Membranes

8 pages, 1968 KiB

Open AccessCommunication

Long-Term Stable 1-butyl-3-methylimidazolium Hexafluorophosphate/Ag Metal Composite Membranes for Facilitated Olefin Transport

by Sang Wook Kang

Membranes 2020, 10(8), 191; https://doi.org/10.3390/membranes10080191 - 18 Aug 2020

Cited by 1 | Viewed by 1848

Abstract

For the preparation of long-term stable ionic liquid/Ag nanoparticles composites, we compared the separation performance of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄⁻)/Ag, and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM⁺PF₆⁻)/Ag composite membranes with time. Separation performance showed that the BMIM [...] Read more.

For the preparation of long-term stable ionic liquid/Ag nanoparticles composites, we compared the separation performance of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄⁻)/Ag, and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM⁺PF₆⁻)/Ag composite membranes with time. Separation performance showed that the BMIM⁺PF₆⁻/Ag metal composite membrane was more stable than the BMIM⁺BF₄⁻/Ag metal composite membrane for more than 160 h. These differences in long-term stability in BMIM⁺PF₆⁻/Ag and BMIM⁺BF₄⁻/Ag metal composite membranes was attributable to the phase separation between ionic liquid and nanoparticles. In particular, the phase separation between ionic liquid and silver nanoparticles was not observed with time in hydrophobic ionic liquid BMIM⁺PF₆⁻, confirmed by X-ray photoelectron spectroscopy. Full article

(This article belongs to the Section Membrane Applications)

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14 pages, 4083 KiB

Open AccessArticle

Preparation and Chemical Protective Clothing Application of PVDF Based Sodium Sulfonate Membrane

by Yue Zhao, Xinbo Wang, Deyin Wang, Heguo Li, Lei Li, Shouxin Zhang, Chuan Zhou, Xiaohui Zheng, Quanfu Men, Jinyi Zhong and Liang Wu

Membranes 2020, 10(8), 190; https://doi.org/10.3390/membranes10080190 - 17 Aug 2020

Cited by 14 | Viewed by 3078

Abstract

Chemical protective clothing (CPC) is major equipment to protect human skin from hazardous chemical warfare agents (CWAs), especially nerve agents and blister agents. CPC performance is mainly dominated by the chemical protective material, which needs to meet various requirements, such as mechanical robustness, [...] Read more.

Chemical protective clothing (CPC) is major equipment to protect human skin from hazardous chemical warfare agents (CWAs), especially nerve agents and blister agents. CPC performance is mainly dominated by the chemical protective material, which needs to meet various requirements, such as mechanical robustness, protective properties, physiological comfort, cost-effectiveness, and dimensional stability. In this study, polyvinylidene fluoride (PVDF) based sodium sulfonate membranes with different ion exchange capacities (IECs) are prepared simply from low-cost materials. Their mechanical properties, contact angles, permeations, and selectivities have been tested and compared with each other. Results show that membranes with IEC in the range of 1.5–2 mmol g⁻¹ have high selectivities of water vapor permeation over CWA simulant vapor permeation and good mechanical properties. Therefore, PVDF-based sodium sulfonate membranes are potential materials for CPC applications. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Conference on Energy-Efficient Separation (iEESEP 2019))

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10 pages, 2286 KiB

Open AccessArticle

Reasons for the Formation and Properties of Soliton-Like Charge Waves in Membrane Systems When Using Overlimiting Current Modes

by Makhamet Urtenov, Natalia Chubyr and Vitaly Gudza

Membranes 2020, 10(8), 189; https://doi.org/10.3390/membranes10080189 - 16 Aug 2020

Cited by 5 | Viewed by 1894

Abstract

The study of ion transport in membrane systems in overlimiting current modes is an important problem of physical chemistry and has an important application value. The influence of the space charge on the transport of salt ions under overlimiting current modes was first [...] Read more.

The study of ion transport in membrane systems in overlimiting current modes is an important problem of physical chemistry and has an important application value. The influence of the space charge on the transport of salt ions under overlimiting current modes was first studied in the work of Rubinstein and Shtilman and later in the works of many authors. The purpose of this research is to study, using the method of mathematical modeling, the reasons of formation and properties of the local maximum (minimum) space charge in membrane systems under overlimiting current conditions. It is shown that, in the diffusion layer of the cation-exchange membrane (CEM), the local maximum of the space charge appears due to the limited capacity (exchange capacity) of the membrane at a given potential jump, i.e., the local maximum of space charge appears due to the presence of a local minimum of space charge at the surface of the CEM. The local maximum of the space charge moves as a single soliton-like wave into the depth of the solution. Unlike real solitons, this charged wave changes its size and shape, albeit quite slowly. In the section of the desalination channel, the situation is completely different. First, the space charge of the anion-exchange membrane (AEM) has a negative value, so we should be talking about the local minimum (or the maximum of the absolute value of the charge). However, this is an insignificant clarification. Secondly, the space charge waves of different signs begin to interact, which leads to a new effect, namely the effect of the breakdown of the space charge. The dependence of the local maximum on the input parameters—the cation diffusion coefficient, the growth rate of the potential jump, and the initial and boundary concentrations—is studied. Full article

(This article belongs to the Special Issue Electromembrane Processes: Experiments and Modelling)

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20 pages, 7271 KiB

Open AccessArticle

Pebax^® 2533/Graphene Oxide Nanocomposite Membranes for Carbon Capture

by Riccardo Casadei, Marco Giacinti Baschetti, Myung Jin Yoo, Ho Bum Park and Loris Giorgini

Membranes 2020, 10(8), 188; https://doi.org/10.3390/membranes10080188 - 15 Aug 2020

Cited by 26 | Viewed by 5495

Abstract

In this work, the behavior of new GO-based mixed matrix membranes was tested in view of their use as CO₂-selective membrane in post combustion carbon capture applications. In particular, the new materials were obtained by mixing of Pebax^® 2533 copolymer [...] Read more.

In this work, the behavior of new GO-based mixed matrix membranes was tested in view of their use as CO₂-selective membrane in post combustion carbon capture applications. In particular, the new materials were obtained by mixing of Pebax^® 2533 copolymer with different types of graphene oxide (GO). Pebax^® 2533 has indeed lower selectivity, but higher permeability than Pebax^® 1657, which is more commonly used for membranes, and it could therefore benefit from the addition of GO, which is endowed with very high selectivity of CO₂ with respect to nitrogen. The mixed matrix membranes were obtained by adding different amounts of GO, from 0.02 to 1% by weight, to the commercial block copolymers. Porous graphene oxide (PGO) and GO functionalized with polyetheramine (PEAGO) were also considered in composites produced with similar procedure, with a loading of 0.02%wt. The obtained films were then characterized by using SEM, DSC, XPS analysis and permeability experiments. In particular, permeation tests with pure CO₂ and N₂ at 35°C and 1 bar of upstream pressure were conducted for the different materials to evaluate their separation performance. It has been discovered that adding these GO-based nanofillers to Pebax^® 2533 matrix does not improve the ideal selectivity of the material, but it allows to increase CO₂ permeability when a low filler content, not higher than 0.02 wt%, is considered. Among the different types of GO, then, porous GO seems the most promising as it shows CO₂ permeability in the order of 400 barrer (with an increase of about 10% with respect to the unloaded block copolymer), obtained without reducing the CO₂/N₂ selectivity of the materials, which remained in the order of 25. Full article

(This article belongs to the Special Issue Membranes: 10th Anniversary)

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18 pages, 2332 KiB

Open AccessArticle

The Effects of Temperature and Humidity on the Microstructure of Sulfonated Syndiotactic–polystyrene Ionic Membranes

by Maria-Maddalena Schiavone, David Hermann Lamparelli, Yue Zhao, Fengfeng Zhu, Zsolt Revay and Aurel Radulescu

Membranes 2020, 10(8), 187; https://doi.org/10.3390/membranes10080187 - 14 Aug 2020

Cited by 8 | Viewed by 2889

Abstract

Polymeric membranes based on the semi-crystalline syndiotactic–polystyrene (sPS) become hydrophilic, and therefore conductive, following the functionalization of the amorphous phase by the solid-state sulfonation procedure. Because the crystallinity of the material, and thus the mechanical strength of the membranes, is maintained and the [...] Read more.

Polymeric membranes based on the semi-crystalline syndiotactic–polystyrene (sPS) become hydrophilic, and therefore conductive, following the functionalization of the amorphous phase by the solid-state sulfonation procedure. Because the crystallinity of the material, and thus the mechanical strength of the membranes, is maintained and the resistance to oxidation decomposition can be improved by doping the membranes with fullerenes, the sPS becomes attractive for proton-exchange membranes fuel cells (PEMFC) and energy storage applications. In the current work we report the micro-structural characterization by small-angle neutron scattering (SANS) method of sulfonated sPS films and sPS–fullerene composite membranes at different temperatures between 20 °C and 80 °C, under the relative humidity (RH) level from 10% to 70%. Complementary characterization of membranes was carried out by FTIR, UV-Vis spectroscopy and prompt–γ neutron activation analysis in terms of composition, following the specific preparation and functionalization procedure, and by XRD with respect to crystallinity. The hydrated ionic clusters are formed in the hydrated membrane and shrink slightly with the increasing temperature, which leads to a slight desorption of water at high temperatures. However, it seems that the conductive properties of the membranes do not deteriorate with the increasing temperature and that all membranes equilibrated in liquid water show an increased conductivity at 80 °C compared to the room temperature. The presence of fullerenes in the composite membrane induces a tremendous increase in the conductivity at high temperatures compared to fullerenes-free membranes. Apparently, the observed effects may be related to the formation of additional hydrated pathways in the composite membrane in conjunction with changes in the dynamics of water and polymer. Full article

(This article belongs to the Special Issue Ionic Conductive Membranes for Fuel Cells)

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13 pages, 1563 KiB

Open AccessArticle

Application of a Solid Ceramic Membrane for Monitoring Volatile Organic Compounds in Industrial Wastewater

by Injeong Kim, Jinseul Yoon and Sang Don Kim

Membranes 2020, 10(8), 186; https://doi.org/10.3390/membranes10080186 - 14 Aug 2020

Cited by 2 | Viewed by 2455

Abstract

A large quantity of volatile organic compounds (VOCs) can be released into water environments from oil spills and chemical exposure accidents. A recently developed solid ceramic dosimeter (SCD) could be used for long-term measuring of low VOCs concentrations in water. However, calibration and [...] Read more.

A large quantity of volatile organic compounds (VOCs) can be released into water environments from oil spills and chemical exposure accidents. A recently developed solid ceramic dosimeter (SCD) could be used for long-term measuring of low VOCs concentrations in water. However, calibration and field testing of these SCDs have thus been far insufficient to apply for VOCs monitoring in a water environment in a chemical industrial area. We conducted laboratory calibration experiments and stability tests of the SCD. The mass accumulation of 14 target VOCs from 2 to 100 μg/L was increased linearly with time in the sampler. The absorption rate of the VOCs was related to Henry’s law constant. The average diffusion coefficient of the 14 VOCs in the SCD wall was 1.02 × 10⁻⁹ m²/s. The SCD was utilized in a petrochemical plant complex in South Korea with an industrial wastewater reservoir. After a total of 7 days of deployment, chloroform, ethylbenzene, and toluene were detected by both passive sampling and grab sampling at the same VOC concentrations. Full article

(This article belongs to the Section Membrane Applications)

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13 pages, 2142 KiB

Open AccessArticle

PVDF-Modified Nafion Membrane for Improved Performance of MFC

by Liping Fan, Junyi Shi and Yaobin Xi

Membranes 2020, 10(8), 185; https://doi.org/10.3390/membranes10080185 - 13 Aug 2020

Cited by 27 | Viewed by 4521

Abstract

Low power production and unstable power supply are important bottlenecks restricting the application of microbial fuel cells (MFCs). It is necessary to explore effective methods to improve MFC performance. By using molasses wastewater as fuel, carbon felt as an electrode, and the mixture [...] Read more.

Low power production and unstable power supply are important bottlenecks restricting the application of microbial fuel cells (MFCs). It is necessary to explore effective methods to improve MFC performance. By using molasses wastewater as fuel, carbon felt as an electrode, and the mixture of K₃[Fe(CN)₆] and NaCl as a catholyte, an MFC experimental system was set up to study the performance of MFCs with three different proton exchange membranes. A Nafion membrane was used as the basic material, and polyvinylidene fluoride (PVDF) and acetone-modified PVDF were used to modify it, respectively. The experimental results show that a PVDF-modified membrane can improve the water absorption effectively and, thus, make the MFC have greater power generation and better wastewater treatment effect. The acetone-modified PVDF can further improve the stability of output power of the MFC. When the acetone-modified PVDF was used to modify the Nafion membrane, the steady output voltage of the MFC was above 0.21 V, and the Chemical Oxygen Demand (COD) removal rate for molasses wastewater was about 66.7%, which were 96.3% and 75.1% higher than that of the MFC with the ordinary Nafion membrane. Membrane modification with acetone-modified PVDF can not only increase the output voltage of the MFC but also improve the stability of its output electrical energy. Full article

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12 pages, 1611 KiB

Open AccessArticle

Integrated Membrane–Electrocoagulation System for Removal of Celestine Blue Dyes in Wastewater

by Muhammad Syaamil Saad, Lila Balasubramaniam, Mohd Dzul Hakim Wirzal, Nur Syakinah Abd Halim, Muhammad Roil Bilad, Nik Abdul Hadi Md Nordin, Zulfan Adi Putra and Fuad Nabil Ramli

Membranes 2020, 10(8), 184; https://doi.org/10.3390/membranes10080184 - 13 Aug 2020

Cited by 26 | Viewed by 3085

Abstract

The textile industry provides for the needs of people especially in apparel and household items. The industry also discharges dye-containing wastewater that is typically challenging to treat. Despite the application of the biological and chemical treatments for the treatment of textile wastewater, these [...] Read more.

The textile industry provides for the needs of people especially in apparel and household items. The industry also discharges dye-containing wastewater that is typically challenging to treat. Despite the application of the biological and chemical treatments for the treatment of textile wastewater, these methods have their own drawbacks such as non-environment friendly, high cost and energy intensive. This research investigates the efficiency of the celestine blue dye removal from simulated textile wastewater by electrocoagulation (EC) method using iron (Fe) electrodes through an electrolytic cell, integrated with nylon 6,6 nanofiber (NF) membrane filtration for the separation of the flocculants from aqueous water. Based on the results, the integrated system achieves a high dye removal efficiency of 79.4%, by using 1000 ppm of sodium chloride as the electrolyte and 2 V of voltage at a constant pH of 7 and 10 ppm celestine blue dye solution, compared to the standalone EC method in which only 43.2% removal was achieved. Atomic absorption spectroscopy analysis was used to identify the traces of iron in the residual EC solution confirming the absence of iron. The EC-integrated membrane system thus shows superior performance compared to the conventional method whereby an additional 10–30% of dye was removed at 1 V and 2 V using similar energy consumptions. Full article

(This article belongs to the Special Issue Enhancing the Efficiency of Membrane Processes for Water Treatment)

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19 pages, 4439 KiB

Open AccessArticle

Synthesis and Characterization of 40 wt % Ce_0.9Pr_0.1O_2–δ–60 wt % Nd_xSr_1−xFe_0.9Cu_0.1O_3−δ Dual-Phase Membranes for Efficient Oxygen Separation

by Guoxing Chen, Zhijun Zhao, Marc Widenmeyer, Ruijuan Yan, Ling Wang, Armin Feldhoff and Anke Weidenkaff

Membranes 2020, 10(8), 183; https://doi.org/10.3390/membranes10080183 - 12 Aug 2020

Cited by 13 | Viewed by 3087

Abstract

Dense, H₂- and CO₂-resistant, oxygen-permeable 40 wt % Ce_0.9Pr_0.1O_2–_δ–60 wt % Nd_xSr_1−xFe_0.9Cu_0.1O₃₋_δdual-phase membranes were prepared in a one-pot process. These [...] Read more.

Dense, H₂- and CO₂-resistant, oxygen-permeable 40 wt % Ce_0.9Pr_0.1O_2–_δ–60 wt % Nd_xSr_1−xFe_0.9Cu_0.1O₃₋_δdual-phase membranes were prepared in a one-pot process. These Nd-containing dual-phase membranes have up to 60% lower material costs than many classically used dual-phase materials. The Ce_0.9Pr_0.1O₂₋_δ–Nd_0.5Sr_0.5Fe_0.9Cu_0.1O₃₋_δ sample demonstrates outstanding activity and a regenerative ability in the presence of different atmospheres, especially in a reducing atmosphere and pure CO₂ atmosphere in comparison with all investigated samples. The oxygen permeation fluxes across a Ce_0.9Pr_0.1O₂₋_δ–Nd_0.5Sr_0.5Fe_0.9Cu_0.1O₃₋_δ membrane reached up to 1.02 mL min⁻¹ cm⁻² and 0.63 mL min⁻¹ cm⁻² under an air/He and air/CO₂ gradient at T = 1223 K, respectively. In addition, a Ce_0.9Pr_0.1O_2–_δ–Nd_0.5Sr_0.5Fe_0.9Cu_0.1O_3–_δ membrane (0.65 mm thickness) shows excellent long-term self-healing stability for 125 h. The repeated membrane fabrication delivered oxygen permeation fluxes had a deviation of less than 5%. These results indicate that this highly renewable dual-phase membrane is a potential candidate for long lifetime, high temperature gas separation applications and coupled reaction–separation processes. Full article

(This article belongs to the Special Issue Oxygen Transport Membranes: Synthesis and Applications)

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18 pages, 3374 KiB

Open AccessArticle

Optimization of Ruthenium Dioxide Solid Contact in Ion-Selective Electrodes

by Nikola Lenar, Beata Paczosa-Bator and Robert Piech

Membranes 2020, 10(8), 182; https://doi.org/10.3390/membranes10080182 - 09 Aug 2020

Cited by 19 | Viewed by 2594

Abstract

Ruthenium dioxide occurs in two morphologically varied structures: anhydrous and hydrous form; both of them were studied in the scope of this work and applied as mediation layers in ion-selective electrodes. The differences between the electrochemical properties of those two materials underlie their [...] Read more.

Ruthenium dioxide occurs in two morphologically varied structures: anhydrous and hydrous form; both of them were studied in the scope of this work and applied as mediation layers in ion-selective electrodes. The differences between the electrochemical properties of those two materials underlie their diverse structure and hydration properties, which was demonstrated in the paper. One of the main differences is the occurrence of structural water in RuO₂•xH₂O, which creates a large inner surface available for ion transport and was shown to be a favorable feature in the context of designing potentiometric sensors. Both materials were examined with SEM microscope, X-ray diffractometer, and contact angle microscope, and the results revealed that the hydrous form can be characterized as a porous structure with a smaller crystallite size and more hydrophobic properties contrary to the anhydrous form. Potentiometric and electrochemical tests carried out on designed GCD/RuO₂/K⁺-ISM and GCD/RuO₂•xH₂O/K⁺-ISM electrodes proved that the loose porous microstructure with chemically bounded water, which is characteristic for the hydrous form, ensures the high electrical capacitance of electrodes (up to 1.2 mF) with consequently more stable potential (with the potential drift of 0.0015 mV/h) and a faster response (of a few seconds). Full article

(This article belongs to the Special Issue Advances in Artificial and Biological Membranes: Mechanisms of Ionic Sensitivity, Ion-Sensor Designs and Applications for Ions Measurement)

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30 pages, 1113 KiB

Open AccessEditor’s ChoiceReview

Polymyxins and Bacterial Membranes: A Review of Antibacterial Activity and Mechanisms of Resistance

by Carole Ayoub Moubareck

Membranes 2020, 10(8), 181; https://doi.org/10.3390/membranes10080181 - 08 Aug 2020

Cited by 100 | Viewed by 11731

Abstract

Following their initial discovery in the 1940s, polymyxin antibiotics fell into disfavor due to their potential clinical toxicity, especially nephrotoxicity. However, the dry antibiotic development pipeline, together with the rising global prevalence of infections caused by multidrug-resistant (MDR) Gram-negative bacteria have both rejuvenated [...] Read more.

Following their initial discovery in the 1940s, polymyxin antibiotics fell into disfavor due to their potential clinical toxicity, especially nephrotoxicity. However, the dry antibiotic development pipeline, together with the rising global prevalence of infections caused by multidrug-resistant (MDR) Gram-negative bacteria have both rejuvenated clinical interest in these polypeptide antibiotics. Parallel to the revival of their use, investigations into the mechanisms of action and resistance to polymyxins have intensified. With an initial known effect on biological membranes, research has uncovered the detailed molecular and chemical interactions that polymyxins have with Gram-negative outer membranes and lipopolysaccharide structure. In addition, genetic and epidemiological studies have revealed the basis of resistance to these agents. Nowadays, resistance to polymyxins in MDR Gram-negative pathogens is well elucidated, with chromosomal as well as plasmid-encoded, transferrable pathways. The aims of the current review are to highlight the important chemical, microbiological, and pharmacological properties of polymyxins, to discuss their mechanistic effects on bacterial membranes, and to revise the current knowledge about Gram-negative acquired resistance to these agents. Finally, recent research, directed towards new perspectives for improving these old agents utilized in the 21st century, to combat drug-resistant pathogens, is summarized. Full article

(This article belongs to the Special Issue Membranes: 10th Anniversary)

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16 pages, 1769 KiB

Open AccessArticle

Technical and Economic Evaluation of WWTP Renovation Based on Applying Ultrafiltration Membrane

by He Bai, Yakai Lin, Hongbin Qu, Jinglong Zhang, Xiaohong Zheng and Yuanhui Tang

Membranes 2020, 10(8), 180; https://doi.org/10.3390/membranes10080180 - 07 Aug 2020

Cited by 12 | Viewed by 2832

Abstract

Nowadays, the standards of discharging are gradually becoming stricter, since much attention has been paid to the protection of natural water resources around the world. Therefore, it is urgent to upgrade the existing wastewater treatment plant (WWTP), to improve the effluent quality, and [...] Read more.

Nowadays, the standards of discharging are gradually becoming stricter, since much attention has been paid to the protection of natural water resources around the world. Therefore, it is urgent to upgrade the existing wastewater treatment plant (WWTP), to improve the effluent quality, and reduce the discharged pollutants to the natural environment. In this paper, taking the “Liaocheng UESH (UE Envirotech) WWTP in Shandong province of China” as an example, the existing problems and the detailed measures for a renovation were systemically discussed by technical and economic evaluation, before and after the renovation. During the renovation, the ultrafiltration membrane was added as the final stage of the designed process route, while upgrading the operation conditions of biochemical process at the same time. After the renovation, the removal rates of chemical oxygen demand (COD_cr), biochemical oxygen demand (BOD₅), total phosphorus (TP) and other major pollutants were improved greatly, and the results fully achieved the standards of surface water class IV. The ultrafiltration system performs a stable permeability around 1.5 LMH/kPa. Besides, the economic performance of the renovation was evaluated via the net present value (NPV) method. The result reveals that the NPV of the renovation of the WWTP within the 20 year life cycle is CNY 72.51 million and the overall investment cost can be recovered within the fourth year after the reoperation of the plant. This research does not only indicate that it is feasible to take an ultrafiltration membrane as the main technology, both from technical and economic perspectives, while upgrading the biochemical process section in the meantime, but also provides a new strategy for the renovation of existing WWTPs to achieve more stringent emission standards. Full article

(This article belongs to the Special Issue Membranes for Water and Wastewater Treatment)

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18 pages, 5568 KiB

Open AccessArticle

Simulation Study on Direct Contact Membrane Distillation Modules for High-Concentration NaCl Solution

by Weiming Ni, Yongli Li, Juezhen Zhao, Gaoyuan Zhang, Xiaoze Du and Yingchao Dong

Membranes 2020, 10(8), 179; https://doi.org/10.3390/membranes10080179 - 05 Aug 2020

Cited by 23 | Viewed by 3656

Abstract

Membrane distillation technology, as a new membrane-based water treatment technology that combines the membrane technology and evaporation process, has the advantages of using low-grade heat, working at atmospheric pressure with simple configuration, etc. In this study, heat and mass transfer were coupled at [...] Read more.

Membrane distillation technology, as a new membrane-based water treatment technology that combines the membrane technology and evaporation process, has the advantages of using low-grade heat, working at atmospheric pressure with simple configuration, etc. In this study, heat and mass transfer were coupled at the membrane surfaces through the user-defined function program. The effects of feed temperature, feed velocity and permeate velocity on temperature polarization were mainly investigated for a high-concentration NaCl solution. The temperature polarization was increased with the increase of feed temperature and the decrease of feed and permeate velocity. The effects of temperature, inlet velocity and solution concentration on the evaporation efficiency of the membrane module for co- and counter-current operations were investigated in detail. The counter-current operation performed better than co-current operation in most cases, except for the condition where the NaCl concentration was relatively low or the module length was long enough. In addition, the optimal membrane thickness for both PVDF and PTFE was studied. The optimal membrane thickness was found in the range of 10 to 20 μm, which corresponded to the highest permeate flux for the selected materials, pore size distribution, and operation conditions. Membrane material with lower thermal conductivity and larger porosity was prone to get higher permeate flux and had larger optimal membrane thickness. Increasing feed velocity or feed temperature could decrease the optimal membrane thickness. Full article

(This article belongs to the Section Inorganic Membranes)

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18 pages, 3758 KiB

Open AccessArticle

Nanofiltration Membrane Characterization and Application: Extracting Lithium in Lepidolite Leaching Solution

by Lin Gao, Huaiyou Wang, Yue Zhang and Min Wang

Membranes 2020, 10(8), 178; https://doi.org/10.3390/membranes10080178 - 03 Aug 2020

Cited by 19 | Viewed by 3664

Abstract

This study concerns the feasibility of extracting lithium and separating aluminum from lepidolite leaching solution by nanofiltration. Four commercial nanofiltration (NF) membranes (DK, DL, NF270, and Duracid NF) were chosen to investigate ion separation performance in simulated lepidolite leaching solution. Membranes were characterized [...] Read more.

This study concerns the feasibility of extracting lithium and separating aluminum from lepidolite leaching solution by nanofiltration. Four commercial nanofiltration (NF) membranes (DK, DL, NF270, and Duracid NF) were chosen to investigate ion separation performance in simulated lepidolite leaching solution. Membranes were characterized according to FT-IR, hydrophobicity, zeta potential, morphology, thickness, pore size, and hydraulic permeability to reveal the effect of membrane properties on separation. NF membranes were investigated including the retention ratio of SO₄²⁻ and Li+, the separation efficiency of Li⁺/Al³⁺, and the effect of other cations (K⁺, Na⁺, Ca²⁺) on the separation of Li⁺/Al³⁺. The results show that DK membrane displayed the appropriate permeate flux and extremely high Li⁺/Al³⁺ separation efficiency with a separation factor of 471.3 compared with other NF membranes owing to its pore size, smooth membrane surface, and appropriate zeta potential. Overall, it is found that nanofiltration has a superior separation efficiency of lithium and aluminum, which may bring deep insights and open an avenue to offer a feasible strategy to extract lithium from lepidolite leaching solution in the future. Full article

(This article belongs to the Section Membrane Applications)

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21 pages, 1504 KiB

Open AccessReview

Macropinocytosis in Different Cell Types: Similarities and Differences

by Xiao Peng Lin, Justine D. Mintern and Paul A. Gleeson

Membranes 2020, 10(8), 177; https://doi.org/10.3390/membranes10080177 - 03 Aug 2020

Cited by 90 | Viewed by 12483

Abstract

Macropinocytosis is a unique pathway of endocytosis characterised by the nonspecific internalisation of large amounts of extracellular fluid, solutes and membrane in large endocytic vesicles known as macropinosomes. Macropinocytosis is important in a range of physiological processes, including antigen presentation, nutrient sensing, recycling [...] Read more.

Macropinocytosis is a unique pathway of endocytosis characterised by the nonspecific internalisation of large amounts of extracellular fluid, solutes and membrane in large endocytic vesicles known as macropinosomes. Macropinocytosis is important in a range of physiological processes, including antigen presentation, nutrient sensing, recycling of plasma proteins, migration and signalling. It has become apparent in recent years from the study of specialised cells that there are multiple pathways of macropinocytosis utilised by different cell types, and some of these pathways are triggered by different stimuli. Understanding the physiological function of macropinocytosis requires knowledge of the regulation and fate of the macropinocytosis pathways in a range of cell types. Here, we compare the mechanisms of macropinocytosis in different primary and immortalised cells, identify the gaps in knowledge in the field and discuss the potential approaches to analyse the function of macropinocytosis in vivo. Full article

(This article belongs to the Special Issue Membrane Transport and Cytoskeleton Dynamics)

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12 pages, 5279 KiB

Open AccessArticle

Low-Temperature Direct Contact Membrane Distillation for the Treatment of Aqueous Solutions Containing Urea

by Alessandra Criscuoli, Alfredo Capuano, Michele Andreucci and Enrico Drioli

Membranes 2020, 10(8), 176; https://doi.org/10.3390/membranes10080176 - 03 Aug 2020

Cited by 9 | Viewed by 2692

Abstract

Research activities on the application of direct contact membrane distillation (DCMD) for processing at low temperature (up to 50 °C) solutions containing urea were presented and discussed. Feeds were urine (also in mixture) and human plasma ultrafiltrate. Moreover, as a case study, the [...] Read more.

Research activities on the application of direct contact membrane distillation (DCMD) for processing at low temperature (up to 50 °C) solutions containing urea were presented and discussed. Feeds were urine (also in mixture) and human plasma ultrafiltrate. Moreover, as a case study, the performance of membrane modules of different sizes and features was investigated for reaching the productivities needed in the treatment of the human plasma ultrafiltrate. In particular, two modules were equipped with the same type of capillaries, but differed in terms of membrane area, while the third module contained a different type of membranes and presented a membrane area in between those of the two previous modules. The three modules were compared, at a parity of operating temperatures and streams velocity, in terms of transmembrane flux, permeate production and size, underlining the directions to follow for a real implementation of the technique. Full article

(This article belongs to the Special Issue Membrane Distillation Process)

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21 pages, 3774 KiB

Open AccessArticle

Novel Carbon Quantum Dots/Silver Blended Polysulfone Membrane with Improved Properties and Enhanced Performance in Tartrazine Dye Removal

by Jin Yee Gan, Woon Chan Chong, Lan Ching Sim, Chai Hoon Koo, Yean Ling Pang, Ebrahim Mahmoudi and Abdul Wahab Mohammad

Membranes 2020, 10(8), 175; https://doi.org/10.3390/membranes10080175 - 03 Aug 2020

Cited by 18 | Viewed by 3569

Abstract

This study produced a novel polysulfone (PSF) membrane for dye removal using lemon-derived carbon quantum dots-grafted silver nanoparticles (Ag/CQDs) as membrane nanofiller. The preparation of CQDs was completed by undergoing hydrothermal treatment to carbonize the pulp-free lemon juice into CQD solution. The CQD [...] Read more.

This study produced a novel polysulfone (PSF) membrane for dye removal using lemon-derived carbon quantum dots-grafted silver nanoparticles (Ag/CQDs) as membrane nanofiller. The preparation of CQDs was completed by undergoing hydrothermal treatment to carbonize the pulp-free lemon juice into CQD solution. The CQD solution was then coupled with Ag nanoparticles to form Ag/CQDs nanohybrid. The synthesized powders were characterized in terms of morphologies, functional groups and surface charges. A set of membranes was fabricated with different loadings of Ag/CQDs powder using the nonsolvent-induced phase separation (NIPS) method. The modified membranes were studied in terms of morphology, elemental composition, hydrophilicity and pore size. In addition, pure water flux, rejection test and fouling analysis of the membranes were evaluated using tartrazine dye. From the results, 0.5 wt % of Ag/CQD was identified as the optimum loading to be incorporated with the pristine PSF membrane. The modified membrane exhibited an excellent pure water permeability and dye rejection with improvements of 169% and 92%, respectively. In addition, the composite membrane also experienced lower flux decline, higher reversible fouling and lower irreversible fouling. This study has proven that the addition of CQD additives into membrane greatly improves the polymeric membrane’s properties and filtration performance. Full article

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

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11 pages, 4999 KiB

Open AccessArticle

Organic-Inorganic Artificial Ion Channel Polyvinylidene Fluoride Membranes for Controllable Selectivity Transport of Alkali Metal Cations

by Ye Tian, Shaohua Jin, Xinxin Zhang, Lihua Wang, Yakai Lin, Yutao Jin and Lijie Li

Membranes 2020, 10(8), 174; https://doi.org/10.3390/membranes10080174 - 31 Jul 2020

Cited by 1 | Viewed by 2036

Abstract

In this article, organic–inorganic hybrid materials with different functional groups were used to form organic–inorganic hybrid dense membranes for selective separation of mono/divalent ions by blending these materials and polyvinylidene fluoride (PVDF) in dimethylacetamide with HCl as the catalyst. The membranes prepared by [...] Read more.

In this article, organic–inorganic hybrid materials with different functional groups were used to form organic–inorganic hybrid dense membranes for selective separation of mono/divalent ions by blending these materials and polyvinylidene fluoride (PVDF) in dimethylacetamide with HCl as the catalyst. The membranes prepared by 3-(ureido benzene) propyltriethoxysilane (H1), 3-(ureido-4-methoxyphenyl) propyltriethoxysilane (H2), 3-(ureido-3-chloro-4-methoxyphenyl) propyltriethoxysilane (H3), 3-(ureidoindazolyl) propyltrieth-oxysilane (H4), or 3-(ureidopentanol) propyltriethoxysilane (H5) were labeled as HM1–HM5, respectively. The transport properties of different chlorides were tested. The effects of different anions on sodium cation transport were also tested. The results showed that HM1–HM4 could transport monovalent Li⁺, Na⁺, and K⁺ except Ca²⁺ and Mg²⁺, and the permeability of Li⁺, Na⁺, and K⁺ through the hybrid membranes followed the order of P_Na+ > P_K+ > P_Li+. Moreover, membranes with different H2 content were also prepared due to HM2 having the best ion transport performance. The ion transport performance increased accordingly with the mass ratio of H2 to PVDF, and the permeability of Na⁺ was twice that of Li⁺ and K⁺ when the mass ratio was 15/10. Under this condition, it was also proved that NH₄⁺ could not transport through the hybrid membrane with various selectivity for different anions as Cl⁻ > NO₃⁻ > HCO₃⁻ > SO₄²⁻. Full article

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

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21 pages, 7191 KiB

Open AccessArticle

Long-Running Comparison of Feed-Water Scaling in Membrane Distillation

by Mohammad Rezaei, Albraa Alsaati, David M. Warsinger, Florian Hell and Wolfgang M. Samhaber

Membranes 2020, 10(8), 173; https://doi.org/10.3390/membranes10080173 - 31 Jul 2020

Cited by 11 | Viewed by 4154

Abstract

Membrane distillation (MD) has shown promise for concentrating a wide variety of brines, but the knowledge is limited on how different brines impact salt scaling, flux decline, and subsequent wetting. Furthermore, past studies have lacked critical details and analysis to enable a physical [...] Read more.

Membrane distillation (MD) has shown promise for concentrating a wide variety of brines, but the knowledge is limited on how different brines impact salt scaling, flux decline, and subsequent wetting. Furthermore, past studies have lacked critical details and analysis to enable a physical understanding, including the length of experiments, the inclusion of salt kinetics, impact of antiscalants, and variability between feed-water types. To address this gap, we examined the system performance, water recovery, scale formation, and saturation index of a lab-scale vacuum membrane distillation (VMD) in long-running test runs approaching 200 h. The tests provided a comparison of a variety of relevant feed solutions, including a synthetic seawater reverse osmosis brine with a salinity of 8.0 g/L, tap water, and NaCl, and included an antiscalant. Saturation modeling indicated that calcite and aragonite were the main foulants contributing to permeate flux reduction. The longer operation times than typical studies revealed several insights. First, scaling could reduce permeate flux dramatically, seen here as 49% for the synthetic brine, when reaching a high recovery ratio of 91%. Second, salt crystallization on the membrane surface could have a long-delayed but subsequently significant impact, as the permeate flux experienced a precipitous decline only after 72 h of continuous operation. Several scaling-resistant impacts were observed as well. Although use of an antiscalant did not reduce the decrease in flux, it extended membrane operational time before surface foulants caused membrane wetting. Additionally, numerous calcium, magnesium, and carbonate salts, as well as silica, reached very high saturation indices (>1). Despite this, scaling without wetting was often observed, and scaling was consistently reversible and easily washed. Under heavy scaling conditions, many areas lacked deposits, which enabled continued operation; existing MD performance models lack this effect by assuming uniform layers. This work implies that longer times are needed for MD fouling experiments, and provides further scaling-resistant evidence for MD. Full article

(This article belongs to the Special Issue In Process Wetting Prevention in Membrane Distillation)

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9 pages, 940 KiB

Open AccessCommunication

Cholera Toxin Subunit B for Sensitive and Rapid Determination of Exosomes by Gel Filtration

by Karolina Sapoń, Dominika Maziarz, Teresa Janas, Aleksander F. Sikorski and Tadeusz Janas

Membranes 2020, 10(8), 172; https://doi.org/10.3390/membranes10080172 - 31 Jul 2020

Cited by 7 | Viewed by 2828

Abstract

We developed a sensitive fluorescence-based assay for determination of exosome concentration. In our assay, Cholera toxin subunit B (CTB) conjugated to a fluorescence probe and a gel filtration technique (size-exclusion chromatography) are used. Exosomal membranes are particularly enriched in raft-forming lipids (cholesterol, sphingolipids, [...] Read more.

We developed a sensitive fluorescence-based assay for determination of exosome concentration. In our assay, Cholera toxin subunit B (CTB) conjugated to a fluorescence probe and a gel filtration technique (size-exclusion chromatography) are used. Exosomal membranes are particularly enriched in raft-forming lipids (cholesterol, sphingolipids, and saturated phospholipids) and in GM1 ganglioside. CTB binds specifically and with high affinity to exosomal GM1 ganglioside residing in rafts only, and it has long been the probe of choice for membrane rafts. The CTB-gel filtration assay allows for detection of as little as 3 × 10⁸ isolated exosomes/mL in a standard fluorometer, which has a sensitivity comparable to other methods using advanced instrumentation. The linear quantitation range for CTB-gel filtration assay extends over one order of magnitude in exosome concentration. Using 80 nM fluorescence-labeled CTB, we quantitated 3 × 10⁸ to 6 × 10⁹ exosomes/mL. The assay ranges exhibited linear fluorescence increases versus exosome concentration (r² = 0.987). The assay was verified for exosomal liposomes. The assay is easy to use, rapid, and does not require any expensive or sophisticated instrumentation. Full article

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

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14 pages, 2150 KiB

Open AccessArticle

A Simple Method to Identify the Dominant Fouling Mechanisms during Membrane Filtration Based on Piecewise Multiple Linear Regression

by Hao Xu, Kang Xiao, Jinlan Yu, Bin Huang, Xiaomao Wang, Shuai Liang, Chunhai Wei, Xianghua Wen and Xia Huang

Membranes 2020, 10(8), 171; https://doi.org/10.3390/membranes10080171 - 29 Jul 2020

Cited by 23 | Viewed by 4826

Abstract

Membrane fouling is a complicated issue in microfiltration and ultrafiltration. Clearly identifying the dominant fouling mechanisms during the filtration process is of great significance for the phased and targeted control of fouling. To this end, we propose a semi-empirical multiple linear regression model [...] Read more.

Membrane fouling is a complicated issue in microfiltration and ultrafiltration. Clearly identifying the dominant fouling mechanisms during the filtration process is of great significance for the phased and targeted control of fouling. To this end, we propose a semi-empirical multiple linear regression model to describe flux decline, incorporating the five fouling mechanisms (the first and second kinds of standard blocking, complete blocking, intermediate blocking, and cake filtration) based on the additivity of the permeate volume contributed by different coexisting mechanisms. A piecewise fitting protocol was established to distinguish the fouling stages and find the significant mechanisms in each stage. This approach was applied to a case study of a microfiltration membrane filtering a model foulant solution composed of polysaccharide, protein, and humic substances, and the model fitting unequivocally revealed that the dominant fouling mechanism evolved in the sequence of initial adaptation, fast adsorption followed by slow adsorption inside the membrane pores, and the gradual growth of a cake/gel layer on the membrane surface. The results were in good agreement with the permeate properties (total organic carbon, ultraviolet absorbance, and fluorescence) during the filtration process. This modeling approach proves to be simple and reliable for identifying the main fouling mechanisms during membrane filtration with statistical confidence. Full article

(This article belongs to the Special Issue Membranes for Water and Wastewater Treatment)

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23 pages, 5329 KiB

Open AccessArticle

Operating Conditions Optimization via the Taguchi Method to Remove Colloidal Substances from Recycled Paper and Cardboard Production Wastewater

by Mayko Rannany S. Sousa, Jaime Lora-García, María-Fernanda López-Pérez, Asunción Santafé-Moros and José M. Gozálvez-Zafrilla

Membranes 2020, 10(8), 170; https://doi.org/10.3390/membranes10080170 - 29 Jul 2020

Cited by 14 | Viewed by 3371

Abstract

Optimization of the ultrafiltration (UF) process to remove colloidal substances from a paper mill’s treated effluent was investigated in this study. The effects of four operating parameters in a UF system (transmembrane pressure (TMP), cross-flow velocity (CFV), temperature and molecular weight cut-off (MWCO)) [...] Read more.

Optimization of the ultrafiltration (UF) process to remove colloidal substances from a paper mill’s treated effluent was investigated in this study. The effects of four operating parameters in a UF system (transmembrane pressure (TMP), cross-flow velocity (CFV), temperature and molecular weight cut-off (MWCO)) on the average permeate flux (J_v), organic matter chemical oxygen demand (COD) rejection rate and the cumulative flux decline (SFD), was investigated by robust experimental design using the Taguchi method. Analysis of variance (ANOVA) for an L₉ orthogonal array were used to determine the significance of the individual factors, that is to say, to determine which factor has more and which less influence over the UF response variables. Analysis of the percentage contribution (P%) indicated that the TMP and MWCO have the greatest contribution to the average permeate flux and SFD. In the case of the COD rejection rate, the results showed that MWCO has the highest contribution followed by CFV. The Taguchi method and the utility concept were employed to optimize the multiple response variables. The optimal conditions were found to be 2.0 bar of transmembrane pressure, 1.041 m/s of the cross-flow velocity, 15 °C of the temperature, and 100 kDa MWCO. The validation experiments under the optimal conditions achieved J_v, COD rejection rate and SFD results of 81.15 L·m⁻²·h⁻¹, 43.90% and 6.01, respectively. Additionally, SST and turbidity decreased by about 99% and 99.5%, respectively, and reduction in particle size from around 458–1281 nm to 12.71–24.36 nm was achieved. The field-emission scanning electron microscopy images under optimal conditions showed that membrane fouling takes place at the highest rate in the first 30 min of UF. The results demonstrate the validity of the approach of using the Taguchi method and utility concept to obtain the optimal membrane conditions for the wastewater treatment using a reduced number of experiments. Full article

(This article belongs to the Special Issue Membranes for Water and Wastewater Treatment)

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23 pages, 16579 KiB

Open AccessReview

Diffusion Dialysis for Acid Recovery from Acidic Waste Solutions: Anion Exchange Membranes and Technology Integration

by Chengyi Zhang, Wen Zhang and Yuxin Wang

Membranes 2020, 10(8), 169; https://doi.org/10.3390/membranes10080169 - 29 Jul 2020

Cited by 40 | Viewed by 6175

Abstract

Inorganic acids are commonly used in mining, metallurgical, metal-processing, and nuclear-fuel-reprocessing industries in various processes, such as leaching, etching, electroplating, and metal-refining. Large amounts of spent acidic liquids containing toxic metal ion complexes are produced during these operations, which pose a serious hazard [...] Read more.

Inorganic acids are commonly used in mining, metallurgical, metal-processing, and nuclear-fuel-reprocessing industries in various processes, such as leaching, etching, electroplating, and metal-refining. Large amounts of spent acidic liquids containing toxic metal ion complexes are produced during these operations, which pose a serious hazard to the living and non-living environment. Developing economic and eco-friendly regeneration approaches to recover acid and valuable metals from these industrial effluents has focused the interest of the research community. Diffusion dialysis (DD) using anion exchange membranes (AEMs) driven by an activity gradient is considered an effective technology with a low energy consumption and little environmental contamination. In addition, the properties of AEMs have an important effect on the DD process. Hence, this paper gives a critical review of the properties of AEMs, including their acid permeability, membrane stability, and acid selectivity during the DD process for acid recovery. Furthermore, the DD processes using AEMs integrated with various technologies, such as pressure, an electric field, or continuous operation are discussed to enhance its potential for industrial applications. Finally, some directions are provided for the further development of AEMs in DD for acid recovery from acidic waste solutions. Full article

(This article belongs to the Special Issue Membranes for Water and Wastewater Treatment)

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16 pages, 2614 KiB

Open AccessArticle

Energy Harvesting from Brines by Reverse Electrodialysis Using Nafion Membranes

by Ahmet H. Avci, Diego A. Messana, Sergio Santoro, Ramato Ashu Tufa, Efrem Curcio, Gianluca Di Profio and Enrica Fontananova

Membranes 2020, 10(8), 168; https://doi.org/10.3390/membranes10080168 - 28 Jul 2020

Cited by 29 | Viewed by 5386

Abstract

Ion exchange membranes (IEMs) have consolidated applications in energy conversion and storage systems, like fuel cells and battery separators. Moreover, in the perspective to address the global need for non-carbon-based and renewable energies, salinity-gradient power (SGP) harvesting by reverse electrodialysis (RED) is attracting [...] Read more.

Ion exchange membranes (IEMs) have consolidated applications in energy conversion and storage systems, like fuel cells and battery separators. Moreover, in the perspective to address the global need for non-carbon-based and renewable energies, salinity-gradient power (SGP) harvesting by reverse electrodialysis (RED) is attracting significant interest in recent years. In particular, brine solutions produced in desalination plants can be used as concentrated streams in a SGP-RED stack, providing a smart solution to the problem of brine disposal. Although Nafion is probably the most prominent commercial cation exchange membrane for electrochemical applications, no study has investigated yet its potential in RED. In this work, Nafion 117 and Nafion 115 membranes were tested for NaCl and NaCl + MgCl₂ solutions, in order to measure the gross power density extracted under high salinity gradient and to evaluate the effect of Mg²⁺ (the most abundant divalent cation in natural feeds) on the efficiency in energy conversion. Moreover, performance of commercial CMX (Neosepta) and Fuji-CEM 80050 (Fujifilm) cation exchange membranes, already widely applied for RED applications, were used as a benchmark for Nafion membranes. In addition, complementary characterization (i.e., electrochemical impedance and membrane potential test) was carried out on the membranes with the aim to evaluate the predominance of electrochemical properties in different aqueous solutions. In all tests, Nafion 117 exhibited superior performance when 0.5/4.0 M NaCl fed through 500 µm-thick compartments at a linear velocity 1.5 cm·s⁻¹. However, the gross power density of 1.38 W·m⁻² detected in the case of pure NaCl solutions decreased to 1.08 W·m⁻² in the presence of magnesium chloride. In particular, the presence of magnesium resulted in a drastic effect on the electrochemical properties of Fuji-CEM-80050, while the impact on other membranes investigated was less severe. Full article

(This article belongs to the Special Issue Ionic Conductive Membranes for Fuel Cells)

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13 pages, 792 KiB

Open AccessArticle

Recent Experiments Support a Microemulsion Origin of Plasma Membrane Domains: Dependence of Domain Size on Physical Parameters

by David W. Allender and M. Schick

Membranes 2020, 10(8), 167; https://doi.org/10.3390/membranes10080167 - 28 Jul 2020

Cited by 6 | Viewed by 2435

Abstract

It is widely, but not universally, believed that the lipids of the plasma membrane are not uniformly distributed, but that “rafts” of sphingolipids and cholesterol float in a “sea” of unsaturated lipids. The physical origin of such heterogeneities is often attributed to a [...] Read more.

It is widely, but not universally, believed that the lipids of the plasma membrane are not uniformly distributed, but that “rafts” of sphingolipids and cholesterol float in a “sea” of unsaturated lipids. The physical origin of such heterogeneities is often attributed to a phase coexistence between the two different domains. We argue that this explanation is untenable for several reasons. Further, we note that the results of recent experiments are inconsistent with this picture. However, they are quite consistent with an alternate explanation, namely, that the plasma membrane is a microemulsion of the two kinds of regions. To show this, we briefly review a simplified version of this theory and its phase diagram. We also explicate the dependence of the predicted domain size on four physical parameters. They are the energy cost of gradients in the composition, the spontaneous curvature of the membrane, its bending modulus and its surface tension. Taking values of the latter two from experiment, we obtain domain sizes for several different cell types that vary from 58 to 88 nm. Full article

(This article belongs to the Special Issue Dynamics and Nano-Organization in Plasma Membranes)

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21 pages, 3474 KiB

Open AccessArticle

Characterization of Selected Polymeric Membranes Used in the Separation and Recovery of Palladium-Based Catalyst Systems

by Bongani Michael Xaba, Sekomeng Johannes Modise, Bamidele Joseph Okoli, Mzimkhulu Ephraim Monapathi and Simphiwe Nelana

Membranes 2020, 10(8), 166; https://doi.org/10.3390/membranes10080166 - 28 Jul 2020

Cited by 8 | Viewed by 2939

Abstract

Membrane separation processes tender a capable option for energy-demanding separation processes. Nanofiltration (NF) and reverse osmosis (RO) membranes are among the most explored, with a latent use in the chemical industry. In this study, four commercial membranes (NF90, NF270, BW30, and XLE) were [...] Read more.

Membrane separation processes tender a capable option for energy-demanding separation processes. Nanofiltration (NF) and reverse osmosis (RO) membranes are among the most explored, with a latent use in the chemical industry. In this study, four commercial membranes (NF90, NF270, BW30, and XLE) were investigated for their applicability based on the key structural performance characteristics in the recycling of Pd-based catalysts from Heck coupling post-reaction mixture. Pure water and organic solvent permeabilities, uncharged solute permeability, swelling, and catalyst rejection studies of the membranes were conducted as well as the morphological characterization using Fourier transform infrared, field emission gun scanning electron microscopy, and atomic force microscopy. Characterization results showed trends consistent with the manufactures’ specifications. Pure water and organic solvent fluxes generally followed the trend NF270 > NF90 > BW30 > XLE, with the solvent choice playing a major role in the separation process. Pd(PPh₃)₂Cl₂ was well rejected by almost all membranes in 2-propanol; however, XLE rejects Pd(OAc)₂ better at high pressure in acetonitrile. Our study, therefore, revealed that the separation and reuse of the two catalysts by NF90 at 10 bar resulted in 97% and 49% product yields with 52% and 10% catalyst retention for Pd(OAc)₂ while Pd(PPh₃)₂Cl_2. gave 87% and 6% yields with 58% and 36% catalyst retention in the first and second cycles, respectively. Considering, the influence of membrane–solute interactions in Pd-catalyst rejection, a careful selection of the polymeric membrane and solvent, a satisfactory separation, and recovery can be achieved. Full article

(This article belongs to the Section Polymeric Membranes)

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23 pages, 2793 KiB

Open AccessArticle

Transport and Electrochemical Characteristics of CJMCED Homogeneous Cation Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions

by Veronika Sarapulova, Natalia Pismenskaya, Dmitrii Butylskii, Valentina Titorova, Yaoming Wang, Tongwen Xu, Yang Zhang and Victor Nikonenko

Membranes 2020, 10(8), 165; https://doi.org/10.3390/membranes10080165 - 25 Jul 2020

Cited by 16 | Viewed by 3715

Abstract

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na₂SO₄, and CaCl₂ solutions, permeability in respect to the NaCl and CaCl₂ [...] Read more.

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na₂SO₄, and CaCl₂ solutions, permeability in respect to the NaCl and CaCl₂ diffusion, transport numbers, current–voltage curves (CVC), and the difference in the pH (ΔpH) of the NaCl solution at the desalination compartment output and input are examined for these membranes in comparison with a well-studied commercial Neosepta CMX cation-exchange membrane produced by Astom Corporation, Japan. It is found that the conductivity, CVC (at relatively low voltages), and water splitting rate (characterized by ΔpH) for both CJMCED membranes are rather close to these characteristics for the CMX membrane. However, the diffusion permeability of the CJMCED membranes is significantly higher than that of the CMX membrane. This is due to the essentially more porous structure of the CJMCED membranes; the latter reduces the counterion permselectivity of these membranes, while allowing much easier transport of large ions, such as anthocyanins present in natural dyes of fruit and berry juices. The new membranes are promising for use in electrodialysis demineralization of brackish water and natural food solutions. Full article

(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume II))

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15 pages, 3513 KiB

Open AccessArticle

Insight into Steam Permeation through Perovskite Membrane via Transient Modeling

by Shujuan Zhuang, Ning Han, Qingchuan Zou, Shuguang Zhang and Feng Song

Membranes 2020, 10(8), 164; https://doi.org/10.3390/membranes10080164 - 25 Jul 2020

Cited by 6 | Viewed by 2386

Abstract

A dynamic model based on BaCe_0.9Y_0.1O_3−δ (BCY10) perovskite membrane for steam permeation process is presented here to essentially investigate the internal mechanism. The transient concentration distribution and flux of the charged species and the electric potential distribution within [...] Read more.

A dynamic model based on BaCe_0.9Y_0.1O_3−δ (BCY10) perovskite membrane for steam permeation process is presented here to essentially investigate the internal mechanism. The transient concentration distribution and flux of the charged species and the electric potential distribution within the membrane on the steam permeation process are analyzed in detail via simulation based on this model. The results indicate that the flux of steam can be improved via elevating operating temperatures, enlarging the difference of the partial steam pressure between two sides of the membrane, increasing the membrane density, and reducing the membrane thickness. Moreover, it was found that the polarization electric potential between both sides of the membrane occurs during the steam permeation process, especially at the steady state of the steam permeation process. The polarization electric potential reaches the maximum value at about 1050 K in this membrane. The evolution of electric potential can explain the influence of the above-mentioned factors on the steam permeation process. This study advances the mechanism of steam permeation through perovskite membrane, which provides a new strategy for the fundamental investigation of related species permeation (oxygen, carbon dioxide, hydrogen, etc.) on inorganic membranes via transient modeling. Full article

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

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12 pages, 9051 KiB

Open AccessArticle

Tuning the Surface Structure of Polyamide Membranes Using Porous Carbon Nitride Nanoparticles for High-Performance Seawater Desalination

by Zongyao Zhou, Xiang Li, Digambar B. Shinde, Guan Sheng, Dongwei Lu, Peipei Li and Zhiping Lai

Membranes 2020, 10(8), 163; https://doi.org/10.3390/membranes10080163 - 24 Jul 2020

Cited by 14 | Viewed by 3429

Abstract

Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C₃N₄) nanoparticle to potentially improve both the water flux and [...] Read more.

Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C₃N₄) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic–organic covalent bonds endowed C₃N₄ with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C₃N₄, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C₃N₄ embedded in the ”ridge” sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination. Full article

(This article belongs to the Special Issue Membranes for Water and Wastewater Treatment)

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12 pages, 2275 KiB

Open AccessArticle

Amphipathic Janus Membrane with Hierarchical Multiscale Hyperporous Structure for Interfacial Catalysis

by Yakai Lin, Yuanyuan Liu, Yicheng Su, Lin Wang, Yuanhui Tang, Tianyin Liu, Liwei Ren and Xiaolin Wang

Membranes 2020, 10(8), 162; https://doi.org/10.3390/membranes10080162 - 23 Jul 2020

Cited by 3 | Viewed by 3247

Abstract

The rational design and realization of multiscale porous structures has been a long-standing challenge in membrane science. Block copolymers (BCPs) with their self-assembly-enabled nanodomains have the potential to make structural breakthroughs. An amphipathic Janus membrane, with a hierarchical multiscale hyperporous structure constituted by [...] Read more.

The rational design and realization of multiscale porous structures has been a long-standing challenge in membrane science. Block copolymers (BCPs) with their self-assembly-enabled nanodomains have the potential to make structural breakthroughs. An amphipathic Janus membrane, with a hierarchical multiscale hyperporous structure constituted by polystyrene-b-poly(4-vinylpyridine) (PS4VP) and polyvinylidene fluoride (PVDF) blocks, was designed and synthesized in this work. Hydrophobic PVDF dominated one side of the membrane, and hydrophilic PS4VP, with nanopores that formed inside the macroporous channels of PVDF via a self-assembly approach, dominated the other side. Candida Rugosa Lipase (CRL), as a model biocatalyst, was immobilized in the PS4VP nanopores via injection. The immobilized lipase was exactly suspended at the interface of the organic and aqueous phases, owing to the amphipathic property of the Janus membrane. The designed structures and catalysis performances were further characterized. The immobilized lipase exhibited a three times higher specific activity than free lipase, and the relative activity still remained above 90% after 10 cycles of reusing, indicating the observable promotion and the guaranteed stability of the Janus membrane in interfacial catalysis. This work provided a general, facile and unique example for the design and synthesis of a hierarchical multiscale hyperporous membrane for interfacial catalysis. Full article

(This article belongs to the Special Issue Polymeric Membrane)

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