Membranes

27 pages, 5353 KiB

Open AccessEditor’s ChoiceReview

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

by Petros Gkotsis, Efrosini Peleka and Anastasios Zouboulis

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

Cited by 5 | Viewed by 4623

Abstract

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

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

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

► Show Figures

Figure 1

20 pages, 8184 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 1503

Abstract

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

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

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

► Show Figures

Graphical abstract

17 pages, 8117 KiB

Open AccessEditor’s ChoiceArticle

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

by Ji-Min Lee and Moon-Sung Kang

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

Cited by 2 | Viewed by 1930

Abstract

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

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

(This article belongs to the Section Polymeric Membranes)

► Show Figures

Graphical abstract

18 pages, 2604 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 1 | Viewed by 1577

Abstract

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

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

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

► Show Figures

Graphical abstract

22 pages, 1869 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 2 | Viewed by 1526

Abstract

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

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

► Show Figures

Figure 1

16 pages, 6238 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 2107

Abstract

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

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

(This article belongs to the Section Membrane Applications)

► Show Figures

Figure 1

18 pages, 1327 KiB

Open AccessEditor’s ChoiceReview

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

by Małgorzata A. Kaczorowska

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

Cited by 2 | Viewed by 1695

Abstract

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

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

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

► Show Figures

Figure 1

15 pages, 2596 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 2 | Viewed by 1529

Abstract

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

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

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

► Show Figures

Figure 1

25 pages, 5593 KiB

Open AccessEditor’s ChoiceReview

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

by Al Mamun, Mohamed Kiari and Lilia Sabantina

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

Cited by 4 | Viewed by 2258

Abstract

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

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

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

► Show Figures

Figure 1

15 pages, 8704 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 1213

Abstract

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

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

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

► Show Figures

Figure 1

18 pages, 2146 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 1 | Viewed by 1204

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 1640 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 5 | Viewed by 1497

Abstract

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

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

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

► Show Figures

Figure 1

21 pages, 2447 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 1 | Viewed by 1034

Abstract

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

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

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

► Show Figures

Figure 1

41 pages, 4959 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 8 | Viewed by 3003

Abstract

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

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

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

► Show Figures

Graphical abstract

16 pages, 11361 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 990

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 3052 KiB

Open AccessEditor’s ChoiceReview

Current and Potential Applications of Green Membranes with Nanocellulose

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

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

Cited by 2 | Viewed by 1379

Abstract

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

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

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

► Show Figures

Figure 1

29 pages, 2156 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 6 | Viewed by 2890

Abstract

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

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

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

► Show Figures

Figure 1

21 pages, 13797 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 3 | Viewed by 1215

Abstract

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

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

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

► Show Figures

Figure 1

25 pages, 2438 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Viewed by 2050

Abstract

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

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

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

► Show Figures

Graphical abstract

18 pages, 3338 KiB

Open AccessEditor’s ChoiceReview

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

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

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

Cited by 4 | Viewed by 3073

Abstract

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

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

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

► Show Figures

Figure 1

24 pages, 1200 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Challenges and Solutions for Global Water Scarcity

by Hilla Shemer, Shlomo Wald and Raphael Semiat

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

Cited by 14 | Viewed by 6791

Abstract

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

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

(This article belongs to the Section Membrane Applications)

► Show Figures

Figure 1

23 pages, 3410 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 4 | Viewed by 1259

Abstract

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

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

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

► Show Figures

Figure 1

37 pages, 6260 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 15 | Viewed by 4033

Abstract

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

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

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

► Show Figures

Figure 1

37 pages, 4819 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Developing Enzyme Immobilization with Fibrous Membranes: Longevity and Characterization Considerations

by Yue Yuan, Jialong Shen and Sonja Salmon

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

Cited by 5 | Viewed by 2477

Abstract

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

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

► Show Figures

Figure 1

13 pages, 4627 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 5 | Viewed by 1098

Abstract

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

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

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

► Show Figures

Figure 1

13 pages, 18311 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Preparation and Lithium-Ion Separation Property of ZIF-8 Membrane with Excellent Flexibility

by Jun Zhao, Rongyu Fan, Shengchang Xiang, Jiapeng Hu and Ximing Zheng

Membranes 2023, 13(5), 500; https://doi.org/10.3390/membranes13050500 - 9 May 2023

Cited by 5 | Viewed by 1967

Abstract

Metal-organic framework (MOF) membranes exhibit immense potential for separation applications due to their regular pore channels and scalable pore sizes. However, structuring a flexible and high-quality MOF membrane remains a challenge due to its brittleness, which severely restricts its practical application. This paper [...] Read more.

Metal-organic framework (MOF) membranes exhibit immense potential for separation applications due to their regular pore channels and scalable pore sizes. However, structuring a flexible and high-quality MOF membrane remains a challenge due to its brittleness, which severely restricts its practical application. This paper presents a simple and effective method in which continuous, uniform, defect-free ZIF-8 film layers of tunable thickness are constructed on the surface of inert microporous polypropylene membranes (MPPM). To provide heterogeneous nucleation sites for ZIF-8 growth, an extensive amount of hydroxyl and amine groups were introduced on the MPPM surface using the dopamine-assisted co-deposition technique. Subsequently, ZIF-8 crystals were grown in-situ on the MPPM surface using the solvothermal method. The resultant ZIF-8/MPPM exhibited a lithium-ion permeation flux of 0.151 mol m⁻² h⁻¹ and a high selectivity of Li⁺/Na⁺ = 1.93, Li⁺/Mg²⁺ = 11.50. Notably, ZIF-8/MPPM has good flexibility, and the lithium-ion permeation flux and selectivity remain unchanged at a bending curvature of 348 m⁻¹. These excellent mechanical characteristics are crucial for the practical applications of MOF membranes. Full article

(This article belongs to the Special Issue Zeolitic Membranes for Gas and Liquid Separation: Synthesis and Applications)

► Show Figures

Figure 1

29 pages, 2652 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Microbial Fuel Cell Construction Features and Application for Sustainable Wastewater Treatment

by Hridoy Roy, Tanzim Ur Rahman, Nishat Tasnim, Jannatul Arju, Md. Mustafa Rafid, Md. Reazul Islam, Md. Nahid Pervez, Yingjie Cai, Vincenzo Naddeo and Md. Shahinoor Islam

Membranes 2023, 13(5), 490; https://doi.org/10.3390/membranes13050490 - 30 Apr 2023

Cited by 28 | Viewed by 9092

Abstract

A microbial fuel cell (MFC) is a system that can generate electricity by harnessing microorganisms’ metabolic activity. MFCs can be used in wastewater treatment plants since they can convert the organic matter in wastewater into electricity while also removing pollutants. The microorganisms in [...] Read more.

