCST) characteristics and the non-solvent thermally induced phase separation method (NTIPS). Coupling with morphological observations, the membrane formation kinetics were analyzed in depth to understand the synergistic effect between the LCST solution properties and fabrication conditions in NTIPS. Utilizing such a synergistic effect, the transition from finger-like macrovoid pores to bi-continuous highly connected pores could be flexibly tuned by increasing the PVDF concentration and the weight ratio of SiO₂/PVDF in the dope solution and by raising the coagulation temperature to above the LCST of the solution. The filtration experiments with surfactant-stabilized oil-water emulsion showed that the permeation flux of the PVDF/SiO₂ composite membranes was higher than 318 L·m⁻²·h⁻¹·bar⁻¹ and the rejection above 99.2%. It was also shown that the PVDF/SiO₂ composite membranes, especially those fabricated above the LCST, demonstrated better hydrophilicity, which resulted in significant enhancement in the anti-fouling properties for oil/water emulsion separation. Compared to the benchmark pure PVDF membrane in oily water purification, the optimal composite membrane T70 was demonstrated via the 3-cycle filtration experiments with a significantly improved flux recovery ratio (F_rr) and minimal reduced irreversible fouling (R_ir). Overall, with the developed method in this work, facile procedure to tune the membrane morphology and pore structure was demonstrated, resulting in high performance composite membranes suitable for oil/water emulsion separation. Full article

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

► Show Figures

Figure 1

22 pages, 6221 KiB

Open AccessEditor’s ChoiceArticle

Prediction of Membrane Failure in a Water Purification Plant Using Nonhomogeneous Poisson Process Models

by Takashi Hashimoto and Satoshi Takizawa

Membranes 2021, 11(11), 800; https://doi.org/10.3390/membranes11110800 - 20 Oct 2021

Cited by 2 | Viewed by 2324

Abstract

The prediction of membrane failure in full-scale water purification plants is an important but difficult task. Although previous studies employed accelerated laboratory-scale tests of membrane failure, it is not possible to reproduce the complex operational conditions of full-scale plants. Therefore, we aimed to [...] Read more.

The prediction of membrane failure in full-scale water purification plants is an important but difficult task. Although previous studies employed accelerated laboratory-scale tests of membrane failure, it is not possible to reproduce the complex operational conditions of full-scale plants. Therefore, we aimed to develop prediction models of membrane failure using actual membrane failure data. Because membrane filtration systems are repairable systems, nonhomogeneous Poisson process (NHPP) models, i.e., power law and log-linear models, were employed; the model parameters were estimated using the membrane failure data from a full-scale plant operated for 13 years. Both models were able to predict cumulative failures for forthcoming years; nonetheless, the power law model showed higher stability and narrower confidence intervals than the log-linear model. By integrating two membrane replacement criteria, namely deterioration of filtrate water quality and reduction of membrane permeability, it was possible to predict the time to replace all the membranes on a water purification plant. Finally, the NHPP models coupled with a nonparametric bootstrap method provided a method to select membrane modules for earlier replacement than others. Although the criteria for membrane replacement may vary among membrane filtration plants, the NHPP models presented in this study could be applied to any other plant with membrane failure data. Full article

(This article belongs to the Special Issue Water and Wastewater Treatment Technologies with Membrane Filtration)

► Show Figures

Graphical abstract

11 pages, 1795 KiB

Open AccessEditor’s ChoiceArticle

Biphenyl-Based Covalent Triazine Framework/Matrimid^® Mixed-Matrix Membranes for CO₂/CH₄ Separation

by Stefanie Bügel, Quang-Dien Hoang, Alex Spieß, Yangyang Sun, Shanghua Xing and Christoph Janiak

Membranes 2021, 11(10), 795; https://doi.org/10.3390/membranes11100795 - 19 Oct 2021

Cited by 6 | Viewed by 3128

Abstract

Processes, such as biogas upgrading and natural gas sweetening, make CO₂/CH₄ separation an environmentally relevant and current topic. One way to overcome this separation issue is the application of membranes. An increase in separation efficiency can be achieved by applying [...] Read more.

Processes, such as biogas upgrading and natural gas sweetening, make CO₂/CH₄ separation an environmentally relevant and current topic. One way to overcome this separation issue is the application of membranes. An increase in separation efficiency can be achieved by applying mixed-matrix membranes, in which filler materials are introduced into polymer matrices. In this work, we report the covalent triazine framework CTF-biphenyl as filler material in a matrix of the glassy polyimide Matrimid^®. MMMs with 8, 16, and 24 wt% of the filler material are applied for CO₂/CH₄ mixed-gas separation measurements. With a CTF-biphenyl loading of only 16 wt%, the CO₂ permeability is more than doubled compared to the pure polymer membrane, while maintaining the high CO₂/CH₄ selectivity of Matrimid^®. Full article

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

► Show Figures

Graphical abstract

18 pages, 50625 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Polyelectrolyte Membranes of Pectin Graft-Copolymers with PVA and Their Composites with Phosphomolybdic Acid for Drug Delivery, Toxic Metal Ion Removal, and Fuel Cell Applications

by Raagala Vijitha, Nagella Sivagangi Reddy, Kasula Nagaraja, Tiruchuru J. Sudha Vani, Marlia M. Hanafiah, Katta Venkateswarlu, Sivarama Krishna Lakkaboyana, Kummari S. V. Krishna Rao and Kummara Madhususdana Rao

Membranes 2021, 11(10), 792; https://doi.org/10.3390/membranes11100792 - 18 Oct 2021

Cited by 16 | Viewed by 3192

Abstract

In this study, a simple method for the fabrication of highly diffusive, adsorptive and conductive eco-friendly polyelectrolyte membranes (PEMs) with sulfonate functionalized pectin and poly(vinyl alcohol)(PVA) was established. The graft-copolymers were synthesized by employing the use of potassium persulfate as a free radical [...] Read more.

In this study, a simple method for the fabrication of highly diffusive, adsorptive and conductive eco-friendly polyelectrolyte membranes (PEMs) with sulfonate functionalized pectin and poly(vinyl alcohol)(PVA) was established. The graft-copolymers were synthesized by employing the use of potassium persulfate as a free radical initiator from pectin (PC), a carbohydrate polymer with 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS) and sodium 4-vinylbenzene sulphonate (SVBS). The PEMs were fabricated from the blends of pectin graft-copolymers (PC-g-AMPS and PC-g-SVBS) and PVA by using a solution casting method, followed by chemical crosslinking with glutaraldehyde. The composite PEMs were fabricated by mixing phosphomolybdic acid with the aforementioned blends. The PEMs were successfully characterized by FTIR, XRD, SEM, and EDAX studies. They were assessed for the controlled release of an anti-cancer drug (5-fluorouracil) and the removal of toxic metal ions (Cu²⁺) from aqueous media. Furthermore, the composite PEMs were evaluated for fuel cell application. The 5-fluorouracil release capacity of the PEMs was found to be 93% and 99.1% at 300 min in a phosphate buffer solution (pH = 7.4). The highest Cu²⁺ removal was observed at 206.7 and 190.1 mg/g. The phosphomolybdic acid-embedded PEMs showed superior methanol permeability, i.e., 6.83 × 10⁻⁵, and 5.94 × 10^−5, compared to the pristine PEMs. Furthermore, the same trend was observed for the proton conductivities, i.e., 13.77 × 10⁻³, and 18.6 × 10⁻³ S/cm at 30 °C. Full article

(This article belongs to the Special Issue Development of Novel Composite Membranes in Water/Wastewater Treatment)

► Show Figures

Graphical abstract

21 pages, 6819 KiB

Open AccessEditor’s ChoiceArticle

An Experimental Performance Study of a Catalytic Membrane Reactor for Ethanol Steam Reforming over a Metal Honeycomb Catalyst

by Nikita Eremeev, Alexey Krasnov, Yuliya Bespalko, Ludmilla Bobrova, Oleg Smorygo and Vladislav Sadykov

Membranes 2021, 11(10), 790; https://doi.org/10.3390/membranes11100790 - 18 Oct 2021

Cited by 7 | Viewed by 2477

Abstract

The present study deals with the combination of ethanol steam reforming over a monolithic catalyst and hydrogen separation by membrane in a lab-scale catalytic membrane reactor (CMR). The catalyst was comprised of honeycomb thin-walled Fechralloy substrate loaded with Ni + Ru/Pr_0.35Ce [...] Read more.

The present study deals with the combination of ethanol steam reforming over a monolithic catalyst and hydrogen separation by membrane in a lab-scale catalytic membrane reactor (CMR). The catalyst was comprised of honeycomb thin-walled Fechralloy substrate loaded with Ni + Ru/Pr_0.35Ce_0.35Zr_0.35O₂ active component. The asymmetric supported membrane consisted of a thin Ni-Cu alloy–Nd tungstate nanocomposite dense permselective layer deposited on a hierarchically structured asymmetric support. It has been shown that the monolithic catalyst-assisted CMR is capable of increasing the driving potential for hydrogen permeation through the same membrane as compared with that of the packed bed catalyst by increasing the retentate hydrogen concentration. Important operating parameters responsible for the low carbon deposition rate as well as the amount of hydrogen produced from 1 mol of ethanol, such as the temperature range of 700–900 °C, the water/ethanol molar ratio of 4 in the feed, have been determined. Regarding the choice of the reagent concentration (ethanol and steam in Ar), its magnitude may directly interfere with the effectiveness of the reaction-separation process in the CMR. Full article

(This article belongs to the Special Issue Novel Supported Membranes for Syngas Generation and Hydrogen Separation)

► Show Figures

Figure 1

17 pages, 7345 KiB

Open AccessEditor’s ChoiceReview

Recent Developments in Nanoporous Graphene Membranes for Organic Solvent Nanofiltration: A Short Review

by Yoon-Tae Nam, Jun-Hyeok Kang, Jae-Dong Jang, Jun-Hyuk Bae, Hee-Tae Jung and Dae-Woo Kim

Membranes 2021, 11(10), 793; https://doi.org/10.3390/membranes11100793 - 18 Oct 2021

Cited by 9 | Viewed by 4564

Abstract

Graphene-based membranes are promising candidates for efficient organic solvent nanofiltration (OSN) processes because of their unique structural characteristics, such as mechanical/chemical stability and precise molecular sieving. Recently, to improve organic solvent permeance and selectivity, nanopores have been fabricated on graphene planes via chemical [...] Read more.

Graphene-based membranes are promising candidates for efficient organic solvent nanofiltration (OSN) processes because of their unique structural characteristics, such as mechanical/chemical stability and precise molecular sieving. Recently, to improve organic solvent permeance and selectivity, nanopores have been fabricated on graphene planes via chemical and physical methods. The nanopores serve as an additional channel for facilitating ultrafast solvent permeation while filtering organic molecules by size exclusion. This review summarizes the recent developments in nanoporous graphene (NG)-based membranes for OSN applications. The membranes are categorized depending on the membrane structure: single-layer NG, multilayer NG, and graphene-based composite membranes hybridized with other porous materials. Techniques for nanopore generation on graphene, as well as the challenges faced and the perspectives required for the commercialization of NG membranes, are also discussed. Full article

(This article belongs to the Special Issue Advancements of 2D Materials-Based Membranes)

► Show Figures

Figure 1

37 pages, 32302 KiB

Open AccessEditor’s ChoiceReview

A Review on Ion-Exchange Membrane Fouling during the Electrodialysis Process in the Food Industry, Part 1: Types, Effects, Characterization Methods, Fouling Mechanisms and Interactions

by Lasâad Dammak, Julie Fouilloux, Myriam Bdiri, Christian Larchet, Estelle Renard, Lassaad Baklouti, Veronika Sarapulova, Anton Kozmai and Natalia Pismenskaya

Membranes 2021, 11(10), 789; https://doi.org/10.3390/membranes11100789 - 16 Oct 2021

Cited by 38 | Viewed by 5807

Abstract

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), [...] Read more.

Electrodialysis (ED) was first established for water desalination and is still highly recommended in this field for its high water recovery, long lifetime and acceptable electricity consumption. Today, thanks to technological progress in ED processes and the emergence of new ion-exchange membranes (IEMs), ED has been extended to many other applications in the food industry. This expansion of uses has also generated several problems such as IEMs’ lifetime limitation due to different ageing phenomena (because of organic and/or mineral compounds). The current commercial IEMs show excellent performance in ED processes; however, organic foulants such as proteins, surfactants, polyphenols or other natural organic matters can adhere on their surface (especially when using anion-exchange membranes: AEMs) forming a colloid layer or can infiltrate the membrane matrix, which leads to the increase in electrical resistance, resulting in higher energy consumption, lower water recovery, loss of membrane permselectivity and current efficiency as well as lifetime limitation. If these aspects are not sufficiently controlled and mastered, the use and the efficiency of ED processes will be limited since, it will no longer be competitive or profitable compared to other separation methods. In this work we reviewed a significant amount of recent scientific publications, research and reviews studying the phenomena of IEM fouling during the ED process in food industry with a special focus on the last decade. We first classified the different types of fouling according to the most commonly used classifications. Then, the fouling effects, the characterization methods and techniques as well as the different fouling mechanisms and interactions as well as their influence on IEM matrix and fixed groups were presented, analyzed, discussed and illustrated. Full article

(This article belongs to the Special Issue In-Depth on the Fouling and Antifouling of Ion-Exchange Membranes)

► Show Figures

Figure 1

22 pages, 7156 KiB

Open AccessEditor’s ChoiceArticle

Assessment of Sieverts Law Assumptions and ‘n’ Values in Palladium Membranes: Experimental and Theoretical Analyses

by Abdulrahman Alraeesi and Tracy Gardner

Membranes 2021, 11(10), 778; https://doi.org/10.3390/membranes11100778 - 12 Oct 2021

Cited by 15 | Viewed by 7436

Abstract

Palladium and palladium alloy membranes are superior materials for hydrogen purification, removal, or reaction processes. Sieverts’ Law suggests that the flux of hydrogen through such membranes is proportional to the difference between the feed and permeate side partial pressures, each raised to the [...] Read more.

Palladium and palladium alloy membranes are superior materials for hydrogen purification, removal, or reaction processes. Sieverts’ Law suggests that the flux of hydrogen through such membranes is proportional to the difference between the feed and permeate side partial pressures, each raised to the 0.5 power (n = 0.5). Sieverts’ Law is widely applied in analyzing the steady state hydrogen permeation through Pd-based membranes, even in some cases where the assumptions made in deriving Sieverts’ Law do not apply. Often permeation data are fit to the model allowing the pressure exponent (n) to vary. This study experimentally assessed the validity of Sieverts’ Law as hydrogen was separated from other gases and theoretically modelled the effects of pressure and temperature on the assumptions and hence the accuracy of the 0.5-power law even with pure hydrogen feed. Hydrogen fluxes through Pd and Pd-Ag alloy foils from feed mixtures (5–83% helium in hydrogen; 473–573 K; with and without a sweep gas) were measured to study the effect of concentration polarization (CP) on hydrogen permeance and the applicability of Sieverts’ Law under such conditions. Concentration polarization was found to dominate hydrogen transport under some experimental conditions, particularly when feed concentrations of hydrogen were low. All mixture feed experiments showed deviation from Sieverts’ Law. For example, the hydrogen flux through Pd foil was found to be proportional to the partial pressure difference (n ≈ 1) rather than being proportional to the difference in the square root of the partial pressures (n = 0.5), as suggested by Sieverts’ Law, indicating the high degree of concentration polarization. A theoretical model accounting for Langmuir adsorption with temperature dependent adsorption equilibrium coefficient was made and used to assess the effect of varying feed pressure from 1–136 atm at fixed temperature, and of varying temperature from 298 to 1273 K at fixed pressure. Adsorption effects, which dominate at high pressure and at low temperature, result in pressure exponents (n) values less than 0.5. With better understanding of the transport steps, a qualitative analysis of literature (n) values of 0.5, 0.5 < n < 1, and n > 1, was conducted suggesting the role of each condition or step on the hydrogen transport based on the empirically fit exponent value. Full article

(This article belongs to the Special Issue Modeling and Simulation of Industrial and Environmental Processes with Membranes)

► Show Figures

Graphical abstract

18 pages, 1375 KiB

Open AccessEditor’s ChoiceArticle

Optimization of Energy Efficiency, Operation Costs, Carbon Footprint and Ecological Footprint with Reverse Osmosis Membranes in Seawater Desalination Plants

by Federico Leon, Alejandro Ramos and Sebastian O. Perez-Baez

Membranes 2021, 11(10), 781; https://doi.org/10.3390/membranes11100781 - 12 Oct 2021

Cited by 16 | Viewed by 3570

Abstract

This article shows the optimization of the reverse osmosis process in seawater desalination plants, taking the example of the Canary Islands, where there are more than 320 units of different sizes, both private and public. The objective is to improve the energy efficiency [...] Read more.

This article shows the optimization of the reverse osmosis process in seawater desalination plants, taking the example of the Canary Islands, where there are more than 320 units of different sizes, both private and public. The objective is to improve the energy efficiency of the system in order to save on operation costs as well as reduce the carbon and ecological footprints. Reverse osmosis membranes with higher surface area have lower energy consumption, as well as energy recovery systems to recover the brine pressure and introduce it in the system. Accounting for the operation, maintenance and handling of the membranes is also important in energy savings, in order to improve the energy efficiency. The energy consumption depends on the permeate water quality required and the model of the reverse osmosis membrane installed in the seawater desalination plant, as it is shown in this study. Full article

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

► Show Figures

Figure 1

17 pages, 3178 KiB

Open AccessEditor’s ChoiceArticle

Improved CO₂/CH₄ Separation Properties of Cellulose Triacetate Mixed–Matrix Membranes with CeO₂@GO Hybrid Fillers

by Chhabilal Regmi, Saeed Ashtiani, Zdeněk Sofer and Karel Friess

Membranes 2021, 11(10), 777; https://doi.org/10.3390/membranes11100777 - 11 Oct 2021

Cited by 13 | Viewed by 2728

Abstract

The study of the effects associated with the compatibility of the components of the hybrid filler with polymer matrix, which ultimately decide on achieving mixed matrix membranes (MMMs) with better gas separation properties, is essential. Herein, a facile solution casting process of simple [...] Read more.

The study of the effects associated with the compatibility of the components of the hybrid filler with polymer matrix, which ultimately decide on achieving mixed matrix membranes (MMMs) with better gas separation properties, is essential. Herein, a facile solution casting process of simple incorporating CeO₂@GO hybrid inorganic filler material is implemented. Significant improvements in material and physico-chemical properties of the synthesized membranes were observed by SEM, XRD, TGA, and stress-strain measurements. Usage of graphene oxide (GO) with polar groups on the surface enabled forming bonds with ceria (CeO₂) nanoparticles and CTA polymer and provided the homogeneous dispersion of the nanofillers in the hybrid MMMs. Moreover, increasing GO loading concentration enhanced both gas permeation in MMMs and CO₂ gas uptakes. The best performance was achieved by the membrane containing 7 wt.% of GO with CO₂ permeability of 10.14 Barrer and CO₂/CH₄ selectivity 50.7. This increase in selectivity is almost fifteen folds higher than the CTA-CeO₂ membrane sample, suggesting the detrimental effect of GO for enhancing the selectivity property of the MMMs. Hence, a favorable synergistic effect of CeO₂@GO hybrid fillers on gas separation performance is observed, propounding the efficient and feasible strategy of using hybrid fillers in the membrane for the potential biogas upgrading process. Full article

(This article belongs to the Special Issue From Novel Material Concept to Scalable Membrane Product for Gas Separation)

► Show Figures

Graphical abstract

10 pages, 1893 KiB

Open AccessEditor’s ChoiceArticle

A Study to Enhance the Nitrate-Nitrogen Removal Rate without Dismantling the NF Module by Building a PFSA Ionomer-Coated NF Module

by In-Kee Park, Jian Hou, Jaehan Yun, Hee-Dae Lee and Chang-Hyun Lee

Membranes 2021, 11(10), 769; https://doi.org/10.3390/membranes11100769 - 9 Oct 2021

Cited by 4 | Viewed by 2450

Abstract

Water resource pollution by nitrate-nitrogen, mainly caused by anthropogenic causes, induces eutrophication of water resources, and indicates the degree of organic pollution. Therefore, this study devised a method for coating PFSA ionomer with excellent chemical resistance without disassembling the module to improve the [...] Read more.

Water resource pollution by nitrate-nitrogen, mainly caused by anthropogenic causes, induces eutrophication of water resources, and indicates the degree of organic pollution. Therefore, this study devised a method for coating PFSA ionomer with excellent chemical resistance without disassembling the module to improve the removal rate of nitrate-nitrogen in water by using a cyclic coating method on a commercially available nanofiltration membrane (NF membrane) module. Nafion was prepared as a supercritical fluid dispersion using a high-temperature and high-pressure reactor, and the particle size and the degree of dispersion of the dispersion were analyzed by DLS. The crystallinity was confirmed through XRD by drying the dispersion in the liquid state. After the dispersion was prepared as a membrane according to the heat treatment conditions, the characteristics according to the particle size were analyzed by tensile strength and TEM. The nitrate-nitrogen removal rate of the NF membrane module coated with the dispersion was increased by 93% compared to that before coating. Therefore, the result showed that the cycle coating method devised in this study could efficiently coat the already commercialized module and improve performance. Full article

(This article belongs to the Special Issue Recent Membrane Research and Development in Korea)

► Show Figures

Graphical abstract

23 pages, 3036 KiB

Open AccessEditor’s ChoiceArticle

Impact of Chlorinated-Assisted Backwash and Air Backwash on Ultrafiltration Fouling Management for Urban Wastewater Tertiary Treatment

by Jiaqi Yang, Mathias Monnot, Lionel Ercolei and Philippe Moulin

Membranes 2021, 11(10), 733; https://doi.org/10.3390/membranes11100733 - 27 Sep 2021

Cited by 5 | Viewed by 2366

Abstract

To improve membrane fouling management, the NaClO-assisted backwash has been developed to improve permeability maintenance and reduce the need for intensive chemical cleanings. This study is aimed to focus on the efficiency of NaClO-assisted backwash in real UF pilot scale and with periodic [...] Read more.

To improve membrane fouling management, the NaClO-assisted backwash has been developed to improve permeability maintenance and reduce the need for intensive chemical cleanings. This study is aimed to focus on the efficiency of NaClO-assisted backwash in real UF pilot scale and with periodic classic backwash (CB) and air backwash (AB). The impacts on hydraulic filtration performance, physicochemical properties of membrane material under different addition frequencies of NaClO, and the performance of chlorinated CB and AB will be discussed. In result, 10 mg Cl₂ L⁻¹ NaClO addition in backwash water is confirmed to greatly improve the overall filtration performance and backwash cleaning efficiency. One condition stands out from the other due to better control of irreversible fouling, less NaClO consumption in 10 years prediction, sustainable and adaptable filtration performance, and less potential damage on the physicochemical properties of the membrane. Additionally, it can be inferred from this experiment that frequent contact with NaClO induced some degradation on the PES-made UF membrane surface properties. To retain the best state of UF membrane on anti-fouling and qualified production, the optimized condition with more frequent NaClO contact was not suggested for long-term filtration. Full article

(This article belongs to the Special Issue Troubleshooting of Membrane Processes in Real Operation)

► Show Figures

Figure 1

22 pages, 5307 KiB

Open AccessEditor’s ChoiceArticle

Experimental Study of a Heat Pump for Simultaneous Cooling and Desalination by Membrane Distillation

by Ahmadou Tidiane Diaby, Paul Byrne, Patrick Loulergue, Ousmane Sow and Thierry Maré

Membranes 2021, 11(10), 725; https://doi.org/10.3390/membranes11100725 - 23 Sep 2021

Cited by 7 | Viewed by 2842

Abstract

Heat pump systems can simultaneously produce cooling energy for space cooling in hotels, office and residential buildings and heat for desalination using membrane distillation (MD). The MD technique uses a heat input at a temperature compatible with the levels of heat pump condensers [...] Read more.

Heat pump systems can simultaneously produce cooling energy for space cooling in hotels, office and residential buildings and heat for desalination using membrane distillation (MD). The MD technique uses a heat input at a temperature compatible with the levels of heat pump condensers (<60 °C). A heat pump prototype coupled with an air-gap membrane distillation unit was constructed and tested. This paper presents the experimental study on a lab-scale prototype and details the two operating modes “continuous” and “controlled” simulating an air conditioning system and a food storage, respectively. The experimental results enable to analyze the performance of the prototype and the physical phenomena involved. Finally, the study shows that this system could be a promising solution to help supplying freshwater to people in hot regions of the world. Full article

(This article belongs to the Special Issue Advanced Membrane Processes in Water Treatment)

► Show Figures

Graphical abstract

17 pages, 39717 KiB

Open AccessEditor’s ChoiceArticle

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

by Esra Eray, Victor Manuel Candelario and Vittorio Boffa

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

Cited by 12 | Viewed by 4702

Abstract

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

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

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

► Show Figures

Graphical abstract

14 pages, 2756 KiB

Open AccessEditor’s ChoiceArticle

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

by Muhammad Kashif Shahid and Younggyun Choi

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

Cited by 8 | Viewed by 3450

Abstract

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

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

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

► Show Figures

Graphical abstract

29 pages, 2414 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 36 | Viewed by 9049

Abstract

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

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

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

► Show Figures

Figure 1

32 pages, 10701 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 24 | Viewed by 5740

Abstract

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

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

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

► Show Figures

Figure 1

24 pages, 3729 KiB

Open AccessEditor’s ChoiceReview

Recent Progress in Mixed-Matrix Membranes for Hydrogen Separation

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

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

Cited by 37 | Viewed by 7439

Abstract

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

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

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

► Show Figures

Graphical abstract

28 pages, 2906 KiB

Open AccessFeature PaperEditor’s ChoiceReview

De Novo Ion-Exchange Membranes Based on Nanofibers

by Shaoling Zhang, Akihiko Tanioka and Hidetoshi Matsumoto

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

Cited by 8 | Viewed by 4272

Abstract

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

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

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

► Show Figures

Figure 1

21 pages, 3192 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 16 | Viewed by 3366

Abstract

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

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

(This article belongs to the Section Polymeric Membranes)

► Show Figures

Figure 1

17 pages, 2415 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 15 | Viewed by 3278

Abstract

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

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

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

► Show Figures

Graphical abstract

13 pages, 1492 KiB

Open AccessEditor’s ChoiceReview

Rush Hour of LATs towards Their Transport Cycle

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

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

Cited by 7 | Viewed by 2698

Abstract

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

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

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

► Show Figures

Figure 1

19 pages, 8262 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 23 | Viewed by 3536

Abstract

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

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

(This article belongs to the Section Membrane Chemistry)

► Show Figures

Figure 1

29 pages, 4366 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 15 | Viewed by 5947

Abstract

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

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

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

► Show Figures

Graphical abstract

18 pages, 2900 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 4 | Viewed by 3581

Abstract

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

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

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

► Show Figures

Graphical abstract

20 pages, 3323 KiB

Open AccessEditor’s ChoiceArticle

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

by Yuki Suga, Ryosuke Takagi and Hideto Matsuyama

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

Cited by 3 | Viewed by 4177

Abstract

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

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

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

► Show Figures

Graphical abstract

15 pages, 6949 KiB

Open AccessEditor’s ChoiceArticle

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

by Dimitra C. Banti, Manassis Mitrakas and Petros Samaras

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

Cited by 16 | Viewed by 3291

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 3546 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 7 | Viewed by 4514

Abstract

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

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

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

► Show Figures

Figure 1

11 pages, 2712 KiB

Open AccessEditor’s ChoiceArticle

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

by Yasushi Mino, Naruki Fukukawa and Hideto Matsuyama

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

Cited by 5 | Viewed by 3284

Abstract

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

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

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

► Show Figures

Figure 1

25 pages, 3687 KiB

Open AccessEditor’s ChoicePerspective

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

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

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

Cited by 48 | Viewed by 5031

Abstract

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

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

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

► Show Figures

Figure 1

14 pages, 2251 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 19 | Viewed by 3520

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 3565 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 83 | Viewed by 5891

Abstract

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

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

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

► Show Figures

Figure 1

20 pages, 4935 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 13 | Viewed by 4674

Abstract

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

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

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

► Show Figures

Figure 1

12 pages, 9321 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 3 | Viewed by 5222

Abstract

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

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

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

► Show Figures

Figure 1

35 pages, 7848 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 4 | Viewed by 2962

Abstract

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

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

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

► Show Figures

Graphical abstract

13 pages, 3390 KiB

Open AccessEditor’s ChoiceArticle

Carbon Dioxide Enrichment PEBAX/MOF Composite Membrane for CO₂ Separation

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

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

Cited by 29 | Viewed by 5278

Abstract

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

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

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

► Show Figures

Figure 1

22 pages, 3356 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 9 | Viewed by 2930

Abstract

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

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

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

► Show Figures

Figure 1

14 pages, 2243 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 20 | Viewed by 3506

Abstract

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

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

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

► Show Figures

Figure 1

15 pages, 865 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in the Prediction of Fouling in Membrane Bioreactors

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

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

Cited by 34 | Viewed by 4663

Abstract

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

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

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

► Show Figures

Figure 1

21 pages, 5063 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 14 | Viewed by 5028

Abstract

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

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

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

► Show Figures

Figure 1

37 pages, 2405 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 25 | Viewed by 7502

Abstract

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

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

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

► Show Figures

Graphical abstract

21 pages, 3980 KiB

Open AccessEditor’s ChoiceReview

Peripheral Membrane Proteins: Promising Therapeutic Targets across Domains of Life

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

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

Cited by 30 | Viewed by 7660

Abstract

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

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

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

► Show Figures

Graphical abstract

12 pages, 3661 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 6 | Viewed by 3068

Abstract

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

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

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

► Show Figures

Graphical abstract

30 pages, 3899 KiB

Open AccessEditor’s ChoiceReview

Characterizing the Structure and Interactions of Model Lipid Membranes Using Electrophysiology

by Joyce El-Beyrouthy and Eric Freeman

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

Cited by 12 | Viewed by 5203

Abstract

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

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

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

► Show Figures

Figure 1

25 pages, 5652 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 115 | Viewed by 20059

Abstract

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

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

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

► Show Figures

Graphical abstract

24 pages, 42226 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 18 | Viewed by 3970

Abstract

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

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

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

► Show Figures

Figure 1

19 pages, 19670 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

by Joanna Konczyk and Wojciech Ciesielski

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

Cited by 9 | Viewed by 2404

Abstract

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

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

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

► Show Figures

Graphical abstract

16 pages, 10154 KiB

Open AccessEditor’s ChoiceReview

S-Layer Ultrafiltration Membranes

by Bernhard Schuster and Uwe B. Sleytr

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

Cited by 11 | Viewed by 3563

Abstract

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

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

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

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI