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Membranes, Volume 13, Issue 1 (January 2023) – 118 articles

Cover Story (view full-size image): In this study, we demonstrate the fabrication of thin PdCu alloy on Ta support for hydrogen separation from mixed gases produced from the reforming of hydrocarbons. Alloying Cu with Pd can increase the durability of the membrane while mitigating the high cost of whole Pd membranes. Furthermore, the hydrogen dissociation mechanism on PdCu is numerically analyzed via a density functional theory simulation. Our findings greatly contribute to the development of cost‑effective and durable membranes for thermocatalytic hydrogen purification to replace energy-intensive Pressure Swing Adsorption (PSA) as the mainstream hydrogen separation. View this paper
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12 pages, 2457 KiB  
Article
Response Mechanism of Polymeric Liquid Junction-Free Reference Electrodes Based on Organic Electrolytes
Membranes 2023, 13(1), 118; https://doi.org/10.3390/membranes13010118 - 16 Jan 2023
Cited by 1 | Viewed by 1246
Abstract
To achieve a transition from conventional liquid-junction reference electrodes (LJF REs) to their all-solid-state alternatives, organic electrolytes are often introduced into the polymeric electrode membranes. In this article, we implement a theoretical approach to the explanation and quantification of the boundary potential stabilization [...] Read more.
To achieve a transition from conventional liquid-junction reference electrodes (LJF REs) to their all-solid-state alternatives, organic electrolytes are often introduced into the polymeric electrode membranes. In this article, we implement a theoretical approach to the explanation and quantification of the boundary potential stabilization phenomenon for the electrodes modified with organic electrolytes (Q+B). For the first time, stabilization of the phase boundary potential due to the partition of lipophilic ions of the Q+B electrolyte between the polymeric and aqueous phases is numerically simulated to predict the LJF electrodes behavior. The impact of the hydrophilic electrolyte on the potential stabilization is demonstrated both numerically and experimentally. The developed model predicted that the small additions of a traditional ion-exchanger enhance performance of the Q+B-based reference electrodes. For some specific cases, the optimal concentrations of Q+B and ion-exchanger in the polymeric phase are suggested to provide stable electrode potential in a broad range of aqueous electrolyte concentrations. In addition, the efficiency of the stabilization was shown to be dependent on the overall Q+B load in the polymeric membrane rather than on the closeness of the partition coefficients of the Q+ and B ions; and on the volume of the aqueous phase. The model results are verified experimentally with poly(vinyl chloride) membranes containing ion-exchanger or hydrophilic electrolyte and Q+B in various proportions. A good agreement between the measured electrode response and the theoretical results is observed in a broad range of solution concentrations. In particular, the cationic function of membranes containing KTpClPB is suppressed, and the electrodes begin to behave as REs starting from 50–60 mol. % of ETH500 electrolyte added to the membrane, relative to the total amount of salt. Full article
(This article belongs to the Special Issue Membrane Development and Applications in Electrochemistry)
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13 pages, 4372 KiB  
Article
Investigation on Human Serum Protein Depositions Inside Polyvinylidene Fluoride-Based Dialysis Membrane Layers Using Synchrotron Radiation Micro-Computed Tomography (SR-μCT)
Membranes 2023, 13(1), 117; https://doi.org/10.3390/membranes13010117 - 16 Jan 2023
Cited by 1 | Viewed by 1416
Abstract
Hemodialysis (HD) membrane fouling with human serum proteins is a highly undesirable process that results in blood activations with further severe consequences for HD patients. Polyvinylidene fluoride (PVDF) membranes possess a great extent of protein adsorption due to hydrophobic interaction between the membrane [...] Read more.
Hemodialysis (HD) membrane fouling with human serum proteins is a highly undesirable process that results in blood activations with further severe consequences for HD patients. Polyvinylidene fluoride (PVDF) membranes possess a great extent of protein adsorption due to hydrophobic interaction between the membrane surface and non-polar regions of proteins. In this study, a PVDF membrane was modified with a zwitterionic (ZW) polymeric structure based on a poly (maleic anhydride-alt-1-decene), 3-(dimethylamino)-1-propylamine derivative and 1,3-propanesultone. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and zeta potential analyses were used to determine the membrane’s characteristics. Membrane fouling with human serum proteins (human serum albumin (HSA), fibrinogen (FB), and transferrin (TRF)) was investigated with synchrotron radiation micro-computed tomography (SR-μCT), which allowed us to trace the protein location layer by layer inside the membrane. Both membranes (PVDF and modified PVDF) were detected to possess the preferred FB adsorption due to the Vroman effect, resulting in an increase in FB content in the adsorbed protein compared to FB content in the protein mixture solution. Moreover, FB was shown to only replace HSA, and no significant role of TRF in the Vroman effect was detected; i.e., TRF content was nearly the same both in the adsorbed protein layer and in the protein mixture solution. Surface modification of the PVDF membrane resulted in increased FB adsorption from both the protein mixture and the FB single solution, which is supposed to be due to the presence of an uncompensated negative charge that is located at the COOH group in the ZW polymer. Full article
(This article belongs to the Special Issue Membranes and Membrane Processes in Medicine)
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19 pages, 7129 KiB  
Article
Fabrication of Mechanically Enhanced, Suturable, Fibrous Hydrogel Membranes
Membranes 2023, 13(1), 116; https://doi.org/10.3390/membranes13010116 - 16 Jan 2023
Cited by 2 | Viewed by 1251
Abstract
Poly(vinyl-alcohol) hydrogels have already been successfully utilised as drug carrier systems and tissue engineering scaffolds. However, lacking mechanical strength and suturability hinders any prospects for clinical and surgical applications. The objective of this work was to fabricate mechanically robust PVA membranes, which could [...] Read more.
Poly(vinyl-alcohol) hydrogels have already been successfully utilised as drug carrier systems and tissue engineering scaffolds. However, lacking mechanical strength and suturability hinders any prospects for clinical and surgical applications. The objective of this work was to fabricate mechanically robust PVA membranes, which could also withstand surgical manipulation and suturing. Electrospun membranes and control hydrogels were produced with 61 kDa PVA. Using a high-speed rotating cylindrical collector, we achieved fibre alignment (fibre diameter: 300 ± 50 nm). Subsequently, we created multilayered samples with different orientations to achieve multidirectional reinforcement. Finally, utilising glutaraldehyde as a cross-linker, we created insoluble fibrous-hydrogel membranes. Mechanical studies were performed, confirming a fourfold increase in the specific loading capacities (from 0.21 to 0.84 Nm2/g) in the case of the monolayer samples. The multilayered membranes exhibited increased resistance from both horizontal and vertical directions, which varies according to the specific arrangement. Finally, the cross-linked fibrous hydrogel samples not only exhibited specific loading capacities significantly higher than their counterpart bulk hydrogels but successfully withstood suturing. Although cross-linking optimisation and animal experiments are required, these membranes have great prospects as alternatives to current surgical meshes, while the methodology could also be applied in other systems as well. Full article
(This article belongs to the Special Issue Surface and Interface Engineering of Polymeric Membrane)
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9 pages, 3107 KiB  
Communication
Assessment of Dye-Absorbed Eggshell Membrane Composites as Solid Polymer Electrolyte of Fuel Cells
Membranes 2023, 13(1), 115; https://doi.org/10.3390/membranes13010115 - 16 Jan 2023
Cited by 1 | Viewed by 1684
Abstract
Recently, polymer electrolytes have been developed for high-performance and eco-friendly fuel cells. Among the candidates, eggshell membrane (ESM) has been promising because of its abundance to assemble various energy devices with low cost and its absorption ability of organic materials. In this work, [...] Read more.
Recently, polymer electrolytes have been developed for high-performance and eco-friendly fuel cells. Among the candidates, eggshell membrane (ESM) has been promising because of its abundance to assemble various energy devices with low cost and its absorption ability of organic materials. In this work, we investigated fuel cells that included ESM-absorbing xanthene-, triphenylmethane-, and azo-type tar dye, which contained abundant hydrophilic groups, as polymer electrolytes. We found out two points: (1) that the fuel cells that included ESM-absorbing xanthene-type dye generated the highest IV performance, and (2) the basic molecular structures of the tar dyes determined the correlation of the maximum power and proton conductivities. Full article
(This article belongs to the Special Issue Proton-Conducting Membranes)
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20 pages, 2759 KiB  
Review
Recovery of Metals from Wastewater—State-of-the-Art Solutions with the Support of Membrane Technology
Membranes 2023, 13(1), 114; https://doi.org/10.3390/membranes13010114 - 16 Jan 2023
Cited by 4 | Viewed by 2705
Abstract
This paper discusses the most important research trends in the recovery of metals from industrial wastewater using membrane techniques in recent years. Particular attention is paid to the preparation of new membranes with the required filtration and separation properties. At the same time, [...] Read more.
This paper discusses the most important research trends in the recovery of metals from industrial wastewater using membrane techniques in recent years. Particular attention is paid to the preparation of new membranes with the required filtration and separation properties. At the same time, possible future applications are highlighted. The aspects discussed are divided into metals in order to clearly and comprehensibly list the most optimal solutions depending on the composition of the wastewater and the possibility of recovering valuable components (metalloids, heavy metals, and platinum group metals). It is shown that it is possible to effectively remove metals from industrial wastewater by appropriate membrane preparation (up to ~100%), including the incorporation of functional groups, nanoparticles on the membrane surface. However, it is also worth noting the development of hybrid techniques, in which membrane techniques are one of the elements of an effective purification procedure. Full article
(This article belongs to the Special Issue Membrane Technologies for Resource Recovery (Volume II))
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22 pages, 7638 KiB  
Review
Recent Advances in Transition Metal Tellurides (TMTs) and Phosphides (TMPs) for Hydrogen Evolution Electrocatalysis
Membranes 2023, 13(1), 113; https://doi.org/10.3390/membranes13010113 - 15 Jan 2023
Cited by 9 | Viewed by 2292
Abstract
The hydrogen evolution reaction (HER) is a developing and promising technology to deliver clean energy using renewable sources. Presently, electrocatalytic water (H2O) splitting is one of the low-cost, affordable, and reliable industrial-scale effective hydrogen (H2) production methods. Nevertheless, the [...] Read more.
The hydrogen evolution reaction (HER) is a developing and promising technology to deliver clean energy using renewable sources. Presently, electrocatalytic water (H2O) splitting is one of the low-cost, affordable, and reliable industrial-scale effective hydrogen (H2) production methods. Nevertheless, the most active platinum (Pt) metal-based catalysts for the HER are subject to high cost and substandard stability. Therefore, a highly efficient, low-cost, and stable HER electrocatalyst is urgently desired to substitute Pt-based catalysts. Due to their low cost, outstanding stability, low overpotential, strong electronic interactions, excellent conductivity, more active sites, and abundance, transition metal tellurides (TMTs) and transition metal phosphides (TMPs) have emerged as promising electrocatalysts. This brief review focuses on the progress made over the past decade in the use of TMTs and TMPs for efficient green hydrogen production. Combining experimental and theoretical results, a detailed summary of their development is described. This review article aspires to provide the state-of-the-art guidelines and strategies for the design and development of new highly performing electrocatalysts for the upcoming energy conversion and storage electrochemical technologies. Full article
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14 pages, 5796 KiB  
Article
Effects of Natural Rhamnolipid Mixture on Dioleoylphosphatidylcholine Model Membrane Depending on Method of Preparation and Sterol Content
Membranes 2023, 13(1), 112; https://doi.org/10.3390/membranes13010112 - 15 Jan 2023
Cited by 1 | Viewed by 1263
Abstract
Rhamnolipids as biosurfactants have a potentially wide range of applications, for example, as “green” surfactants or components of drug delivery systems, which is associated with the features of their interaction with cell membranes. However, as noted in the literature, those kind of features [...] Read more.
Rhamnolipids as biosurfactants have a potentially wide range of applications, for example, as “green” surfactants or components of drug delivery systems, which is associated with the features of their interaction with cell membranes. However, as noted in the literature, those kind of features have not been sufficiently studied now. This paper presents a study of the interaction of a natural mixture of rhamnolipids produced by bacteria of the rhizosphere zone of plants Pseudomonas aeruginosa with model membranes—liposomes based on dioleoylphosphatidylcholine (DOPC), depending on the method of their preparation and the content of sterols—ergosterol, cholesterol, lanosterol. Liposomes with rhamnolipids were prepared by two protocols: with film method from a mixture of DOPC and rhamnolipids; with film method from DOPC and injection of water solution of rhamnolipids. Joint analysis of the data of 31P NMR spectroscopy and ATR-FTIR spectroscopy showed that in the presence of rhamnolipids, the mobility of the head group of the DOPC phospholipid increases, the conformational disorder of the hydrophobic tail increases, and the degree of hydration of the C=O and P=O groups of the phospholipid decreases. It can be assumed that, when prepared from a mixture, rhamnolipids are incorporated into the membrane in the form of clusters and are located closer to the middle of the bilayer; while when prepared by injection, rhamnolipid molecules migrate into the membrane in the form of individual molecules and are located closer to the head part of phospholipids. The sterol composition of the model membrane also affects the interaction of rhamnolipids with the membrane. Here it is worth noting the possible presence of type of interaction between rhamnolipids and ergosterol differ from other investigated sterols, due to which rhamnolipid molecules are embedded in the area where ergosterol is located. Full article
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11 pages, 2603 KiB  
Article
Esterification of Acetic Acid by Flow-Type Membrane Reactor with AEI Zeolite Membrane
Membranes 2023, 13(1), 111; https://doi.org/10.3390/membranes13010111 - 14 Jan 2023
Cited by 3 | Viewed by 1520
Abstract
AEI-type zeolite membrane for dehydration was prepared, and a flow-type membrane reactor for the esterification of acetic acid and ethanol by AEI membrane was developed. A synthesized AEI membrane had suitable molecular sieving property for gas separation (H2/i-butane and [...] Read more.
AEI-type zeolite membrane for dehydration was prepared, and a flow-type membrane reactor for the esterification of acetic acid and ethanol by AEI membrane was developed. A synthesized AEI membrane had suitable molecular sieving property for gas separation (H2/i-butane and CO2/CH4) and pervaporation (H2O/acetic acid). AEI membrane showed H2O permeance of 6.2 × 10−7 mol m−2 s−1 Pa−1 with a separation factor of 67 at 363 K for the equimolar mixture of H2O/acetic acid. AEI membrane maintained stable performance under acidic conditions. The yield of ethyl acetate at 363 K in a flow-type membrane reactor with AEI membrane successfully exceeded the equilibrium of 69.1%, reaching 89.0%. The flow rate of feed solution strongly affected the conversion of acetic acid and the space–time yield (STY) of ethyl acetate. Due to the more significant proportion of water selectively removed from the reaction system at a lower feed flow rate, the thermodynamic equilibrium shifted significantly, resulting in higher conversions. In contrast, STY increased with increasing feed flow rate. Our flow-type membrane reactor exhibited a relatively large STY of 430 kg m−3 h−1 compared with the batch-type membrane reactor previously reported. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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17 pages, 4110 KiB  
Article
Platinum Nanoparticles Immobilized on Electrospun Membranes for Catalytic Oxidation of Volatile Organic Compounds
Membranes 2023, 13(1), 110; https://doi.org/10.3390/membranes13010110 - 14 Jan 2023
Cited by 1 | Viewed by 1202
Abstract
Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally [...] Read more.
Structured catalytic membranes with high porosity and a low pressure drop are particularly suitable for industrial processes carried out at high space velocities. One of these processes is the catalytic total oxidation of volatile organic compounds, which is an economically feasible and environmentally friendly way of emission abatement. Noble metal catalysts are typically preferred due to high activity and stability. In this paper, the preparation of a thermally stable polybenzimidazole electrospun membrane, which can be used as a support for a platinum catalyst applicable in the total oxidation of volatile organic compounds, is reported for the first time. In contrast to commercial pelletized catalysts, high porosity of the membrane allowed for easy accessibility of the platinum active sites to the reactants and the catalytic bed exhibited a low pressure drop. We have shown that the preparation conditions can be tuned in order to obtain catalysts with a desired platinum particle size. In the gas-phase oxidation of ethanol, acetone, and toluene, the catalysts with Pt particle sizes 2.1 nm and 26 nm exhibited a lower catalytic activity than that with a Pt particle size of 12 nm. Catalysts with a Pt particle size of 2.1 nm and 12 nm were prepared by equilibrium adsorption, and the higher catalytic activity of the latter catalyst was ascribed to more reactive adsorbed oxygen species on larger Pt nanoparticles. On the other hand, the catalyst with a Pt particle size of 26 nm was prepared by a solvent evaporation method and contained less active polycrystalline platinum. Last but not least, the catalyst containing only 0.08 wt.% of platinum achieved high conversion (90%) of all the model volatile organic compounds at moderate temperatures (lower than 335 °C), which is important for reducing the costs of the abatement technology. Full article
(This article belongs to the Special Issue Catalysis in Membrane Reactors 2022)
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15 pages, 3866 KiB  
Article
Synthesis and Characterization of a Composite Anion Exchange Membrane for Water Electrolyzers (AEMWE)
Membranes 2023, 13(1), 109; https://doi.org/10.3390/membranes13010109 - 14 Jan 2023
Cited by 8 | Viewed by 4382
Abstract
Anion exchange membranes (AEM) have gained attention recently as a promising candidate for low-cost water electrolysis systems to produce hydrogen, linked with renewable energy resources as a sustainable alternative to fossil fuels. The development of potential materials for producing and analyzing AEM is [...] Read more.
Anion exchange membranes (AEM) have gained attention recently as a promising candidate for low-cost water electrolysis systems to produce hydrogen, linked with renewable energy resources as a sustainable alternative to fossil fuels. The development of potential materials for producing and analyzing AEM is an imperative step towards commercialization and plays a competitive role in the hydrogen production industry. In this article, we developed a composite anion exchange membrane prepared by activating a commercial support structure (Celgard® 3401) with a commercially available functional group (Fumion® FAA-3) through a phase-inversion process. Fourier-transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analysis demonstrated the phase-inversion procedure as an effective methodology. Furthermore, the cell performance test result (with Celgard/Fumion) was very promising and even better in comparison with a commercial membrane commonly applied in alkaline electrolysis (Fumasep). We also developed a testing procedure for membrane performance evaluation during electrolysis which is very critical considering the effect of CO2 absorption on membrane conductivity. Full article
(This article belongs to the Special Issue Membrane Development and Applications in Electrochemistry)
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32 pages, 11350 KiB  
Review
Recent Advancements in the Recovery and Reuse of Organic Solvents Using Novel Nanomaterial-Based Membranes for Renewable Energy Applications
Membranes 2023, 13(1), 108; https://doi.org/10.3390/membranes13010108 - 13 Jan 2023
Cited by 4 | Viewed by 2093
Abstract
The energy crisis in the world is increasing rapidly owing to the shortage of fossil fuel reserves. Climate change and an increase in global warming necessitates a change in focus from petroleum-based fuels to renewable fuels such as biofuels. The remodeling of existing [...] Read more.
The energy crisis in the world is increasing rapidly owing to the shortage of fossil fuel reserves. Climate change and an increase in global warming necessitates a change in focus from petroleum-based fuels to renewable fuels such as biofuels. The remodeling of existing separation processes using various nanomaterials is of a growing interest to industrial separation methods. Recently, the design of membrane technologies has been the most focused research area concerning fermentation broth to enhance performance efficiency, while recovering those byproducts to be used as value added fuels. Specifically, the use of novel nano material membranes, which brings about a selective permeation of the byproducts, such as organic solvent, from the fermentation broth, positively affects the fermentation kinetics by eliminating the issue of product inhibition. In this review, which and how membrane-based technologies using novel materials can improve the separation performance of organic solvents is considered. In particular, technical approaches suggested in previous studies are discussed with the goal of emphasizing benefits and problems faced in order to direct research towards an optimized membrane separation performance for renewable fuel production on a commercial scale. Full article
(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in North America)
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21 pages, 3973 KiB  
Article
Impact of Hierarchical Cation-Exchange Membranes’ Chemistry and Crosslinking Level on Electrodialysis Demineralization Performances of a Complex Food Solution
Membranes 2023, 13(1), 107; https://doi.org/10.3390/membranes13010107 - 13 Jan 2023
Cited by 3 | Viewed by 2339
Abstract
Hierarchical cation-exchange membranes (hCEMs) fabricated by blade coating and UV crosslinking of ionomer on top of a porous substrate demonstrated promising results in performing NaCl demineralization. In the food industry, complex solutions are used and hCEMs were never investigated before for these food [...] Read more.
Hierarchical cation-exchange membranes (hCEMs) fabricated by blade coating and UV crosslinking of ionomer on top of a porous substrate demonstrated promising results in performing NaCl demineralization. In the food industry, complex solutions are used and hCEMs were never investigated before for these food applications. The performances of two different coating chemistries (urethane acrylate based: UL, and acrylic acid based: EbS) and three crosslinking degrees (UL5, UL6, UL7 for UL formulations, and EbS-1, EbS-2, EbS-3 for EbS formulations) were formulated. The impacts of hCEMs properties and crosslinking density on whey demineralization performances by electrodialysis (ED) were evaluated and compared to CMX, a high performing CEM for whey demineralization by ED. The crosslinking density had an impact on the hCEMs area specific resistance, and on the ionic conductance for EbS membrane. However, 70% demineralization of 18% whey solution was reached for the first time for hCEMs without any fouling observed, and with comparable performances to the CMX benchmark. Although some properties were impacted by the crosslinking density, the global performances in ED (limiting current, demineralization duration, global system resistance, energy consumption, current efficiency) for EbS and UL6 membranes were similar to the CMX benchmark. These promising results suggest the possible application of these hCEMs (UL6, EbS-2, and EbS-3) for whey demineralization by ED and more generally complex products as an alternative in the food industry. Full article
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12 pages, 3127 KiB  
Article
Fouling and Mitigation Behavior of Foulants on Ion Exchange Membranes with Surface Property in Reverse Electrodialysis
Membranes 2023, 13(1), 106; https://doi.org/10.3390/membranes13010106 - 13 Jan 2023
Cited by 2 | Viewed by 1754
Abstract
In this study, two different types of ion exchange membranes are used to investigate the tendency of membrane fouling with respect to surface roughness and hydrophilicity. Commercially available membranes reinforced by electrospun nanofiber have rough and hydrophilic surfaces, and lab-made pore-filling membranes exhibit [...] Read more.
In this study, two different types of ion exchange membranes are used to investigate the tendency of membrane fouling with respect to surface roughness and hydrophilicity. Commercially available membranes reinforced by electrospun nanofiber have rough and hydrophilic surfaces, and lab-made pore-filling membranes exhibit a smooth and hydrophobic surface. Three different organic surfactants (i.e., cationic, anionic and non-ionic surfactants) are chosen as foulants with similar molecular weights. It is confirmed that membrane fouling by electrical attraction mainly occurs, in which anionic and cationic foulants influence anion and cation exchange membranes, respectively. Thus, less fouling is obtained on both membranes for the non-charged foulant. The membranes with a rough surface show a higher fouling tendency than those with a smooth surface in the short-term continuous fouling tests. However, during the cyclic operations of fouling and mitigation of the commercially available membranes, the irregularities of a rough membrane surface cause a rapid increase in electrical resistance from the beginning of fouling due to excessive adsorption on the surface, but the fouling is easily mitigated due to the hydrophilic surface. On the other hand, the membranes with a smooth surface show alleviated fouling from the beginning of fouling, but the irreversible fouling occurs as foulants accumulate on the hydrophobic surface which causes membrane fouling to be favorable. Full article
(This article belongs to the Special Issue Surface and Interface Engineering of Polymeric Membrane)
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20 pages, 4205 KiB  
Article
Composite Proton-Conducting Membrane with Enhanced Phosphoric Acid Doping of Basic Films Radiochemically Grafted with Binary Vinyl Heterocyclic Monomer Mixtures
Membranes 2023, 13(1), 105; https://doi.org/10.3390/membranes13010105 - 13 Jan 2023
Cited by 3 | Viewed by 1731
Abstract
A composite proton conducting membrane (PCM) was prepared by radiation-induced grafting (RIG) of binary mixtures of 4-vinyl pyridine (4-VP) and 1-vinylimidazole (1-VIm) onto poly(ethylene-co-tetrafluoroethylene) (ETFE) film followed by phosphoric acid (PA) doping. The grafting parameters such as absorbed dose, temperature, monomer [...] Read more.
A composite proton conducting membrane (PCM) was prepared by radiation-induced grafting (RIG) of binary mixtures of 4-vinyl pyridine (4-VP) and 1-vinylimidazole (1-VIm) onto poly(ethylene-co-tetrafluoroethylene) (ETFE) film followed by phosphoric acid (PA) doping. The grafting parameters such as absorbed dose, temperature, monomer concentration, time, and monomer ratio were varied to control the degree of grafting (DG%). The effect of the reactivity ratio of 4-VP and 1-VIm on the composition and degree of monomer unit alternation in the formed graft copolymer was investigated. The changes in the chemical and physical properties endowed by grafting and subsequent PA acid doping were monitored using analytical instruments. The mechanical properties and proton conductivity of the obtained membrane were evaluated and its performance was tested in H2/O2 fuel cell at 120 °C under anhydrous and partially wet conditions. The acid doping level was affected by the treatment parameters and enhanced by increasing DG. The proton conductivity was boosted by incorporating the combination of pyridine and imidazole rings originating from the formed basic graft copolymer of 4-VP/1-VIm dominated by 4-VP units in the structure. The proton conductivity showed a strong dependence on the temperature. The membrane demonstrated superior properties compared to its counterpart obtained by grafting 4-VP alone. The membrane also showed a strong potential for application in proton exchange membrane fuel cells (PEMFC) operating at 120 °C. Full article
(This article belongs to the Special Issue Proton-Conducting Membranes)
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23 pages, 6332 KiB  
Article
Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale
Membranes 2023, 13(1), 99; https://doi.org/10.3390/membranes13010099 - 12 Jan 2023
Cited by 4 | Viewed by 2295
Abstract
This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) [...] Read more.
This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1 and 2.6 g L−1) were evaluated on a demonstration plant. Filtration periods of 2–8 h were achieved when using the MF membrane, while these increased to 34–69 days with the UF membrane. This wide difference was due to severe fouling when operating the MF membrane, which was dramatically reduced by the UF membrane. Use of raw wastewater and higher solids concentration showed a significant benefit in the filtration performance when using the UF module. The physical fouling control strategies tested (air sparging and backwashing) proved to be ineffective in controlling UF membrane fouling, although these strategies had a significant impact on MF membrane fouling, extending the operating period from some hours to 5–6 days. The fouling evaluation showed that a cake layer seemed to be the predominant reversible fouling mechanism during each independent filtration cycle. However, as continuous filtration advanced, a large accumulation of irreversible fouling appeared, which could have been related to intermediate/complete pore blocking in the case of the MF membrane, while it could have been produced by standard pore blocking in the case of the UF membrane. Organic matter represented more than 70% of this irreversible fouling in all the experimental conditions evaluated. Full article
(This article belongs to the Special Issue Membrane Technologies for Resource Recovery (Volume II))
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15 pages, 2450 KiB  
Article
Current-Voltage and Transport Characteristics of Heterogeneous Ion-Exchange Membranes in Electrodialysis of Solutions Containing a Heterocyclic Amino Acid and a Strong Electrolyte
Membranes 2023, 13(1), 98; https://doi.org/10.3390/membranes13010098 - 12 Jan 2023
Cited by 3 | Viewed by 1216
Abstract
The alterations in current-voltage and transport characteristics of highly basic and strongly acidic ion-exchange membranes, during the electrodialysis of solutions containing a heterocyclic amino acid and a strong electrolyte, were studied. An increase in the catalytic activity of the water splitting process at [...] Read more.
The alterations in current-voltage and transport characteristics of highly basic and strongly acidic ion-exchange membranes, during the electrodialysis of solutions containing a heterocyclic amino acid and a strong electrolyte, were studied. An increase in the catalytic activity of the water splitting process at the surface of heterogeneous MK-40 and MA-41 membranes upon prolonged contact with proline and tryptophan solutions was found. A significant effect of electroconvection on the components mass transfer through the cation-exchange membrane in the intensive current mode of electrodialysis was revealed for the solution containing a heterocyclic amino acid along with mineral salt (NaCl). This led to a reduction in the length of the “plateau” of the membrane’s current-voltage characteristics, in comparison with the characteristics for an individual sodium chloride solution with the same concentration. The changes in the characteristics of the studied ion-exchange membranes caused by contact with solutions containing heterocyclic amino acids during electrodialysis were reversible when applying electrochemical regeneration (cleaning in place) using the overlimiting current mode, corresponding to the region of facilitated transport for these ampholytes. Full article
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14 pages, 3202 KiB  
Article
Improving the Separation Properties of Polybenzimidazole Membranes by Adding Acetonitrile for Organic Solvent Nanofiltration
Membranes 2023, 13(1), 104; https://doi.org/10.3390/membranes13010104 - 12 Jan 2023
Cited by 1 | Viewed by 1636
Abstract
In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding [...] Read more.
In research on membranes, the addition of co-solvents to the polymer dope solution is a common method for tuning the morphology and separation performance. For organic solvent nanofiltration (OSN) applications, we synthesized polybenzimidazole (PBI) membranes with high separation properties and stability by adding acetonitrile (MeCN) to the dope solution, followed by crosslinking with dibromo-p-xylene. Accordingly, changes in the membrane structure and separation properties were investigated when MeCN was added. PBI/MeCN membranes with a dense and thick active layer and narrow finger-like macrovoids exhibited superior rejection properties in the ethanol solution compared with the pristine PBI membrane. After crosslinking, they displayed superior rejection properties (96.56% rejection of 366-g/mol polypropylene glycol). In addition, the membranes demonstrated stable permeances for various organic solvents, including acetone, methanol, ethanol, toluene, and isopropyl alcohol. Furthermore, to evaluate the feasibility of the modified PBI OSN membranes, ecamsule, a chemical product in the fine chemical industry, was recovered. Correspondingly, the efficient recovery of ecamsule from a toluene/methanol solution using the OSN process with PBI/MeCN membranes demonstrated their applicability in many fine chemical industries. Full article
(This article belongs to the Topic Membrane Separation Technology Research)
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20 pages, 2690 KiB  
Article
Is It Possible to Prepare a “Super” Anion-Exchange Membrane by a Polypyrrole-Based Modification?
Membranes 2023, 13(1), 103; https://doi.org/10.3390/membranes13010103 - 12 Jan 2023
Cited by 4 | Viewed by 1852
Abstract
In spite of wide variety of commercial ion-exchange membranes, their characteristics, in particular, electrical conductivity and counterion permselectivity, are unsatisfactory for some applications, such as electrolyte solution concentration. This study is aimed at obtaining an anion-exchange membrane (AEM) of high performance in concentrated [...] Read more.
In spite of wide variety of commercial ion-exchange membranes, their characteristics, in particular, electrical conductivity and counterion permselectivity, are unsatisfactory for some applications, such as electrolyte solution concentration. This study is aimed at obtaining an anion-exchange membrane (AEM) of high performance in concentrated solutions. An AEM is prepared with a polypyrrole (PPy)-based modification of a heterogeneous AEM with quaternary ammonium functional groups. Concentration dependences of the conductivity, diffusion permeability and Cl transport number in NaCl solutions are measured and simulated using a new version of the microheterogeneous model. The model describes changes in membrane swelling with increasing concentration and the effect of these changes on the transport characteristics. It is assumed that PPy occupies macro- and mesopores of the host membrane where it replaces non-selective electroneutral solution. Increasing conductivity and selectivity are explained by the presence of positively charged PPy groups. It is found that the conductivity of a freshly prepared membrane reaches 20 mS/cm and the chloride transport number > 0.99 in 4 M NaCl. A choice of input parameters allows quantitative agreement between the experimental and simulation results. However, PPy has shown itself to be an unstable material. This article discusses what parameters a membrane can have to show such exceptional characteristics. Full article
(This article belongs to the Special Issue Ion-Exchange Membranes and Processes, Fourth Edition)
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18 pages, 2902 KiB  
Article
Design of an Antibiotic-Releasing Polymer: Physicochemical Characterization and Drug Release Patterns
Membranes 2023, 13(1), 102; https://doi.org/10.3390/membranes13010102 - 12 Jan 2023
Cited by 4 | Viewed by 1408
Abstract
Conventional drug delivery has its share of shortcomings, especially its rapid drug release with a relatively short duration of therapeutic drug concentrations, even in topical applications. Prolonged drug release can be effectively achieved by modifying the carrier in a drug delivery system. Among [...] Read more.
Conventional drug delivery has its share of shortcomings, especially its rapid drug release with a relatively short duration of therapeutic drug concentrations, even in topical applications. Prolonged drug release can be effectively achieved by modifying the carrier in a drug delivery system. Among the several candidates for carriers studied over the years, poly (ether ether ketone), a biocompatible thermoplastic, was chosen as a suitable carrier. Its inherent hydrophobicity was overcome by controlled sulfonation, which introduced polar sulfonate groups onto the polymer backbone. Optimization of the sulfonation process was completed by the variation of the duration, temperature of the sulfonation, and concentration of sulfuric acid. The sulfonation was confirmed by EDS and the degree of sulfonation was determined by an NMR analysis (61.6% and 98.9%). Various physical properties such as morphology, mechanical strength, and thermal stability were studied using scanning electron microscopy, tensile testing, and thermogravimetric analysis. Cytotoxicity tests were performed on the SPEEK samples to study the variation in biocompatibility against a Vero cell line. The drug release kinetics of ciprofloxacin (CP) and nalidixic acid sodium salt (NA)-loaded membranes were studied in deionized water as well as SBF and compared against the absorbance of standardized solutions of the drug. The data were then used to determine the diffusion, distribution, and permeability coefficients. Various mathematical models were used to fit the obtained data to establish the order and mechanism of drug release. Studies revealed that drug release occurs by diffusion and follows zero-order kinetics. Full article
(This article belongs to the Special Issue Lipid/Polymeric Membrane Based Drug Delivery Systems)
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15 pages, 5908 KiB  
Article
Thermoradiationally Modified Polytetrafluoroethylene as a Basis for Membrane Fabrication: Resistance to Hydrogen Penetration, the Effect of Ion Treatment on the Chemical Structure and Surface Morphology, Evaluation of the Track Radius
Membranes 2023, 13(1), 101; https://doi.org/10.3390/membranes13010101 - 12 Jan 2023
Viewed by 1212
Abstract
A study of the properties of thermoradiationally modified polytetrafluoroethylene and its importance for use as the basis of polymer membranes is presented. The hydrogen permeability of a TRM-PTFE film was studied in comparison with an original PTFE film, and showed a three-fold decrease [...] Read more.
A study of the properties of thermoradiationally modified polytetrafluoroethylene and its importance for use as the basis of polymer membranes is presented. The hydrogen permeability of a TRM-PTFE film was studied in comparison with an original PTFE film, and showed a three-fold decrease in hydrogen permeability. Further, TRM-PTFE films were irradiated with accelerated Xe ions with an energy of 1 MeV with fluences from 1 × 108 to 1 × 1011. The changes induced by ion treatment were analyzed by infrared spectroscopy of disturbed total internal reflection (IR-ATR) and by atomic force microscopy (ASM). IR-ATR indicated the absence of destruction in the fluence range from 1 × 108 to 3 × 1010 cm−2 (in the area of isolated tracks) and the beginning of overlap of latent tracks on fluences from 3 × 1010 to 1 × 1011 cm−2. Topographic images with AFM showed layered lamellar structures that collapsed at a fluence of 108 cm−2. The destruction was accompanied by a decrease in roughness about seven times the size of the track core observed by the ASM method, fully corresponding to the value obtained on the basis of calculations using modeling in an SRIM program. Full article
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19 pages, 3736 KiB  
Article
Synthesis, Characterization, and Performance of Semi-Refined Kappa Carrageenan-Based Film Incorporating Cassava Starch
Membranes 2023, 13(1), 100; https://doi.org/10.3390/membranes13010100 - 12 Jan 2023
Cited by 3 | Viewed by 1877
Abstract
This paper reports the incorporation of cassava starch (CS) at various concentrations into a previously developed ZnO/SiO2-semi-refined kappa carrageenan-based film (SRκC) bionanocomposite and evaluates its performance as minced chicken edible packaging. The incorporation of CS into SRκC-based films aims to provide [...] Read more.
This paper reports the incorporation of cassava starch (CS) at various concentrations into a previously developed ZnO/SiO2-semi-refined kappa carrageenan-based film (SRκC) bionanocomposite and evaluates its performance as minced chicken edible packaging. The incorporation of CS into SRκC-based films aims to provide multifunctional food packaging with enhanced surface morphology, thickness, mechanical properties, and transparency. The effect of the incorporation of various mixing ratios of CS and SRκC (CS:SRκC ratios of 1:3, 1:1, and 3:1) was investigated. The results show that the surface morphology, thickness, and mechanical properties of the SRκC-based films are increased by incorporating CS. Interestingly, a significant shelf-life improvement of up to 6 days is obtained for the application of the CS:SRκC 1:3 film as minced chicken packaging. It is concluded that the incorporation of CS into SRκC-based film is promising for extending the shelf life of minced chicken samples. Full article
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20 pages, 3456 KiB  
Article
Bilayer Lipid Membrane as Memcapacitance: Capacitance–Voltage Pinched Hysteresis and Negative Insertion Conductance
Membranes 2023, 13(1), 97; https://doi.org/10.3390/membranes13010097 - 11 Jan 2023
Cited by 2 | Viewed by 1304
Abstract
Inelastic (dissipative) effects of different natures in lipid bilayer membranes can lead to hysteresis phenomena. Early, it was shown that lipid bilayer membranes, under the action of a periodic sinusoidal voltage, demonstrate pinched-hysteresis loops in the experimental capacitance–voltage dependences and are almost the [...] Read more.
Inelastic (dissipative) effects of different natures in lipid bilayer membranes can lead to hysteresis phenomena. Early, it was shown that lipid bilayer membranes, under the action of a periodic sinusoidal voltage, demonstrate pinched-hysteresis loops in the experimental capacitance–voltage dependences and are almost the only example of the physical implementation of memcapacitance. Here, we propose an equivalent circuit and mathematical framework for analyzing the dynamic nonlinear current response of a lipid bilayer membrane as an externally controlled memcapacitance. Solving a nonlinear differential equation for the equivalent circuit of a membrane in the form of a parallel connection of a nonlinear viscoelastic capacitor and an active resistance using the small parameter method, we obtain explicit analytical dependences for the current response of the membrane and pinched-hysteresis loops. The explicit solutions and their comparison with experimental data allow us to identify the lumped equivalent circuit parameters that govern the memcapacitor behavior of the membrane and hence the magnitude of the hysteresis. We quantify the memcapacitance hysteresis in terms of negative work done by the control signal. An analysis of the formulas leads to the conclusion that the determining factor for the appearance of pinched hysteresis is the type of nonlinear dependence of the device capacitance on voltage. Full article
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23 pages, 5515 KiB  
Article
Functional Characterization of Four Known Cav2.1 Variants Associated with Neurodevelopmental Disorders
Membranes 2023, 13(1), 96; https://doi.org/10.3390/membranes13010096 - 11 Jan 2023
Cited by 2 | Viewed by 1735
Abstract
Cav2.1 channels are expressed throughout the brain and are the predominant Ca2+ channels in the Purkinje cells. These cerebellar neurons fire spontaneously, and Cav2.1 channels are involved in the regular pacemaking activity. The loss of precision of the firing pattern of Purkinje [...] Read more.
Cav2.1 channels are expressed throughout the brain and are the predominant Ca2+ channels in the Purkinje cells. These cerebellar neurons fire spontaneously, and Cav2.1 channels are involved in the regular pacemaking activity. The loss of precision of the firing pattern of Purkinje cells leads to ataxia, a disorder characterized by poor balance and difficulties in performing coordinated movements. In this study, we aimed at characterizing functional and structural consequences of four variations (p.A405T in I-II loop and p.R1359W, p.R1667W and p.S1799L in IIIS4, IVS4, and IVS6 helices, respectively) identified in patients exhibiting a wide spectrum of disorders including ataxia symptoms. Functional analysis using two major Cav2.1 splice variants (Cav2.1+e47 and Cav2.1−e47) in Xenopus laevis oocytes, revealed a lack of effect upon A405T substitution and a significant loss-of-function caused by R1359W, whereas R1667W and S1799L caused both channel gain-of-function and loss-of-function, in a splice variant-dependent manner. Structural analysis revealed the loss of interactions with S1, S2, and S3 helices upon R1359W and R1667W substitutions, but a lack of obvious structural changes with S1799L. Computational modeling suggests that biophysical changes induced by Cav2.1 pathogenic mutations might affect action potential frequency in Purkinje cells. Full article
(This article belongs to the Special Issue The Xenopus Oocyte: A Tool for Membrane Biology)
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18 pages, 4316 KiB  
Article
Nanovesicles as Vanillin Carriers for Antimicrobial Applications
Membranes 2023, 13(1), 95; https://doi.org/10.3390/membranes13010095 - 11 Jan 2023
Cited by 6 | Viewed by 1575
Abstract
Vanillin is a natural compound easily extracted from plants. It has neuroprotective, anti-carcinogenic, antioxidant, antimicrobial, and anti-biofilm properties. It also presents high volatility, high hydrophilicity, and low bioavailability. Nanomaterials can be used to improve pharmacodynamics, solubility, and stability and to enhance pharmacokinetics. In [...] Read more.
Vanillin is a natural compound easily extracted from plants. It has neuroprotective, anti-carcinogenic, antioxidant, antimicrobial, and anti-biofilm properties. It also presents high volatility, high hydrophilicity, and low bioavailability. Nanomaterials can be used to improve pharmacodynamics, solubility, and stability and to enhance pharmacokinetics. In this work, non-ionic surfactant vesicles were synthesized as vanillin carriers: neutral niosomes formed by Span60 and cholesterol, positive charged niosomes formulated with cetyltrimethylammonium bromide (CTAB), and negatively charged niosomes formulated with sodium dodecyl sulfate (SDS). Niosomes synthesis was carried out with two commonly used methods: thin film hydration (TFH) and ethanol injection method (EIM). The niosomes synthesized were used to prepare two different materials: (i) a powder containing the lyophilized noisome with vanillin systems and (ii) a gelatin matrix film containing niosomes with vanillin. Lyophilization was carried out using maltodextrin as a cryoprotectant. The lyophilization of colloidal structures allows for storage at room temperature for long periods of time, keeping their organoleptic characteristics invariable. Niosomes were characterized before and after the lyophilization process in terms of morphological characterization, size, polydispersity index (PDI), and zeta potential. Moreover, niosomes cargo was evaluated by calculating the encapsulation efficiency (EE) and loading capacity (LC). Results showed that the use of the TFH method allowed us to obtain niosomes of 255 nm with high EE (up to 40%) and LC values higher than EIM. The lyophilization process decreased the LC of the vesicles prepared, but this decrease was mitigated by up to 20% when ionic surfactants were used on the membrane bilayer. Gelatin films are biodegradable materials suitable for food packing applications. The incorporation of a natural compound with antimicrobial activity would be a clear advantage for such an application. The films prepared were characterized in terms of morphology, water solubility, color, and transparency. Niosomes synthesized by thin film hydration had better chemical and physical properties to load vanillin. Especially in the case of application in films, niosomes with a negative charge, formed by SDS, and vanillin loaded gave better mechanical and chemical characteristics to the film. Full article
(This article belongs to the Special Issue Biodegradable Films Characterization and Food Packaging)
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17 pages, 1628 KiB  
Article
Enantiodiscriminating Lipophilic Liquid Membrane-Based Assay for High-Throughput Nanomolar Enantioenrichment of Chiral Building Blocks
Membranes 2023, 13(1), 94; https://doi.org/10.3390/membranes13010094 - 11 Jan 2023
Viewed by 1446
Abstract
The reported optical resolution method was designed to support high-throughput enantioseparation of molecular building blocks obtained by automated small-scale synthetic methods. Lipophilic esters of common resolving agents were prepared and used as liquid membranes on the indifferent polymer surface of a microtiter assay. [...] Read more.
The reported optical resolution method was designed to support high-throughput enantioseparation of molecular building blocks obtained by automated small-scale synthetic methods. Lipophilic esters of common resolving agents were prepared and used as liquid membranes on the indifferent polymer surface of a microtiter assay. Chiral model compounds were enriched in one of the enantiomers starting from the aqueous solutions of their racemic mixture. Enantiodiscrimination was provided by forming diastereomeric coordination complexes of lipophilic enantiopure esters with the enantiomers of the chiral building blocks inside the liquid membranes. This enantiomeric recognition resulted in a greater distribution ratio of the preferred isomer in the membrane phase, thus the process enables a simultaneous enantioenrichment of the solutions outside the membrane. This paper reports a novel microplate-integrated stereoselective membrane enrichment technique satisfying the need for automatable enantioseparation on a subpreparative scale. Full article
(This article belongs to the Special Issue Membrane-Based Technologies in Pharmaceutical Sciences)
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16 pages, 3334 KiB  
Article
Evaluation of a Novel Cuboid Hollow Fiber Hemodialyzer Design Using Computational Fluid Dynamics
Membranes 2023, 13(1), 93; https://doi.org/10.3390/membranes13010093 - 11 Jan 2023
Cited by 2 | Viewed by 1897
Abstract
Conventional hollow fiber hemodialyzers have a cylindrical shell-and-tube design. Due to their circular cross-section and radial flow distribution and collection in the headers, the flow of blood in the header as well as in the hollow fiber membranes is non-uniform. The creation of [...] Read more.
Conventional hollow fiber hemodialyzers have a cylindrical shell-and-tube design. Due to their circular cross-section and radial flow distribution and collection in the headers, the flow of blood in the header as well as in the hollow fiber membranes is non-uniform. The creation of high shear stress and high shear rate zones or stagnation zones could result in problems, such as cell lysis and blood clotting. In this paper, a novel cuboid hemodialyzer design is proposed as an alternative to the conventional cylindrical hemodialyzer. The primary motivation behind the proposed design is to create uniform flow conditions and thereby minimize some of the above-mentioned adverse effects. The most salient feature of the proposed design is a cuboid shell within which the hollow fiber membrane bundle is potted. The lumen of the fibers is fed from one side using a flow distributor consisting of embedded primary and secondary channels, while the fibers are drained from the other side using a flow collector, which also has embedded primary and secondary channels. The flow characteristics of the lumen side of the cuboid hemodialyzer were compared with those of a conventional hemodialyzer based on computational fluid dynamics (CFD) simulations. The results of CFD simulations clearly indicated that the flow of liquid within the cuboid dialyzer was significantly more uniform. Consequently, the shear rate and shear stress were also more uniform. By adopting this new design, some of the problems associated with the conventional hemodialyzer design could potentially be addressed. Full article
(This article belongs to the Special Issue State-of-the-Art Membrane Science and Technology in North America)
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14 pages, 2544 KiB  
Article
Isolation of Carboxylic Acids and NaOH from Kraft Black Liquor with a Membrane-Based Process Sequence
Membranes 2023, 13(1), 92; https://doi.org/10.3390/membranes13010092 - 10 Jan 2023
Cited by 1 | Viewed by 1530
Abstract
In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used [...] Read more.
In kraft pulping, large quantities of biomass degradation products dissolved in the black liquor are incinerated for power generation and chemical recovery. The black liquor is, however, a promising feedstock for carboxylic acids and lignin. Efficient fractionation of black liquor can be used to isolate these compounds and recycle the pulping chemicals. The present work discusses the fractionation of industrial black liquor by a sequence of nanofiltration and bipolar membrane electrodialysis units. Nanofiltration led to retention of the majority of lignin in the retentate and to a significant concentration increase in low-molecular-weight carboxylic acids, such as formic, acetic, glycolic and lactic acids, in the permeate. Subsequent treatment with bipolar membrane electrodialysis showed the potential for simultaneous recovery of acids in the acid compartment and the pulping chemical NaOH in the base compartment. The residual lignin was completely retained by the used membranes. Diffusion of acids to the base compartment and the low current density, however, limited the yield of acids and the current efficiency. In experiments with a black liquor model solution under optimized conditions, NaOH and acid recoveries of 68–72% were achieved. Full article
(This article belongs to the Section Membrane Applications)
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14 pages, 4073 KiB  
Article
Preparation of Lateral Flow PVDF Membrane via Combined Vapor- and Non-Solvent-Induced Phase Separation (V-NIPS)
Membranes 2023, 13(1), 91; https://doi.org/10.3390/membranes13010091 - 10 Jan 2023
Cited by 4 | Viewed by 1825
Abstract
A large pore size Poly(vinylidene fluoride) (PVDF) membrane was prepared by the V-NIPS method using PVDF/N, N-dimethylacetamide (DMAc)/Polyvinyl pyrrolidone (PVP)/Polyethylene glycol (PEG) system. Firstly, the effect of different additive ratios on the membrane morphology and pore size was studied, and it was found [...] Read more.
A large pore size Poly(vinylidene fluoride) (PVDF) membrane was prepared by the V-NIPS method using PVDF/N, N-dimethylacetamide (DMAc)/Polyvinyl pyrrolidone (PVP)/Polyethylene glycol (PEG) system. Firstly, the effect of different additive ratios on the membrane morphology and pore size was studied, and it was found that when the PVP:PEG ratio was 8:2, PVDF membranes with a relatively large pore size tend to be formed; the pore size is about 7.5 µm. Then, the effects of different exposure time on the membrane morphology and pore size were investigated, and it was found that as the vapor temperature increased, the pores on the surface of the membrane first became slightly smaller and then increased. Finally, the effects of different vapor temperatures on the membrane properties were discussed. The results showed that the as-prepared membrane exhibited suitable capillary flow rate and similar performance compared with a commercially available membrane in colloidal gold tests. The likely cause is that the amount of negative charge is less and the capillary migration rate is too fast. This paper provides a reference for the preparation of PVDF colloidal gold detection membrane. Full article
(This article belongs to the Topic Membrane Separation Technology Research)
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10 pages, 9065 KiB  
Communication
A 3D Printed Membrane Reactor System for Electrochemical CO2 Conversion
Membranes 2023, 13(1), 90; https://doi.org/10.3390/membranes13010090 - 10 Jan 2023
Cited by 3 | Viewed by 1462
Abstract
Nowadays, CO2 electroreduction is gaining special interest as achieving net zero CO2 emissions is not going to be enough to avoid or mitigate the negative effects of climate change. However, the cost of CO2 electroreduction is still very high because [...] Read more.
Nowadays, CO2 electroreduction is gaining special interest as achieving net zero CO2 emissions is not going to be enough to avoid or mitigate the negative effects of climate change. However, the cost of CO2 electroreduction is still very high because of the low efficiency of conversion (around 20%). Therefore, it is necessary to optimize the reaction conditions. Thus, a miniaturized novel membrane reactor was designed and manufactured in this study, with a shorter distance between the electrodes and a reduced volume, compared with CNC-manufactured reactors, using novel stereolithography-based 3D printing. The reduced distance between the two electrodes reduced the electrical resistance and therefore lowered the overpotential necessary to trigger the reaction from −1.6 V to −1.2 V, increasing the efficiency. In addition, the reduction in the volume of the reactor increased the catalyst area/volume ratio, which also boosted the concentration of the products (from FE 18% to FE 21%), allowing their better identification. Furthermore, the smaller volume and reduced complexity of the reactor also improved the testing capacity and decreased the cost of experimentation. The novel miniaturized reactor can help researchers to perform more experiments in a cost/time-effective way, facilitating the optimization of the reaction conditions. Full article
(This article belongs to the Special Issue Advances in Polymeric Membranes for Carbon Capture and Storage (CCS))
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20 pages, 2236 KiB  
Article
Polysulfone Membranes Doped with Human Neutrophil Elastase Inhibitors: Assessment of Bioactivity and Biocompatibility
Membranes 2023, 13(1), 89; https://doi.org/10.3390/membranes13010089 - 10 Jan 2023
Viewed by 1168
Abstract
The use of polysulfone (PSU) hemodialysis (HD) membranes modified with bioactive compounds has gained relevance in chronic kidney disease (CKD) management. Compounds based on the 4-oxo-β-lactam scaffold have outstanding inhibitory ability and selectivity for human neutrophil elastase (HNE). The present work aimed to [...] Read more.
The use of polysulfone (PSU) hemodialysis (HD) membranes modified with bioactive compounds has gained relevance in chronic kidney disease (CKD) management. Compounds based on the 4-oxo-β-lactam scaffold have outstanding inhibitory ability and selectivity for human neutrophil elastase (HNE). The present work aimed to evaluate the bioactivity and biocompatibility of PSU-based HD membranes doped with HNE inhibitors (HNEIs). For this, two 4-oxo-β-lactam derivates (D4L-1 and D4L-2) synthesized in house were used, as well as a commercial HNEI (Sivelestat), for comparison purposes. Their HNE inhibition efficacy was evaluated in in vitro and ex vivo (incubations with human plasma) assay conditions. All biomaterials were bioactive and hemocompatible. The inhibitory capacity of the HNEIs and HNEI-PSU membranes in vitro was D4L-1 > D4L-2 > Sivelestat and D4L-2 > Sivelestat > D4L-1, respectively. In ex vivo conditions, both HNEIs and HNEI-PSU materials presented the same relative inhibitory ability (D4L-1 > D4L-2 > Sivelestat). The difference observed between in vitro and ex vivo conditions is most likely due to the inherent lipophilicity/hydrophobicity of each HNEI influencing their affinity and accessibility to HNE when trapped in the membrane. Compared to Sivelestat, both D4L-1 and D4L-2 (and the respective doped membranes) have more potent inhibition capabilities. In conclusion, this work reports the successful development of PSU membranes functionalized with HNEIs. Full article
(This article belongs to the Section Membrane Applications)
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