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Membranes, Volume 12, Issue 5 (May 2022) – 105 articles

Cover Story (view full-size image): Methods for extracting NH4+-NH3 and phosphates from natural sources and residual effluents from human and animal life, as well as industrial effluents, are classified. The prospects for the use of membrane processes in the transition to a circular economy are considered in the field of nutrients. Particular attention is paid to processes based on ion-exchange membranes. The successes and bottlenecks of such processes are discussed. Modern ideas about the mechanisms of transport of NH4+-NH3 and phosphates in ion-exchange membranes in the presence and absence of an electric field are presented. Furthermore, innovations for improving the performance of electromembrane processes are examined. View this paper
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16 pages, 3662 KiB  
Article
Ultrafiltration Membranes Functionalized with Copper Oxide and Zwitterions for Fouling Resistance
by Cannon Hackett, Mojtaba Abolhassani, Lauren F. Greenlee and Audie K. Thompson
Membranes 2022, 12(5), 544; https://doi.org/10.3390/membranes12050544 - 23 May 2022
Cited by 5 | Viewed by 2162
Abstract
Polymeric membrane fouling is a long-standing challenge for water filtration. Metal/metal oxide nanoparticle functionalization of the membrane surface can impart anti-fouling properties through the reactivity of the metal species and the generation of radical species. Copper oxide nanoparticles (CuO NPs) are effective at [...] Read more.
Polymeric membrane fouling is a long-standing challenge for water filtration. Metal/metal oxide nanoparticle functionalization of the membrane surface can impart anti-fouling properties through the reactivity of the metal species and the generation of radical species. Copper oxide nanoparticles (CuO NPs) are effective at reducing organic fouling when used in conjunction with hydrogen peroxide, but leaching of copper ions from the membrane has been observed, which can hinder the longevity of the CuO NP activity at the membrane surface. Zwitterions can reduce organic fouling and stabilize NP attachment, suggesting a potential opportunity to combine the two functionalizations. Here, we coated polyethersulfone (PES) ultrafiltration membranes with polydopamine (PDA) and attached the zwitterionic compound, thiolated 2-methacryloyloxyethyl phosphorylcholine (MPC-SH), and CuO NPs. Functionalized membranes resulted in a higher flux recovery ratio (0.694) than the unfunctionalized PES control (0.599). Copper retention was high (>96%) for functionalized membranes. The results indicate that CuO NPs and MPC-SH can reduce organic fouling with only limited copper leaching. Full article
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3 pages, 201 KiB  
Editorial
Water Treatment Process
by Szilárd S. Bucs, Nadia Farhat and Luca Fortunato
Membranes 2022, 12(5), 543; https://doi.org/10.3390/membranes12050543 - 23 May 2022
Cited by 3 | Viewed by 1593
Abstract
Water scarcity is the main factor driving the enhancement of available technologies and the development of new technologies [...] Full article
(This article belongs to the Special Issue Water Treatment Process)
18 pages, 3159 KiB  
Article
Variables and Mechanisms Affecting Electro-Membrane Extraction of Bio-Succinic Acid from Fermentation Broth
by Alina Anamaria Malanca, Enrico Mancini, Mohamed Yusuf, Gabriel Kjær Khensir, Seyed Soheil Mansouri, Ioannis V. Skiadas, Hariklia N. Gavala and Manuel Pinelo
Membranes 2022, 12(5), 542; https://doi.org/10.3390/membranes12050542 - 23 May 2022
Cited by 4 | Viewed by 2247
Abstract
The production of succinic acid from fermentation is a promising approach for obtaining building-block chemicals from renewable sources. However, the limited bio-succinic yield from fermentation and the complexity of purification has been making the bio-succinic acid production not competitive with petroleum-based succinic acid. [...] Read more.
The production of succinic acid from fermentation is a promising approach for obtaining building-block chemicals from renewable sources. However, the limited bio-succinic yield from fermentation and the complexity of purification has been making the bio-succinic acid production not competitive with petroleum-based succinic acid. Membrane electrolysis has been identified to be a promising technology in both production and separation stages of fermentation processes. This work focuses on identifying the key operational parameters affecting the performance of the electrolytic cell for separating succinic acid from fermentation broth through an anionic exchange membrane. Indeed, while efforts are mainly focused on studying the performance of an integrated fermenter-electrolytic cell system, a lack of understanding remains in how to tune the electrolytic cell and which main parameters are involved. The results show that a single electrolytic cell of operating volume 250 mL was able to extract up to 3 g L−1 h−1 of succinic acid. The production of OH ions by water electrolysis can act as a buffer for the fermenter and it could be tuned as a function of the extraction rate. Furthermore, as the complexity of the solution in terms of the quantity and composition of the ions increased, the energy required for the separation process decreased. Full article
(This article belongs to the Special Issue Membrane Synthesis and Progress in Membrane Reactor)
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17 pages, 3762 KiB  
Article
Influence of Degassing Treatment on the Ink Properties and Performance of Proton Exchange Membrane Fuel Cells
by Pengcheng Liu, Daijun Yang, Bing Li, Cunman Zhang and Pingwen Ming
Membranes 2022, 12(5), 541; https://doi.org/10.3390/membranes12050541 - 22 May 2022
Cited by 2 | Viewed by 2918
Abstract
Degradation occurs in catalyst inks because of the catalytic oxidation of the solvent. Identification of the generation process of impurities and their effects on the properties of HSC ink and LSC ink is crucial in mitigating them. In this study, gas chromatography-mass spectrometry [...] Read more.
Degradation occurs in catalyst inks because of the catalytic oxidation of the solvent. Identification of the generation process of impurities and their effects on the properties of HSC ink and LSC ink is crucial in mitigating them. In this study, gas chromatography-mass spectrometry (GC-MS) and cyclic voltammetry (CV) showed that oxidation of NPA and EA was the primary cause of impurities such as acetic acid, aldehyde, propionic acid, propanal, 1,1-dipropoxypropane, and propyl propionate. After the degassing treatment, the degradation of the HSC ink was suppressed, and the concentrations of acetic acid, propionic acid, and propyl propionate plummeted from 0.0898 wt.%, 0.00224 wt.%, and 0.00046 wt.% to 0.0025 wt.%, 0.0126 wt.%, and 0.0003 wt.%, respectively. The smaller particle size and higher zeta potential in the degassed HSC ink indicated the higher utilization of Pt, thus leading to optimized mass transfer in the catalyst layer (CL) during working conditions. The electrochemical performance test result shows that the MEA fabricated from the degassed HSC ink had a peak power density of 0.84 W cm−2, which was 0.21 W cm−2 higher than that fabricated from the normal HSC ink. However, the introduction of propionic acid in the LSC ink caused the Marangoni flux to inhibit the coffee ring effect and promote the uniform deposition of the catalyst. The RDE tests indicated that the electrode deposited from the LSC ink with propionic acid possessed a mass activity of 84.4 mA∙mgPt−1, which was higher than the 60.5 mA∙mgPt−1 of the electrode deposited from the normal LSC ink. Full article
(This article belongs to the Topic Electromaterials for Environment & Energy)
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14 pages, 2692 KiB  
Communication
Development and Industrial-Scale Fabrication of Next-Generation Low-Energy Membranes for Desalination
by Li May Goh, Zhiwei Thong, Weikun Paul Li, Shu Ting Ooi, Farhanah Esa, Kok Seng Ng, Adil Dhalla and Chakravarthy Gudipati
Membranes 2022, 12(5), 540; https://doi.org/10.3390/membranes12050540 - 22 May 2022
Cited by 4 | Viewed by 2198
Abstract
Spiral-wound modules have been the most common configuration of packing flat-sheet membranes since the early development of polyamide (PA) membranes for water treatment applications. Conventional spiral-wound modules (SWMs) for desalination applications typically consist of several leaf sets, with each leaf set comprising feed [...] Read more.
Spiral-wound modules have been the most common configuration of packing flat-sheet membranes since the early development of polyamide (PA) membranes for water treatment applications. Conventional spiral-wound modules (SWMs) for desalination applications typically consist of several leaf sets, with each leaf set comprising feed spacers, membranes, and a permeate carrier (PC) wrapped around a permeate-collecting tube. The membrane area that can be packed into a given module diameter is limited by the overall leaf set thickness, restricting module productivity for a given membrane permeability. We describe here a novel industrial-scale method for successfully coating the polysulfone (PSf) ultrafiltration (UF) support layer directly onto a permeate carrier, instead of conventional non-woven fabric, as a precursor to the polyamide TFC coating, resulting in twofold benefits: (a) drastically simplifying the membrane fabrication process by eliminating the use of non-woven fabric and (b) increasing the throughput of each membrane module by facilitating the packing of a larger membrane area in a standard module housing. By combining the permeate carrier and membrane into a single sheet, the need for the non-woven support layer was eliminated, leading to a significantly reduced leaf set thickness, enabling a much larger membrane area to be packed in a given volume, leading to lower energy consumption per cubic meter of produced water. Molecular-weight cutoff (MWCO) values in the range of 36–96 kDa were found to be dependent on PC thickness and material. Nevertheless, the reinforced membranes were successfully fabricated with a ~9% reduction in membrane leaf thickness compared to a conventional membrane. Preliminary trials of coating a thin-film composite PA layer resulted in defect-free reverse osmosis (RO) membranes with a salt rejection of 94% and a flux of 40 L m−2 h−1 when tested against a 2000 mg/L NaCl feed solution at an operating pressure of 15 bar. Results from the testing of the 1812 and 2514 elements validated the novel concept and paved the way for further improvements towards full-scale RO membranes with the potential to be the next low-energy workhorse of the water industry. Full article
(This article belongs to the Special Issue Polymeric Membranes as Promising Pathways to Low-Carbon Future)
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69 pages, 14301 KiB  
Review
State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond
by Hui Shen Lau, Siew Kei Lau, Leong Sing Soh, Seang Uyin Hong, Xie Yuen Gok, Shouliang Yi and Wai Fen Yong
Membranes 2022, 12(5), 539; https://doi.org/10.3390/membranes12050539 - 22 May 2022
Cited by 24 | Viewed by 8808
Abstract
The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air [...] Read more.
The aggravation of environmental problems such as water scarcity and air pollution has called upon the need for a sustainable solution globally. Membrane technology, owing to its simplicity, sustainability, and cost-effectiveness, has emerged as one of the favorable technologies for water and air purification. Among all of the membrane configurations, hollow fiber membranes hold promise due to their outstanding packing density and ease of module assembly. Herein, this review systematically outlines the fundamentals of hollow fiber membranes, which comprise the structural analyses and phase inversion mechanism. Furthermore, illustrations of the latest advances in the fabrication of organic, inorganic, and composite hollow fiber membranes are presented. Key findings on the utilization of hollow fiber membranes in microfiltration (MF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), pervaporation, gas and vapor separation, membrane distillation, and membrane contactor are also reported. Moreover, the applications in nuclear waste treatment and biomedical fields such as hemodialysis and drug delivery are emphasized. Subsequently, the emerging R&D areas, precisely on green fabrication and modification techniques as well as sustainable materials for hollow fiber membranes, are highlighted. Last but not least, this review offers invigorating perspectives on the future directions for the design of next-generation hollow fiber membranes for various applications. As such, the comprehensive and critical insights gained in this review are anticipated to provide a new research doorway to stimulate the future development and optimization of hollow fiber membranes. Full article
(This article belongs to the Section Membrane Chemistry)
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14 pages, 3640 KiB  
Article
Understanding Aging Mechanisms in the Context of UV Irradiation of a Low Fouling and Self-Cleaning PVDF-PVP-TiO2 Hollow-Fiber Membrane
by Emma Roubaud, William Maréchal, Olivier Lorain, Lina Lamaa, Laure Peruchon, Cédric Brochier, Julie Mendret, Jean-Pierre Mericq, Stephan Brosillon, Catherine Faur and Christel Causserand
Membranes 2022, 12(5), 538; https://doi.org/10.3390/membranes12050538 - 21 May 2022
Cited by 3 | Viewed by 1875
Abstract
In the context of designing a photocatalytic self-cleaning/low-fouling membrane, the stability of PVDF-PVP-TiO2 hollow-fiber membranes under UV irradiation has been studied. The effect of irradiation power, aqueous environment composition and fouling state on the properties of the membranes has been investigated. With [...] Read more.
In the context of designing a photocatalytic self-cleaning/low-fouling membrane, the stability of PVDF-PVP-TiO2 hollow-fiber membranes under UV irradiation has been studied. The effect of irradiation power, aqueous environment composition and fouling state on the properties of the membranes has been investigated. With this aim, SEM observations, chemical analysis and tensile strength measurements have been conducted. The results indicate that pristine membranes that undergo UV irradiation in ultra-pure water are significantly degraded due to attacks of OH° radicals. However, when methylene blue, used as a model pollutant, is introduced in the aqueous environment, OH° radicals preferentially react with this molecule rather than the membranes, successfully preserving the original properties of the latter. The presence of an adsorbed BSA layer (pre-fouling by immersion) on the surface of the membrane delays membrane aging, as the BSA layer is degraded by radicals instead of the membrane material. The degradation of the BSA layer also validates the self-cleaning properties of the membrane. However, when membranes are pre-fouled by filtration of a 2 g/L BSA solution, delay to aging is less. This is because OH° radicals do not reach BSA molecules that are trapped inside the membrane pores, and therefore react with the membrane material. Full article
(This article belongs to the Special Issue Advance in Photocatalytic Membrane Reactor)
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12 pages, 3001 KiB  
Article
Sustainable Wax Coatings Made from Pine Needle Extraction Waste for Nanopaper Hydrophobization
by Sergejs Beluns, Oskars Platnieks, Jekaterina Sevcenko, Mara Jure, Gerda Gaidukova, Liga Grase and Sergejs Gaidukovs
Membranes 2022, 12(5), 537; https://doi.org/10.3390/membranes12050537 - 20 May 2022
Cited by 4 | Viewed by 2799
Abstract
We combine renewable and waste materials to produce hydrophobic membranes in the present work. Cellulose nanopaper prepared from paper waste was used as a structural component for the membrane. The pine wax was reclaimed from pine needle extraction waste and can be regarded [...] Read more.
We combine renewable and waste materials to produce hydrophobic membranes in the present work. Cellulose nanopaper prepared from paper waste was used as a structural component for the membrane. The pine wax was reclaimed from pine needle extraction waste and can be regarded as a byproduct. The dip-coating and spray-coating methods were comprehensively compared. In addition, the solubility of wax in different solvents is reported, and the concentration impact on coating quality is presented as the change in the contact angle value. The sensile drop method was used for wetting measurements. Spray-coating yielded the highest contact angle with an average of 114°, while dip-coating reached an average value of 107°. Scanning electron microscopy (SEM) was used for an in-depth comparison of surface morphology. It was observed that coating methods yield significantly different microstructures on the surface of cellulose fibers. The wax is characterized by nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry (DSC). Pine wax has a melting temperature of around 80 °C and excellent thermal stability in oxygen, with a degradation peak above 290 °C. Fourier transform infrared spectroscopy (FTIR) was used to identify characteristic groups of components and show the changes on coated nanopaper. Overall, the results of this work yield important insight into wax-coated cellulose nanopapers and a comparison of spray- and dip-coating methods. The prepared materials have a potential application as membranes and packaging materials. Full article
(This article belongs to the Collection Feature Papers in Membrane Engineering and Applications)
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22 pages, 9326 KiB  
Article
Silver/Snail Mucous PVA Nanofibers: Electrospun Synthesis and Antibacterial and Wound Healing Activities
by Aalaa A. El-Attar, Hamdy B. El-Wakil, Ahmed H. Hassanin, Basant A. Bakr, Tahani M. Almutairi, Mohamed Hagar, Bassma H. Elwakil and Zakia A. Olama
Membranes 2022, 12(5), 536; https://doi.org/10.3390/membranes12050536 - 20 May 2022
Cited by 17 | Viewed by 3248
Abstract
Healthcare textiles are gaining great attention in the textile industry. Electrospun nanofibers are considered the golden soldiers due to their strength, flexibility, and eco-friendly properties. The present study aimed to evaluate the potency of polyvinyl alcohol (PVA) nanofibers loaded with newly biosynthesized silver [...] Read more.
Healthcare textiles are gaining great attention in the textile industry. Electrospun nanofibers are considered the golden soldiers due to their strength, flexibility, and eco-friendly properties. The present study aimed to evaluate the potency of polyvinyl alcohol (PVA) nanofibers loaded with newly biosynthesized silver nanoparticles (Ag-NPs) as a wound healing dressing. Chocolate-band snail (Eobania vermiculata) mucus (which is part of the Mollusca defense system) was used as a novel reducing and stabilizing agent. Data indicated the effectiveness of Eobania vermiculata’s mucus in silver nanoparticle synthesis after a 24 h incubation time. The biosynthesized AgNPs-SM showed a 13.15 nm particle size, −22.5 mV ζ potential, and 0.37 PDI, which proved the stability of the synthesized nanoparticles. Eobania vermiculata mucus and AgNPs-SM showed potent antibacterial activity, especially against Pseudomonas aeruginosa. The electrospinning technique was applied in the fabrication of PVA/AgNPs-SM nanofibers, which were homogenous with a fine diameter of about 100–170 nm and showed a significantly high antimicrobial activity. In vitro and in vivo studies revealed that PVA/AgNPs-SM nanofibers were safe and efficiently enhanced the wound healing process (typical histological picture of the proliferative phase with compact and well aligned collagen fibers in the dermal tissue after 12 days) together with bacterial growth inhibition in the infected skin area. Full article
(This article belongs to the Special Issue Electrospun Nanofiber Membranes: From Synthesis to Applications)
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15 pages, 1192 KiB  
Article
Application of Clove Oil and Sonication Process on the Influence of the Functional Properties of Mung Bean Flour-Based Edible Film
by Ittiporn Keawpeng, Somwang Lekjing, Balaji Paulraj and Karthikeyan Venkatachalam
Membranes 2022, 12(5), 535; https://doi.org/10.3390/membranes12050535 - 20 May 2022
Cited by 6 | Viewed by 2329
Abstract
The present study was aimed to investigate the effects of sonication and clove oil incorporation on the improvement of physical, antioxidant, and antimicrobial properties and lipid oxidation inhibiting abilities of mung bean flour (MF)-based films. There were three groups of films tested (1) [...] Read more.
The present study was aimed to investigate the effects of sonication and clove oil incorporation on the improvement of physical, antioxidant, and antimicrobial properties and lipid oxidation inhibiting abilities of mung bean flour (MF)-based films. There were three groups of films tested (1) MF: mung bean flour alone, (2) MFC: MF incorporated with 2% clove oil (C), and (3) MFCU: MFC prepared with sonication (25 kHz, 100% amplitude, 10 min). Film thickness and bulk density showed slight differences, and moisture content, solubility, and water vapor permeability significantly differed between the formulations. Tensile strength, elongation at break, and Young’s modulus were highest for the MFCU films, followed by MFC and MF in rank order. Furthermore, the Fourier-transform infrared spectroscopy results also demonstrated that the clove oil and sonication treatment had improved the interconnections of the biopolymers, thus increasing the physical strength of the film. Phytochemicals in terms of total phenolics and total flavonoids were elevated in the MFCU films and contributed to stronger radical scavenging abilities (p < 0.05). MFC and MFCU films showed a strong antibacterial control of the Gram-positive Staphylococcus aureus (S. aureus) and also of the Gram-negative Campylobacter jejuni (C. jejuni). Overall, the lipid oxidation indicators Thiobarbituric acid reactive substances (TBARS, peroxide value, p-anisidine value, and totox value) showed significantly high inhibition, attributed to radical scavenging activities in the MFCU and MFC samples. The mung bean flour films incorporated with clove oil and prepared with sonication have good potential as packaging materials for food due to strong physical, antimicrobial, and antioxidant properties, as well as lipid oxidation inhibiting abilities. Full article
(This article belongs to the Special Issue Advances on Bio-Based Materials for Food Packaging Applications)
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13 pages, 1091 KiB  
Article
Infrared Spectroscopic Study of Multi-Component Lipid Systems: A Closer Approximation to Biological Membrane Fluidity
by Maria C. Klaiss-Luna and Marcela Manrique-Moreno
Membranes 2022, 12(5), 534; https://doi.org/10.3390/membranes12050534 - 20 May 2022
Cited by 6 | Viewed by 2812
Abstract
Membranes are essential to cellular organisms, and play several roles in cellular protection as well as in the control and transport of nutrients. One of the most critical membrane properties is fluidity, which has been extensively studied, using mainly single component systems. In [...] Read more.
Membranes are essential to cellular organisms, and play several roles in cellular protection as well as in the control and transport of nutrients. One of the most critical membrane properties is fluidity, which has been extensively studied, using mainly single component systems. In this study, we used Fourier transform infrared spectroscopy to evaluate the thermal behavior of multi-component supported lipid bilayers that mimic the membrane composition of tumoral and non-tumoral cell membranes, as well as microorganisms such as Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus. The results showed that, for tumoral and non-tumoral membrane models, the presence of cholesterol induced a loss of cooperativity of the transition. However, in the absence of cholesterol, the transitions of the multi-component lipid systems had sigmoidal curves where the gel and fluid phases are evident and where main transition temperatures were possible to determine. Additionally, the possibility of designing multi-component lipid systems showed the potential to obtain several microorganism models, including changes in the cardiolipin content associated with the resistance mechanism in Staphylococcus aureus. Finally, the potential use of multi-component lipid systems in the determination of the conformational change of the antimicrobial peptide LL-37 was studied. The results showed that LL-37 underwent a conformational change when interacting with Staphylococcus aureus models, instead of with the erythrocyte membrane model. The results showed the versatile applications of multi-component lipid systems studied by Fourier transform infrared spectroscopy. Full article
(This article belongs to the Special Issue Model Lipid Membrane)
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15 pages, 5176 KiB  
Article
Array of Graphene Variable Capacitors on 100 mm Silicon Wafers for Vibration-Based Applications
by Millicent N. Gikunda, Ferdinand Harerimana, James M. Mangum, Sumaya Rahman, Joshua P. Thompson, Charles Thomas Harris, Hugh O. H. Churchill and Paul M. Thibado
Membranes 2022, 12(5), 533; https://doi.org/10.3390/membranes12050533 - 19 May 2022
Cited by 5 | Viewed by 2599
Abstract
Highly flexible, electrically conductive freestanding graphene membranes hold great promise for vibration-based applications. This study focuses on their integration into mainstream semiconductor manufacturing methods. We designed a two-mask lithography process that creates an array of freestanding graphene-based variable capacitors on 100 mm silicon [...] Read more.
Highly flexible, electrically conductive freestanding graphene membranes hold great promise for vibration-based applications. This study focuses on their integration into mainstream semiconductor manufacturing methods. We designed a two-mask lithography process that creates an array of freestanding graphene-based variable capacitors on 100 mm silicon wafers. The first mask forms long trenches terminated by square wells featuring cone-shaped tips at their centers. The second mask fabricates metal traces from each tip to its contact pad along the trench and a second contact pad opposite the square well. A graphene membrane is then suspended over the square well to form a variable capacitor. The same capacitor structures were also built on 5 mm by 5 mm bare dies containing an integrated circuit underneath. We used atomic force microscopy, optical microscopy, and capacitance measurements in time to characterize the samples. Full article
(This article belongs to the Special Issue Latest Development of Carbon Membranes)
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12 pages, 666 KiB  
Review
Role of Lipoproteins in the Pathophysiology of Breast Cancer
by Santhi Latha Pandrangi, Prasanthi Chittineedi, Rajasekhar Chikati, Juan Alejandro Neira Mosquera, Sungey Naynee Sánchez Llaguno, Gooty Jaffer Mohiddin, Suseela Lanka, Sphoorthi Shree Chalumuri and Narendra Maddu
Membranes 2022, 12(5), 532; https://doi.org/10.3390/membranes12050532 - 19 May 2022
Cited by 11 | Viewed by 3195
Abstract
Breast cancer is one of the most common malignancies in women and the leading cause of cancer mortality. Hypercholesterolemia and obesity are potential risk factors for the incidence of breast cancer, and their detection can enhance cancer prevention. In this paper, we discuss [...] Read more.
Breast cancer is one of the most common malignancies in women and the leading cause of cancer mortality. Hypercholesterolemia and obesity are potential risk factors for the incidence of breast cancer, and their detection can enhance cancer prevention. In this paper, we discuss the current state of investigations on the importance of lipoproteins, such as low denisity lipoproteins (LDL) and high density lipoproteins (HDL), and cholesterol transporters in the progression of breast cancer, and the therapeutic strategies to reduce breast cancer mortality. Although some research has been unsuccessful at uncovering links between the roles of lipoproteins and breast cancer risk, major scientific trials have found a straight link between LDL levels and incidence of breast cancer, and an inverse link was found between HDL and breast cancer development. Cholesterol and its transporters were shown to have significant importance in the development of breast cancer in studies on breast cancer cell lines and experimental mice models. Instead of cholesterol, 27-hydroxycholesterol, which is a cholesterol metabolite, is thought to promote propagation and metastasis of estrogen receptor-positive breast cancer cell lines. Alteration of lipoproteins via oxidation and HDL glycation are thought to activate many pathways associated with inflammation, thereby promoting cellular proliferation and migration, leading to metastasis while suppressing apoptosis. Medications that lower cholesterol levels and apolipoprotein A-I mimics have appeared to be possible therapeutic agents for preventing excessive cholesterol’s role in promoting the development of breast cancer. Full article
(This article belongs to the Special Issue The Role of Lipoproteins and Cell Membrane Lipids in Disease)
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18 pages, 3984 KiB  
Article
Surface Optimization of Commercial Porous Ti Substrates by EPD of Titanium Nitride
by Cecilia Mortalò, Maria Cannio, Valentina Zin, Enrico Miorin, Francesco Montagner, Luca Pasquali, Monica Montecchi, Dino Norberto Boccaccini, Monica Fabrizio and Silvia Maria Deambrosis
Membranes 2022, 12(5), 531; https://doi.org/10.3390/membranes12050531 - 19 May 2022
Cited by 1 | Viewed by 2242
Abstract
In this work, the infiltration of TiN powders by electrophoretic deposition (EPD) in aqueous media was considered as alternative method to reduce the size craters and the roughness of commercial porous Ti substrates. Ti substrates can be used as suitable supports for the [...] Read more.
In this work, the infiltration of TiN powders by electrophoretic deposition (EPD) in aqueous media was considered as alternative method to reduce the size craters and the roughness of commercial porous Ti substrates. Ti substrates can be used as suitable supports for the deposition of dense hydrogen separation TiNx-based membranes by physical vapor deposition (PVD) techniques. The influence of various EPD deposition parameters on surface morphology and roughness of TiN-infiltrated substrates were investigated in order to optimize their surface properties. The results suggest that a multi-step EPD procedure is an effective technique for reducing substrate surface defects of commercial porous Ti substrates which could then be successfully used as proper supports for the deposition of dense and defect-free TiNx layers, also aligning the thermal mismatch between the active layer and the porous substrate. Full article
(This article belongs to the Topic Inorganic Thin Film Materials)
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22 pages, 7581 KiB  
Article
Versatile and Resistant Electroless Pore-Plated Pd-Membranes for H2-Separation: Morphology and Performance of Internal Layers in PSS Tubes
by David Martinez-Diaz, Valeria Michienzi, José Antonio Calles, Raúl Sanz, Alessio Caravella and David Alique
Membranes 2022, 12(5), 530; https://doi.org/10.3390/membranes12050530 - 18 May 2022
Cited by 4 | Viewed by 1782
Abstract
Pd-membranes are interesting in multiple ultra-pure hydrogen production processes, although they can suffer inhibition by certain species or abrasion under fluidization conditions in membrane reactors, thus requiring additional protective layers to ensure long and stable operation. The ability to incorporate intermediate and palladium [...] Read more.
Pd-membranes are interesting in multiple ultra-pure hydrogen production processes, although they can suffer inhibition by certain species or abrasion under fluidization conditions in membrane reactors, thus requiring additional protective layers to ensure long and stable operation. The ability to incorporate intermediate and palladium films with enough adherence on both external and internal surfaces of tubular porous supports becomes crucial to minimize their complexity and cost. This study addresses the incorporation of CeO2 and Pd films onto the internal side of PSS tubes for applications in which further protection could be required. The membranes so prepared, with a Pd-thickness around 12–15 μm, show an excellent mechanical resistance and similar performance to those prepared on the external surface. A good fit to Sieverts’ law with an H2-permeance of 4.571 × 10−3 mol m−2 s−1 Pa−0.5 at 400 °C, activation energy around 15.031 kJ mol−1, and complete ideal perm-selectivity was observed. The permeate fluxes reached in H2 mixtures with N2, He, or CO2 decreased with dilution and temperature due to the inherent concentration-polarization. The presence of CO in mixtures provoked a higher decrease because of a further inhibition effect. However, the original flux was completely recovered after feeding again with pure hydrogen, maintaining stable operation for at least 1000 h. Full article
(This article belongs to the Special Issue Elucidating Mass Transfer Processes in Membranes for Gas Separation)
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14 pages, 5570 KiB  
Article
Electrospun, Resorbable, Drug-Eluting, Nanofibrous Membranes Promote Healing of Allograft Tendons
by Chun-Jui Weng, Yu-Chen Wu, Ming-Yi Hsu, Fu-Pang Chang and Shih-Jung Liu
Membranes 2022, 12(5), 529; https://doi.org/10.3390/membranes12050529 - 18 May 2022
Cited by 4 | Viewed by 1779
Abstract
In spite of advances in medical technology, the repair of Achilles tendon ruptures remains challenging. Reconstruction with an autograft tendon provides the advantage of a higher healing rate; nevertheless, the development of donor-site morbidity cannot be ignored. We developed biodegradable, drug-eluting, nanofibrous membranes [...] Read more.
In spite of advances in medical technology, the repair of Achilles tendon ruptures remains challenging. Reconstruction with an autograft tendon provides the advantage of a higher healing rate; nevertheless, the development of donor-site morbidity cannot be ignored. We developed biodegradable, drug-eluting, nanofibrous membranes employing an electrospinning technique and evaluated their effectiveness on the healing of allograft tendons. Poly-D-L-lactide-glycolide was used as the polymeric material for the nanofibers, while doxycycline was selected as the drug for delivery. The in vitro and in vivo drug-release profiles were investigated. The biomechanical properties of allografted Achilles tendons repaired using the nanofibrous membranes were tested in euthanized rabbits at 2-, 4-, and 6-week time intervals. Histological examination was performed for the evaluation of tissue reaction and tendon healing. The level of postoperative animal activity was also monitored using an animal behavior cage. The experimental results showed that the degradable nanofibers used as a vehicle could provide sustained release of doxycycline for 42 days after surgery with very low systemic drug concentration. Allograft Achilles tendon reconstruction assisted by drug-loaded nanofibers was associated with better biomechanical properties at 6 weeks post-surgery. In addition, the animals exhibited a better level of activity after surgery. The use of drug-eluting, nanofibrous membranes could enhance healing in Achilles tendon allograft reconstruction surgery. Full article
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16 pages, 2722 KiB  
Article
Separation of Drugs by Commercial Nanofiltration Membranes and Their Modelling
by Vignesh Nayak, Jiří Cuhorka and Petr Mikulášek
Membranes 2022, 12(5), 528; https://doi.org/10.3390/membranes12050528 - 17 May 2022
Cited by 17 | Viewed by 2971
Abstract
Pharmaceutical drugs have recently emerged as one the foremost water pollutants in the environment, triggering a severe threat to living species. With their complex chemical nature and the intricacy involved in the removal process in mind, the present work investigates the performance of [...] Read more.
Pharmaceutical drugs have recently emerged as one the foremost water pollutants in the environment, triggering a severe threat to living species. With their complex chemical nature and the intricacy involved in the removal process in mind, the present work investigates the performance of commercially available polyamide thin-film composite tubular nanofiltration (NF) membranes (AFC 40 and AFC 80) in removing polluting pharmaceutical drugs, namely caffeine, paracetamol and naproxen. The structural parameters of the NF membranes were estimated by water permeability measurements and retention measurements with aqueous solutions of organic, uncharged (glycerol) solutes. The effect of various operating conditions on the retention of solutes by the AFC 40 and AFC 80 membranes, such as applied transmembrane pressure, tangential feed flow velocity, feed solution concentration and ionic strength, were evaluated. It was found that the rejection of drugs was directly proportional to transmembrane pressure and feed flow rate. Due to the size difference between caffeine (MW = 194.9 g/mol), naproxen (MW = 230.2 g/mol) and paracetamol (MW = 151.16 g/mol), the AFC 40 membrane proved to be efficient for caffeine and naproxen, with rejection efficiencies of 88% and 99%, respectively. In contrast, the AFC 80 membrane proved to be better for paracetamol, with a rejection efficiency of 96% (and rejection efficiency of 100% for caffeine and naproxen). It was also observed that the rejection efficiency of the AFC 80 membrane did not change with changes in external operating conditions compared to the AFC 40 membrane. The membrane performance was predicted using the Spiegler–Kedem model based on irreversible thermodynamics, which was successfully used to explain the transport mechanism of solutes through the AFC 40 and AFC 80 membranes in the NF process. Full article
(This article belongs to the Special Issue Selected Papers from Euromembrane 2021)
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17 pages, 6672 KiB  
Article
Microstructure and Hydrothermal Stability of Microporous Niobia-Silica Membranes: Effect of Niobium Doping Contents
by Jiachen Xia, Jing Yang, Hao Zhang, Yingming Guo and Ruifeng Zhang
Membranes 2022, 12(5), 527; https://doi.org/10.3390/membranes12050527 - 17 May 2022
Viewed by 1537
Abstract
Methyl-modified niobium-doped silica (Nb/SiO2) materials with various Nb/Si molar ratios (nNb) were fabricated using tetraethoxysilane and methyltriethoxysilane as the silica source and niobium pentachloride as the niobium source by the sol–gel method, and the Nb/SiO2 membranes were prepared [...] Read more.
Methyl-modified niobium-doped silica (Nb/SiO2) materials with various Nb/Si molar ratios (nNb) were fabricated using tetraethoxysilane and methyltriethoxysilane as the silica source and niobium pentachloride as the niobium source by the sol–gel method, and the Nb/SiO2 membranes were prepared thereof by the dip-coating process under an N2 calcining atmosphere. Their microstructures were characterized and gas permeances tested. The results showed that the niobium element existed in the formation of the Nb-O groups in the Nb/SiO2 materials. When the niobium doping content and the calcining temperature were large enough, the Nb2O5 crystals could be formed in the SiO2 frameworks. With the increase of nNb and calcination temperature, the formed particle sizes increased. The doping of Nb could enhance the H2/CO2 and H2/N2 permselectivities of SiO2 membranes. When nNb was equal to 0.08, the Nb/SiO2 membrane achieved a maximal H2 permeance of 4.83 × 10−6 mol·m−2·Pa−1·s−1 and H2/CO2 permselectivity of 15.49 at 200 °C and 0.1 MPa, which also exhibited great hydrothermal stability and thermal reproducibility. Full article
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30 pages, 7266 KiB  
Article
Molecular Characterization of Membrane Gas Separation under Very High Temperatures and Pressure: Single- and Mixed-Gas CO2/CH4 and CO2/N2 Permselectivities in Hybrid Networks
by Sylvie Neyertz, David Brown, Saman Salimi, Farzaneh Radmanesh and Nieck E. Benes
Membranes 2022, 12(5), 526; https://doi.org/10.3390/membranes12050526 - 17 May 2022
Cited by 4 | Viewed by 2976
Abstract
This work illustrates the potential of using atomistic molecular dynamics (MD) and grand-canonical Monte Carlo (GCMC) simulations prior to experiments in order to pre-screen candidate membrane structures for gas separation, under harsh conditions of temperature and pressure. It compares at 300 °C and [...] Read more.
This work illustrates the potential of using atomistic molecular dynamics (MD) and grand-canonical Monte Carlo (GCMC) simulations prior to experiments in order to pre-screen candidate membrane structures for gas separation, under harsh conditions of temperature and pressure. It compares at 300 °C and 400 °C the CO2/CH4 and CO2/N2 sieving properties of a series of hybrid networks based on inorganic silsesquioxanes hyper-cross-linked with small organic PMDA or 6FDA imides. The inorganic precursors are the octa(aminopropyl)silsesquioxane (POSS), which degrades above 300 °C, and the octa(aminophenyl)silsesquioxane (OAPS), which has three possible meta, para or ortho isomers and is expected to resist well above 400 °C. As such, the polyPOSS-imide networks were tested at 300 °C only, while the polyOAPS-imide networks were tested at both 300 °C and 400 °C. The feed gas pressure was set to 60 bar in all the simulations. The morphologies and densities of the pure model networks at 300 °C and 400 °C are strongly dependent on their precursors, with the amount of significant free volume ranging from ~2% to ~20%. Since measurements at high temperatures and pressures are difficult to carry out in a laboratory, six isomer-specific polyOAPS-imides and two polyPOSS-imides were simulated in order to assess their N2, CH4 and CO2 permselectivities under such harsh conditions. The models were first analyzed under single-gas conditions, but to be closer to the real processes, the networks that maintained CO2/CH4 and CO2/N2 ideal permselectivities above 2 were also tested with binary-gas 90%/10% CH4/CO2 and N2/CO2 feeds. At very high temperatures, the single-gas solubility coefficients vary in the same order as their critical temperatures, but the differences between the penetrants are attenuated and the plasticizing effect of CO2 is strongly reduced. The single-gas diffusion coefficients correlate well with the amount of available free volume in the matrices. Some OAPS-based networks exhibit a nanoporous behavior, while the others are less permeable and show higher ideal permselectivities. Four of the networks were further tested under mixed-gas conditions. The solubility coefficient improved for CO2, while the diffusion selectivity remained similar for the CO2/CH4 pair and disappeared for the CO2/N2 pair. The real separation factor is, thus, mostly governed by the solubility. Two polyOAPS-imide networks, i.e., the polyorthoOAPS-PMDA and the polymetaOAPS-6FDA, seem to be able to maintain their CO2/CH4 and CO2/N2 sieving abilities above 2 at 400 °C. These are outstanding performances for polymer-based membranes, and consequently, it is important to be able to produce isomer-specific polyOAPS-imides for use as gas separation membranes under harsh conditions. Full article
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11 pages, 4518 KiB  
Article
Optimization of Giant Unilamellar Vesicle Electroformation for Phosphatidylcholine/Sphingomyelin/Cholesterol Ternary Mixtures
by Zvonimir Boban, Ivan Mardešić, Witold Karol Subczynski, Dražan Jozić and Marija Raguz
Membranes 2022, 12(5), 525; https://doi.org/10.3390/membranes12050525 - 16 May 2022
Cited by 6 | Viewed by 2310
Abstract
Artificial vesicles are important tools in membrane research because they enable studying membrane properties in controlled conditions. Giant unilamellar vesicles (GUVs) are specially interesting due to their similarity in size to eukaryotic cells. We focus on optimization of GUV production from phosphatidylcholine/sphingomyelin/cholesterol mixtures [...] Read more.
Artificial vesicles are important tools in membrane research because they enable studying membrane properties in controlled conditions. Giant unilamellar vesicles (GUVs) are specially interesting due to their similarity in size to eukaryotic cells. We focus on optimization of GUV production from phosphatidylcholine/sphingomyelin/cholesterol mixtures using the electroformation method. This mixture has been extensively researched lately due to its relevance for the formation of lipid rafts. We measured the effect of voltage, frequency, lipid film thickness, and cholesterol (Chol) concentration on electroformation successfulness using spin-coating for reproducible lipid film deposition. Special attention is given to the effect of Chol concentrations above the phospholipid bilayer saturation threshold. Such high concentrations are of interest to groups studying the role of Chol in the fiber cell plasma membranes of the eye lens or development of atherosclerosis. Utilizing atomic force and fluorescence microscopy, we found the optimal lipid film thickness to be around 30 nm, and the best frequency–voltage combinations in the range of 2–6 V and 10–100 Hz. Increasing the Chol content, we observed a decrease in GUV yield and size. However, the effect was much less pronounced when the optimal lipid film thickness was used. The results underline the need for simultaneous optimization of both electrical parameters and thickness in order to produce high-quality GUVs for experimental research. Full article
(This article belongs to the Special Issue Artificial Models of Biological Membranes)
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10 pages, 2126 KiB  
Article
Comparative Evaluation of the Performance of Sterile Filters for Bioburden Protection and Final Fill in Biopharmaceutical Processes
by Jimin Na, Dongwoo Suh, Young Hoon Cho and Youngbin Baek
Membranes 2022, 12(5), 524; https://doi.org/10.3390/membranes12050524 - 16 May 2022
Cited by 3 | Viewed by 2914
Abstract
Sterile filtration processes are widely used in the production of biotherapeutics for microorganism removal and product sterility. Sterile filtration processes can be applied to buffer preparation and cell culture media preparation in biotherapeutics processes, and to final sterilization or final filling in downstream [...] Read more.
Sterile filtration processes are widely used in the production of biotherapeutics for microorganism removal and product sterility. Sterile filtration processes can be applied to buffer preparation and cell culture media preparation in biotherapeutics processes, and to final sterilization or final filling in downstream processes. Owing to their broad range of applications in bioprocessing, various 0.2/0.22 μm sterile filters with different polymer materials (i.e., hydrophilic PVDF and PES) and nominal pore sizes are commercially available. The objective of this study was to evaluate two different commercial sterile filters in terms of filtration performance in various sterile filtration processes of biopharmaceutical production. The results demonstrate the importance of choosing the appropriate filter considering the process type and target removal/transport product to ensure efficient sterile filtration in the production of biotherapeutics. Full article
(This article belongs to the Special Issue Bioprocessing with Membranes: Filtration and Chromatography)
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15 pages, 3802 KiB  
Article
Fabrication of Polyacrylonitrile UF Membranes by VIPS Method with Acetone as Co-Solvent
by Alexey Yushkin, Alexey Balynin, Mikhail Efimov, Konstantin Pochivalov, Inna Petrova and Alexey Volkov
Membranes 2022, 12(5), 523; https://doi.org/10.3390/membranes12050523 - 15 May 2022
Cited by 7 | Viewed by 2620
Abstract
For the first time, a systematic study was carried out of the replacement of the low-volatility solvents N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide (DMSO) with the high-volatility solvent acetone in the casting solution of polyacrylonitrile (PAN). The effect of acetone’s presence in the casting solution [...] Read more.
For the first time, a systematic study was carried out of the replacement of the low-volatility solvents N-methyl-2-pyrrolidone (NMP) or dimethylsulfoxide (DMSO) with the high-volatility solvent acetone in the casting solution of polyacrylonitrile (PAN). The effect of acetone’s presence in the casting solution on the performance of ultrafiltration membranes fabricated via vapor-induced phase separation (VIPS) was investigated. It was possible to replace 40% of NMP and 50% of DMSO with acetone, which resulted in the reduction of the casting solution viscosity from 70.6 down to 41.3 Pa∙s (20% PAN, NMP), and from 68.3 down to 20.6 Pa∙s (20% PAN, DMSO). It was found that 20 min of exposure to water vapor (relative humidity—85%) was sufficient to govern the phase separation, which was mainly induced by the water vapor. Regardless of the casting solution composition (15 or 20% PAN; DMSO or NMP), all membranes formed via VIPS possessed a sponge-like porous structure. The addition of acetone to the casting solution allowed the reduction of the transport pore size from 35–48 down to 8.5–25.6, depending on the casting solution composition. By varying the acetone content at constant polymer concentration, it was possible to decrease the molecular weight cut-off (MWCO) from 69 to 10 kg/mol. Membranes prepared from 20% PAN solution in an acetone/DMSO mixture had the lowest MWCO of 10 kg/mol with a water permeance of 5.1 L/(m2·h·bar). Full article
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13 pages, 3232 KiB  
Communication
An AFM Approach Applied in a Study of α-Crystallin Membrane Association: New Insights into Lens Hardening and Presbyopia Development
by Nawal K. Khadka, Raju Timsina and Laxman Mainali
Membranes 2022, 12(5), 522; https://doi.org/10.3390/membranes12050522 - 14 May 2022
Cited by 5 | Viewed by 2309
Abstract
The lens of the eye loses elasticity with age, while α-crystallin association with the lens membrane increases with age. It is unclear whether there is any correlation between α-crystallin association with the lens membrane and loss in lens elasticity. This research investigated α-crystallin [...] Read more.
The lens of the eye loses elasticity with age, while α-crystallin association with the lens membrane increases with age. It is unclear whether there is any correlation between α-crystallin association with the lens membrane and loss in lens elasticity. This research investigated α-crystallin membrane association using atomic force microscopy (AFM) for the first time to study topographical images and mechanical properties (breakthrough force and membrane area compressibility modulus (KA), as measures of elasticity) of the membrane. α-Crystallin extracted from the bovine lens cortex was incubated with a supported lipid membrane (SLM) prepared on a flat mica surface. The AFM images showed the time-dependent interaction of α-crystallin with the SLM. Force spectroscopy revealed the presence of breakthrough events in the force curves obtained in the membrane regions where no α-crystallin was associated, which suggests that the membrane’s elasticity was maintained. The force curves in the α-crystallin submerged region and the close vicinity of the α-crystallin associated region in the membrane showed no breakthrough event within the defined peak force threshold, indicating loss of membrane elasticity. Our results showed that the association of α-crystallin with the membrane deteriorates membrane elasticity, providing new insights into understanding the molecular basis of lens hardening and presbyopia. Full article
(This article belongs to the Special Issue Advances in Model Membrane Systems)
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13 pages, 4429 KiB  
Article
A Facile and Sustainable Enhancement of Anti-Oxidation Stability of Nafion Membrane
by Prem P. Sharma and Dukjoon Kim
Membranes 2022, 12(5), 521; https://doi.org/10.3390/membranes12050521 - 13 May 2022
Cited by 9 | Viewed by 2507
Abstract
OH radicals are the main cause of chemical degradation of Nafion membranes in fuel cell operation. Although the cerium ion (Ce3+/4+, Ce) is reported as an effective OH radical quencher, its membrane application has critical limitations associated with the [...] Read more.
OH radicals are the main cause of chemical degradation of Nafion membranes in fuel cell operation. Although the cerium ion (Ce3+/4+, Ce) is reported as an effective OH radical quencher, its membrane application has critical limitations associated with the reduction of membrane proton conductivity and its leaking. In this study, the Ce-grafted graphitic carbon nitrides (g-C3N4) (CNCe) nano-particles are synthesized and embedded in Nafion membranes to prolong the OH radical scavenging effect. The synthesis of CNCe nano-particles is evaluated by X-ray diffraction, energy dispersive X-ray analysis, and transmission electron microscopy. Compared with the pristine and Ce-blended Nafion membranes, the CNCe imbedded ones show tremendous improvement in long-term anti-oxidation stability. While the fluoride emission rates of Nafion are 0.0062 mg·cm−2·h−1 at the anode and 0.0034 mg·cm−2·h−1 at the cathode, those of Nafion/CNCe membranes are 0.0037 mg·cm−2·h−1 at the anode and 0.0023 mg·cm−2·h−1 at the cathode. The single cell test for Nafion/CNCe membranes at 80 °C and 50% relative humidity illustrates much better durability than those for Nafion and Nafion/Ce, indicating its superior scavenging effect on OH radicals. Full article
(This article belongs to the Topic Polymer Electrolytes)
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9 pages, 4906 KiB  
Article
A Facile Method to Synthesize b-Oriented Silicalite-1 Thin Film
by Montree Thongkam, Somsak Woramongkolchai, Sairoong Saowsupa and Pesak Rungrojchaipon
Membranes 2022, 12(5), 520; https://doi.org/10.3390/membranes12050520 - 13 May 2022
Viewed by 1798
Abstract
Silicalite-1 thin film was prepared with the following batch composition—3TPAOH:25TEOS:1450H2O:100EtOH—and synthesized using the hydrothermal technique. Silicalite-1 colloidal crystals were successfully coated on the surface of the silica substrate by the dip-coating method. The investigation of silicalite-1 thin film with organic structure-directing [...] Read more.
Silicalite-1 thin film was prepared with the following batch composition—3TPAOH:25TEOS:1450H2O:100EtOH—and synthesized using the hydrothermal technique. Silicalite-1 colloidal crystals were successfully coated on the surface of the silica substrate by the dip-coating method. The investigation of silicalite-1 thin film with organic structure-directing agents (SDA), using a seeding technique with various colloidal seed concentrations, number of dip-coating steps, and crystallization time, were systematically discussed and obtained interesting results. Silicalite-1 powder and Silicalite-1 membrane, the patterns of which showed a unique characteristic crystallography of MFI topology, were characterized by XRD, which indicated the preferred orientation along the b-axis perpendicular to the substrate surface. The morphology and crystal size aspect of Silicalite-1 were also examined by a scanning electron microscope (SEM). Full article
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10 pages, 2204 KiB  
Review
Recent Progress of Adsorptive Ultrafiltration Membranes in Water Treatment—A Mini Review
by Tong Yu, Jing Zhou, Feng Liu, Bao-Ming Xu and Yong Pan
Membranes 2022, 12(5), 519; https://doi.org/10.3390/membranes12050519 - 13 May 2022
Cited by 18 | Viewed by 3564
Abstract
Adsorptive ultrafiltration mixed matrix membranes (MMMs) are a new strategy, developed in recent years, to remove harmful cations and small-molecule organics from wastewater and drinking water, which achieve ultrafiltration and adsorption functions in one unit and are considered to be among the promising [...] Read more.
Adsorptive ultrafiltration mixed matrix membranes (MMMs) are a new strategy, developed in recent years, to remove harmful cations and small-molecule organics from wastewater and drinking water, which achieve ultrafiltration and adsorption functions in one unit and are considered to be among the promising technologies that have exhibited efficiency and competence in water reuse. This mini review concerns the research progress of adsorptive ultrafiltration MMMs for removing heavy metal ions and small-molecule organics. We firstly introduce the types and classifications of adsorptive ultrafiltration MMMs (their classifications can be established based on the type of the adsorbent used). Furthermore, we discuss the removal mechanism of adsorptive ultrafiltration MMMs, as well as summarizing the main fabrication techniques for adsorptive ultrafiltration membranes. In addition, we identified some of the issues and challenges of the practical application for adsorptive ultrafiltration. Full article
(This article belongs to the Special Issue Mixed-Matrix Membranes and Polymeric Membranes)
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3 pages, 187 KiB  
Editorial
Nanofiltration Membranes: Recent Advances and Environmental Applications
by Mohammad Peydayesh
Membranes 2022, 12(5), 518; https://doi.org/10.3390/membranes12050518 - 13 May 2022
Cited by 4 | Viewed by 2672
Abstract
Nanofiltration (NF) is a cutting-edge filtration technology that may be considered a true paradigm shift in membrane science [...] Full article
14 pages, 2038 KiB  
Article
Comparison of Effects of Different Sacrificial Hydrogen Bonds on Performance of Polyurethane/Graphene Oxide Membrane
by Wen Fu, Li Wang, Zhuohang Huang, Xiaoyan Huang, Zhijin Su, Yixing Liang, Zhitin Gao and Qingyu Pan
Membranes 2022, 12(5), 517; https://doi.org/10.3390/membranes12050517 - 13 May 2022
Cited by 2 | Viewed by 1754
Abstract
Processing robust mechanical properties is important for elastomeric materials. In this work, different molecular weights of polyethylene glycols (PEG) were used to modify graphene oxide (GO) in order to study the relationship between the number of hydrogen bonds and the properties of the [...] Read more.
Processing robust mechanical properties is important for elastomeric materials. In this work, different molecular weights of polyethylene glycols (PEG) were used to modify graphene oxide (GO) in order to study the relationship between the number of hydrogen bonds and the properties of the polyurethane/graphene oxide membrane. The fact of PEG was successfully grafted onto the surface of GO was certified by Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy. The graft ratio was indicated by thermogravimetric analysis. The presence of hydrogen bonds in PUR/MGO composites membrane was proved by the cyclic loading-unloading test and stress relaxation test. The thermal stability and low-temperature resistance performance of PUR/MGO had been improved compared with PUR/GO. When the molecular weight of PEG grafted on the surface of GO was 600, the tensile strength and elongation at break of the composite membrane were optimal. The reason for the improvement of physical and mechanical properties was that the dispersion of filler in the rubber matrix and the compatibility between filler and rubber had been improved. Full article
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18 pages, 5405 KiB  
Article
Discharge Characteristics, Plasma Electrolytic Oxidation Mechanism and Properties of ZrO2 Membranes in K2ZrF6 Electrolyte
by Li Wang, Wen Fu, Guangkun Yi, Ziyang Chen, Zhitin Gao and Qingyu Pan
Membranes 2022, 12(5), 516; https://doi.org/10.3390/membranes12050516 - 12 May 2022
Cited by 5 | Viewed by 1619
Abstract
ZrO2 was coated on AZ31 magnesium alloy substrate by plasma electrolytic oxidation with K2ZrF6 and NaH2PO4 electrolytes. The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical [...] Read more.
ZrO2 was coated on AZ31 magnesium alloy substrate by plasma electrolytic oxidation with K2ZrF6 and NaH2PO4 electrolytes. The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical emission spectroscopy. The surface morphology and element composition of the membranes were observed by scanning electron microscope. The ion transfer of the substrate was studied by atomic absorption spectroscopy. The phase composition and corrosion characteristics of the PEO membranes were examined with XRD and an electrochemical workstation, respectively. The heat and mass transfer models during the PEO process were introduced. The contributions of ions to the membranes and active species were also analyzed. The results indicated that the ion transfer at different stages exhibits different tendencies. At the first and transition stages, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tends to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate. The intensity of active species is related to the energy state of the working electrode’s surface. The higher the energy, the greater the probability that the active species will be excited to generate energy level transitions, and the higher the plasma concentration. Full article
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18 pages, 5252 KiB  
Article
A Novel Proline-Rich Cathelicidin from the Alpaca Vicugna pacos with Potency to Combat Antibiotic-Resistant Bacteria: Mechanism of Action and the Functional Role of the C-Terminal Region
by Pavel V. Panteleev, Victoria N. Safronova, Roman N. Kruglikov, Ilia A. Bolosov, Ivan V. Bogdanov and Tatiana V. Ovchinnikova
Membranes 2022, 12(5), 515; https://doi.org/10.3390/membranes12050515 - 12 May 2022
Cited by 5 | Viewed by 2558
Abstract
Over recent years, a growing number of bacterial species have become resistant to clinically relevant antibiotics. Proline-rich antimicrobial peptides (PrAMPs) having a potent antimicrobial activity and a negligible toxicity toward mammalian cells attract attention as new templates for the development of antibiotic drugs. [...] Read more.
Over recent years, a growing number of bacterial species have become resistant to clinically relevant antibiotics. Proline-rich antimicrobial peptides (PrAMPs) having a potent antimicrobial activity and a negligible toxicity toward mammalian cells attract attention as new templates for the development of antibiotic drugs. Here, we mined genomes of all living Camelidae species and found a novel family of Bac7-like proline-rich cathelicidins which inhibited bacterial protein synthesis. The N-terminal region of a novel peptide from the alpaca Vicugna pacos named VicBac is responsible for inhibition of bacterial protein synthesis with an IC50 value of 0.5 µM in the E. coli cell-free system whereas the C-terminal region allows the peptide to penetrate bacterial membranes effectively. We also found that the full-length VicBac did not induce bacterial resistance after a two-week selection experiment, unlike the N-terminal truncated analog, which depended on the SbmA transport system. Both pro- and anti-inflammatory action of VicBac and its N-terminal truncated variant on various human cell types was found by multiplex immunoassay. The presence of the C-terminal tail in the natural VicBac does not provide for specific immune-modulatory effects in vitro but enhances the observed impact compared with the truncated analog. The pronounced antibacterial activity of VicBac, along with its moderate adverse effects on mammalian cells, make this molecule a promising scaffold for the development of peptide antibiotics. Full article
(This article belongs to the Special Issue Modern Studies on Membrane-Targeting Antimicrobial Peptides)
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