Membranes

14 pages, 5184 KiB

Open AccessArticle

Thermal Lamination of Electrospun Nanofiber Membrane with Woven Fabric and Yarn Embedding Effect

by Ziyuan Gao, Le Xu, Hongxia Wang, Xin Wei, Kaikai Chen, Wenyu Wang, Suzhen Zhang and Tong Lin

Membranes 2025, 15(3), 95; https://doi.org/10.3390/membranes15030095 - 20 Mar 2025

Viewed by 386

Abstract

This study investigated the effectiveness of two lamination methods for integrating electrospun nanofiber membranes with woven nylon fabric for personal protective applications. The first method used a thermoplastic urethane (TPU) nonwoven adhesive, while the second method incorporated both the adhesive and a yarn, [...] Read more.

This study investigated the effectiveness of two lamination methods for integrating electrospun nanofiber membranes with woven nylon fabric for personal protective applications. The first method used a thermoplastic urethane (TPU) nonwoven adhesive, while the second method incorporated both the adhesive and a yarn, with the yarn embedding by sewing. Lamination with the TPU nonwoven adhesive slightly improved the adhesion between the nanofiber membrane and the nylon fabric. However, it decreased the air permeability, with the degree of the decrease depending on the areal density of the TPU adhesive. As the areal density of the TPU increased from 10 g/m² to 30 g/m², the air permeability decreased from 107.6 mm/s to 43.4 mm/s. The lamination resulted in a slight increase in the filtration efficiency for oil aerosol particles (0.3 µm, PM0.3, at a flow rate of 32 L/min) to 96.4%, with a pressure drop of 83 Pa. Embedding non-fusible yarns in the laminate increased the nanofiber/fabric adhesion and permeability. Still, the filtration efficiency and pressure drop were reduced to 74.4% and 38 Pa, respectively, due to numerous pinholes formed in the nanofiber layer during the sewing process. Conversely, incorporating fusible TPU yarns not only improved the interlayer adhesion by 175% compared to using TPU fabric adhesive alone but also increased the air permeability to 136.1 mm/s. However, the filtration performance (87.7%, 72 Pa) was slightly lower than that of the unlaminated nanofiber/fabric pack because the TPU yarns sealed the pinholes during lamination. Lamination embedded with hot-melt yarns provides a versatile approach for combining nanofiber membranes with conventional fabrics. It can be used to develop nanofiber-functionalized textiles for a wide range of applications, including fire protection, electrical insulation, sound absorption, filtration, marine applications, and more. Full article

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

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58 pages, 3504 KiB

Open AccessReview

Fouling of Reverse Osmosis (RO) and Nanofiltration (NF) Membranes by Low Molecular Weight Organic Compounds (LMWOCs), Part 2: Countermeasures and Applications

by Yasushi Maeda

Membranes 2025, 15(3), 94; https://doi.org/10.3390/membranes15030094 - 17 Mar 2025

Viewed by 394

Abstract

Fouling, particularly from organic fouling and biofouling, poses a significant challenge in the RO/NF treatment of marginal waters, especially wastewater. Part 1 of this review detailed LMWOC fouling mechanisms. Part 2 focuses on countermeasures and applications. Effective fouling prevention relies on pretreatment, early [...] Read more.

Fouling, particularly from organic fouling and biofouling, poses a significant challenge in the RO/NF treatment of marginal waters, especially wastewater. Part 1 of this review detailed LMWOC fouling mechanisms. Part 2 focuses on countermeasures and applications. Effective fouling prevention relies on pretreatment, early detection, cleaning, optimized operation, and in situ membrane modification. Accurate fouling prediction is crucial. Preliminary tests using flat-sheet membranes or small-diameter modules are recommended. Currently, no specific fouling index exists for LMWOC fouling. Hydrophobic membranes, such as polyamide, are proposed as alternatives to the standard silt density index (SDI) filter. Once LMWOC fouling potential is assessed, suitable pretreatment methods can be implemented. These include adsorbents, specialized water filters, oxidative decomposition, and antifoulants. In situations where pretreatment is impractical, alternative strategies like high pH operation might be considered. Membrane cleaning becomes necessary upon fouling; however, standard cleaning often fails to fully restore the original flow. Specialized CIP chemicals, including organic solvent-based and oxidative agents, are required. Conversely, LMWOC fouling typically leads to a stabilized flow rate reduction rather than a continuous decline. Aggressive cleaning may be avoided if the resulting operating pressure increase is acceptable. When a significant flow rate drop occurs and LMWOC fouling is suspected, analysis of the fouled membrane is necessary for identification. Standard FT-IR often fails to detect LMWOCs. Solvent extraction followed by GC-MS is required. Pyrolysis GC-MS, which eliminates the extraction step, shows promise. The review concludes by examining how LMWOCs can be strategically utilized to enhance membrane rejection and restore deteriorated membranes. Full article

(This article belongs to the Special Issue Membrane Fouling Control: Mechanism, Properties, and Applications)

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20 pages, 4431 KiB

Open AccessArticle

Simulation of Carbon Dioxide Absorption in a Hollow Fiber Membrane Contactor Under Non-Isothermal Conditions

by Youkang Jin, Lei Wang, Jinpeng Bi, Wei Zhao, Hui Zhang, Yuexia Lv and Xi Chen

Membranes 2025, 15(3), 93; https://doi.org/10.3390/membranes15030093 - 14 Mar 2025

Viewed by 395

Abstract

CO₂ capture by membrane gas absorption technology has been considered a promising alternative to mitigate or stabilize atmospheric CO₂ concentrations. The non-isothermal nature of the CO₂ absorption process in hollow fiber membrane contactors is a critical factor that significantly influences [...] Read more.

CO₂ capture by membrane gas absorption technology has been considered a promising alternative to mitigate or stabilize atmospheric CO₂ concentrations. The non-isothermal nature of the CO₂ absorption process in hollow fiber membrane contactors is a critical factor that significantly influences CO₂ removal performance. In the present study, a non-isothermal mathematical model and a two-dimensional computational simulation were carried out to evaluate the CO₂ separation by three typical absorbents in a polyvinylidene fluoride hollow fiber membrane contactor under non-wetting operation mode. The simulation results exhibited good matching with the published experimental data with the deviations in the range of lower than 5%, which validated the reliability of the developed numerical model. A significant temperature increase ranging from 2 to 15 K was observed along the length of the hollow fiber membrane contactor, which further facilitated the absorption and reaction process in this study. The results showed that potassium glycinate exhibited the highest absorption capacity, followed by monoethanolamine and 1-ethyl-3-methylimidazolium. In addition, the mass transfer could be enhanced by increasing the liquid flow rate, absorbent concentration, module length, and membrane porosity, while increasing the gas velocity and CO₂ inlet concentration were unfavorable for the CO₂ removal process. Full article

(This article belongs to the Special Issue Membranes and Membrane Reactors for Gas Purification and Production: Towards More Sustainable Processes)

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37 pages, 2692 KiB

Open AccessArticle

Fractionation of a Procyanidin-Rich Grape Seed Extract by a Preparative Integrated Ultrafiltration/Reverse Osmosis/Solid-Phase Extraction Procedure

by Esperanza Guerrero-Hurtado, Alba Gutiérrez-Docio, Rebeca Fiedorowicz and Marin Prodanov

Membranes 2025, 15(3), 92; https://doi.org/10.3390/membranes15030092 - 14 Mar 2025

Viewed by 374

Abstract

The consumption of grape seed extracts is known for its contribution to animal and human health and is associated with its relevant procyanidin content. However, there is a little scientific unanimity whether these properties are due to the procyanidin content or to the [...] Read more.

The consumption of grape seed extracts is known for its contribution to animal and human health and is associated with its relevant procyanidin content. However, there is a little scientific unanimity whether these properties are due to the procyanidin content or to the length of their polymers. The main reason for this doubt is the technical difficulties related to their separation. Therefore, a preparative separation of grape seed extract was carried out using an integrated ultra/diafiltration procedure with membranes of 300, 30, 5, and 1 kDa molecular mass cut-offs, reverse osmosis and solid-phase extraction to obtain fractions of very high (>300 kDa), high (300–30 kDa), intermediate (30–5 kDa), low molecular mass (5–1 kDa), very-low-mass polar molecules and ions (<1 kDa), and very-low-mass dipole molecules (<1 kDa). Process parameters, mass transfer across the membranes and the quality of separation of each fraction are described and discussed in depth. A high degree of purification was achieved for the higher-molecular-mass fractions (>300, 300–30, and 30–5 kDa), as well as the big majority of procyanidin polymers and oligomers from very-low-molecular-mass species. All fractions were characterized for their procyanidin content by normal phase high-performance liquid chromatography coupled to a photodiode array detector (NP-HPLC-PAD). This analytical technique has shown for the first time that not only do oligomeric procyanidins elute at an increasing order of elution, but polymeric ones also do the same. Full article

(This article belongs to the Special Issue Membrane Technologies in Food Processing)

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26 pages, 7036 KiB

Open AccessArticle

Comparison of Different Polymeric Membranes in Direct Contact Membrane Distillation and Air Gap Membrane Distillation Configurations

by Cristiane Raquel Sousa Mesquita, Abdul Orlando Cárdenas Gómez, Carolina Palma Naveira Cotta and Renato Machado Cotta

Membranes 2025, 15(3), 91; https://doi.org/10.3390/membranes15030091 - 13 Mar 2025

Viewed by 504

Abstract

Membrane distillation (MD) is an evolving thermal separation technique most frequently aimed at water desalination, compatible with low-grade heat sources such as waste heat from thermal engines, solar collectors, and high-concentration photovoltaic panels. This study presents a comprehensive theoretical–experimental evaluation of three commercial [...] Read more.

Membrane distillation (MD) is an evolving thermal separation technique most frequently aimed at water desalination, compatible with low-grade heat sources such as waste heat from thermal engines, solar collectors, and high-concentration photovoltaic panels. This study presents a comprehensive theoretical–experimental evaluation of three commercial membranes of different materials (PE, PVDF, and PTFE), tested for two distinct MD modules—a Direct Contact Membrane Distillation (DCMD) module and an Air Gap Membrane Distillation (AGMD) module—analyzing the impact of key operational parameters on the performance of the individual membranes in each configuration. The results showed that increasing the feed saline concentration from 7 g/L to 70 g/L led to distillate flux reductions of 12.2% in the DCMD module and 42.9% in the AGMD one, averaged over the whole set of experiments. The increase in feed temperature from 65 °C to 85 °C resulted in distillate fluxes up to 2.36 times higher in the DCMD module and 2.70 times higher in the AGMD one. The PE-made membrane demonstrated the highest distillate fluxes, while the PVDF and PTFE membranes exhibited superior performance under high-salinity conditions in the AGMD module. Membranes with high contact angles, such as PTFE with 143.4°, performed better under high salinity conditions. Variations in operational parameters, such as flow rate and temperature, markedly affect the temperature and concentration polarization effects. The analyses underscored the necessity of a careful selection of membrane type for each distillation configuration by the specific characteristics of the process and its operational conditions. In addition to experimental findings, the proposed heat and mass transfer-reduced model showed good agreement with experimental data, with deviations within ±15%, effectively capturing the influence of operational parameters. Theoretical predictions showed good agreement with experimental data, confirming the model’s validity, which can be applied to optimization methodologies to improve the membrane distillation process. Full article

(This article belongs to the Section Membrane Applications for Water Treatment)

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24 pages, 22607 KiB

Open AccessArticle

Fabrication of a Novel PES/CNTs@TiO₂ Membrane Combining Photo-Electrocatalysis and Filtration for Organic Pollutant Removal

by Yue Lu, Xuan Xing, Yi Jiang and Jianxin Xia

Membranes 2025, 15(3), 90; https://doi.org/10.3390/membranes15030090 - 10 Mar 2025

Viewed by 637

Abstract

Membrane filtration has been widely used in wastewater treatment; contaminants attached to the membrane surface led to flux loss and service life reduction. In the present study, a photo-electrocatalysis membrane was fabricated with CNTs@TiO₂ deposited on a commercial polyethersulfone (PES) membrane (PES/CNTs@TiO [...] Read more.

Membrane filtration has been widely used in wastewater treatment; contaminants attached to the membrane surface led to flux loss and service life reduction. In the present study, a photo-electrocatalysis membrane was fabricated with CNTs@TiO₂ deposited on a commercial polyethersulfone (PES) membrane (PES/CNTs@TiO₂). XRD and SEM characterization proved that the CNTs@TiO₂ composites were successfully fabricated using the one-pot hydrothermal method. Additionally, vacuum filtration was used to distribute the as-prepared powder on the PES membrane. In CNTs@TiO₂, TiO₂ particles were deposited on the outer layer of CNTs, which benefits light adsorption and photocatalytic reaction. The hydrophilicity, light absorption ability, and electron transfer rate of the PES/CNTs@TiO₂ membrane were enhanced compared with the pristine PES membranes. Organic compound removal was improved in the photo-electrocatalysis filtration system with the improvement of 32.41% for methyl orange (MO), 26.24% for methyl blue (MB), 7.86% for sulfamethoxazole (SMZ), and 25.19% for florfenicol (FF), respectively. Moreover, the hydrophilicity and removal rate could be restored after pure water cleaning, demonstrating excellent reusability. The quenching experiment showed that ·OH and ·O₂⁻ were the main reactive oxygen species. This work provides a convenient form of photo-electrocatalysis filtration technology using modified commercial membranes, which has great potential for practical application. Full article

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

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12 pages, 587 KiB

Open AccessArticle

Adhesive Force Between Biconcave Red Blood Cell Membrane and Bulk Substrate

by Weihua Mu

Membranes 2025, 15(3), 89; https://doi.org/10.3390/membranes15030089 - 10 Mar 2025

Viewed by 502

Abstract

Adhesion between a red blood cell and substrates is essential to many biophysical processes and has significant implications for medical applications. This study derived a theoretical formula for the adhesive force between a red blood cell and a bulk substrate, incorporating the Hamaker [...] Read more.

Adhesion between a red blood cell and substrates is essential to many biophysical processes and has significant implications for medical applications. This study derived a theoretical formula for the adhesive force between a red blood cell and a bulk substrate, incorporating the Hamaker constant to account for van der Waals interactions. The derivation is based on a biconcave shape of an RBC, described by the well-known Ouyang–Helfrich equation and its analytical solution developed by Ouyang. The theoretical predictions align with experimental observations and the empirical spherical model, revealing a

F \propto D^{- 2.5}

relationship for biconcave RBCs versus

F \propto D^{- 2}

for spheres. While the current study focuses on idealized geometries and static conditions, future work will extend these findings to more complex environmental conditions, such as dynamic flow and interactions with plasma proteins, thereby broadening the applicability of the model. This work bridges foundational research in cell membrane mechanics with practical applications in hemostatic materials, platelet adhesion, and biomaterials engineering. The findings provide insights for designing advanced biological sensors, surgical tools, and innovative medical materials with enhanced biocompatibility and performance. Full article

(This article belongs to the Special Issue Design Principles and Biomedical Applications of Multifunctional Biological Membranes)

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25 pages, 9793 KiB

Open AccessArticle

Analysis of CO₂ Absorption in Gas/Liquid Membrane Contactors with Inserted Descending Hydraulic Diameters of 3D-Printed Turbulence Promoters

by Chii-Dong Ho, Yi-Wun Wang, Zheng-Zhong Chen and Thiam Leng Chew

Membranes 2025, 15(3), 88; https://doi.org/10.3390/membranes15030088 - 9 Mar 2025

Viewed by 706

Abstract

The decline in absorption flux across membrane modules is attributed to the increase in concentration polarization resistance in flat-plate membrane contactors for CO₂ absorption using monoethanolamine (MEA) as the absorbent. Researchers have discovered that this effect can be mitigated by inserting turbulence [...] Read more.

The decline in absorption flux across membrane modules is attributed to the increase in concentration polarization resistance in flat-plate membrane contactors for CO₂ absorption using monoethanolamine (MEA) as the absorbent. Researchers have discovered that this effect can be mitigated by inserting turbulence promoters, which enhance turbulence intensity at the cost of increased power consumption, thereby improving CO₂ absorption flux. The performance of flat-plate membrane contactors for CO₂ absorption was further enhanced by reducing the hydraulic diameters of embedded 3D-printed turbulence promoters, considering the increased power consumption. The mass-balance modeling, incorporating chemical reactions, was developed theoretically and conducted experimentally on a flat-plate gas/liquid polytetrafluoroethylene/polypropylene (PTFE/PP) membrane module in the present study. A one-dimensional theoretical analysis, based on the resistance-in-series model and the plug-flow model, was conducted to predict absorption flux and concentration distributions. An economic analysis was also performed on modules with promoter-filled channels, considering different array configurations and geometric shapes of turbulence promoters, weighing both absorption flux improvement and power consumption increment. Device performances were evaluated and compared with those of modules using uniform promoter widths. Additionally, the Sherwood number for the CO₂ membrane absorption module was generalized into a simplified expression to predict the mass transfer coefficient for modules with inserted 3D-printed turbulence promoters. Results showed that the ratio of absorption flux improvement to power consumption increment in descending hydraulic-diameter operations is higher than in uniform hydraulic-diameter operations. Full article

(This article belongs to the Section Membrane Applications for Gas Separation)

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20 pages, 4935 KiB

Open AccessArticle

Characterization, Performance, and Toxicological Assessment of Polysulfone-Sulfonated Polyether Ether Ketone Membranes for Water Separation Applications

by Muhammad Usman Yousaf, Lucca Madeo Cortarelli, Nerissa I. Jebet, Jason M. Unrine, Nirupam Aich, Olga V. Tsyusko and Isabel C. Escobar

Membranes 2025, 15(3), 87; https://doi.org/10.3390/membranes15030087 - 8 Mar 2025

Viewed by 1898

Abstract

The removal of small molecular weight charged compounds from aqueous solutions using membrane remains a challenge. In this study, polysulfone (PSf)- and sulfonated polyether ether ketone (SPEEK)-based membranes were fabricated via non-solvent induced phase separation process (NIPS) using N-Methyl-2-Pyrrolidone (NMP) as solvent and [...] Read more.

The removal of small molecular weight charged compounds from aqueous solutions using membrane remains a challenge. In this study, polysulfone (PSf)- and sulfonated polyether ether ketone (SPEEK)-based membranes were fabricated via non-solvent induced phase separation process (NIPS) using N-Methyl-2-Pyrrolidone (NMP) as solvent and water as non-solvent. Membranes were characterized structurally and morphologically, followed by toxicity assessment conducted before and after filtration, both with and without annealing at various pH values to evaluate potential leaching of trapped solvent from the membrane pores. Additionally, membrane performance was characterized using binary mixtures of cationic and anionic dyes. The results demonstrated selective filtration behavior, with cationic dyes being preferentially rejected due to size exclusion and electrostatic interactions. Additionally, a key focus of this work was the investigation of solvent leaching, framed within a Safe(r)-by-Design (SbD) approach aimed at enhancing functional performance while minimizing environmental toxicity. Toxicity assessments using a model organism, a nematode Caenorhabditis elegans, revealed that annealing reduced solvent leaching and thus permeate toxicity, particularly at neutral pH values, by facilitating trapped solvent release prior to membrane use. These findings provide insights for the importance of including an SbD approach during membrane casting to fabricate membranes with desirable properties while minimizing toxicity. Full article

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

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12 pages, 21558 KiB

Open AccessArticle

Ceramic Nanofiltration Membranes: Creating Nanopores by Calcination of Atmospheric-Pressure Molecular Layer Deposition Grown Titanicone Layers

by Harpreet Sondhi, Mingliang Chen, Michiel Pieter Nijboer, Arian Nijmeijer, Fred Roozeboom, Mikhael Bechelany, Alexey Kovalgin and Mieke Luiten-Olieman

Membranes 2025, 15(3), 86; https://doi.org/10.3390/membranes15030086 - 8 Mar 2025

Viewed by 669

Abstract

Ceramic membrane technology, whether applied as a stand-alone separation technology or in combination with energy-intensive approaches like distillation, is a promising solution for lower energy alternatives with minimal carbon footprints. To improve the separation of solutes in the nanofiltration range from industrial wastewater [...] Read more.

Ceramic membrane technology, whether applied as a stand-alone separation technology or in combination with energy-intensive approaches like distillation, is a promising solution for lower energy alternatives with minimal carbon footprints. To improve the separation of solutes in the nanofiltration range from industrial wastewater streams, ceramic nanofiltration (NF) membranes with reproducible sub-nanometre pore sizes are required. To achieve this, the emerging technique of molecular layer deposition (MLD) is employed to develop ceramic NF membranes, and its efficiency and versatility make it a powerful tool for preparing uniform nanoscale high-porosity membranes. Our work, which involved vapor-phase titanium tetrachloride as a precursor and ethylene glycol as a co-reactant, followed by calcination in air at 350 °C, resulted in NF membranes with pore sizes (radii) around ~0.8 ± 0.1 nm and a demineralized water permeability of 13 ± 1 L·m⁻²·h⁻¹·bar⁻¹.The high-water flux with >90% rejection of polyethylene glycol molecules with a molecular size larger than 380 ± 6 Dalton indicates the efficiency of the MLD technique in membrane functionalization and size-selective separation processes, and its potential for industrial applications. Full article

(This article belongs to the Special Issue Preparation, Characterization, and Application of Advanced Separation Membrane Materials)

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22 pages, 8618 KiB

Open AccessArticle

Suitability of Electrodialysis with Monovalent Selective Anion-Exchange Membranes for Fractionation of Aqueous Mixture Containing Reactive Dye and Mineral Salt

by Katarzyna Majewska-Nowak, Arif Eftekhar Ahmed, Martyna Grzegorzek and Karolina Baraniec

Membranes 2025, 15(3), 85; https://doi.org/10.3390/membranes15030085 - 7 Mar 2025

Viewed by 684

Abstract

To fulfil the goals of the circular economy, the treatment of textile wastewater should be focused on the recovery of valuable components. Monovalent anion-selective electrodialysis (MASED) was applied for the separation of reactive dyes from mineral salts. Standard cation-exchange membranes (CM membranes) and [...] Read more.

To fulfil the goals of the circular economy, the treatment of textile wastewater should be focused on the recovery of valuable components. Monovalent anion-selective electrodialysis (MASED) was applied for the separation of reactive dyes from mineral salts. Standard cation-exchange membranes (CM membranes) and monovalent selective anion-exchange membranes (MVA membranes) were used in the electrodialysis (ED) stack. The separation efficiency was evaluated for model solutions of various reactive dyes (varying in molecular weight and chemical reactivity) containing NaCl. In the course of MASED, the mineral salt was successfully removed from the dye solutions with an efficacy of 97.4–99.4%, irrespectively of the composition of the treated solution. The transport of dye molecules through the ion-exchange membranes (IEMs) from diluate to concentrate compartments was irrelevant. Nonetheless, a significant adsorption of dye particles on the membranes was observed. Around 11–40% of the initial dye mass was deposited in the ED stack. Dye adsorption intensity was significantly affected by dye reactivity. This study showed the potential of the MASED process for the separation of the reactive dye from the mineral salt on condition that antifouling membrane properties are improved. The obtained streams (the concentrate rich in mineral salt and the diluate containing the reactive dye) can be reused in the dye-house textile operations; however, some loss of dye mass should be included. Full article

(This article belongs to the Special Issue Research on Electrodialytic Processes)

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18 pages, 8753 KiB

Open AccessArticle

Enhanced Protein Separation Performance of Cellulose Acetate Membranes Modified with Covalent Organic Frameworks

by Shurui Shao, Maoyu Liu, Baifu Tao, Kayode Hassan Lasisi, Wenqiao Meng, Xing Wu and Kaisong Zhang

Membranes 2025, 15(3), 84; https://doi.org/10.3390/membranes15030084 - 6 Mar 2025

Viewed by 875

Abstract

As a porous crystalline material, covalent organic frameworks (COFs) have attracted significant attention due to their extraordinary features, such as an ordered pore structure and excellent stability. Synthesized through the aldehyde amine condensation reaction, TpPa-1 COFs (Triformylphloroglucinol-p-Phenylenediamine-1 COFs) were blended with cellulose acetate [...] Read more.

As a porous crystalline material, covalent organic frameworks (COFs) have attracted significant attention due to their extraordinary features, such as an ordered pore structure and excellent stability. Synthesized through the aldehyde amine condensation reaction, TpPa-1 COFs (Triformylphloroglucinol-p-Phenylenediamine-1 COFs) were blended with cellulose acetate (CA) to form a casting solution. The TpPa-1 COF/CA ultrafiltration membrane was then prepared using the non-solvent-induced phase inversion (NIPS) method. The influence of TpPa-1 COFs content on the hydrophilicity, stability and filtration performance of the modified membrane was studied. Due to the hydrophilic groups in TpPa-1 COFs and the network structure formed by covalent bonds, the modified CA membranes exhibited higher hydrophilicity and lower protein adsorption compared with the pristine CA membrane. The porous crystalline structure of TpPa-1 COFs increased the water permeation path in the CA membrane, improving the permeability of the modified membrane while maintaining an outstanding bovine serum albumin (BSA) rejection. Furthermore, the addition of TpPa-1 COFs reduced protein adsorption on the CA membrane and overcame the trade-off between permeability and selectivity in CA membrane bioseparation applications. This approach provides a sustainable method for enhancing membrane performance while enhancing the application of membranes in protein purification. Full article

(This article belongs to the Special Issue Membrane Separation and Water Treatment: Modeling and Application)

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16 pages, 3140 KiB

Open AccessArticle

Study on Organo-Silica-Derived Membranes Using a Robeson-like Plot

by Lucas Bünger, Tim van Gestel, Tim Kurtz, Krassimir Garbev, Peter Stemmermann, Wilhelm A. Meulenberg, Olivier Guillon and Dieter Stapf

Membranes 2025, 15(3), 83; https://doi.org/10.3390/membranes15030083 - 5 Mar 2025

Viewed by 510

Abstract

For industrial CO₂ utilization, the supply of concentrated CO₂ within a continuous, high-volume stream at high temperatures remains a substantial requirement. Membrane processes offer a simple and efficient method to provide CO₂ in this form. While several organo-silica-based membranes have [...] Read more.

For industrial CO₂ utilization, the supply of concentrated CO₂ within a continuous, high-volume stream at high temperatures remains a substantial requirement. Membrane processes offer a simple and efficient method to provide CO₂ in this form. While several organo-silica-based membranes have been developed for CO₂/N₂ separation under these conditions, there is no standardized framework guiding comparability and optimization. Therefore, we present these membranes in a Robeson-like plot across various temperatures. Utilizing a standard 1,2-bis(triethoxysilyl)-ethane (BTESE) precursor and a simplified sol–gel method, we prepared a microporous membrane layer and characterized it for an exemplary comparison. This characterization includes key parameters for mixed-gas applications: (1) temperature-dependent single- and mixed-gas permeances to observe interactions, (2) the impact of the driving forces in mixtures (vacuum and concentration) to distinguish between permselectivity and the separation factor clearly, and (3) influence of the support structure to enable permeability calculations at elevated temperatures. Furthermore, a quick interpretation method for assessing the membrane’s microstructure is presented. A qualitative microstructure assessment can be achieved by analyzing the temperature dependencies of the three major diffusion mechanisms that simultaneously occur—Knudsen, surface, and activated diffusion. Full article

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

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34 pages, 1949 KiB

Open AccessReview

Remediation of Micro- and Nanoplastics by Membrane Technologies

by Michał Bodzek and Piotr Bodzek

Membranes 2025, 15(3), 82; https://doi.org/10.3390/membranes15030082 - 5 Mar 2025

Viewed by 650

Abstract

Micro- and nanoplastics (NPs) cannot be completely removed from water/wastewater in conventional wastewater treatment plants (WWTPs) and drinking water treatment plants (DWTPs). According to the literature analysis, membrane processes, one of the advanced treatment technologies, are the most effective and promising technologies for [...] Read more.

Micro- and nanoplastics (NPs) cannot be completely removed from water/wastewater in conventional wastewater treatment plants (WWTPs) and drinking water treatment plants (DWTPs). According to the literature analysis, membrane processes, one of the advanced treatment technologies, are the most effective and promising technologies for the removal of microplastics (MPs) from water and wastewater. In this article, firstly, the properties of MPs commonly found in water and wastewater treatment and their removal efficiencies are briefly reviewed. In addition, research on the use of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and membrane bioreactors (MBR) for the remediation of MPs and NPs from water/wastewater is reviewed, and the advantages/disadvantages of each removal method are discussed. Membrane filtration is also compared with other methods used to remove MPs. Furthermore, the problem of membrane fouling by MPs during filtration and the potential for MPs to be released from the polymeric membrane structure are discussed. Finally, based on the literature survey, the current status and gaps in research on MPs removal by membrane technologies are identified, and recommendations for further research are made. Full article

(This article belongs to the Section Membrane Applications for Water Treatment)

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24 pages, 1362 KiB

Open AccessReview

Pressure-Driven Membrane Processes for Removing Microplastics

by Priscila Edinger Pinto, Alexandre Giacobbo, Gabriel Maciel de Almeida, Marco Antônio Siqueira Rodrigues and Andréa Moura Bernardes

Membranes 2025, 15(3), 81; https://doi.org/10.3390/membranes15030081 - 5 Mar 2025

Viewed by 1010

Abstract

The intense consumption of polymeric materials combined with poor waste management results in the dissemination of their fragments in the environment as micro- and nanoplastics. They are easily dispersed in stormwater, wastewater, and landfill leachate and carried towards rivers, lakes, and oceans, causing [...] Read more.

The intense consumption of polymeric materials combined with poor waste management results in the dissemination of their fragments in the environment as micro- and nanoplastics. They are easily dispersed in stormwater, wastewater, and landfill leachate and carried towards rivers, lakes, and oceans, causing their contamination. In aqueous matrices, the use of membrane separation processes has stood out for the efficiency of removing these particulate contaminants, achieving removals of up to 100%. For this review article, we researched the removal of microplastics and nanoplastics by membrane processes whose driving force is the pressure gradient. The analysis focuses on the challenges found in the operation of microfiltration, ultrafiltration, nanofiltration, and reverse-osmosis systems, as well as on the innovations applied to the membranes, with comparisons of treatment systems and the peculiarities of each system and each aqueous matrix. We also point out weaknesses and opportunities for future studies so that these techniques, known to be capable of removing many other contaminants of emerging concern, can subsequently be widely applied in the removal of micro- and nanoplastics. Full article

(This article belongs to the Special Issue Recent Advances in Polymeric Membranes—Preparation and Applications)

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10 pages, 4242 KiB

Open AccessArticle

Veratridine-Induced Oscillations in Nav 1.7 but Not Nav 1.5 Sodium Channels Are Revealed by Membrane Potential Sensitive Dye

by Sarah C. R. Lummis, Samantha C. Salvage, Christopher L.-H. Huang and Antony P. Jackson

Membranes 2025, 15(3), 80; https://doi.org/10.3390/membranes15030080 - 5 Mar 2025

Viewed by 623

Abstract

Voltage-gated sodium channels (Navs) are critical for membrane potential depolarisation in cells, with especially important roles in neuronal and cardiomyocyte membranes. Their malfunction results in a range of disorders, and they are the target of many widely used drugs. A rapid yet accurate [...] Read more.

Voltage-gated sodium channels (Navs) are critical for membrane potential depolarisation in cells, with especially important roles in neuronal and cardiomyocyte membranes. Their malfunction results in a range of disorders, and they are the target of many widely used drugs. A rapid yet accurate functional assay is therefore desirable both to probe for novel active compounds and to better understand the many different Nav isoforms. Here, we use fluorescence to monitor Nav function: cells expressing either the cardiac Nav 1.5 or pain-associated Nav 1.7 were loaded with fluorescent membrane potential sensitive dye and then stimulated with veratridine. Cells expressing Nav 1.5 show a concentration-dependent slow rise and then a plateau in fluorescence. In contrast, cells expressing Nav 1.7 show a more rapid rise and then unexpected oscillatory behavior. Inhibition by flecainide and mexiletine demonstrates that these oscillations are Nav-dependent. Thus, we show that this fluorescent membrane potential dye can provide useful functional data and that we can readily distinguish between these two Nav isoforms because of the behavior of cells expressing them when activated by veratridine. We consider these distinct behaviors may be due to different interactions of veratridine with the different Nav isoforms, although more studies are needed to understand the mechanism underlying the oscillations. Full article

(This article belongs to the Section Biological Membranes)

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29 pages, 6219 KiB

Open AccessReview

The Importance of Bilayer Asymmetry in Biological Membranes: Insights from Model Membranes

by Igor S. Oliveira, Guilherme X. Pinheiro, Maria Luana B. Sa, Pedro Henrique L. O. Gurgel, Samuel U. Pizzol, Rosangela Itri, Vera B. Henriques and Thais A. Enoki

Membranes 2025, 15(3), 79; https://doi.org/10.3390/membranes15030079 - 3 Mar 2025

Viewed by 721

Abstract

This mini-review intends to highlight the importance of bilayer asymmetry. Biological membranes are complex structures that are a physical barrier separating the external environment from the cellular content. This complex bilayer comprises an extensive lipid repertory, suggesting that the different lipid structures might [...] Read more.

This mini-review intends to highlight the importance of bilayer asymmetry. Biological membranes are complex structures that are a physical barrier separating the external environment from the cellular content. This complex bilayer comprises an extensive lipid repertory, suggesting that the different lipid structures might play a role in the membrane. Interestingly, this vast repertory of lipids is asymmetrically distributed between leaflets that form the lipid bilayer. Here, we discuss the properties of the plasma membrane from the perspective of experimental model membranes, consisting of simplified and controlled in vitro systems. We summarize some crucial features of the exoplasmic (outer) and cytoplasmic (inner) leaflets observed through investigations using symmetric and asymmetric membranes. Symmetric model membranes for the exoplasmic leaflet have a unique lipid composition that might form a coexistence of phases, namely the liquid disordered and liquid order phases. These phase domains may appear in different sizes and shapes depending on lipid composition and lipid–lipid interactions. In contrast, symmetric model membranes for the cytoplasmic leaflet form a fluid phase. We discuss the outcomes reported in the literature for asymmetric bilayers, which vary according to lipid compositions and, consequently, reflect different intra- and inter-leaflet interactions. Interestingly, the asymmetric bilayer could show induced domains in the inner leaflet, or it could decrease the tendency of the outer leaflet to phase separation. If cells regulate the lipid composition of the plasma membrane, they can adjust the existence and sizes of the domains by tuning the lipid composition. Full article

(This article belongs to the Special Issue Advances in Symmetric and Asymmetric Lipid Membranes)

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17 pages, 2695 KiB

Open AccessArticle

Enhancing the Performance of Tangential Flow Microfiltration for Bioreactor Clarification

by Amir Hossein Mostafavi, Liang-Kai Chu, Xianghong Qian, John Paul Smelko, Da Zhang, Andrew Zydney and Sumith Ranil Wickramasinghe

Membranes 2025, 15(3), 78; https://doi.org/10.3390/membranes15030078 - 3 Mar 2025

Viewed by 1098

Abstract

Tangential flow microfiltration is easily adapted for batch and continuous bioreactor clarification. The permeate can be introduced directly to the subsequent capture step. However, the commercial use of tangential flow filtration (TFF) is limited by membrane fouling, leading to a compromised performance. Here, [...] Read more.

Tangential flow microfiltration is easily adapted for batch and continuous bioreactor clarification. The permeate can be introduced directly to the subsequent capture step. However, the commercial use of tangential flow filtration (TFF) is limited by membrane fouling, leading to a compromised performance. Here, we explored the possibility of reducing membrane fouling by integrating a hydrocyclone as the primary clarification operation. The overflow from the hydrocyclone was introduced directly as the feed to the microfiltration module. Chinese hamster ovary cells were used as the feed stream to investigate the feasibility of this integrated process. A range of cell viabilities from 0% (cell lysate) to 96% were investigated. The cell densities ranged from 0.9 to 10 million cells per mL. Two commercially available hollow fiber microfiltration membranes were used, an essentially symmetric membrane and a reverse asymmetric membrane where the more open support structure faced the feed stream. The reverse asymmetric membrane was more resistant to fouling in the absence of an integrated hydrocyclone. Integrating a hydrocyclone led to a reduction in the flux decline for the symmetric membrane, but did not affect the performance of the reverse asymmetric membrane. The careful choice of membrane morphology and pore size is important when designing an integrated process. Full article

(This article belongs to the Special Issue Application of Membrane Materials in Bioseparation and Downstream Processing)

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16 pages, 6337 KiB

Open AccessArticle

Preparation of Crown Ether-Containing Polyamide Membranes via Interfacial Polymerization and Their Desalination Performance

by Liqing Xing, Liping Lin, Jiaxin Guo, Xinping He and Chunhai Yi

Membranes 2025, 15(3), 77; https://doi.org/10.3390/membranes15030077 - 3 Mar 2025

Viewed by 618

Abstract

The large-scale application of aromatic polyamide (PA) thin-film composite (TFC) membranes for reverse osmosis has provided an effective way to address worldwide water scarcity. However, the water permeability and salt rejection capabilities of the PA membrane remain limited. In this work, cyclic micropores [...] Read more.

The large-scale application of aromatic polyamide (PA) thin-film composite (TFC) membranes for reverse osmosis has provided an effective way to address worldwide water scarcity. However, the water permeability and salt rejection capabilities of the PA membrane remain limited. In this work, cyclic micropores based on crown ether were introduced into the PA layer using a layer-by-layer interfacial polymerization (LbL-IP) method. After interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the di(aminobenzo)-18-crown-6 (DAB18C6) solution in methanol was poured on the membrane to react with the residual TMC. The cyclic micropores of DAB18C6 provided the membrane with rapid water transport channels and improved ion rejection due to its hydrophilicity and size sieving effect. The membranes were characterized by FTIR, XPS, SEM, and AFM. Compared to unmodified membranes, the water contact angle decreased from 54.1° to 31.6° indicating better hydrophilicity. Moreover, the crown ether-modified membrane exhibited both higher permeability and enhanced rejection performance. The permeability of the crown ether-modified membrane was more than ten times higher than unmodified membranes with a rejection above 95% for Na₂SO₄, MgSO₄, MgCl_2, and NaCl solution. These results highlight the potential of this straightforward surface grafting strategy and the modified membranes for advanced water treatment technologies, particularly in addressing seawater desalination challenges. Full article

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

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30 pages, 4960 KiB

Open AccessArticle

Modelling Gas Transport in Multiphasic Materials: Application to Semicrystalline Membranes

by Lorenzo Merlonghi, Marco Giacinti Baschetti and Maria Grazia De Angelis

Membranes 2025, 15(3), 76; https://doi.org/10.3390/membranes15030076 - 2 Mar 2025

Viewed by 785

Abstract

The description of gas permeation across heterogeneous materials has been studied with many methods, mainly focusing on composites with high aspect ratios and low filler volume fractions. In the present work, the extension of these approaches to semicrystalline polymers is studied, considering a [...] Read more.

The description of gas permeation across heterogeneous materials has been studied with many methods, mainly focusing on composites with high aspect ratios and low filler volume fractions. In the present work, the extension of these approaches to semicrystalline polymers is studied, considering a wide range of crystalline volume fractions to tackle applications ranging from membranes to barrier materials. A numerical approach focused on tortuosity effects related to the presence of impermeable crystalline domains was considered. Algorithms based on random sequential adsorption and Voronoi tessellation were used to reproduce the morphology of semicrystalline polymers. The flux reduction across the microstructures generated due to the presence of impermeable crystals was calculated by solving local mass balance through a finite volume method. Using this strategy, it was possible to investigate the effect of crystallites’ arrangement, size distribution, orientation and shape on the relative permeability and the tortuosity of semicrystalline membranes. The results were analyzed considering existing macroscopic models and new analytical equations were proposed in order to account on such morphological effects for the prediction of the tortuosity in semicrystalline polymers. Full article

(This article belongs to the Special Issue Mathematical and Computational Modelling in Membrane Separations: From Preparation to Processes)

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16 pages, 4460 KiB

Open AccessArticle

Tailoring the Performance of a Composite PEI Nanofiltration Membrane via Incorporating Activated PDA for Efficient Dye Sieving and Salt Separation

by Wanting Li, Jiaye Liu, Weifu Wang, Shichun Chen, Fengwei Jia, Xiang Li, Ying Zhao, Wenjuan Zhang, Dan Song and Jun Ma

Membranes 2025, 15(3), 75; https://doi.org/10.3390/membranes15030075 - 2 Mar 2025

Viewed by 815

Abstract

Efficient dye sieving and salt separation can facilitate the recycling of valuable resources in textile wastewater treatment. This study focuses on developing a high-performance nanofiltration membrane (NF) by co-depositing activated polydopamine (O-PDA), oxidized with KMnO₄, and polyethyleneimine (PEI) onto a polysulfone [...] Read more.

Efficient dye sieving and salt separation can facilitate the recycling of valuable resources in textile wastewater treatment. This study focuses on developing a high-performance nanofiltration membrane (NF) by co-depositing activated polydopamine (O-PDA), oxidized with KMnO₄, and polyethyleneimine (PEI) onto a polysulfone support membrane (PSF), thereby enabling effective dye sieving and salt separation. Due to the high hydrophilicity of PDA and the formation of high molecular polymers after oxidation, it was anticipated that O-PDA would crosslink the PEI layer, providing rapid permeating channels. Filtration experiments demonstrated that the formation of O-PDA significantly enhanced the salt retention rate of nanofiltration membranes, achieving a nearly threefold increase in NaCl retention from 15% to 45.7%. It was observed that the retention performance of O-PDA could be adjusted by controlling its loading or oxidation level. Furthermore, despite a notable reduction in permeability, the dye removal efficiency of the O-PDA/PEI membrane increased substantially to 99.5%. Long-term filtration experiments also confirmed both the stability and anti-fouling properties of this membrane design. Clearly, owing to its excellent operational stability and anti-fouling characteristics, the O-PDA/PEI membrane exhibits great potential for applications in dye sieving and salt separation. Full article

(This article belongs to the Special Issue Membrane and Other Innovative Technologies for Water Purification: Design, Development, and Application)

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21 pages, 6032 KiB

Open AccessArticle

The Biphasic Effect of Lipopolysaccharide on Membrane Potential

by Maria E. Hadjisavva and Robin L. Cooper

Membranes 2025, 15(3), 74; https://doi.org/10.3390/membranes15030074 - 2 Mar 2025

Viewed by 688

Abstract

Lipopolysaccharide (LPS) from certain strains of Gram-negative bacteria can induce a rapid (<1 s) hyperpolarization of membrane potential, followed by a gradual depolarization exceeding the initial resting membrane potential. Through overexpression of a Drosophila ORK1 two-pore-domain K⁺ channel (K2P) in larval muscles [...] Read more.

Lipopolysaccharide (LPS) from certain strains of Gram-negative bacteria can induce a rapid (<1 s) hyperpolarization of membrane potential, followed by a gradual depolarization exceeding the initial resting membrane potential. Through overexpression of a Drosophila ORK1 two-pore-domain K⁺ channel (K2P) in larval muscles and altering the external concentrations of K⁺ and Na⁺ ions, it is clear that the hyperpolarization is due to activating K2P channels and the depolarization is due to promoting an inward Na⁺ leak. When the external Na⁺ concentration is negligible, the LPS-delayed depolarization is dampened. The hyperpolarization induced by LPS can exceed −100 mV when external K⁺ and Na⁺ concentrations are lowered. These results indicate direct action by LPS on ion channels independently of immune responses. Such direct actions may need to be considered when developing clinical treatments for certain forms of bacterial septicemia. Full article

(This article belongs to the Section Biological Membranes)

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15 pages, 4356 KiB

Open AccessArticle

Surfactant-Enhanced Cleaning Solutions for Ceramic Membranes: A Comparative Study on Humic Acid and BSA Fouling

by Navneet Kallapalli and Onita D. Basu

Membranes 2025, 15(3), 73; https://doi.org/10.3390/membranes15030073 - 2 Mar 2025

Viewed by 825

Abstract

Control of natural organic matter (NOM) reversible and irreversible fouling with ceramic membranes for drinking water applications with chemically enhanced backwash (CEB) protocols is limited. This research examines the efficiency of various chemical combinations with non-ionic surfactants to control the NOM fouling caused [...] Read more.

Control of natural organic matter (NOM) reversible and irreversible fouling with ceramic membranes for drinking water applications with chemically enhanced backwash (CEB) protocols is limited. This research examines the efficiency of various chemical combinations with non-ionic surfactants to control the NOM fouling caused by humic acid (HA) and protein foulants. Two commercially available non-ionic surfactants, Tween 80 and Triton X100, combined with conventional cleaning solutions, were analyzed with respect to membrane fouling and cleaning using the resistance in series (RIS) model, membrane permeability, carbon mass balance, and contact angle measurements. The results demonstrated that in all cases, CEB outperformed hydraulic backwashing; in addition, the inclusion of surfactants demonstrated enhanced the fouling control with protein foulants more than humic acid. The transmembrane pressure (TMP) with surfactant CEB was controlled to within a range of 83–105 kPa compared to hydraulic backwash at approx. 128 kPa for HA and BSA. The carbon mass balance analysis indicates that Tween 80 surfactant-based CEB demonstrated effective fouling control, leaving only 20% irreversible fouling with HA and 30% with BSA while the hydraulic backwash resulted in 57% irreversible fouling of carbon on the membrane for HA and BSA. Full article

(This article belongs to the Special Issue Ceramic Membranes for Removal of Emerging Pollutants)

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17 pages, 5040 KiB

Open AccessArticle

Experimental and Simulation Study of Proton Exchange Membrane Fuel Cell with 12 µm Thick Membrane over the Temperature Range of 80 °C to 120 °C

by Yunfei Zhang, Zhengrui Xiao, Xiaoyang Zhao, Jian Wang, Yadong Wang and Jun Yu

Membranes 2025, 15(3), 72; https://doi.org/10.3390/membranes15030072 - 1 Mar 2025

Viewed by 690

Abstract

Recent advancements have been made in understanding the mechanisms and perspectives of fuel cells operating at elevated temperatures. However, the changes in electrochemical processes within the membrane electrode assembly remain unclear. This study aims to investigate the performance variation laws of membrane electrode [...] Read more.

Recent advancements have been made in understanding the mechanisms and perspectives of fuel cells operating at elevated temperatures. However, the changes in electrochemical processes within the membrane electrode assembly remain unclear. This study aims to investigate the performance variation laws of membrane electrode assemblies composed of Gore12 during operation at an increasing temperature ranging from 80 to 120 °C, utilizing overpotential decomposition and electrochemical impedance analysis. The experimental results indicate that increasing back pressure can improve the performance of fuel cells, particularly at higher temperatures. The charge transfer resistance initially decreases and then increases with temperature. Furthermore, combined with the simulation results, it is demonstrated that Gore12’s thin membrane structure provides excellent self-humidification, which ensures efficient proton conduction at low relative humidity. These findings offer new insights into improving the performance of PEMFCs and enabling stable operation at high temperatures. Full article

(This article belongs to the Section Membrane Applications for Energy)

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17 pages, 5147 KiB

Open AccessArticle

Bacterial Contamination of Ultrafiltration Installation Applied to Carwash Wastewater Treatment

by Piotr Woźniak and Marek Gryta

Membranes 2025, 15(3), 71; https://doi.org/10.3390/membranes15030071 - 1 Mar 2025

Viewed by 507

Abstract

An ultrafiltration (UF) installation was used to separate the actual wastewater from a car wash. Following these studies, the plant was washed several times; however, severe membrane fouling was observed during the filtration of sterile deionised (DI) water. As a result, the permeate [...] Read more.

An ultrafiltration (UF) installation was used to separate the actual wastewater from a car wash. Following these studies, the plant was washed several times; however, severe membrane fouling was observed during the filtration of sterile deionised (DI) water. As a result, the permeate flux decreased by more than 50% after 5 h of the UF process. The source of the fouling was the release of deposits, particularly bacteria, from the surfaces of plant elements such as pipes and pumps. The paper presents the effectiveness of biofilm removal from the surface of the equipment during a cyclically repeated washing process. Chemical washing was carried out using acid solutions and alkaline cleaning solutions containing NaOH (pH = 11.5–12). After installation cleaning, the filtration tests were carried out using DI water as a feed. It was determined how biofouling, which develops under these conditions, reduces permeate flux. Despite 3 h of installation washing, there was a 50% reduction in flux after 10 h of UF. Repeating the installation wash (4 h) resulted in a similar decrease in flux after 4 days of UF. Stabilisation of the flux at a level of 500 LMH was achieved after an additional 5 h of washing, including application of hot (323–333 K) alkaline cleaning solutions. The number of bacteria in the biofilm collected from the surface of the membranes, the pump inlet and the surface of the polyvinyl chloride (PVC) hoses forming the pipeline was also investigated. Despite repeated chemical cleaning, the number of bacteria on the pump and hose surfaces was 50–100 CFU/cm². Studies were carried out to determine which bacterial species survived the chemical cleaning of the installation. Gram-positive and Gram-negative bacteria were determined, and taxonomic characteristics of the isolated bacteria were identified. Full article

(This article belongs to the Special Issue Membrane Fouling during Water/Wastewater Treatment Processes)

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16 pages, 3689 KiB

Open AccessArticle

Gas and Steam Permeation Properties of Cation-Exchanged ZSM-5 Membrane

by Yuichiro Hirota, Masaki Nakai, Kasumi Tani, Koya Sakane, Ayumi Ikeda, Yasuhisa Hasegawa and Sadao Araki

Membranes 2025, 15(3), 70; https://doi.org/10.3390/membranes15030070 - 1 Mar 2025

Viewed by 499

Abstract

NaZSM-5 powder and membranes were hydrothermally prepared. Their (1) steam (H₂O) adsorption properties and (2) the permeation and separation of gas and H₂O were evaluated before and after the cation exchange of Na⁺ to K⁺ or Cs [...] Read more.

NaZSM-5 powder and membranes were hydrothermally prepared. Their (1) steam (H₂O) adsorption properties and (2) the permeation and separation of gas and H₂O were evaluated before and after the cation exchange of Na⁺ to K⁺ or Cs⁺. The quantity of adsorbed H₂O decreased as the size of the cation increased, indicating that the micropore volume and effective pore size of ZSM-5 decreased after cation exchange. The H₂ and N₂ permeances after cation exchange were less than 5% of the values before cation exchange, indicating a significant reduction in gas permeability. In contrast, the reduction of the H₂O permeance values of the ZSM-5 membranes before and after K⁺ or Cs⁺ exchange was lower than that of H₂, resulting in improved H₂O/H₂ separation performance. Compared with the NaZSM-5 membrane, the K⁺- or Cs⁺-exchanged ZSM-5 membranes exhibited superior H₂O permselectivity, particularly at dilute H₂O concentrations (<1 vol%). Full article

(This article belongs to the Special Issue Preparation, Characterization, and Application of Advanced Separation Membrane Materials)

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25 pages, 3360 KiB

Open AccessArticle

Hybrid Mechanical Vapor Compression and Membrane Distillation System: Concept and Analysis

by Emad Ali, Jamel Orfi and Salim Mokraoui

Membranes 2025, 15(3), 69; https://doi.org/10.3390/membranes15030069 - 28 Feb 2025

Viewed by 459

Abstract

The concept of integrating mechanical vapor compression (MVC) with direct contact membrane distillation (DCMD) is presented and analyzed. The hybrid system utilizes the DCMD to harvest the thermal energy of the MVC reject brine to preheat a portion of the seawater intake and [...] Read more.

The concept of integrating mechanical vapor compression (MVC) with direct contact membrane distillation (DCMD) is presented and analyzed. The hybrid system utilizes the DCMD to harvest the thermal energy of the MVC reject brine to preheat a portion of the seawater intake and simultaneously produce additional fresh water. Based on the operating temperature, the hybrid system requires specific energy consumption between 9.6 to 24.3 kWh/m³, which is equivalent to 25 to 37% less than the standalone MVC. Similarly, the freshwater production of the hybrid system can range between 1.03 and 1.1 kg/h, which is equivalent to a 3% and 10% increase relative to the standalone MVC when operating at brine temperatures of 50 and 90 °C, respectively. However, this enhancement is achieved at the expense of an average of 60% larger total surface area. This is partially due to the incorporation of the surface area of the MD modules and mostly to reduced temperature differences. Altering the permeate-to-feed ratio of the DCMD module led to a marginal change in the overall production without any enhancement in the compression power consumption. Increasing the MD module length by 50% resulted in a 3% enlargement in the overall production rate and a 10% reduction in power consumption. A modified hybrid structure that additionally utilizes the distillate heat is sought. A 5% increase in water production at the expense of a 45% rise in the specific compression energy of the modified structure over the original hybrid system is obtained. Full article

(This article belongs to the Section Membrane Applications for Water Treatment)

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10 pages, 2749 KiB

Open AccessArticle

Titanium Nitride as an Intermetallic Diffusion Barrier for Hydrogen Permeation in Palladium–Vanadium Composite Membranes

by Cameron M. Burst, Chao Li, Douglas Way and Colin A. Wolden

Membranes 2025, 15(3), 68; https://doi.org/10.3390/membranes15030068 - 21 Feb 2025

Viewed by 750

Abstract

Hydrogen purification is a critical industrial process, and there are ongoing efforts to develop low-cost alternatives to palladium foil membranes. Titanium nitride (TiN) is studied as an interdiffusion barrier to enable hydrogen permeation in composite palladium–vanadium membranes. TiN was deposited via reactive sputtering, [...] Read more.

Hydrogen purification is a critical industrial process, and there are ongoing efforts to develop low-cost alternatives to palladium foil membranes. Titanium nitride (TiN) is studied as an interdiffusion barrier to enable hydrogen permeation in composite palladium–vanadium membranes. TiN was deposited via reactive sputtering, and films with the desired (200) orientation were obtained in the metallic regime at 400 °C under a 200 V bias to the substrate. The permeability of thin-film TiN was determined with palladium-based sandwich structures. TiN layers up to 10 nm resulted in a minimal decrease in flux (~20%) relative to a freestanding PdCu foil, which was attributed to the interfacial resistance. At greater thicknesses, the TiN layer was rate-limiting, and it was found that the effective permeability of the sputtered TiN thin films was ~6 × 10⁻¹² mol s⁻¹ m⁻¹ Pa^−0.5. Composite Pd|TiN|V|TiN|Pd membranes exhibited permeability values up to three times greater than pure palladium, exhibiting stability at 450 °C for over 100 h, with the lack of intermetallic diffusion and alloy formation being confirmed with XRD. The membranes were unstable at 500 °C, which was attributed to the instability of the thin Pd layer and loss of catalytic activity. Full article

(This article belongs to the Special Issue A Commemorative Special Issue in Honor of Dr. Moises Carreon)

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19 pages, 2640 KiB

Open AccessArticle

Efficiency of an Ultrafiltration Process for the Depollution of Pretreated Olive Mill Wastewater

by Mohammed Zine, Noureddine Touach, El Mostapha Lotfi and Philippe Moulin

Membranes 2025, 15(3), 67; https://doi.org/10.3390/membranes15030067 - 20 Feb 2025

Viewed by 520

Abstract

The depollution of constructed wetland-pretreated olive mill wastewater (OMW) using a membrane filtration system was experimentally studied. Dead-end filtration (DEF) was employed to evaluate suitable MF/UF membranes and select the appropriate molecular weight cut-off for optimal OMW treatment. Removal efficiencies for COD (chemical [...] Read more.

The depollution of constructed wetland-pretreated olive mill wastewater (OMW) using a membrane filtration system was experimentally studied. Dead-end filtration (DEF) was employed to evaluate suitable MF/UF membranes and select the appropriate molecular weight cut-off for optimal OMW treatment. Removal efficiencies for COD (chemical oxygen demand) and TOC (total organic carbon) using DEF reached maximum values of 88.14% and 11.17%, respectively. Adsorption of raw and pretreated OMW on granular activated carbon was also carried out for a comparative study against DEF and pretreatment. The semi-industrial-scale experiments were conducted using commercial ceramic ultrafiltration (UF) membranes (150 and 50 kDa) in cross-flow filtration (CFF) mode at a permeate flux around 200 L h⁻¹ m⁻² and a trans-membrane pressure (TMP) of 3.5–3.8 bars. This post-treatment had a significant impact on COD removal efficiency from pretreated OMW, reaching 78.5%. The coupled process proposed in this study achieved removal efficiencies of 97%, 97%, and 99.9% of COD, TOC, and turbidity, respectively. Full article

(This article belongs to the Special Issue Membrane Processes for Water Recovery in Food Processing Industries)

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15 pages, 7827 KiB

Open AccessArticle

Changes in the Separation Properties of Aged PVDF Ultrafiltration Membranes During Long-Term Treatment of Car Wash Wastewater

by Wirginia Tomczak, Marek Gryta, Piotr Woźniak and Monika Daniluk

Membranes 2025, 15(3), 66; https://doi.org/10.3390/membranes15030066 - 20 Feb 2025

Viewed by 461

Abstract

Car wash wastewater (CWW) is complex waste that may be effectively treated by the ultrafiltration (UF) process. However, one of the most important challenges in implementing this process on an industrial scale is the fouling phenomenon membrane aging. Indeed, these may lead to [...] Read more.

Car wash wastewater (CWW) is complex waste that may be effectively treated by the ultrafiltration (UF) process. However, one of the most important challenges in implementing this process on an industrial scale is the fouling phenomenon membrane aging. Indeed, these may lead to a reduction in UF performance possibly associated with a loss in integrity of the fouled/aged membrane. Therefore, the main aim of the current study was to provide a comprehensive investigation on the changes in the separation properties of aged FP100 ultrafiltration membranes made of polyvinylidene fluoride (PVDF) with respect to their application for long-term treatment of CWW. For this purpose, studies were conducted for new membranes and membranes previously used for over 5 years in a pilot plant. As a feed, solutions of dextran, solutions of model organism Escherichia coli and synthetic CWW were used. It has been found that PVDF membranes demonstrated poor stability when in frequent contact with chemicals periodically applied for membrane cleaning. Indeed, the aged membranes were characterised by the increased porosity. However, it is important to note that membranes aging had no significant impact on the permeate quality during the UF process of synthetic CWW. Indeed, the obtained permeate was characterised by the turbidity lower than 0.25 NTU. Likewise, with regard to the separation of E. coli, the aged PVDF membranes ensured the high process efficiency and over 99.99% bacterial retention. In the interest of the growing potential of PVDF membrane in CWW treatment, the results obtained in the current work complement the findings made in this field. Full article

(This article belongs to the Section Membrane Applications for Water Treatment)

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