A microbial fuel cell (MFC) is a system that can generate electricity by harnessing microorganisms’ metabolic activity. MFCs can be used in wastewater treatment plants since they can convert the organic matter in wastewater into electricity while also removing pollutants. The microorganisms in the anode electrode oxidize the organic matter, breaking down pollutants and generating electrons that flow through an electrical circuit to the cathode compartment. This process also generates clean water as a byproduct, which can be reused or released back into the environment. MFCs offer a more energy-efficient alternative to traditional wastewater treatment plants, as they can generate electricity from the organic matter in wastewater, offsetting the energy needs of the treatment plants. The energy requirements of conventional wastewater treatment plants can add to the overall cost of the treatment process and contribute to greenhouse gas emissions. MFCs in wastewater treatment plants can increase sustainability in wastewater treatment processes by increasing energy efficiency and reducing operational cost and greenhouse gas emissions. However, the build-up to the commercial-scale still needs a lot of study, as MFC research is still in its early stages. This study thoroughly describes the principles underlying MFCs, including their fundamental structure and types, construction materials and membrane, working mechanism, and significant process elements influencing their effectiveness in the workplace. The application of this technology in sustainable wastewater treatment, as well as the challenges involved in its widespread adoption, are discussed in this study. Full article

(This article belongs to the Special Issue Separation Principles and Applications of Membrane Technology)

► Show Figures

Figure 1

21 pages, 5993 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Bioinspired Nanoplatforms Based on Graphene Oxide and Neurotrophin-Mimicking Peptides

by Luigi Redigolo, Vanessa Sanfilippo, Diego La Mendola, Giuseppe Forte and Cristina Satriano

Membranes 2023, 13(5), 489; https://doi.org/10.3390/membranes13050489 - 30 Apr 2023

Cited by 2 | Viewed by 1817

Abstract

Neurotrophins (NTs), which are crucial for the functioning of the nervous system, are also known to regulate vascularization. Graphene-based materials may drive neural growth and differentiation, and, thus, have great potential in regenerative medicine. In this work, we scrutinized the nano–biointerface between the [...] Read more.

Neurotrophins (NTs), which are crucial for the functioning of the nervous system, are also known to regulate vascularization. Graphene-based materials may drive neural growth and differentiation, and, thus, have great potential in regenerative medicine. In this work, we scrutinized the nano–biointerface between the cell membrane and hybrids made of neurotrophin-mimicking peptides and graphene oxide (GO) assemblies (pep−GO), to exploit their potential in theranostics (i.e., therapy and imaging/diagnostics) for targeting neurodegenerative diseases (ND) as well as angiogenesis. The pep−GO systems were assembled via spontaneous physisorption onto GO nanosheets of the peptide sequences BDNF(1-12), NT3(1-13), and NGF(1-14), mimicking the brain-derived neurotrophic factor (BDNF), the neurotrophin 3 (NT3), and the nerve growth factor (NGF), respectively. The interaction of pep−GO nanoplatforms at the biointerface with artificial cell membranes was scrutinized both in 3D and 2D by utilizing model phospholipids self-assembled as small unilamellar vesicles (SUVs) or planar-supported lipid bilayers (SLBs), respectively. The experimental studies were paralleled via molecular dynamics (MD) computational analyses. Proof-of-work in vitro cellular experiments with undifferentiated neuroblastoma (SH-SY5Y), neuron-like, differentiated neuroblastoma (dSH-SY5Y), and human umbilical vein endothelial cells (HUVECs) were carried out to shed light on the capability of the pep−GO nanoplatforms to stimulate the neurite outgrowth as well as tubulogenesis and cell migration. Full article

(This article belongs to the Special Issue Nanotechnologies and Nanoparticles Interaction with Bio-Membranes)

► Show Figures

Figure 1

31 pages, 5141 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Engineering Metal-Organic-Framework (MOF)-Based Membranes for Gas and Liquid Separation

by Yutian Duan, Lei Li, Zhiqiang Shen, Jian Cheng and Kewu He

Membranes 2023, 13(5), 480; https://doi.org/10.3390/membranes13050480 - 29 Apr 2023

Cited by 6 | Viewed by 5207

Abstract

Separation is one of the most energy-intensive processes in the chemical industry, and membrane-based separation technology contributes significantly to energy conservation and emission reduction. Additionally, metal-organic framework (MOF) materials have been widely investigated and have been found to have enormous potential in membrane [...] Read more.

Separation is one of the most energy-intensive processes in the chemical industry, and membrane-based separation technology contributes significantly to energy conservation and emission reduction. Additionally, metal-organic framework (MOF) materials have been widely investigated and have been found to have enormous potential in membrane separation due to their uniform pore size and high designability. Notably, pure MOF films and MOF mixed matrix membranes (MMMs) are the core of the “next generation” MOF materials. However, there are some tough issues with MOF-based membranes that affect separation performance. For pure MOF membranes, problems such as framework flexibility, defects, and grain orientation need to be addressed. Meanwhile, there still exist bottlenecks for MMMs such as MOF aggregation, plasticization and aging of the polymer matrix, poor interface compatibility, etc. Herein, corresponding methods are introduced to solve these problems, including inhibiting framework flexibility, regulating synthesis conditions, and enhancing the interaction between MOF and substrate. A series of high-quality MOF-based membranes have been obtained based on these techniques. Overall, these membranes revealed desired separation performance in both gas separation (e.g., CO₂, H₂, and olefin/paraffin) and liquid separation (e.g., water purification, organic solvent nanofiltration, and chiral separation). Full article

(This article belongs to the Special Issue Research Progress of Metal-Organic-Framework (MOF) Membranes)

► Show Figures

Figure 1

18 pages, 3314 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Nanocarbon-Based Mixed Matrix Pebax-1657 Flat Sheet Membranes for CO₂/CH₄ Separation

by Athanasios N. Vasileiou, George V. Theodorakopoulos, Dionysios S. Karousos, Mirtat Bouroushian, Andreas A. Sapalidis and Evangelos P. Favvas

Membranes 2023, 13(5), 470; https://doi.org/10.3390/membranes13050470 - 28 Apr 2023

Cited by 5 | Viewed by 1614

Abstract

In the present work, Pebax-1657, a commercial multiblock copolymer (poly(ether-block-amide)), consisting of 40% rigid amide (PA6) groups and 60% flexible ether (PEO) linkages, was selected as the base polymer for preparing dense flat sheet mixed matrix membranes (MMMs) using the solution casting method. [...] Read more.

In the present work, Pebax-1657, a commercial multiblock copolymer (poly(ether-block-amide)), consisting of 40% rigid amide (PA6) groups and 60% flexible ether (PEO) linkages, was selected as the base polymer for preparing dense flat sheet mixed matrix membranes (MMMs) using the solution casting method. Carbon nanofillers, specifically, raw and treated (plasma and oxidized) multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) were incorporated into the polymeric matrix in order to improve the gas-separation performance and polymer’s structural properties. The developed membranes were characterized by means of SEM and FTIR, and their mechanical properties were also evaluated. Well-established models were employed in order to compare the experimental data with theoretical calculations concerning the tensile properties of MMMs. Most remarkably, the tensile strength of the mixed matrix membrane with oxidized GNPs was enhanced by 55.3% compared to the pure polymeric membrane, and its tensile modulus increased 3.2 times compared to the neat one. In addition, the effect of nanofiller type, structure and amount to real binary CO₂/CH₄ (10/90 vol.%) mixture separation performance was evaluated under elevated pressure conditions. A maximum CO₂/CH₄ separation factor of 21.9 was reached with CO₂ permeability of 384 Barrer. Overall, MMMs exhibited enhanced gas permeabilities (up to fivefold values) without sacrificing gas selectivity compared to the corresponding pure polymeric membrane. Full article

(This article belongs to the Special Issue Structure and Performance of Porous Polymer Membranes)

► Show Figures

Figure 1

17 pages, 8302 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electrophoretic Deposition and Characterization of Thin-Film Membranes Li₇La₃Zr₂O₁₂

by Efim Lyalin, Evgeniya Il’ina, Elena Kalinina, Boris Antonov, Alexander Pankratov and Danil Pereverzev

Membranes 2023, 13(5), 468; https://doi.org/10.3390/membranes13050468 - 27 Apr 2023

Cited by 3 | Viewed by 1252

Abstract

In the presented study, films from tetragonal Li₇La₃Zr₂O₁₂ were obtained by electrophoretic deposition (EPD) for the first time. To obtain a continuous and homogeneous coating on Ni and Ti substrates, iodine was added to the Li [...] Read more.

In the presented study, films from tetragonal Li₇La₃Zr₂O₁₂ were obtained by electrophoretic deposition (EPD) for the first time. To obtain a continuous and homogeneous coating on Ni and Ti substrates, iodine was added to the Li₇La₃Zr₂O₁₂ suspension. The EPD regime was developed to carry out the stable process of deposition. The influence of annealing temperature on phase composition, microstructure, and conductivity of membranes obtained was studied. It was established that the phase transition from tetragonal to low-temperature cubic modification of solid electrolyte was observed after its heat treatment at 400 °C. This phase transition was also confirmed by high-temperature X-ray diffraction analysis of Li₇La₃Zr₂O₁₂ powder. Increasing the annealing temperature leads to the formation of additional phases in the form of fibers and their growth from 32 (dried film) to 104 μm (annealed at 500 °C). The formation of this phase occurred due to the chemical reaction of Li₇La₃Zr₂O₁₂ films obtained by electrophoretic deposition with air components during heat treatment. The total conductivity of Li₇La₃Zr₂O₁₂ films obtained has values of ~10⁻¹⁰ and ~10⁻⁷ S cm⁻¹ at 100 and 200 °C, respectively. The method of EPD can be used to obtain solid electrolyte membranes based on Li₇La₃Zr₂O₁₂ for all-solid-state batteries. Full article

(This article belongs to the Special Issue Fabrication, Characterization and Application of Organic/Inorganic Film Membranes and Advanced Materials (Volume II))

► Show Figures

Graphical abstract

15 pages, 2354 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

New Meloxicam Derivatives—Synthesis and Interaction with Phospholipid Bilayers Measured by Differential Scanning Calorimetry and Fluorescence Spectroscopy

by Jadwiga Maniewska, Justyna Gąsiorowska, Żaneta Czyżnikowska, Krystyna Michalak and Berenika M. Szczęśniak-Sięga

Membranes 2023, 13(4), 416; https://doi.org/10.3390/membranes13040416 - 6 Apr 2023

Cited by 1 | Viewed by 1606

Abstract

The purpose of the present paper was to assess the ability of five newly designed and synthesized meloxicam analogues to interact with phospholipid bilayers. Calorimetric and fluorescence spectroscopic measurements revealed that, depending on the details of the chemical structure, the studied compounds penetrated [...] Read more.

The purpose of the present paper was to assess the ability of five newly designed and synthesized meloxicam analogues to interact with phospholipid bilayers. Calorimetric and fluorescence spectroscopic measurements revealed that, depending on the details of the chemical structure, the studied compounds penetrated bilayers and affected mainly their polar/apolar regions, closer to the surface of the model membrane. The influence of meloxicam analogues on the thermotropic properties of DPPC bilayers was clearly visible because these compounds reduced the temperature and cooperativity of the main phospholipid phase transition. Additionally, the studied compounds quenched the fluorescence of prodan to a higher extent than laurdan, what pointed to a more pronounced interaction with membrane segments close to its surface. We presume that a more pronounced intercalation of the studied compounds into the phospholipid bilayer may be related to the presence of the molecule of a two-carbon aliphatic linker with a carbonyl group and fluorine substituent/trifluoromethyl group (compounds PR25 and PR49) or the three-carbon linker together with the trifluoromethyl group (PR50). Moreover, computational investigations of the ADMET properties have shown that the new meloxicam analogues are characterized by beneficial expected physicochemical parameters, so we may presume that they will have a good bioavailability after an oral administration. Full article

(This article belongs to the Special Issue Biological Membrane and Bioactive Compounds Interactions)

► Show Figures

Graphical abstract

22 pages, 9347 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Anatase TiO₂/PVDF Composite Membrane for Oil-in-Water Emulsion Separation and Dye Photocatalytic Degradation

by Chengcai Li, Hewei Yu, Biao Huang, Guojin Liu, Yuhai Guo, Hailin Zhu and Bin Yu

Membranes 2023, 13(3), 364; https://doi.org/10.3390/membranes13030364 - 22 Mar 2023

Cited by 4 | Viewed by 2226

Abstract

At present, the types of pollutants in wastewater are more and more complicated, however, the multifunctional membrane materials are in short supply. To prepare a membrane with both high efficient oil-in-water emulsion separation performance and photocatalytic degradation performance of organic dyes, the bifunctional [...] Read more.

At present, the types of pollutants in wastewater are more and more complicated, however, the multifunctional membrane materials are in short supply. To prepare a membrane with both high efficient oil-in-water emulsion separation performance and photocatalytic degradation performance of organic dyes, the bifunctional separation membrane was successfully prepared by electrostatic spinning technology of PVDF/PEMA and in situ deposition of anatase TiO₂ nanoparticles containing Ti³⁺ and oxygen vacancies (O_v). The prepared composite membrane has excellent hydrophilic properties (WCA = 15.65), underwater oleophobic properties (UOCA = 156.69), and photocatalytic performance. These composite membranes have high separation efficiency and outstanding anti-fouling performance, the oil removal efficiency reaches 98.95%, and the flux recovery rate (FRR) reaches 99.19% for soybean oil-in-water emulsion. In addition, the composite membrane has outstanding photocatalytic degradation performance, with 97% and 90.2% degradation of RhB and AG-25 under UV conditions, respectively. Several oil-in-water separation and dye degradation experiments show that the PVDF composite membrane has excellent reuse performance. Based on these results, this study opens new avenues for the preparation of multifunctional reusable membranes for the water treatment field. Full article

► Show Figures

Graphical abstract

13 pages, 9333 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Circular Economy Approach in Treatment of Galvanic Wastewater Employing Membrane Processes

by Anna Kowalik-Klimczak, Anna Gajewska-Midziałek, Zofia Buczko, Monika Łożyńska, Maciej Życki, Wioletta Barszcz, Tinatin Ciciszwili, Adrian Dąbrowski, Sonia Kasierot, Jadwiga Charasińska and Tadeusz Gorewoda

Membranes 2023, 13(3), 325; https://doi.org/10.3390/membranes13030325 - 11 Mar 2023

Cited by 4 | Viewed by 2306

Abstract

According to the idea of sustainable development, humanity should make every effort to care for the natural environment along with economic development. Decreasing water resources in the world makes it necessary to take action to reduce the consumption of this resource. This article [...] Read more.

According to the idea of sustainable development, humanity should make every effort to care for the natural environment along with economic development. Decreasing water resources in the world makes it necessary to take action to reduce the consumption of this resource. This article presents the results of research conducted to improve the use of recyclable materials in line with the circular economy model. The research focused on the development of a technological solution for the recovery of raw materials from galvanic wastewater. The concept of a galvanic wastewater treatment system presented in the article includes wastewater pre-treatment in the ultrafiltration (UF) process and water recovery in the reverse osmosis (RO) process. In addition, the purpose of the work was to manage post-filtration waste (RO retentate) containing high concentrations of zinc in the process of galvanizing metal details. The obtained results indicate that it is possible to reduce the amount of sewage from the galvanizing industry by reusing the recovered water as technical water in the process line. The carried-out model tests of galvanizing confirmed the possibility of using RO retentate for the production of metal parts. The achieved results are a proposal to solve the problem of reducing the impact of galvanic wastewater on the environment and to improve the profitability of existing galvanizing technologies by reducing the consumption of water and raw materials. Full article

(This article belongs to the Special Issue Towards the Circular Economy—Membrane Processes for the Recovery of Water and Nutrients from Wastewater)

► Show Figures

Graphical abstract

20 pages, 3536 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stability of Superhydrophobicity and Structure of PVDF Membranes Treated by Vacuum Oxygen Plasma and Organofluorosilanisation

by Ramón Jiménez-Robles, Marta Izquierdo, Vicente Martínez-Soria, Laura Martí, Alicia Monleón and José David Badia

Membranes 2023, 13(3), 314; https://doi.org/10.3390/membranes13030314 - 9 Mar 2023

Cited by 5 | Viewed by 1989

Abstract

Superhydrophobic poly(vinylidene fluoride) (PVDF) membranes were obtained by a surface treatment consisting of oxygen plasma activation followed by functionalisation with a mixture of silica precursor (SiP) (tetraethyl-orthosilicate [TEOS] or 3-(triethoxysilyl)-propylamine [APTES]) and a fluoroalkylsilane (1H,1H,2H,2H-perfluorooctyltriethoxysilane), and were benchmarked with coated membranes without plasma [...] Read more.

Superhydrophobic poly(vinylidene fluoride) (PVDF) membranes were obtained by a surface treatment consisting of oxygen plasma activation followed by functionalisation with a mixture of silica precursor (SiP) (tetraethyl-orthosilicate [TEOS] or 3-(triethoxysilyl)-propylamine [APTES]) and a fluoroalkylsilane (1H,1H,2H,2H-perfluorooctyltriethoxysilane), and were benchmarked with coated membranes without plasma activation. The modifications acted mainly on the surface, and the bulk properties remained stable. From a statistical design of experiments on surface hydrophobicity, the type of SiP was the most relevant factor, achieving the highest water contact angles (WCA) with the use of APTES, with a maximum WCA higher than 155° for membranes activated at a plasma power discharge of 15 W during 15 min, without membrane degradation. Morphological changes were observed on the membrane surfaces treated under these plasma conditions, showing a pillar-like structure with higher surface porosity. In long-term stability tests under moderate water flux conditions, the WCA of coated membranes which were not activated by oxygen plasma decreased to approximately 120° after the first 24 h (similar to the pristine membrane), whilst the WCA of plasma-treated membranes was maintained around 130° after 160 h. Thus, plasma pre-treatment led to membranes with a superhydrophobic performance and kept a higher hydrophobicity after long-term operations. Full article

(This article belongs to the Special Issue Surface Modification and Performance Enhancement in Membrane Separation Technologies)

► Show Figures

Graphical abstract

12 pages, 7977 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Novel Nafion/Graphitic Carbon Nitride Nanosheets Composite Membrane for Steam Electrolysis at 110 °C

by Taipu Chen, Bo Lv, Shucheng Sun, Jinkai Hao and Zhigang Shao

Membranes 2023, 13(3), 308; https://doi.org/10.3390/membranes13030308 - 7 Mar 2023

Cited by 3 | Viewed by 3321

Abstract

Hydrogen is expected to have an important role in future energy systems; however, further research is required to ensure the commercial viability of hydrogen generation. Proton exchange membrane steam electrolysis above 100 °C has attracted significant research interest owing to its high electrolytic [...] Read more.

Hydrogen is expected to have an important role in future energy systems; however, further research is required to ensure the commercial viability of hydrogen generation. Proton exchange membrane steam electrolysis above 100 °C has attracted significant research interest owing to its high electrolytic efficiency and the potential to reduce the use of electrical energy through waste heat utilization. This study developed a novel composite membrane fabricated from graphitic carbon nitride (g-C₃N₄) and Nafion and applied it to steam electrolysis with excellent results. g-C₃N₄ is uniformly dispersed among the non−homogeneous functionalized particles of the polymer, and it improves the thermostability of the membranes. The amino and imino active sites on the nanosheet surface enhance the proton conductivity. In ultrapure water at 90 °C, the proton conductivity of the Nafion/0.4 wt.% g-C₃N₄ membrane is 287.71 mS cm⁻¹. Above 100 °C, the modified membranes still exhibit high conductivity, and no sudden decreases in conductivity were observed. The Nafion/g-C₃N₄ membranes exhibit excellent performance when utilized as a steam electrolyzer. Compared with that of previous studies, this approach achieves better electrolytic behavior with a relatively low catalyst loading. Steam electrolysis using a Nafion/0.4 wt.% g-C₃N₄ membranes achieves a current density of 2260 mA cm⁻² at 2 V, which is approximately 69% higher than the current density achieved using pure Nafion membranes under the same conditions. Full article

(This article belongs to the Special Issue Membranes in Fuel Cell and Electrolyzer Applications)

► Show Figures

Graphical abstract

10 pages, 1321 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Efficient Recovery of Organic Matter from Municipal Wastewater by a High-Rate Membrane Bioreactor Equipped with Flat-Sheet Ceramic Membranes

by Michael Joseph Rocco, Akira Hafuka, Toru Tsuchiya and Katsuki Kimura

Membranes 2023, 13(3), 300; https://doi.org/10.3390/membranes13030300 - 3 Mar 2023

Cited by 4 | Viewed by 1446

Abstract

High-rate processes have been investigated for the recovery of organic matter from municipal wastewater. High-rate membrane bioreactors (HR-MBRs) may simultaneously achieve the increased recovery of carbon and high effluent quality, although control of membrane fouling is extremely difficult. To address the severe fouling [...] Read more.

High-rate processes have been investigated for the recovery of organic matter from municipal wastewater. High-rate membrane bioreactors (HR-MBRs) may simultaneously achieve the increased recovery of carbon and high effluent quality, although control of membrane fouling is extremely difficult. To address the severe fouling in HR-MBRs, the combination of granular scouring and frequent chemically enhanced backwashing was examined. The use of robust flat-sheet ceramic membranes enabled the application of those cleaning strategies. Experiments were carried out at an existing wastewater treatment plant. To operate as a high-rate system, the bioreactor solid residence time and hydraulic residence time were set at 0.5 days and 1.6 h, respectively. Although a relatively high flux of 20 L m⁻² h⁻¹ was applied, the proposed HR-MBR exhibited a very low fouling rate of 1.3 kPa/day. The system could recover >70% of the carbon from raw wastewater, whereas the concentration of chemical oxygen demand in the effluent was lowered to <20 mg/L. The performance of the proposed HR-MBR observed in this study was clearly superior to those reported in previous related studies. Full article

(This article belongs to the Special Issue Green Membrane Technology)

► Show Figures

Graphical abstract

20 pages, 2183 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Evaluation of Forward Osmosis and Low-Pressure Reverse Osmosis with a Tubular Membrane for the Concentration of Municipal Wastewater and the Production of Biogas

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

Membranes 2023, 13(3), 266; https://doi.org/10.3390/membranes13030266 - 23 Feb 2023

Cited by 2 | Viewed by 2019

Abstract

Currently, freshwater scarcity is one of the main issues that the world population has to face. To address this issue, new wastewater treatment technologies have been developed such as membrane processes. Among them, due to the energy disadvantages of pressure-driven membrane processes, Forward [...] Read more.

Currently, freshwater scarcity is one of the main issues that the world population has to face. To address this issue, new wastewater treatment technologies have been developed such as membrane processes. Among them, due to the energy disadvantages of pressure-driven membrane processes, Forward Osmosis (FO) and Low-Pressure Reverse Osmosis (LPRO) have been introduced as promising alternatives. In this study, the behavior of a 2.3 m² tubular membrane TFO-D90 when working with municipal wastewater has been studied. Its performances have been evaluated and compared in two operating modes such as FO and LPRO. Parameters such as fouling, flow rates, water flux, draw solution concentration, organic matter concentration, as well as its recovery have been studied. In addition, the biogas production capacity has been evaluated with the concentrated municipal wastewater obtained from each process. The results of this study indicate that the membrane can work in both processes (FO and LPRO) but, from the energy and productivity point of view, FO is considered more appropriate mainly due to its lower fouling level. This research may offer a new point of view on low-energy and energy recovery wastewater treatment and the applicability of FO and LPRO for wastewater concentration. Full article

(This article belongs to the Special Issue Recent Advances in Membrane Materials and Membrane Processes for Water and Wastewater Treatment (Volume II))

► Show Figures

Graphical abstract

16 pages, 1260 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Prolonging the Life Span of Membrane in Submerged MBR by the Application of Different Anti-Biofouling Techniques

by Noman Sohail, Ramona Riedel, Bogdan Dorneanu and Harvey Arellano-Garcia

Membranes 2023, 13(2), 217; https://doi.org/10.3390/membranes13020217 - 9 Feb 2023

Cited by 3 | Viewed by 2257

Abstract

The membrane bioreactor (MBR) is an efficient technology for the treatment of municipal and industrial wastewater for the last two decades. It is a single stage process with smaller footprints and a higher removal efficiency of organic compounds compared with the conventional activated [...] Read more.

The membrane bioreactor (MBR) is an efficient technology for the treatment of municipal and industrial wastewater for the last two decades. It is a single stage process with smaller footprints and a higher removal efficiency of organic compounds compared with the conventional activated sludge process. However, the major drawback of the MBR is membrane biofouling which decreases the life span of the membrane and automatically increases the operational cost. This review is exploring different anti-biofouling techniques of the state-of-the-art, i.e., quorum quenching (QQ) and model-based approaches. The former is a relatively recent strategy used to mitigate biofouling. It disrupts the cell-to-cell communication of bacteria responsible for biofouling in the sludge. For example, the two strains of bacteria Rhodococcus sp. BH4 and Pseudomonas putida are very effective in the disruption of quorum sensing (QS). Thus, they are recognized as useful QQ bacteria. Furthermore, the model-based anti-fouling strategies are also very promising in preventing biofouling at very early stages of initialization. Nevertheless, biofouling is an extremely complex phenomenon and the influence of various parameters whether physical or biological on its development is not completely understood. Advancing digital technologies, combined with novel Big Data analytics and optimization techniques offer great opportunities for creating intelligent systems that can effectively address the challenges of MBR biofouling. Full article

(This article belongs to the Special Issue A Commemorative Issue in Honor of Docent Constantin Luca: pH in Membrane Processes)

► Show Figures

Graphical abstract

16 pages, 3130 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Model Catanionic Vesicles from Biomimetic Serine-Based Surfactants: Effect of the Combination of Chain Lengths on Vesicle Properties and Vesicle-to-Micelle Transition

by Isabel S. Oliveira, Sandra G. Silva, Maria Luísa do Vale and Eduardo F. Marques

Membranes 2023, 13(2), 178; https://doi.org/10.3390/membranes13020178 - 1 Feb 2023

Viewed by 1850

Abstract

Mixtures of cationic and anionic surfactants often originate bilayer structures, such as vesicles and lamellar liquid crystals, that can be explored as model membranes for fundamental studies or as drug and gene nanocarriers. Here, we investigated the aggregation properties of two catanionic mixtures [...] Read more.

Mixtures of cationic and anionic surfactants often originate bilayer structures, such as vesicles and lamellar liquid crystals, that can be explored as model membranes for fundamental studies or as drug and gene nanocarriers. Here, we investigated the aggregation properties of two catanionic mixtures containing biomimetic surfactants derived from serine. The mixtures are designated as 12Ser/8-8Ser and 14Ser/10-10Ser, where mSer is a cationic, single-chained surfactant and n-nSer is an anionic, double-chained one (m and n being the C atoms in the alkyl chains). Our goal was to investigate the effects of total chain length and chain length asymmetry of the catanionic pair on the formation of catanionic vesicles, the vesicle properties and the vesicle/micelle transitions. Ocular observations, surface tension measurements, video-enhanced light microscopy, cryogenic scanning electron microscopy, dynamic and electrophoretic light scattering were used to monitor the self-assembly process and the aggregate properties. Catanionic vesicles were indeed found in both systems for molar fractions of cationic surfactant ≥0.40, always possessing positive zeta potentials (ζ = +35–50 mV), even for equimolar sample compositions. Furthermore, the 14Ser/10-10Ser vesicles were only found as single aggregates (i.e., without coexisting micelles) in a very narrow compositional range and as a bimodal population (average diameters of 80 and 300 nm). In contrast, the 12Ser/8-8Ser vesicles were found for a wider sample compositional range and as unimodal or bimodal populations, depending on the mixing ratio. The aggregate size, pH and zeta potential of the mixtures were further investigated. The unimodal 12Ser/8-8Ser vesicles (<D_H> ≈ 250 nm, pH ≈ 7–8, ζ ≈ +32 mV and a cationic/anionic molar ratio of ≈2:1) are particularly promising for application as drug/gene nanocarriers. Both chain length asymmetry and total length play a key role in the aggregation features of the two systems. Molecular insights are provided by the main findings. Full article

(This article belongs to the Special Issue Study on Drug-Membrane Interactions, Volume II)

► Show Figures

Graphical abstract

16 pages, 9582 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Scaling Up of Steric Exclusion Membrane Chromatography for Lentiviral Vector Purification

by Jennifer Julia Labisch, Richard Paul, G. Philip Wiese and Karl Pflanz

Membranes 2023, 13(2), 149; https://doi.org/10.3390/membranes13020149 - 24 Jan 2023

Cited by 3 | Viewed by 3473

Abstract

Lentiviral vectors (LVs) are widely used in clinical trials of gene and cell therapy. Low LV stability incentivizes constant development and the improvement of gentle process steps. Steric exclusion chromatography (SXC) has gained interest in the field of virus purification but scaling up [...] Read more.

Lentiviral vectors (LVs) are widely used in clinical trials of gene and cell therapy. Low LV stability incentivizes constant development and the improvement of gentle process steps. Steric exclusion chromatography (SXC) has gained interest in the field of virus purification but scaling up has not yet been addressed. In this study, the scaling up of lentiviral vector purification by SXC with membrane modules was approached. Visualization of the LVs captured on the membrane during SXC showed predominant usage of the upper membrane layer. Furthermore, testing of different housing geometries showed a strong influence on the uniform usage of the membrane. The main use of the first membrane layer places a completely new requirement on the scaling of the process and the membrane modules. When transferring the SXC process to smaller or larger membrane modules, it became apparent that scaling of the flow rate is a critical factor that must be related to the membrane area of the first layer. Performing SXC at different scales demonstrated that a certain critical minimum surface area-dependent flow rate is necessary to achieve reproducible LV recoveries. With the presented scaling approach, we were able to purify 980 mL LVs with a recovery of 68%. Full article

(This article belongs to the Special Issue Bioprocessing with Membranes: Filtration and Chromatography)

► Show Figures

Graphical abstract

18 pages, 4017 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Phosphatidylcholine Liposomes Reprogram Macrophages toward an Inflammatory Phenotype

by David M. Cauvi, Dennis Hawisher, Julia Derunes and Antonio De Maio

Membranes 2023, 13(2), 141; https://doi.org/10.3390/membranes13020141 - 21 Jan 2023

Cited by 2 | Viewed by 2162

Abstract

Phospholipids are the major components of cellular membranes and cell-derived vesicles such as exosomes. They are also key components of artificial lipid nanoparticles, allowing the encapsulation and transport of various biological or chemical cargos. Both artificial and natural vesicles could be captured by [...] Read more.

Phospholipids are the major components of cellular membranes and cell-derived vesicles such as exosomes. They are also key components of artificial lipid nanoparticles, allowing the encapsulation and transport of various biological or chemical cargos. Both artificial and natural vesicles could be captured by cells delivering important information that could modulate cellular functions. However, the potential contribution of phospholipids within vesicles altering cellular physiology has been largely underestimated. Here, we showed that macrophages exposed to liposomes made exclusively with palmitoyl oleoyl phosphatidylcholine (POPC) in vivo resulted in a dramatic alteration of the transcriptome profile. Differential gene expression analysis indicated that the exposure to POPC liposomes resulted in a change in the expression of 1598 genes. Moreover, 146 genes were upregulated, and 69 genes were downregulated by incubation with POPC liposomes in contrast to palmitoyl oleoyl phosphatidylserine (POPS) exposure. Signaling pathway impact analysis revealed that 24 signaling pathways were significantly modulated after exposure to POPC liposomes, including the activation of the NF-κB pathway. Indeed, the expression of several cytokines (TNF-α, IL-6, and IL-10) and chemokines (Cxcl1 and Cxcl2) were increased. These observations were validated by the exposure of macrophages to POPC liposomes in culture conditions. In addition, the proteomic analysis of peritoneal cells exposed to POPC liposomes performed by mass spectrometry revealed that the expression of 107 proteins was downregulated after POPC exposure, whereas the expression of 12 proteins was significantly upregulated by this treatment, including seven proteins involved in the neutrophil degranulation pathway. This observation was confirmed by flow cytometry analysis showing the rapid recruitment of neutrophils into the peritoneal cavity after POPC exposure. Overall, these findings demonstrate that the presence of phospholipids within artificial and natural vesicles could be responsible for changes in the function of target cells. Full article

(This article belongs to the Special Issue Recent Studies on the Behaviour of Lipid Membranes)

► Show Figures

Graphical abstract

16 pages, 3872 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Key Parameters Impacting the Crystal Formation in Antisolvent Membrane-Assisted Crystallization

by Sara Chergaoui, Damien P. Debecker, Tom Leyssens and Patricia Luis

Membranes 2023, 13(2), 140; https://doi.org/10.3390/membranes13020140 - 21 Jan 2023

Cited by 5 | Viewed by 2143

Abstract

Antisolvent crystallization is commonly used in the formation of heat-sensitive compounds as it is the case for most active pharmaceutical ingredients. Membranes have the ability to control the antisolvent mass transfer to the reaction medium, providing excellent mixing that inhibits the formation of [...] Read more.

Antisolvent crystallization is commonly used in the formation of heat-sensitive compounds as it is the case for most active pharmaceutical ingredients. Membranes have the ability to control the antisolvent mass transfer to the reaction medium, providing excellent mixing that inhibits the formation of local supersaturations responsible for the undesired properties of the resulting crystals. Still, optimization of the operating conditions is required. This work investigates the impact of solution velocity, the effect of antisolvent composition, the temperature and gravity, using glycine-water-ethanol as a model crystallization system, and polypropylene flat sheet membranes. Results proved that in any condition, membranes were consistent in providing a narrow crystal size distribution (CSD) with coefficient of variation (CV) in the range of 0.5–0.6 as opposed to 0.7 obtained by batch and drop-by-drop crystallization. The prism-like shape of glycine crystals was maintained as well, but slightly altered when operating at a temperature of 35 °C with the appearance of smoother crystal edges. Finally, the mean crystal size was within 23 to 40 µm and did not necessarily follow a clear correlation with the solution velocities or antisolvent composition, but increased with the application of higher temperature or gravity resistance. Besides, the monoclinic form of α-glycine was perfectly maintained in all conditions. The results at each condition correlated directly with the antisolvent transmembrane flux that ranged between 0.0002 and 0.001 kg/m². s. In conclusion, membrane antisolvent crystallization is a robust solution offering consistent crystal properties under optimal operating conditions. Full article

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

► Show Figures

Graphical abstract

14 pages, 2544 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Isolation of Carboxylic Acids and NaOH from Kraft Black Liquor with a Membrane-Based Process Sequence

by Silvia Maitz, Lukas Wernsperger and Marlene Kienberger

Membranes 2023, 13(1), 92; https://doi.org/10.3390/membranes13010092 - 10 Jan 2023

Cited by 1 | Viewed by 1800

Abstract

In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used [...] Read more.

In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used to isolate these compounds and recycle the pulping chemicals. The present work discusses the fractionation of industrial black liquor by a sequence of nanofiltration and bipolar membrane electrodialysis units. Nanofiltration led to retention of the majority of lignin in the retentate and to a significant concentration increase in low-molecular-weight carboxylic acids, such as formic, acetic, glycolic and lactic acids, in the permeate. Subsequent treatment with bipolar membrane electrodialysis showed the potential for simultaneous recovery of acids in the acid compartment and the pulping chemical NaOH in the base compartment. The residual lignin was completely retained by the used membranes. Diffusion of acids to the base compartment and the low current density, however, limited the yield of acids and the current efficiency. In experiments with a black liquor model solution under optimized conditions, NaOH and acid recoveries of 68–72% were achieved. Full article

(This article belongs to the Section Membrane Applications)

► Show Figures

Graphical abstract

16 pages, 5303 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Open Pore Ultrafiltration Hollow Fiber Membrane Fabrication Method via Dual Pore Former with Dual Dope Solution Phase

by Kyunghoon Jang, Thanh-Tin Nguyen, Eunsung Yi, Chang Seong Kim, Soo Wan Kim and In S. Kim

Membranes 2022, 12(11), 1140; https://doi.org/10.3390/membranes12111140 - 13 Nov 2022

Cited by 2 | Viewed by 2147

Abstract

Hollow-fiber membranes are widely used in various fields of membrane processes because of their numerous properties, e.g., large surface area, high packing density, mass production with uniform quality, obvious end-of-life indicators, and so on. However, it is difficult to control the pores and [...] Read more.

Hollow-fiber membranes are widely used in various fields of membrane processes because of their numerous properties, e.g., large surface area, high packing density, mass production with uniform quality, obvious end-of-life indicators, and so on. However, it is difficult to control the pores and internal properties of hollow-fiber membranes due to their inherent structure: a hollow inside surrounded by a wall membrane. Herein, we aimed to control pores and the internal structure of hollow-fiber membranes by fabricating a dual layer using a dual nozzle. Two different pore formers, polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP), were separately prepared in the dope solutions and used for spinning the dual layer. Our results show that nanoscale pores could be formed on the lumen side (26.8–33.2 nm), and the open pores continuously increased in size toward the shell side. Due to robust pore structure, our fabricated membrane exhibited a remarkable water permeability of 296.2 ± 5.7 L/m²·h·bar and an extremely low BSA loss rate of 0.06 ± 0.02%, i.e., a high BSA retention of 99.94%. In consideration of these properties, the studied membranes are well-suited for use in either water treatment or hemodialysis. Overall, our membranes could be considered for the latter application with a high urea clearance of 257.6 mL/min, which is comparable with commercial membranes. Full article

(This article belongs to the Special Issue Separation Principles and Applications of Membrane Technology)

► Show Figures

Figure 1

15 pages, 4311 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Bioselective PES Membranes Based on Chitosan Functionalization and Virus-Imprinted NanoMIPs for Highly Efficient Separation of Human Pathogenic Viruses from Water

by Carmen Andreina Olivares Moreno and Zeynep Altintas

Membranes 2022, 12(11), 1117; https://doi.org/10.3390/membranes12111117 - 9 Nov 2022

Cited by 3 | Viewed by 1969

Abstract

Waterborne viruses are a public health concern due to relatively small infection doses. Particularly, adenoviruses (AdVs) are more resistant than RNA viruses to water purification treatments in terms of ultraviolet (UV) irradiation, pH, and chlorination tolerance. Moreover, AdVs are one of the most [...] Read more.

Waterborne viruses are a public health concern due to relatively small infection doses. Particularly, adenoviruses (AdVs) are more resistant than RNA viruses to water purification treatments in terms of ultraviolet (UV) irradiation, pH, and chlorination tolerance. Moreover, AdVs are one of the most predominant waterborne viruses. Membrane separations have proven superior removal capabilities of waterborne pathogens over other separation methods. However, virus removal at ultratrace levels is still a significant challenge for current membrane technology. This study successfully addressed this challenge by developing a bioselective polyethersulfone (PES) membrane by a joint strategy involving chitosan hydrophilic surface modification and the immobilization of adenovirus-specific molecularly imprinted nanoparticles (nanoMIPs). The topological and chemical changes taking place on the membrane surface were characterized by using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, hydrophilicity and membrane performance were investigated in terms of swelling behavior, permeation flux, and surface fouling studies. The membrane efficacy was evaluated by filtration experiments, where the virus concentration of the loading solution before filtration and the permeates after filtration was quantified. The novel bioselective membrane showed excellent virus removal capabilities by separating 99.99% of the viruses from the water samples. Full article

(This article belongs to the Special Issue Advances in Molecularly Imprinted Membranes)

► Show Figures

Graphical abstract

22 pages, 4166 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Exploring Membrane Binding Targets of Disordered Human Tau Aggregates on Lipid Rafts Using Multiscale Molecular Dynamics Simulations

by Kwan H. Cheng, Angela Graf, Amber Lewis, Thuong Pham and Aakriti Acharya

Membranes 2022, 12(11), 1098; https://doi.org/10.3390/membranes12111098 - 4 Nov 2022

Cited by 8 | Viewed by 1982

Abstract

The self-aggregation of tau, a microtubule-binding protein, has been linked to the onset of Alzheimer’s Disease. Recent studies indicate that the disordered tau aggregates, or oligomers, are more toxic than the ordered fibrils found in the intracellular neurofibrillary tangles of tau. At present, [...] Read more.

The self-aggregation of tau, a microtubule-binding protein, has been linked to the onset of Alzheimer’s Disease. Recent studies indicate that the disordered tau aggregates, or oligomers, are more toxic than the ordered fibrils found in the intracellular neurofibrillary tangles of tau. At present, details of tau oligomer interactions with lipid rafts, a model of neuronal membranes, are not known. Using molecular dynamics simulations, the lipid-binding events, membrane-damage, and protein folding of tau oligomers on various lipid raft surfaces were investigated. Tau oligomers preferred to bind to the boundary domains (Lod) created by the coexisting liquid-ordered (Lo) and liquid-disordered (Ld) domains in the lipid rafts. Additionally, stronger binding of tau oligomers to the ganglioside (GM1) and phosphatidylserine (PS) domains, and subsequent protein-induced lipid chain order disruption and beta-sheet formation were detected. Our results suggest that GM1 and PS domains, located exclusively in the outer and inner leaflets, respectively, of the neuronal membranes, are specific membrane domain targets, whereas the Lod domains are non-specific targets, of tau oligomers binding to neurons. The molecular details of these specific and non-specific tau bindings to lipid rafts may provide new insights into understanding membrane-associated tauopathies leading to Alzheimer’s Disease. Full article

(This article belongs to the Special Issue Lipid Membranes and Their Applications)

► Show Figures

Figure 1

17 pages, 6994 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Obtaining and Characterizing the Osmium Nanoparticles/n–Decanol Bulk Membrane Used for the p–Nitrophenol Reduction and Separation System

by Aurelia Cristina Nechifor, Alexandru Goran, Szidonia-Katalin Tanczos, Florentina Mihaela Păncescu, Ovidiu-Cristian Oprea, Alexandra Raluca Grosu, Cristian Matei, Vlad-Alexandru Grosu, Bogdan Ștefan Vasile and Paul Constantin Albu

Membranes 2022, 12(10), 1024; https://doi.org/10.3390/membranes12101024 - 21 Oct 2022

Cited by 6 | Viewed by 1568

Abstract

Liquid membranes based on nanoparticles follow a continuous development, both from obtaining methods and characterization of techniques points of view. Lately, osmium nanoparticles have been deposited either on flat membranes, with the aim of initiating some reaction processes, or on hollow fiber membranes, [...] Read more.

Liquid membranes based on nanoparticles follow a continuous development, both from obtaining methods and characterization of techniques points of view. Lately, osmium nanoparticles have been deposited either on flat membranes, with the aim of initiating some reaction processes, or on hollow fiber membranes, with the aim of increasing the contact surface with the phases of the membrane system. This paper presents the obtainment and characterization of a liquid membrane based on osmium nanoparticles (Os–NP) dispersed in ndecanol (nDol) for the realization of a membrane system with a large contact surface between the phases, but without using a liquid membrane support. The dispersion of osmium nanoparticles in n-decanol is carried out by the method of reducing osmium tetroxide with 1–undecenoic acid (UDA). The resulting membrane was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy analysis (EDAX), thermoanalysis (TG, DSC), Fourier transform infra-red (FTIR) spectroscopy and dynamic light scattering (DLS). In order to increase the mass transfer surface, a design for the membrane system was realized with the dispersion of the membrane through the receiving phase and the dispersion of the source phase through the membrane (DBLM-dispersion bulk liquid membrane). The process performance was tested for the reduction of p–nitrophenol (pNP) from the source phase, using sodium tetra-borohydride (NaBH₄), to p–aminophenol (pAP), which was transported and collected in the receiving phase. The obtained results show that membranes based on the dispersion of osmium nanoparticles in n–decanol can be used with an efficiency of over 90% for the reduction of p–nitrophenol and the separation of p–aminophenol. Full article

(This article belongs to the Special Issue A Commemorative Issue in Honor of Docent Constantin Luca: pH in Membrane Processes)

► Show Figures

Graphical abstract

20 pages, 2649 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermally Rearranged Mixed Matrix Membranes from Copoly(o-hydroxyamide)s and Copoly(o-hydroxyamide-amide)s with a Porous Polymer Network as a Filler—A Comparison of Their Gas Separation Performances

by Cenit Soto, Bibiana Comesaña-Gandara, Ángel Marcos, Purificación Cuadrado, Laura Palacio, Ángel E. Lozano, Cristina Álvarez, Pedro Prádanos and Antonio Hernandez

Membranes 2022, 12(10), 998; https://doi.org/10.3390/membranes12100998 - 14 Oct 2022

Cited by 3 | Viewed by 1793

Abstract

Copoly(o-hydroxyamide)s (HPA) and copoly(o-hydroxyamide-amide)s (PAA) have been synthesized to be used as continuous phases in mixed matrix membranes (MMMs). These polymeric matrices were blended with different loads (15 and 30 wt.%) of a relatively highly microporous porous polymer network (PPN). SEM images of [...] Read more.

Copoly(o-hydroxyamide)s (HPA) and copoly(o-hydroxyamide-amide)s (PAA) have been synthesized to be used as continuous phases in mixed matrix membranes (MMMs). These polymeric matrices were blended with different loads (15 and 30 wt.%) of a relatively highly microporous porous polymer network (PPN). SEM images of the manufactured MMMs exhibited good compatibility between the two phases for all the membranes studied, and their mechanical properties have been shown to be good enough even after thermal treatment. The WAX results show that the addition of PPN as a filler up to 30% does not substantially change the intersegmental distance and the polymer packing. It seems that, for all the membranes studied, the free volume that determines gas transport is in the high end of the possible range. This means that gas flow occurs mainly between the microvoids in the polymer matrix around the filler. In general, both HPA- and PAA-based MMMs exhibited a notable improvement in gas permeability, due to the presence of PPN, for all gases tested, with an almost constant selectivity. In summary, although the thermal stability of the PAA is limited by the thermal stability of the polyamide side chain, their mechanical properties were better. The permeability was higher for the PAA membranes before their thermal rearrangement, and these values increased after the addition of moderate amounts of PPN. Full article

(This article belongs to the Special Issue Advanced Membrane-based Technologies: Fabrication, Characterization, and Applications)

► Show Figures

Graphical abstract

18 pages, 6133 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Membrane Emulsification—A Novel Solution for Treatment and Reuse of Produced Water from Oil Field

by Aamer Ali, Usman Taqui Syed, Thomas Skovfoged Bak and Cejna Anna Quist-Jensen

Membranes 2022, 12(10), 971; https://doi.org/10.3390/membranes12100971 - 2 Oct 2022

Cited by 2 | Viewed by 2764

Abstract

Produced water (PW) is, by volume, the largest waste product of the oil- and gas-exploration industry and contains pollutants such as hydrocarbons and heavy metals. To meet the stringent environmental regulations, PW must be treated before discharging into the environment. The current study [...] Read more.

Produced water (PW) is, by volume, the largest waste product of the oil- and gas-exploration industry and contains pollutants such as hydrocarbons and heavy metals. To meet the stringent environmental regulations, PW must be treated before discharging into the environment. The current study proposes a novel treatment method where PW is used to prepare oil-in-water emulsion with potential applications within the oil-exploration industry. The emulsions are prepared by applying hollow fiber membrane emulsification (ME) on PW, which inherently contains oil, as to-be-dispersed phase. The results demonstrate that the average droplet size of the emulsions is a function of pressure applied on to-be-dispersed phase and could be customized from 0.24 to 0.65 µm by varying the pressure from 0.25 to 1 bar, respectively. Stability of the emulsions was verified under high pressure and a temperature and storage period of more than 24 h. The calculations showed that an ME unit with <100 kg weight and <1 m³ volume is appropriate to transform the daily average volume of PW from the Danish part of the North Sea into the emulsions. The study provides a novel route, which also complies well with the requirements (low-weight and small spatial footprints) of the offshore oil rigs, to treat and reuse PW within the oil production process and, therefore, eliminates its environmental footprint. Full article

(This article belongs to the Special Issue Membrane Science towards Sustainable Development Goals (SDGs))

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI