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Membranes
Volume 11
Issue 2
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Membranes, Volume 11, Issue 2 (February 2021) – 87 articles

Cover Story (view full-size image): Block copolymer-based magnetic-responsive membranes are smart membranes which due to the presence of iron oxide nanoparticle are susceptible to magnetic stimuli exhibited by a change in their porous structure. One of the hallmarks of these hybrid materials is to mitigate fouling, a primary membrane separation-related issue. This work demonstrates the use of these novel membranes, synthesized via reversible addition–fragmentation chain transfer polymerization. The impact of the magnetic responsiveness of hybrid membranes on protein permeation was evaluated under ON/OFF cyclic magnetic field conditions, using bovine serum albumin as the model protein. The magnetic field allowed for a lower decay of the permeate flux and an improved protein transmission, suggesting the potential contribution of these magnetic-responsive block copolymer membranes for the development of improved bioseparations. View this [...] Read more.
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18 pages, 7141 KiB  
Article
Novel Module-Based Membrane Reactor Design Approach for Improved Operability Performance
by Brent A. Bishop and Fernando V. Lima
Membranes 2021, 11(2), 157; https://doi.org/10.3390/membranes11020157 - 23 Feb 2021
Cited by 6 | Viewed by 3380
Abstract
This work aims to address the design and control challenges caused by the integration of phenomena and the loss of degrees of freedom (DOF) that occur in the intensification of membrane reactor units. First, a novel approach to designing membrane reactor units is [...] Read more.
This work aims to address the design and control challenges caused by the integration of phenomena and the loss of degrees of freedom (DOF) that occur in the intensification of membrane reactor units. First, a novel approach to designing membrane reactor units is proposed. This approach consists of designing smaller modules based on specific phenomena such as heat exchange, reactions, and mass transport and combining them in series to produce the final modular membrane-based unit. This approach to designing membrane reactors is then assessed using a process operability analysis for the first time to maximize the operability index, as a way of quantifying the operational performance of intensified processes. This work demonstrates that by designing membrane reactors in this way, the operability of the original membrane reactor design can be significantly improved, translating to an improvement in achievability for a potential control structure implementation. Full article
(This article belongs to the Special Issue Membrane Reactors for Process Intensification: Recent Advances and Key Applications)
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Figure 1
<p>An example arrangement of three modules to make a larger intensified unit. Here a membrane separator (M), a membrane reactor (MR), and a reactor (R) are combined.</p> Full article ">Figure 2
<p>A breakdown of the individual phenomena that take place in each unit operation.</p> Full article ">Figure 3
<p>Each piece of modular equipment consists of individual modules in series. These modules have been fully developed in AVEVA Process Simulation and can be a heat exchanger, reactor, membrane separator, or membrane reactor.</p> Full article ">Figure 4
<p>Schematic of the process operability concept. The fraction of the DOS covered by the green region would correspond to the operability index (OI) for the design.</p> Full article ">Figure 5
<p>Schematic of a shell and tube WGS-MR for hydrogen recovery and carbon capture.</p> Full article ">Figure 6
<p>Image of the countercurrent WGS-MR setup where the syngas process flow control valve (FC1) and the sweep gas control valve (FC2) manual positions are changed to generate the AIS.</p> Full article ">Figure 7
<p>Computational framework developed for determining the optimum N-mod design.</p> Full article ">Figure 8
<p>The mapping of the input space of control valve positions (AIS) to the output space of carbon capture and hydrogen recovery (AOS).</p> Full article ">Figure 9
<p>Plot showing all viable 2-mod design AOS’s given the same AIS. Here, the red AOS represents the membrane reactor AOS that is shown in <a href="#membranes-11-00157-f008" class="html-fig">Figure 8</a>. In addition, M<sub>1</sub>, M<sub>2</sub>,… M<sub>N</sub>, denote the mapping of each module-based design.</p> Full article ">Figure 10
<p>The optimum 2-mod design that maximizes the size of the AOS. In this case, this design can achieve a 65% larger space than the base case membrane reactor.</p> Full article ">Figure 11
<p>Plot showing all viable 3-mod design AOS’s given the same AIS. Here, the red AOS represents the membrane reactor AOS that was first shown in <a href="#membranes-11-00157-f008" class="html-fig">Figure 8</a>.</p> Full article ">Figure 12
<p>The optimum 3-mod design that maximizes the size of the AOS. In this case, this design can achieve a 67% larger space than the base case membrane reactor.</p> Full article ">Figure 13
<p>The optimum 4-mod design that maximizes the size of the AOS. In this case, this design can achieve a 76% larger space than the base case membrane reactor.</p> Full article ">Figure 14
<p>The AOS of the original membrane reactor is shown (in blue/green). The area of the overlap (green) with the DOS (white) has an OI of 0.129 meaning the membrane reactor can achieve 12.9% of the DOS.</p> Full article ">Figure 15
<p>The AOS of the optimum 4-mod design is shown (in blue/green). The area of the overlap (green) with the DOS (white) has an OI of 0.176, approximately a 37% improvement from the base case.</p> Full article ">
9 pages, 876 KiB  
Perspective
Recent Developments in High-Performance Membranes for CO2 Separation
by Zi Tong and Ali K. Sekizkardes
Membranes 2021, 11(2), 156; https://doi.org/10.3390/membranes11020156 - 23 Feb 2021
Cited by 26 | Viewed by 6271
Abstract
In this perspective article, we provide a detailed outlook on recent developments of high-performance membranes used in CO2 separation applications. A wide range of membrane materials including polymers of intrinsic microporosity, thermally rearranged polymers, metal–organic framework membranes, poly ionic liquid membranes, and [...] Read more.
In this perspective article, we provide a detailed outlook on recent developments of high-performance membranes used in CO2 separation applications. A wide range of membrane materials including polymers of intrinsic microporosity, thermally rearranged polymers, metal–organic framework membranes, poly ionic liquid membranes, and facilitated transport membranes were surveyed from the recent literature. In addition, mixed matrix and polymer blend membranes were covered. The CO2 separation performance, as well as other membrane properties such as film flexibility, processibility, aging, and plasticization, were analyzed. Full article
(This article belongs to the Special Issue Advanced Membranes for Carbon Capture)
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Figure 1
<p>Schematic of CO<sub>2</sub> and amine carrier interaction and an ultrafast CO<sub>2</sub>-selective transport channel inside a facilitated transport membrane.</p> Full article ">Figure 2
<p>Robeson Upper Bound 2008 plot depicting CO<sub>2</sub> permeability and CO<sub>2</sub>/N<sub>2</sub> selectivity of gas separation membranes based on polyvinylamine PVAm, metal–organic frameworks (MOFs), polyethylene oxide (PEO), thermally rearranged (TR) polymers, polymers of intrinsic micro porosity (PIMs), and conventional membranes [<a href="#B15-membranes-11-00156" class="html-bibr">15</a>].</p> Full article ">
17 pages, 1498 KiB  
Review
Membrane Protein Stabilization Strategies for Structural and Functional Studies
by Ekaitz Errasti-Murugarren, Paola Bartoccioni and Manuel Palacín
Membranes 2021, 11(2), 155; https://doi.org/10.3390/membranes11020155 - 22 Feb 2021
Cited by 22 | Viewed by 6705
Abstract
Accounting for nearly two-thirds of known druggable targets, membrane proteins are highly relevant for cell physiology and pharmacology. In this regard, the structural determination of pharmacologically relevant targets would facilitate the intelligent design of new drugs. The structural biology of membrane proteins is [...] Read more.
Accounting for nearly two-thirds of known druggable targets, membrane proteins are highly relevant for cell physiology and pharmacology. In this regard, the structural determination of pharmacologically relevant targets would facilitate the intelligent design of new drugs. The structural biology of membrane proteins is a field experiencing significant growth as a result of the development of new strategies for structure determination. However, membrane protein preparation for structural studies continues to be a limiting step in many cases due to the inherent instability of these molecules in non-native membrane environments. This review describes the approaches that have been developed to improve membrane protein stability. Membrane protein mutagenesis, detergent selection, lipid membrane mimics, antibodies, and ligands are described in this review as approaches to facilitate the production of purified and stable membrane proteins of interest for structural and functional studies. Full article
(This article belongs to the Special Issue Experimental and Computational Methods for Membrane Protein Design)
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Figure 1
<p>Schematic representation of the split GFP assay as reporter of membrane protein expression and stability in the membrane. The split GFP assay consists of two plasmids: one containing the target membrane protein fused to GFP strand 11 (<b>left</b>) and another plasmid expressing GFP strands 1 to 10 (<b>right</b>). Protein expression is controlled by two promoters activated by different inducers (I1 and I2). Inducing these two genes sequentially allows the identification of target membrane protein variants that are expressed and inserted into the plasma membrane of the expression system, since the two fragments of the GFP complements resulting in fluorescence emission. Variants confined into inclusion bodies show no fluorescence as no complementation occurs.</p> Full article ">Figure 2
<p>Membrane protein incorporation into a nanodisc. Detergent (black micelle)-solubilized membrane protein (blue) is incubated with a mixture of membrane scaffold protein (MSP; green) and detergent-solubilized lipids (tan). Nanodisc assembly is initiated after detergent removal.</p> Full article ">Figure 3
<p>Nanobodies in membrane protein structural biology. (<b>a</b>) Traditional monoclonal antibodies (mAb) and their fragments (Fab) vs. heavy chain antibodies (HcAb) and nanobodies (Nb). (<b>b</b>) Nanobody structure (PDB ID: 6f2g) [<a href="#B101-membranes-11-00155" class="html-bibr">101</a>], showing complementary determining regions (CDR) 1 (magenta), 2 (blue), and 3 (orange) and the disulfide bridge established between Cys 22 and Cys 96. (<b>c</b>) Extensive interactions were found between the side chains and backbones of the nanobody CDR3 (orange) and the bacterial amino acid transporter BasC (PDB ID: 6f2g) [<a href="#B101-membranes-11-00155" class="html-bibr">101</a>]. CDR3 interacts with residues from BasC transmembrane domains (TMs) 1, 6, 8 and 9.</p> Full article ">
23 pages, 5221 KiB  
Article
A Unified, One Fluid Model for the Drag of Fluid and Solid Dispersals by Permeate Flux towards a Membrane Surface
by Amgad Salama, Shuyu Sun and Tao Zhang
Membranes 2021, 11(2), 154; https://doi.org/10.3390/membranes11020154 - 22 Feb 2021
Cited by 1 | Viewed by 2342
Abstract
The drag of dispersals towards a membrane surface is a consequence of the filtration process. It also represents the first step towards the development of the problem of fouling. In order to combat membrane fouling, it is important to understand such drag mechanisms [...] Read more.
The drag of dispersals towards a membrane surface is a consequence of the filtration process. It also represents the first step towards the development of the problem of fouling. In order to combat membrane fouling, it is important to understand such drag mechanisms and provide a modeling framework. In this work, a new modeling and numerical approach is introduced that is based on a one-domain model in which both the dispersals and the surrounding fluid are dealt with as a fluid with heterogeneous property fields. Furthermore, because of the fact that the geometry of the object assumes axial symmetry and the configuration remains fixed, the location of the interface may be calculated using geometrical relationships. This alleviates the need to define an indicator function and solve a hyperbolic equation to update the configuration. Furthermore, this approach simplifies the calculations and significantly reduces the computational burden required otherwise if one incorporates a hyperbolic equation to track the interface. To simplify the calculations, we consider the motion of an extended cylindrical object. This allows a reduction in the dimensions of the problem to two, thereby reducing the computational burden without a loss of generality. Furthermore, for this particular case there exists an approximate analytical solution that accounts for the effects of the confining boundaries that usually exist in real systems. We use such a setup to provide the benchmarking of the different averaging techniques for the calculations of properties at the cell faces and center, particularly in the cells involving the interface. Full article
(This article belongs to the Special Issue Flow and Transport in Membranes: Modeling and Experimental Verification)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Surface forces at the two sides of the interface between two phases. Jump in the normal stress is correlated with the curvature of the interface. Tangential stress does not experience jump under the no-slip condition.</p> Full article ">Figure 2
<p>Schematic diagram of the gradient function of the phase function, <math display="inline"><semantics> <mi>φ</mi> </semantics></math>. The gradient is zero in every way except at the interface, where it jumps as a positive delta function on half the interface and a negative delta function over the second half. Therefore, its integral over the whole interface is zero.</p> Full article ">Figure 3
<p>Schematic of the domain where Faxén [<a href="#B39-membranes-11-00154" class="html-bibr">39</a>] expansion apply.</p> Full article ">Figure 4
<p>Schematic of the staggered grid for the three equations.</p> Full article ">Figure 5
<p>Discrete determination of the average velocity over the cells that are completely inside the boundary.</p> Full article ">Figure 6
<p>Schematic representation of the domain.</p> Full article ">Figure 7
<p>Evaluation of the second order derivative closer to the interface.</p> Full article ">Figure 8
<p>Evaluating the density in the interface region.</p> Full article ">Figure 9
<p>Schematic of the computational domain.</p> Full article ">Figure 10
<p>Succession of particle motion (<span class="html-italic">ρ<sub>s</sub></span> = 3000, <span class="html-italic">ρ<sub>f</sub></span> = 1000, μ<sub>s</sub> = 1000, μ<sub>f</sub> = 17.72).</p> Full article ">Figure 11
<p>Velocity profiles (<b>a</b>), streamlines (<b>b</b>), and vorticity contours (<b>c</b>).</p> Full article ">Figure 12
<p>Velocity vectors of the fluid.</p> Full article ">Figure 13
<p>x (red) and y (blue) positions of the particle with time.</p> Full article ">Figure 14
<p>Y-component velocity with time.</p> Full article ">Figure 15
<p>Comparisons between the terminal settling velocity and the simulated one for different diameter to width ratios. In these simulations, the following parameters are held fixed: μ<sub>f</sub> = 0.001 Pa·s, μ<sub>p</sub> = 1000 Pa·s, Mesh n<sub>x</sub> = 40, n<sub>y</sub> = 80.</p> Full article ">Figure 16
<p>Comparisons between the terminal settling velocity and the simulated one for different algorithms for calculating the density in the cells encompassing the interface. In these simulations, the following parameters are held fixed: <math display="inline"><semantics> <mrow> <msub> <mi>k</mi> <mi>x</mi> </msub> </mrow> </semantics></math> = d/L<sub>x</sub> = 4, μ<sub>f</sub> = 0.001 Pa·s, μ<sub>p</sub> = 1000 Pa·s, Mesh n<sub>x</sub> = 40, n<sub>y</sub> = 80.</p> Full article ">Figure 17
<p>Comparisons between the terminal settling velocity and the simulated one for different viscosity ratios. In these simulations, the following parameters are held fixed: <math display="inline"><semantics> <mrow> <msub> <mi>k</mi> <mi>x</mi> </msub> </mrow> </semantics></math> = d/L<sub>x</sub> = 4, μ<sub>f</sub> = 0.001 Pa·s, Mesh density n<sub>x</sub> = 40, n<sub>y</sub> = 80.</p> Full article ">Figure 18
<p>Comparisons between the terminal settling velocity and the simulated one for different spatial resolutions. In these simulations, the following parameters are held fixed: <math display="inline"><semantics> <mrow> <msub> <mi>k</mi> <mi>x</mi> </msub> </mrow> </semantics></math> = d/L<sub>x</sub> = 4, μ<sub>f</sub> = 0.001 Pa·s, μ<sub>p</sub> = 1000 Pa·s.</p> Full article ">
20 pages, 6435 KiB  
Article
Insights into the Influence of Membrane Permeability and Structure on Osmotically-Driven Membrane Processes
by Jing Wei, Qianhong She and Xin Liu
Membranes 2021, 11(2), 153; https://doi.org/10.3390/membranes11020153 - 22 Feb 2021
Cited by 15 | Viewed by 3665
Abstract
The success of osmotically-driven membrane (OM) technology relies critically on high-performance membranes. Yet trade-off of membrane properties, often further complicated by the strongly non-linear dependence of OM performance on them, imposes important constraint on membrane performance. This work systematically characterized four typical commercial [...] Read more.
The success of osmotically-driven membrane (OM) technology relies critically on high-performance membranes. Yet trade-off of membrane properties, often further complicated by the strongly non-linear dependence of OM performance on them, imposes important constraint on membrane performance. This work systematically characterized four typical commercial osmotic membranes in terms of intrinsic separation parameters, structure and surface properties. The osmotic separation performance and membrane scaling behavior of these membranes were evaluated to elucidate the interrelationship of these properties. Experimental results revealed that membranes with smaller structural parameter (S) and higher water/solute selectivity underwent lower internal concentration polarization (ICP) and exhibited higher forward osmosis (FO) efficiency (i.e., higher ratio of experimental water flux over theoretical water flux). Under the condition with low ICP, membrane water permeability (A) had dominant effect on water flux. In this case, the investigated thin film composite membrane (TFC, A = 2.56 L/(m2 h bar), S = 1.14 mm) achieved a water flux up to 82% higher than that of the asymmetric cellulose triacetate membrane (CTA-W(P), A = 1.06 L/(m2 h bar), S = 0.73 mm). In contrast, water flux became less dependent on the A value but was affected more by membrane structure under the condition with severe ICP, and the membrane exhibited lower FO efficiency. The ratio of water flux (Jv TFC/Jv CTA-W(P)) decreased to 0.55 when 0.5 M NaCl feed solution and 2 M NaCl draw solution were used. A framework was proposed to evaluate the governing factors under different conditions and to provide insights into the membrane optimization for targeted OM applications. Full article
(This article belongs to the Special Issue Membrane-based Technologies for Water and Energy Sustainability)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic illustration of osmotic pressure profile across the membrane in osmotically-driven membrane processes. (<b>a</b>) Active-layer-facing-draw-solution (AL-DS) mode. (<b>b</b>) Active-layer-facing-feed-solution (AL-FS) mode. Δ<span class="html-italic">π<sub>effective</sub></span> is the effective osmotic pressure difference. Δ<span class="html-italic">π<sub>CICP</sub></span>, Δ<span class="html-italic">π<sub>DICP</sub></span>, Δ<span class="html-italic">π<sub>CECP</sub></span>, and Δ<span class="html-italic">π<sub>DECP</sub></span> are the osmotic pressure difference loss caused by concentrative internal concentration polarization (ICP), dilutive ICP, concentrative external concentration polarization (ECP), and dilutive ECP [<a href="#B18-membranes-11-00153" class="html-bibr">18</a>].</p> Full article ">Figure 2
<p>Structure and surface morphology of the thin film composite membrane (TFC) and cellulose triacetate membrane (CTA-W(P)). (<b>a</b>) Field-emission scanning electron microscopy (FESEM) micrograph of TFC cross-section at 500×. (<b>b</b>) FESEM micrograph of the surface of TFC active layer at 100,000×. (<b>c</b>) Atomic force microscopy (AFM) image of the surface of TFC active layer. (<b>d</b>) FESEM micrograph of CTA-W(P) cross-section at 500×. (<b>e</b>) FESEM micrograph of the surface of CTA-W(P) active layer at 100,000×. (<b>f</b>) AFM image of the surface of CTA-W(P) active layer.</p> Full article ">Figure 2 Cont.
<p>Structure and surface morphology of the thin film composite membrane (TFC) and cellulose triacetate membrane (CTA-W(P)). (<b>a</b>) Field-emission scanning electron microscopy (FESEM) micrograph of TFC cross-section at 500×. (<b>b</b>) FESEM micrograph of the surface of TFC active layer at 100,000×. (<b>c</b>) Atomic force microscopy (AFM) image of the surface of TFC active layer. (<b>d</b>) FESEM micrograph of CTA-W(P) cross-section at 500×. (<b>e</b>) FESEM micrograph of the surface of CTA-W(P) active layer at 100,000×. (<b>f</b>) AFM image of the surface of CTA-W(P) active layer.</p> Full article ">Figure 3
<p>Fourier transform infrared spectroscopy (FTIR) spectra of (<b>a</b>) TFC, and (<b>b</b>) CTA-W(P), CTA-woven (W), and CTA-nonwoven (NW) membranes.</p> Full article ">Figure 3 Cont.
<p>Fourier transform infrared spectroscopy (FTIR) spectra of (<b>a</b>) TFC, and (<b>b</b>) CTA-W(P), CTA-woven (W), and CTA-nonwoven (NW) membranes.</p> Full article ">Figure 4
<p>Forward osmosis (FO) water flux of TFC and CTA-W(P) membranes with different feed and draw solutions. The tests were performed in (<b>a</b>) AL-DS mode, and (<b>b</b>) AL-FS mode. Pure water, 10 mM and 0.5 M NaCl were used as feed solution (FS), which are denoted as DI, 0.01 M and 0.5 M. 0.2 M, 0.5 M, and 2 M NaCl were used as draw solution (DS), which are denoted as 0.2 M, 0.5 M, and 2 M.</p> Full article ">Figure 5
<p>Water flux of TFC and CTA-W(P) in FO scaling tests. Testing conditions: FS for baseline tests was 0.163 M NaCl; FS for scaling tests was a mixed solution containing 72 mM Na<sub>2</sub>SO<sub>4</sub>, 26.1 mM CaCl<sub>2</sub>, and 10 mM NaCl; crossflow velocities of FS and DS on membrane were 23.2 cm/s; 2–3 M NaCl were used as DS to achieve initial water flux of 15 ± 1 L/(m<sup>2</sup> h).</p> Full article ">Figure 6
<p>Pressure-retarded osmosis (PRO) performance of TFC and CTA-W(P) membranes: (<b>a</b>) water flux, (<b>b</b>) power density, and (<b>c</b>) salt flux/water flux ratio. Testing conditions: 10 mM NaCl as FS, 1 M NaCl as DS, and active-layer-facing-draw-solution (AL-DS) mode.</p> Full article ">Figure 7
<p>FO water flux of membranes with different water permeability (<span class="html-italic">A</span>) and mass diffusion coefficient (<span class="html-italic">K<sub>m</sub></span>). The data was obtained from the experiments in the current work and the literature, and the membrane properties are presented in <a href="#membranes-11-00153-t0A1" class="html-table">Table A1</a> and <a href="#app1-membranes-11-00153" class="html-app">Table S1</a>. Data in (<b>a</b>,<b>b</b>) were evaluated with FS of 0–10 mM NaCl and DS of 0.5–0.75 M NaCl. Data in (<b>c</b>,<b>d</b>) were evaluated with FS of 0.5–0.6 M NaCl and DS of 1.5–2 M NaCl.</p> Full article ">Figure 8
<p>The FO efficiency of benchmark membrane (CTA-W(P)) and <span class="html-italic">J<sub>v TFC</sub>/J<sub>v CTA-W(P)</sub></span> in different testing conditions. DI water, 0.01 M and 0.5 M NaCl were used as FS; 0.2 M, 0.5 M, and 2 M NaCl were used as DS, as in the legend.</p> Full article ">Figure A1
<p>FESEM micrographs of the cross-sections (at 500×) of (<b>a</b>) CTA-W and (<b>b</b>) CTA-NW.</p> Full article ">Figure A2
<p>Illustration of tensile testing with tension in (<b>a</b>) axial direction and (<b>b</b>) diagonal direction.</p> Full article ">Figure A3
<p>FO water flux and salt flux/water flux of the TFC, CTA-W(P), CTA-W, and CTA-NW membranes. Testing conditions: 10 mM NaCl as FS, and 0.5 M or 2 M NaCl as DS.</p> Full article ">
14 pages, 2748 KiB  
Article
Recovery of Acid and Base from Sodium Sulfate Containing Lithium Carbonate Using Bipolar Membrane Electrodialysis
by Wenjie Gao, Qinxiang Fang, Haiyang Yan, Xinlai Wei and Ke Wu
Membranes 2021, 11(2), 152; https://doi.org/10.3390/membranes11020152 - 22 Feb 2021
Cited by 33 | Viewed by 6653
Abstract
Lithium carbonate is an important chemical raw material that is widely used in many contexts. The preparation of lithium carbonate by acid roasting is limited due to the large amounts of low-value sodium sulfate waste salts that result. In this research, bipolar membrane [...] Read more.
Lithium carbonate is an important chemical raw material that is widely used in many contexts. The preparation of lithium carbonate by acid roasting is limited due to the large amounts of low-value sodium sulfate waste salts that result. In this research, bipolar membrane electrodialysis (BMED) technology was developed to treat waste sodium sulfate containing lithium carbonate for conversion of low-value sodium sulfate into high-value sulfuric acid and sodium hydroxide. Both can be used as raw materials in upstream processes. In order to verify the feasibility of the method, the effects of the feed salt concentration, current density, flow rate, and volume ratio on the desalination performance were determined. The conversion rate of sodium sulfate was close to 100%. The energy consumption obtained under the best experimental conditions was 1.4 kWh·kg?1. The purity of the obtained sulfuric acid and sodium hydroxide products reached 98.32% and 98.23%, respectively. Calculated under the best process conditions, the total process cost of BMED was estimated to be USD 0.705 kg?1 Na2SO4, which is considered low and provides an indication of the potential economic and environmental benefits of using applying this technology. Full article
(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume II))
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Figure 1
<p>A flow chart of the preparation of lithium carbonate by acid roasting and bipolar membrane electrodialysis (BMED) technology.</p> Full article ">Figure 2
<p>Schematic diagram of the BMED membrane reactor used in the experiment.</p> Full article ">Figure 3
<p>Effect of feed concentration on BMED performance: (<b>a</b>) acid concentration and alkali concentration, (<b>b</b>) electrical conductivity, (<b>c</b>) voltage drop across the apparatus, and (<b>d</b>) energy consumption and current efficiency.</p> Full article ">Figure 4
<p>Effect of current density on BMED performance: (<b>a</b>) acid concentration and alkali concentration, (<b>b</b>) electrical conductivity, (<b>c</b>) voltage drop across the apparatus, and (<b>d</b>) energy consumption and current efficiency.</p> Full article ">Figure 5
<p>Effect of flow rate on BMED performance: (<b>a</b>) acid concentration and alkali concentration, (<b>b</b>) electrical conductivity, (<b>c</b>) voltage drop across the apparatus, and (<b>d</b>) energy consumption and current efficiency.</p> Full article ">Figure 6
<p>Effect of volume ratio on BMED performance: (<b>a</b>) acid concentration and alkali concentration, (<b>b</b>) electrical conductivity, (<b>c</b>) voltage drop across the apparatus, and (<b>d</b>) energy consumption and current efficiency.</p> Full article ">Figure 7
<p>Comparison of BMED experiments using simulated feed and pure feed: (<b>a</b>) the experimental process and (<b>b</b>) the experimental results.</p> Full article ">Scheme 1
<p>Reaction scheme for the synthesis of lithium carbonate by chlorination roasting, acid roasting, and alkali roasting.</p> Full article ">
25 pages, 5230 KiB  
Article
Improvement of Barrier Properties of Biodegradable Polybutylene Succinate/Graphene Nanoplatelets Nanocomposites Prepared by Melt Process
by Raphaël Cosquer, Sébastien Pruvost and Fabrice Gouanvé
Membranes 2021, 11(2), 151; https://doi.org/10.3390/membranes11020151 - 22 Feb 2021
Cited by 25 | Viewed by 3876
Abstract
Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence [...] Read more.
Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence of these fillers did not significantly modify the morphology, crystalline microstructure of the matrix or its thermal stability. However, a slight reinforcement effect of PBS was reported in the presence of GnP. The water sorption isotherm modelling with Guggenheim, Andersen and De Boer (GAB) equation and Zimm-Lundberg theory allowed a phenomenological analysis at the molecular scale. The presence of GnP did not modify the water sorption capacity of the PBS matrix. From a kinetic point of view, a decrease of the diffusion coefficient with the increasing GnP content was obtained and was attributed to a tortuosity effect. The influence of water activity was discussed over a range of 0.5 to 1 and 0 to 0.9 for water and dioxygen permeability. Improvement of the barrier properties by 38% and 35% for water and dioxygen permeability respectively were obtained. Full article
(This article belongs to the Special Issue Advances on Bio-Based Materials for Food Packaging Applications)
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Figure 1
<p>Chemical structure of Polybutylene Succinate (PBS) repeating unit.</p> Full article ">Figure 2
<p>Transmission electron micrographs of Polybutylene Succinate/Graphene nanoplatelets (PBS/GnP) nanocomposites films (<b>a</b>) PBS/GnP0.1; (<b>b</b>) PBS/GnP0.5; (<b>c</b>) PBS/GnP1; (<b>d</b>) PBS/GnP2.</p> Full article ">Figure 3
<p>(<b>A</b>): WAXS patterns of GnP powder, PBS neat matrix and the different nanocomposites films and (<b>B</b>): deconvolution of WAXS patterns and assignation of the different peaks for neat PBS matrix.</p> Full article ">Figure 4
<p>DSC thermograms of (<b>A</b>) first heating scan (<b>B</b>) cooling scan of neat PBS and corresponding composites.</p> Full article ">Figure 5
<p>Evolution of the weight loss as a function the temperature for PBS and corresponding composites.</p> Full article ">Figure 6
<p>Evolution of (<b>A</b>) storage modulus (G’), (<b>B</b>) loss modulus (G<sup>″</sup>) and (<b>C</b>) tan δ as a function of the temperature of PBS and corresponding composites, at 10 Hz.</p> Full article ">Figure 7
<p>(<b>A</b>): Sorption Isotherm curves at T = 25 °C of the neat PBS matrix and the different nanocomposites and (<b>B</b>): mass gain in the amorphous phase of neat PBS with GAB model as function of the water activity and average number of water molecules sorbed per amorphous unit of PBS (Ni) as function of water activity.</p> Full article ">Figure 8
<p>Evolution for neat PBS of Mean cluster size as a function of: (<b>A</b>) water activity and (<b>B</b>) average number of water molecules sorbed in a single amorphous unit of polymer and (<b>C</b>): evolution of Ni/MCS as a function of the water activity for neat PBS.</p> Full article ">Figure 9
<p>(<b>A</b>) Evolution of diffusion coefficient D as a function of water activity for neat PBS and associated nanocomposites. (<b>B</b>) Evolution diffusion coefficient as a function of Mean Size Cluster for neat PBS.</p> Full article ">Figure 10
<p>Evolution of the water permeability (<b>A</b>) and relative water permeability (<b>B</b>) as a function of water activity of neat PBS and corresponding composites.</p> Full article ">Figure 11
<p>Evolution of the dioxygen permeability (<b>A</b>) and relative dioxygen permeability (<b>B</b>) as a function of water activity of neat PBS and corresponding composites.</p> Full article ">Figure 12
<p>Evolution of the water and oxygen relative permeability as a function of GnP volume fraction for a water activity = 0.7 and Bharadwaj model.</p> Full article ">
13 pages, 2511 KiB  
Review
Recent Impact of Microfluidics on Skin Models for Perspiration Simulation
by Genís Rabost-Garcia, Josep Farré-Lladós and Jasmina Casals-Terré
Membranes 2021, 11(2), 150; https://doi.org/10.3390/membranes11020150 - 21 Feb 2021
Cited by 11 | Viewed by 4228
Abstract
Skin models offer an in vitro alternative to human trials without their high costs, variability, and ethical issues. Perspiration models, in particular, have gained relevance lately due to the rise of sweat analysis and wearable technology. The predominant approach to replicate the key [...] Read more.
Skin models offer an in vitro alternative to human trials without their high costs, variability, and ethical issues. Perspiration models, in particular, have gained relevance lately due to the rise of sweat analysis and wearable technology. The predominant approach to replicate the key features of perspiration (sweat gland dimensions, sweat rates, and skin surface characteristics) is to use laser-machined membranes. Although they work effectively, they present some limitations at the time of replicating sweat gland dimensions. Alternative strategies in terms of fabrication and materials have also showed similar challenges. Additional research is necessary to implement a standardized, simple, and accurate model representing sweating for wearable sensors testing. Full article
(This article belongs to the Special Issue Microfluidics and MEMS Technology for Membranes)
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<p>Scheme of the different purpose and applications of skin models.</p> Full article ">Figure 2
<p>(<b>a</b>) Scheme showing human eccrine sweat gland structure and its microfluidic equivalent model. Adapted with permission from [<a href="#B32-membranes-11-00150" class="html-bibr">32</a>]. Copyright 2015, AIP. (<b>b</b>) Absolute regional median sweat rates of male athletes at a fixed exercise intensity (75% VO<sub>2</sub>) measured gravimetrically using absorbent pads. Reprinted with permission from [<a href="#B33-membranes-11-00150" class="html-bibr">33</a>]. Copyright 2010, Springer Nature. (<b>c</b>) SEM photography of human skin. Adapted with permission from [<a href="#B34-membranes-11-00150" class="html-bibr">34</a>]. Copyright 2013, Royal Society of Chemistry. (<b>d</b>) In vivo skin roughness, RMS values, obtained by a speckle device (black) and fringe projection systems (clear). Reprinted with permission from [<a href="#B35-membranes-11-00150" class="html-bibr">35</a>]. Copyright 2010, Intechopen.</p> Full article ">Figure 3
<p>Perspiration models in literature. (<b>a</b>) Schematic of the bi-layer membrane design and its comparison with the sweat gland structure (left). Depiction of the experimental set-up and image of the integrated membrane (right). Reprinted with permission from [<a href="#B34-membranes-11-00150" class="html-bibr">34</a>]. Copyright 2013, Royal Society of Chemistry. (<b>b</b>) Scheme showing the layers of the perspiration model by Hansen et al. [<a href="#B45-membranes-11-00150" class="html-bibr">45</a>] (left). Adapted with permission from [<a href="#B45-membranes-11-00150" class="html-bibr">45</a>]. Copyright 2020, American Chemical Society. Microscopy image of the surface of the artificial skin by Eiler et al. [<a href="#B46-membranes-11-00150" class="html-bibr">46</a>] (right). Adapted with permission from [<a href="#B46-membranes-11-00150" class="html-bibr">46</a>]. Copyright 2020, Elsevier. (<b>c</b>) Experimental set-up of the artificial sweat pore system used by Koh et al. [<a href="#B45-membranes-11-00150" class="html-bibr">45</a>] and SEM image of the perforated membrane. Reprinted with permission from [<a href="#B45-membranes-11-00150" class="html-bibr">45</a>]. Copyright 2016, The American Association for the Advancement of Science.</p> Full article ">Figure 4
<p>Alternative approaches for perspiration models. (<b>a</b>) Image of the sweating arm prototype developed by Brueck et al. [<a href="#B49-membranes-11-00150" class="html-bibr">49</a>] showing the arm mold and the fluid tanks for sweat solution (left). In vitro test with a wearable device that monitors sweat rate (right). Adapted with permission from [<a href="#B49-membranes-11-00150" class="html-bibr">49</a>]. Copyright 2019, MDPI. (<b>b</b>) Schematic cross-section of the artificial skin used by Garcia-Cordero et al. [<a href="#B52-membranes-11-00150" class="html-bibr">52</a>]. Adapted with permission from [<a href="#B52-membranes-11-00150" class="html-bibr">52</a>]. Copyright 2018, IEEE. (<b>c</b>) Schematic of the artificial perspiration membrane for heat dissipation developed by Kim et al. [<a href="#B53-membranes-11-00150" class="html-bibr">53</a>]. Adapted with permission from [<a href="#B53-membranes-11-00150" class="html-bibr">53</a>]. Copyright 2020, John Wiley and Sons.</p> Full article ">Figure 5
<p>Workflow proposed for microfluidic sweat wearable characterization, using Twine et al.’s [<a href="#B54-membranes-11-00150" class="html-bibr">54</a>] work as an example. Initial laboratory experiments (Stage 1) for proof-of-concept, followed by the use of artificial skin (Stage 2) for more realistic in vitro testing for device optimization prior to human trials (Stage 3) for final validation. Adapted with permission from [<a href="#B54-membranes-11-00150" class="html-bibr">54</a>]. Copyright 2018, Royal Society of Chemistry.</p> Full article ">
5 pages, 220 KiB  
Editorial
Electromembrane Processes: Experiments and Modelling
by Luigi Gurreri, Alessandro Tamburini and Giorgio Micale
Membranes 2021, 11(2), 149; https://doi.org/10.3390/membranes11020149 - 20 Feb 2021
Cited by 4 | Viewed by 2164
Abstract
This Special Issue of Membranes journal focuses on electromembrane processes and is motivated by the increasing interest of the scientific community towards their characterization by experiments and modelling for several applications [...] Full article
(This article belongs to the Special Issue Electromembrane Processes: Experiments and Modelling)
15 pages, 10236 KiB  
Article
A Molecular Model of PEMFC Catalyst Layer: Simulation on Reactant Transport and Thermal Conduction
by Wenkai Wang, Zhiguo Qu, Xueliang Wang and Jianfei Zhang
Membranes 2021, 11(2), 148; https://doi.org/10.3390/membranes11020148 - 20 Feb 2021
Cited by 31 | Viewed by 4737
Abstract
Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt [...] Read more.
Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt catalyst in CL, the interfacial interactions in the three-phase interface, i.e., carbon, Pt, and ionomer should be first clarified. In this study, a molecular model containing carbon, Pt, and ionomer compositions is built and the radial distribution functions (RDFs), diffusion coefficient, water cluster morphology, and thermal conductivity are investigated after the equilibrium molecular dynamics (MD) and nonequilibrium MD simulations. The results indicate that increasing water content improves water aggregation and cluster interconnection, both of which benefit the transport of oxygen and proton in the CL. The growing amount of ionomer promotes proton transport but generates additional resistance to oxygen. Both the increase of water and ionomer improve the thermal conductivity of the C. The above-mentioned findings are expected to help design catalyst layers with optimized Pt content and enhanced reaction efficiency, and further improve the performance of PEMFCs. Full article
(This article belongs to the Special Issue Development of Novel Materials for Proton Exchange Membrane Fuel Cells)
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<p>Schematic diagram of the proton exchange membrane fuel cell (PEMFC) catalyst layer between the PEM and GDL.</p> Full article ">Figure 2
<p>Molecular model of the multi-component catalyst layer between the PEM and GDL (<b>a</b>) molecular model of the catalyst later; (<b>b</b>) secondary pore; and (<b>c</b>) primary pore.</p> Full article ">Figure 3
<p>Chemical structure of the ionomer monomer.</p> Full article ">Figure 4
<p>Schematic diagram of the heat transfer settings.</p> Full article ">Figure 5
<p>Radial distribution functions (RDF) values of the multi-components as a function of water content: (<b>a</b>) Pt–C; (<b>b</b>) Pt–H<sup>+</sup>; (<b>c</b>) Pt–O<sub>2</sub>; (<b>d</b>) S–S; (<b>e</b>) Pt–S; (<b>f</b>) S–H<sub>2</sub>O; (<b>g</b>) S–H<sup>+</sup>; and (<b>h</b>) O<sub>2</sub>–O<sub>2</sub>.</p> Full article ">Figure 6
<p>RDF values of the multi-components as a function of ionomer-to-carbon ratios: (<b>a</b>) Pt–C; (<b>b</b>) Pt–H<sup>+</sup>; (<b>c</b>) Pt–O<sub>2</sub>; (<b>d</b>) S–S; (<b>e</b>) Pt–S; (<b>f</b>) S–H<sub>2</sub>O; (<b>g</b>) S–H<sup>+</sup>; and (<b>h</b>) O<sub>2</sub>–O<sub>2</sub>.</p> Full article ">Figure 7
<p>Diffusion coefficient of oxygen and hydronium ions as a function of water content.</p> Full article ">Figure 8
<p>Water distribution and cluster form in catalyst layer (CL) at different water contents: (<b>a</b>) water clusters distribution at λ = 1; (<b>b</b>) water clusters distribution at λ = 4; (<b>c</b>) water clusters distribution at λ = 7; and (<b>d</b>) water clusters distribution at λ = 10.</p> Full article ">Figure 8 Cont.
<p>Water distribution and cluster form in catalyst layer (CL) at different water contents: (<b>a</b>) water clusters distribution at λ = 1; (<b>b</b>) water clusters distribution at λ = 4; (<b>c</b>) water clusters distribution at λ = 7; and (<b>d</b>) water clusters distribution at λ = 10.</p> Full article ">Figure 9
<p>Diffusion coefficient of oxygen and hydronium ions at different ionomer-to-carbon ratios.</p> Full article ">Figure 10
<p>Water distribution and cluster form in CL at different ionomer-to-carbon ratios: (<b>a</b>) I/C = 0.4; (<b>b</b>) I/C = 0.8; (<b>c</b>) I/C = 1.2; and (<b>d</b>) I/C = 1.6.</p> Full article ">Figure 11
<p>Thermal conductivity of CL with (<b>a</b>) different water contents and (<b>b</b>) different ionomer-to-carbon ratios.</p> Full article ">Figure 12
<p>Temperature distribution of CL and its uneven gradient with different λ.</p> Full article ">
13 pages, 2496 KiB  
Article
Efficient Fluoride Removal from Aqueous Solution Using Zirconium-Based Composite Nanofiber Membranes
by Alaa Mohamed, Elvia P. Valadez Sanchez, Evgenia Bogdanova, Britta Bergfeldt, Ammar Mahmood, Roman V. Ostvald and Tawheed Hashem
Membranes 2021, 11(2), 147; https://doi.org/10.3390/membranes11020147 - 20 Feb 2021
Cited by 24 | Viewed by 3957
Abstract
Herein, composite nanofiber membranes (CNMs) derived from UiO-66 and UiO-66-NH2 Zr-metal-organic frameworks (MOFs) were successfully prepared, and they exhibited high performance in adsorptive fluoride removal from aqueous media. The resultant CNMs were confirmed using different techniques, such as X-ray diffraction (XRD), field [...] Read more.
Herein, composite nanofiber membranes (CNMs) derived from UiO-66 and UiO-66-NH2 Zr-metal-organic frameworks (MOFs) were successfully prepared, and they exhibited high performance in adsorptive fluoride removal from aqueous media. The resultant CNMs were confirmed using different techniques, such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Brunauer–Emmett–Teller (BET) in addition to Fourier-transform infrared spectroscopy (FTIR). The parameters that govern the fluoride adsorption were evaluated, including adsorbent dose, contact time, and pH value, in addition to initial concentration. The crystalline structures of CNMs exhibited high hydrothermal stability and remained intact after fluoride adsorption. It could also be observed that the adsorbent dose has a significant effect on fluoride removal at high alkaline values. The results show that UiO-66-NH2 CNM exhibited high fluoride removal due to electrostatic interactions that strongly existed between F? and metal sites in MOF in addition to hydrogen bonds formed with MOF amino groups. The fluoride removal efficiency reached 95% under optimal conditions of 20 mg L?1, pH of 8, and 40% adsorbent dose at 60 min. The results revealed that UiO-66-NH2 CNM possesses a high maximum adsorption capacity (95 mg L?1) over UiO-66 CNM (75 mg L?1), which exhibited better fitting with the pseudo-second-order model. Moreover, when the initial fluoride concentration increased from 20 to 100 mg/L, fluoride adsorption decreased by 57% (UiO-66 CNM) and 30% (UiO-66-NH2 CNM) after 60 min. After three cycles, CNM revealed the regeneration ability, demonstrating that UiO-66-NH2 CNMs are auspicious adsorbents for fluoride from an aqueous medium. Full article
(This article belongs to the Section Membrane Applications)
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<p>FE-SEM images of (<b>a</b>) UiO-66, (<b>b</b>) UiO-66-NH<sub>2</sub>, (<b>c</b>) polyvinylidene fluoride (PVDF) nanofibers, (<b>d</b>) pristine UiO-66-NH<sub>2</sub> composite nanofiber membrane (CNM), and (<b>e</b>) UiO-66-NH<sub>2</sub> CNM following the adsorption process.</p> Full article ">Figure 1 Cont.
<p>FE-SEM images of (<b>a</b>) UiO-66, (<b>b</b>) UiO-66-NH<sub>2</sub>, (<b>c</b>) polyvinylidene fluoride (PVDF) nanofibers, (<b>d</b>) pristine UiO-66-NH<sub>2</sub> composite nanofiber membrane (CNM), and (<b>e</b>) UiO-66-NH<sub>2</sub> CNM following the adsorption process.</p> Full article ">Figure 1 Cont.
<p>FE-SEM images of (<b>a</b>) UiO-66, (<b>b</b>) UiO-66-NH<sub>2</sub>, (<b>c</b>) polyvinylidene fluoride (PVDF) nanofibers, (<b>d</b>) pristine UiO-66-NH<sub>2</sub> composite nanofiber membrane (CNM), and (<b>e</b>) UiO-66-NH<sub>2</sub> CNM following the adsorption process.</p> Full article ">Figure 2
<p>Patterns of XRD for UiO-66-NH<sub>2</sub>, UiO-66, PVDF nanofiber, and UiO-66-NH<sub>2</sub> CNM prior to and following adsorption at pH 12.</p> Full article ">Figure 3
<p>FTIR spectra of UiO-66, UiO-66-NH<sub>2</sub>, PVDF nanofibers, and UiO-66-NH<sub>2</sub> CNM before and after adsorption.</p> Full article ">Figure 4
<p>Fluoride adsorption capacity of CNMs as a function of contact time.</p> Full article ">Figure 5
<p>Effect of (<b>a</b>) adsorbent dose, (<b>b</b>) contact time, (<b>c</b>) pH, and (<b>d</b>) concentration on the removal efficiency of UiO-66-NH<sub>2</sub>.</p> Full article ">Figure 5 Cont.
<p>Effect of (<b>a</b>) adsorbent dose, (<b>b</b>) contact time, (<b>c</b>) pH, and (<b>d</b>) concentration on the removal efficiency of UiO-66-NH<sub>2</sub>.</p> Full article ">Figure 6
<p>(<b>a</b>) Regeneration studies and (<b>b</b>) SEM image of CNM after various cycles (20 mg L<sup>−1</sup>, pH of 8, and at 60 min).</p> Full article ">
20 pages, 9252 KiB  
Article
Optimization of Fuel Cell Performance Using Computational Fluid Dynamics
by Tabbi Wilberforce, Oluwatosin Ijaodola, Ogungbemi Emmanuel, James Thompson, Abdul Ghani Olabi, Mohammad Ali Abdelkareem, Enas Taha Sayed, Khaled Elsaid and Hussein M. Maghrabie
Membranes 2021, 11(2), 146; https://doi.org/10.3390/membranes11020146 - 20 Feb 2021
Cited by 22 | Viewed by 6060
Abstract
A low cost bipolar plate materials with a high fuel cell performance is important for the establishment of Proton Exchange Membrane (PEM ) fuel cells into the competitive world market. In this research, the effect of different bipolar plates material such as Aluminum [...] Read more.
A low cost bipolar plate materials with a high fuel cell performance is important for the establishment of Proton Exchange Membrane (PEM ) fuel cells into the competitive world market. In this research, the effect of different bipolar plates material such as Aluminum (Al), Copper (Cu), and Stainless Steel (SS) of a single stack of proton exchange membrane (PEM) fuel cells was investigated both numerically and experimentally. Firstly, a three dimensional (3D) PEM fuel cell model was developed, and simulations were conducted using commercial computational fluid dynamics (CFD) ANSYS FLUENT to examine the effect of each bipolar plate materials on cell performance. Along with cell performance, significant parameters distributions like temperature, pressure, a mass fraction of hydrogen, oxygen, and water is presented. Then, an experimental study of a single cell of Al, Cu, and SS bipolar plate material was used in the verification of the numerical investigation. Finally, polarization curves of numerical and experimental results was compared for validation, and the result shows that Al serpentine bipolar plate material performed better than Cu and SS materials. The outcome of the investigation was in tandem to the fact that due to adsorption on metal surfaces, hydrogen molecules is more stable on Al surface than Cu and SS surfaces. Full article
(This article belongs to the Special Issue Development of Novel Materials for Proton Exchange Membrane Fuel Cells)
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<p>Exploded view of a single PEM fuel cell [<a href="#B6-membranes-11-00146" class="html-bibr">6</a>].</p> Full article ">Figure 2
<p>Water transport mechanism in a PEM fuel cell.</p> Full article ">Figure 3
<p>A three-dimensional view of the single PEM fuel cell and its components. (<b>a</b>) Inlet channel (<b>b</b>) outlet channel.</p> Full article ">Figure 4
<p>Temperature distribution at the anode region (GDL/CL) for each material at 298K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 5
<p>Temperature distribution at the cathode region (GDL/CL) for each material at 298K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 6
<p>Temperature distribution at the anode region (GDL/CL) for each material at 323K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 7
<p>Temperature distribution at the cathode region (GDL/CL) for each material at 323K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 8
<p>Temperature distribution at the cathode region (GDL/CL) for each materials at 338K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 9
<p>Temperature distribution at the cathode region (GDL/CL) for each material at 338K: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 10
<p>Pressure distribution at the anode region (GDL/CL) for each material with temperature 323 K at 1.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 11
<p>Pressure distribution at the cathode region (GDL/CL) for each material with temperature 323 K at 1.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 12
<p>Pressure distribution at the anode region (GDL/CL) for each material with temperature 323 K at 2.0 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 13
<p>Pressure distribution at the cathode region (GDL/CL) for each material with temperature 323 K at 2.0 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 14
<p>Pressure distribution at the anode region (GDL/CL) for each material with temperature 323 K at 2.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 15
<p>Pressure distribution at the cathode region (GDL/CL) for each material with temperature 323 K at 2.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 16
<p>Contours of hydrogen mass fraction at the anode region (GDL/CL) for each material with temperature 323 K at pressure 1.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 17
<p>Contours of oxygen mass fraction at the cathode region (GDL/CL) for each material with temperature 323 K at pressure 1.5 bar: (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel.</p> Full article ">Figure 18
<p>Water mass fraction at the membrane for (<b>a</b>) Aluminum, (<b>b</b>) Copper, (<b>c</b>) Steel bipolar plate materials at 338 K, 1.5 bar.</p> Full article ">Figure 19
<p>Comparison between numerical and experimental results of various bipolar plate materials.</p> Full article ">
19 pages, 2292 KiB  
Article
Layer-by-Layer Coating of MK-40 Heterogeneous Membrane with Polyelectrolytes Creates Samples with Low Electrical Resistance and Weak Generation of H+ and OH? Ions
by Kseniia Tsygurina, Olesya Rybalkina, Konstantin Sabbatovskiy, Evgeniy Kirichenko, Vladimir Sobolev and Ksenia Kirichenko
Membranes 2021, 11(2), 145; https://doi.org/10.3390/membranes11020145 - 20 Feb 2021
Cited by 8 | Viewed by 2230
Abstract
Ion exchange membranes covered with layers of polyelectrolytes of alternating charges are characterized by very high monovalent selectivity. This allows the use of such membranes for electrodialytic fractionation of multicomponent solutions. However, the very existence of the boundary at which differently charged layers [...] Read more.
Ion exchange membranes covered with layers of polyelectrolytes of alternating charges are characterized by very high monovalent selectivity. This allows the use of such membranes for electrodialytic fractionation of multicomponent solutions. However, the very existence of the boundary at which differently charged layers come in contact can hinder a membrane’s effectiveness by limiting its ion permeability, raising levels of H+ and OH? ions (thus shifting the pH) and increasing the electrical resistance of the membrane, which leads to increased energy consumption. To test how these properties would be changed, we created cheap layer-by-layer-modified membranes based on the heterogeneous MK-40 membrane, on which we adsorbed layers of polyallylamine and sulfonated polystyrene. We created samples with 3, 4, and 5 layers of polyelectrolytes and characterized them. We showed that the application of layers did not decrease the efficiency of the membrane, since the electrical resistance of the modified samples, which increased after application of the first oppositely charged layer, declined with the application of the following layers and became comparable to that of the substrate, while their limiting current density was higher and the shift of pH of treated solution was low in magnitude and comparable with that of the substrate membrane. Full article
(This article belongs to the Section Membrane Applications)
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<p>The algorithm used to create modified samples. MK-40 is a brand of commercial heterogeneous cation exchange membranes. The numbers in denotations show the amount of applied layers. The membranes for which the upper layer was formed by PAA (polyallylamine) and was assumed to be positively charged are marked in red. The membranes for which the upper layer was formed by PSS (polystyrene sulfonate) and was assumed to be negatively charged are marked in blue.</p> Full article ">Figure 2
<p>Cell and circuitry for registration of current–voltage curves. Blue lines denote the hydraulic connections and red lines denote electric circuits. Note: 1 is the desalination chamber; 2 is the auxiliary chamber; 3 is the electrode chambers; 4 is the capillaries, connected to 5, which represents Luggin electrodes; 6 is the tank gathering solution from desalination and auxiliary chambers; 7 is the tank gathering solution from electrode chambers; 8 is voltmeter and power supply; 9 is the interstitial tank in the desalination track holding the glass electrode and conductivity cell; 10 is the pH meter and conductometer. Note: C* is a studied membrane; C and A are auxiliary cation exchange and anion exchange membranes, respectively.</p> Full article ">Figure 3
<p>Increments of thickness of modified membranes in comparison with membranes with one less adsorbed layer. Error margins are sums of confidence intervals calculated for ten repeated measurements for these two membranes at α = 0.05. MK-40 is a heterogeneous cation exchange membrane, MK-40+1 is a MK-40 coated with homogenizing layer of perfluorsulfonic acid, MK-40+2 is a MK-40+1 with an additional adsorbed layer of polyallylamine, MK-40+3 is a MK-40+2 with an additional adsorbed layer of sodium polystyrene sulfonate, MK-40+4 is a MK-40+3 with an additional adsorbed layer of polyallylamine and MK-40+5 is a MK-40+4 with an additional adsorbed layer of sodium polystyrene sulfonate. Text denotes the composition of the top layer (LF-4SC for perfluorosulfonic acid, PAA for polyallylamine and PSS for sodium polystyrene sulfonate) and its position in a row of layers of the same nature, numbered from the first one applied to the last.</p> Full article ">Figure 4
<p>Determination of the experimental limiting current of the MK-40 membrane by the graphical method.</p> Full article ">Figure 5
<p>(<b>a</b>) The current–voltage curves of the MK-40 membrane and layer-by-layer-modified samples based on the membrane (sans MK-40+1), created using PAA. (<b>b</b>) The current–voltage curves of all studied membranes in “dimensionless current density vs. potential drop reduced by Ohmic component” coordinates, allowing comparison between different cell geometries. (<b>c</b>) The experimental limiting currents of these membranes related to the theoretical limiting current density calculated by the Lévêque equation. The dashed line shows the theoretical limiting current density calculated by the Lévêque equation.</p> Full article ">Figure 5 Cont.
<p>(<b>a</b>) The current–voltage curves of the MK-40 membrane and layer-by-layer-modified samples based on the membrane (sans MK-40+1), created using PAA. (<b>b</b>) The current–voltage curves of all studied membranes in “dimensionless current density vs. potential drop reduced by Ohmic component” coordinates, allowing comparison between different cell geometries. (<b>c</b>) The experimental limiting currents of these membranes related to the theoretical limiting current density calculated by the Lévêque equation. The dashed line shows the theoretical limiting current density calculated by the Lévêque equation.</p> Full article ">Figure 6
<p>The current–voltage curve of the MK-40 membrane modified with MF-4SC and PEI, given for comparison. The dashed line shows the theoretical limiting current density calculated by the Lévêque equation. LCD denotes the limiting current density, PEI denotes polyethyleneimine and PAA denotes polyallylamine.</p> Full article ">Figure 7
<p>The areal resistance values of the membranes in 0.02 M NaCl solution, calculated from initial sections of the current–voltage curves using the difference method.</p> Full article ">Figure 8
<p>Change in pH of the treated NaCl solution after passing through the desalination chamber: (<b>a</b>) dependence of pH on current density for all membranes except MK-40+1; (<b>b</b>) dependence of pH on dimensionless current density <span class="html-italic">i</span>/<span class="html-italic">i</span><sub>lim</sub><sup>theor</sup>, whereby i<sub>lim</sub><sup>theor</sup> was calculated using the Lévêque equation. LCD denotes the limiting current density.</p> Full article ">Figure 9
<p>Concentration changes for cations during electrodialysis desalination of a 0.015 M NaCl + 0.0075 M CaCl<sub>2</sub> solution in a system with a MK-40+5 modified membrane at constant <span class="html-italic">i</span> = 1.5 mA/cm<sup>2</sup>. The theoretical limiting current density is estimated as 2.7 mA/cm<sup>2</sup>.</p> Full article ">
3 pages, 198 KiB  
Editorial
Membrane Distillation Process
by Alessandra Criscuoli
Membranes 2021, 11(2), 144; https://doi.org/10.3390/membranes11020144 - 18 Feb 2021
Cited by 9 | Viewed by 2750
Abstract
The water stress that we have been experiencing in the last few years is driving the development of new technologies for the purification and recovery of water [...] Full article
(This article belongs to the Special Issue Membrane Distillation Process)
15 pages, 2587 KiB  
Article
Highly Dispersed CeOx Hybrid Nanoparticles for Perfluorinated Sulfonic Acid Ionomer–Poly(tetrafluoethylene) Reinforced Membranes with Improved Service Life
by Juhee Ahn, Mobina Irshad Ali, Jun Hyun Lim, Yejun Park, In Kee Park, Denis Duchesne, Lisa Chen, Juyoung Kim and Chang Hyun Lee
Membranes 2021, 11(2), 143; https://doi.org/10.3390/membranes11020143 - 18 Feb 2021
Cited by 11 | Viewed by 3229
Abstract
CeOx hybrid nanoparticles were synthesized and evaluated for use as radical scavengers, in place of commercially available Ce(NO3)3 and CeO2 nanoparticles, to avoid deterioration of the initial electrochemical performance and/or spontaneous aggregation/precipitation issues encountered in polymer electrolyte membranes. [...] Read more.
CeOx hybrid nanoparticles were synthesized and evaluated for use as radical scavengers, in place of commercially available Ce(NO3)3 and CeO2 nanoparticles, to avoid deterioration of the initial electrochemical performance and/or spontaneous aggregation/precipitation issues encountered in polymer electrolyte membranes. When CeOx hybrid nanoparticles were used for membrane formation, the resulting membranes exhibited improved proton conductivity (improvement level = 2–15% at 30–90 °C), and thereby electrochemical single cell performance, because the –OH groups on the hybrid nanoparticles acted as proton conductors. In spite of a small amount (i.e., 1.7 mg/cm3) of introduction, their antioxidant effect was sufficient enough to alleviate the radical-induced decomposition of perfluorinated sulfonic acid ionomer under a Fenton test condition and to extend the chemical durability of the resulting reinforced membranes under fuel cell operating conditions. Full article
(This article belongs to the Special Issue Polymer Electrolyte Membranes)
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<p>(<b>a</b>,<b>d</b>) FE-SEM and (<b>b</b>,<b>c</b>,<b>e</b>,<b>f</b>) EDX mapping images ((<b>b</b>,<b>e</b>) cerium and (<b>c</b>,<b>f</b>) oxygen element) of (<b>a</b>–<b>c</b>) CeO<sub>x</sub>_A–3M ionomer hybrid nanoparticles and (<b>d</b>–<b>f</b>) CeO<sub>x</sub>_B–3M ionomer hybrid nanoparticles in the solid state obtained after drying each dispersion.</p> Full article ">Figure 2
<p>Proton conductivity of perfluorinated sulfonic acid–poly(tetrafluoroethylene) (PFSA–PTFE) reinforced membranes in deionized water. The freestanding membrane (FSM) was made up of 3M 725EW ionomer.</p> Full article ">Figure 3
<p>The hydrogen permeability of PFSA–PTFE reinforced membranes measured via time-lag method.</p> Full article ">Figure 4
<p>The concentration of fluoride ions detected after the chemical degradation of PFSA–PTFE reinforced membranes in a Fenton solution at 80 °C for 2 h.</p> Full article ">Figure 5
<p>The current–voltage polarization curves of PFSA–PTFE reinforced membranes obtained at 65 °C according to changes in applied pressure ((<b>a</b>,<b>b</b>) 1.0 bar<sub>g</sub> and (<b>c</b>,<b>d</b>) 2.0 bar<sub>g</sub>) and humidity ((<b>a</b>,<b>c</b>) 50% relative humidity (RH) and (<b>b</b>,<b>d</b>) 100% RH) values.</p> Full article ">Figure 6
<p>(<b>a</b>) Open-circuit voltage (OCV) values of PFSA–PTFE reinforced membranes as a function of operation time at 90 °C and 30% RH under the pressure of 1.5 bar<sub>g</sub>. (<b>b</b>) Hydrogen crossover obtained with the interval of 100 h via linear sweep voltammetry (LSV) analysis, which was conducted at 65 °C and 50% RH under the pressure of 1.0 bar<sub>g</sub>.</p> Full article ">
15 pages, 4342 KiB  
Article
The Permeability and Selectivity of the Polyamide Reverse Osmosis Membrane were Significantly Enhanced by PhSiCl3
by Junjie Yu, Kaifeng Gu, Binbin Yang, Kaizhen Wang, Yong Zhou and Congjie Gao
Membranes 2021, 11(2), 142; https://doi.org/10.3390/membranes11020142 - 18 Feb 2021
Cited by 3 | Viewed by 2888
Abstract
The work briefly introduces the nano-composite reverse osmosis (RO) membrane with more permeability and selective performance, and we adopted the phenyltrichlorosilane precursor with better chemical stability and greater spatial resistance. The phenyltrichlorosilane concentration was mainly discussed in this work. The in-situ hydrolysis of [...] Read more.
The work briefly introduces the nano-composite reverse osmosis (RO) membrane with more permeability and selective performance, and we adopted the phenyltrichlorosilane precursor with better chemical stability and greater spatial resistance. The phenyltrichlorosilane concentration was mainly discussed in this work. The in-situ hydrolysis of phenyltrichlorosilane and the occurrence of ammonia hydrolysis make it effectively incorporated into the polyamide film. The covalent bond and hydrogen bond of phenyltrichlorosilane and polyamide (PA) can be realized. The phenyl group can extend in the polyamide polymer network and give the film corresponding functions. There will be fewer non-selective defects between phenyltrichlorosilane and PA. Under the premise of maintaining the water-salt selectivity of the membrane, along with the increase of benzene trichlorosilane loading, the 300% pure water flux can be achieved and the desalination rate remains at 98.1–98.9%. This reverse osmosis (RO) is suitable for household water purification. Full article
(This article belongs to the Section Polymeric Membranes)
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<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 1 Cont.
<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 1 Cont.
<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 1 Cont.
<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 1 Cont.
<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 1 Cont.
<p>SEM images under different magnifications of the membranes with different PTS loading: (<b>A</b>,<b>a</b>) TFC membrane; (<b>B</b>,<b>b</b>) thin-film nanocomposite (TFN)-0.1 membrane; (<b>C</b>,<b>c</b>) TFN-0.2 membrane; (<b>D</b>,<b>d</b>) TFN-0.3 membrane; (<b>E</b>,<b>e</b>) TFN-0.4 membrane; (<b>F</b>,<b>f</b>) TFN-0.5 membrane.</p> Full article ">Figure 2
<p>Interfacial polymerization process.</p> Full article ">Figure 3
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 3 Cont.
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 3 Cont.
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 3 Cont.
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 3 Cont.
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 3 Cont.
<p>SEM image and porosity of the membranes with different PTS loading: (<b>A</b>) TFC membrane; (<b>B</b>) TFN 0.1 membrane; (<b>C</b>) TFN 0.2 membrane; (<b>D</b>) TFN 0.3 membrane; (<b>E</b>) TFN 0.4 membrane; (<b>F</b>) TFN 0.5 membrane.</p> Full article ">Figure 4
<p>TEM images of the thin-film composite (TFC) and TFN membranes.</p> Full article ">Figure 5
<p>The dynamic water contact angle (<b>A</b>) and zeta potential (<b>B</b>) characteristics of the membranes with different PTS loads.</p> Full article ">Figure 6
<p>ATR-FTIR spectra of the membranes with different PTS loads.</p> Full article ">Figure 7
<p>C 1s high-resolution spectra of the top surfaces for the membranes with different covalent silicon composition: (<b>A</b>) TFC membrane; (<b>B</b>) TFN-0.1 membrane; (<b>C</b>) TFN-0.2 membrane.</p> Full article ">Figure 8
<p>TGA curves of membranes with different PTS loading: (<b>A</b>) from 30 °C to 700 °C; (<b>B</b>) temperature of 5% weight loss; (<b>C</b>) the maximum temperature loss rate from 50 °C to 400 °C; (<b>D</b>) temperature of maximum loss rate from 520 °C to 540 °C.</p> Full article ">Figure 9
<p>The membranes transport properties: (<b>A</b>) Pure water permeability coefficient; flux and rejection analysis of different NaCl concentrations and test pressures: 500 ppm and 7.0 bar (<b>B</b>); 1500 ppm and 10.0 bar (<b>C</b>); 2000 ppm and 15.5 bar (<b>D</b>); 32,000 ppm and 55.2 bar (<b>E</b>).</p> Full article ">Scheme 1
<p>The membrane preparation process-interfacial polymerization between TMC/PTS in Isopar G and MPD in H<sub>2</sub>O.</p> Full article ">
13 pages, 4305 KiB  
Article
Reliable Sea Water Ro Operation with High Water Recovery and No-Chlorine/No-Sbs Dosing in Arabian Gulf, Saudi Arabia
by Hiroki Miyakawa, Mohammed Maghram Al Shaiae, Troy N. Green, Yohito Ito, Yuichi Sugawara, Makoto Onishi, Yoshinari Fusaoka, Mohammed Farooque Ayumantakath and Ahmed Saleh Al Amoudi
Membranes 2021, 11(2), 141; https://doi.org/10.3390/membranes11020141 - 17 Feb 2021
Cited by 13 | Viewed by 4111
Abstract
For providing advanced desalination the combination of the improvement of water recovery ratio in the reverse osmosis (RO) process and the No-Chlorine/No-Sodium Bisulfite (SBS) Dosing process was studied. In order to prevent membrane fouling even in high recovery water operations, an advanced two-stage [...] Read more.
For providing advanced desalination the combination of the improvement of water recovery ratio in the reverse osmosis (RO) process and the No-Chlorine/No-Sodium Bisulfite (SBS) Dosing process was studied. In order to prevent membrane fouling even in high recovery water operations, an advanced two-stage design was implemented to (1) control the permeate flux through the RO membrane module, (2) optimize the system to reduce contaminant build-up and (3) eliminate the use of chlorine and SBS, which can accelerate membrane fouling. The system was evaluated by monitoring the biofouling and the microorganisms proliferation on the membrane surface based on membrane biofilm formation rate (mBFR). The pilot plant was operated in the condition of a water recovery rate of 55%. As a result, the system was operated for longer than four months without membrane cleaning (clean in place; CIP) and the possibility of operation for seven months without CIP was confirmed by the extrapolation of the pressure values. In addition, the mBFR is a reliable tool for water quality assessment, based on a comparison between the fouling tendency estimated from the mBFR and the actual membrane surface condition from autopsy study and the effectiveness No-Chlorine/No-SBS Dosing process was verified from mBFR of pretreated seawater. Full article
(This article belongs to the Special Issue Seawater Reverse Osmosis Desalination)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>System schematics of the pilot plant.</p> Full article ">Figure 2
<p>Appearance of the pilot plant.</p> Full article ">Figure 3
<p>Flow diagram of reverse osmosis (RO) system.</p> Full article ">Figure 4
<p>Appearance of the flat sheet membrane cell.</p> Full article ">Figure 5
<p>Flow of the flat sheet membrane cell.</p> Full article ">Figure 6
<p>Biofouling monitoring index.</p> Full article ">Figure 7
<p>Evaluation points of membrane biofilm formation rate (mBFR) in the pilot testing.</p> Full article ">Figure 8
<p>Dual media sand filtration (DMF) treated water quality and operation history.</p> Full article ">Figure 9
<p>Changes in feed pressure, permeate flowrate, Total Dissolved Solids (TDS) and temperature.</p> Full article ">Figure 10
<p>Changes in the normalized permeate flow rate and ΔP<sub>25</sub>.</p> Full article ">Figure 11
<p>Surface conditions of the lead and last RO element (collection on 81st day of operation).</p> Full article ">Figure 12
<p>Changes in ΔP<sub>25</sub> of the flat sheet membrane cells.</p> Full article ">Figure 13
<p>Results of Biofilm development.</p> Full article ">
10 pages, 1952 KiB  
Article
Effect of Nano Silicon Dioxide Coating Films on the Quality Characteristics of Fresh-Cut Cantaloupe
by Rokayya Sami, Manal Almatrafi, Abeer Elhakem, Mona Alharbi, Nada Benajiba and Mahmoud Helal
Membranes 2021, 11(2), 140; https://doi.org/10.3390/membranes11020140 - 17 Feb 2021
Cited by 20 | Viewed by 2983
Abstract
The prime objective of the research was to explore the coating effects of chitosan and nano-silicon dioxide with nisin as an antimicrobial agent on physicochemical properties, microbiological stability, and sensorial quality changes during the storage at 4 °C. The combination of nano-material and [...] Read more.
The prime objective of the research was to explore the coating effects of chitosan and nano-silicon dioxide with nisin as an antimicrobial agent on physicochemical properties, microbiological stability, and sensorial quality changes during the storage at 4 °C. The combination of nano-material and chitosan in addition to nisin was effective for reducing the postharvest attributes of fresh-cut cantaloupes in addition to the highest score in sensory evaluation. Chitosan coating treatment enhanced the microbiological quality 2.50 log CFU/g and 1.87 log CFU/g for aerobic counts and mold/yeasts populations, respectively. In a word, the combination of chitosan/nano-silica/nisin treatment was the best condition for fresh-cut cantaloupe shelf life extension by maintaining color, vitamin C 22.29 mg/100g, peroxidase activity 8.06 U/min.g, and other microbiological tests up to storage time of 8 days. Full article
(This article belongs to the Section Inorganic Membranes)
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<p>Effects of coating treatments on fluid loss for cantaloupes during storage at 4 °C for 8 days. Data are mean ± SD, <span class="html-italic">n</span> = 3.</p> Full article ">Figure 2
<p>Effects of coating treatments on pH (<b>a</b>), total soluble solids (TSS) (<b>b</b>), total (TA) (<b>c</b>), and retention (Vc) (<b>d</b>) contents of cantaloupe fruit; data are mean ± SD, <span class="html-italic">n</span> = 3.</p> Full article ">Figure 3
<p>Effects of coating treatments on malondialdehyde content (MDA) (<b>a</b>), polyphenol oxidase (PPO) (<b>b</b>) and peroxidase (POD) (<b>c</b>) activities of cantaloupe fruit; <sup>a;b;c;d;e</sup> mean significant differences between treatments at <span class="html-italic">p</span> ≥ 0.05.</p> Full article ">Figure 4
<p>Effects of coating treatments on microbial quality, (<b>a</b>) total aerobic plate count, (<b>b</b>) yeast and mold counts, and (<b>c</b>) water activity of cantaloupe fruit; data are mean ± SD, <span class="html-italic">n</span> = 3.</p> Full article ">Figure 4 Cont.
<p>Effects of coating treatments on microbial quality, (<b>a</b>) total aerobic plate count, (<b>b</b>) yeast and mold counts, and (<b>c</b>) water activity of cantaloupe fruit; data are mean ± SD, <span class="html-italic">n</span> = 3.</p> Full article ">Figure 5
<p>Sensory evaluation of fresh-cut cantaloupe fruits.</p> Full article ">
33 pages, 2610 KiB  
Review
A Review on Polymer Nanocomposites and Their Effective Applications in Membranes and Adsorbents for Water Treatment and Gas Separation
by Oluranti Agboola, Ojo Sunday Isaac Fayomi, Ayoola Ayodeji, Augustine Omoniyi Ayeni, Edith E. Alagbe, Samuel E. Sanni, Emmanuel E. Okoro, Lucey Moropeng, Rotimi Sadiku, Kehinde Williams Kupolati and Babalola Aisosa Oni
Membranes 2021, 11(2), 139; https://doi.org/10.3390/membranes11020139 - 16 Feb 2021
Cited by 117 | Viewed by 10123
Abstract
Globally, environmental challenges have been recognised as a matter of concern. Among these challenges are the reduced availability and quality of drinking water, and greenhouse gases that give rise to change in climate by entrapping heat, which result in respirational illness from smog [...] Read more.
Globally, environmental challenges have been recognised as a matter of concern. Among these challenges are the reduced availability and quality of drinking water, and greenhouse gases that give rise to change in climate by entrapping heat, which result in respirational illness from smog and air pollution. Globally, the rate of demand for the use of freshwater has outgrown the rate of population increase; as the rapid growth in town and cities place a huge pressure on neighbouring water resources. Besides, the rapid growth in anthropogenic activities, such as the generation of energy and its conveyance, release carbon dioxide and other greenhouse gases, warming the planet. Polymer nanocomposite has played a significant role in finding solutions to current environmental problems. It has found interest due to its high potential for the reduction of gas emission, and elimination of pollutants, heavy metals, dyes, and oil in wastewater. The revolution of integrating developed novel nanomaterials such as nanoparticles, carbon nanotubes, nanofibers and activated carbon, in polymers, have instigated revitalizing and favourable inventive nanotechnologies for the treatment of wastewater and gas separation. This review discusses the effective employment of polymer nanocomposites for environmental utilizations. Polymer nanocomposite membranes for wastewater treatment and gas separation were reviewed together with their mechanisms. The use of polymer nanocomposites as an adsorbent for toxic metals ions removal and an adsorbent for dye removal were also discussed, together with the mechanism of the adsorption process. Patents in the utilization of innovative polymeric nanocomposite membranes for environmental utilizations were discussed. Full article
(This article belongs to the Special Issue Composite Membranes: Preparation and Applications)
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Graphical abstract
Full article ">Figure 1
<p>Schematic representation of different nanomaterials and their diameters. Carbon nanotubes are known to have diameters in the range of a nanometer. Nanoparticle properties change as it gets to nanoscale. The nanosheet is regarded as another type of nanoparticle. Nanofibers can be prepared from diverse polymers and hence, have diverse sizes.</p> Full article ">Figure 2
<p>Membranes fabricated with nanomaterials, such as mono-component nanomaterial membranes fabricated with the integration of nanoparticles, nanofibers, carbon nanotubes, and nanosheets, and their composites (in conjunction with unique polymeric or inorganic materials) (Adapted from Ref. [<a href="#B37-membranes-11-00139" class="html-bibr">37</a>], with consent from Elsevier).</p> Full article ">Figure 3
<p>Schematic illustration of the membrane separation process using polymer membrane with selective inter-activities of the gas molecules with the pores across the membranes with the aid of Knudsen’s diffusion.</p> Full article ">Figure 4
<p>Classes of functionalization (covalent and non-covalent) approaches for adsorbent materials. Chemical modifications permit enhancement of their chemical and physical properties. The physical modifications are grouped into thermal treatment techniques and deionized water treatment techniques. Biological modifications involve the bioadsorbtion treatment method.</p> Full article ">Figure 5
<p>Illustration of the pressure swing adsorption technique. The technology works under pressure by using the adsorbent’s differences in gas adsorption rate to separate some gases from a gaseous mixture (Adapted from Ref. [<a href="#B174-membranes-11-00139" class="html-bibr">174</a>]).</p> Full article ">Figure 6
<p>Rotation of the Kuhn segments resulting in alteration of polymer shape as a result of thermal vibration of atoms.</p> Full article ">Figure 7
<p>Illustration of the addition of nanoparticles into polymer matrices; it results in the alteration of optical, mechanical, and electrical properties in relation to the host polymer.</p> Full article ">
20 pages, 4037 KiB  
Review
Advanced Technologies for Stabilization and High Performance of Seawater RO Membrane Desalination Plants
by Hiroo Takabatake, Masahide Taniguchi and Masaru Kurihara
Membranes 2021, 11(2), 138; https://doi.org/10.3390/membranes11020138 - 16 Feb 2021
Cited by 30 | Viewed by 7968
Abstract
Seawater desalination plants that use reverse osmosis (RO) membranes have become a core part of social infrastructure, and should be designed to meet the needs of product water quality and production capacity, while considering various environmental factors such as the seawater quality, temperature [...] Read more.
Seawater desalination plants that use reverse osmosis (RO) membranes have become a core part of social infrastructure, and should be designed to meet the needs of product water quality and production capacity, while considering various environmental factors such as the seawater quality, temperature and geographical features. Furthermore, stable operation while overcoming various problems should be achieved alongside the increasing demands for energy saving and cost reduction. As no universal plant apparatus and operation technology meets these various requirements, the plants need to be customized for individual solutions. This paper reviews and summarizes the proven technologies, including their advantages/disadvantages, and points to cutting-edge technologies related to the design and operation maintenance of seawater intake, pre-treatment and the RO desalination process. Full article
(This article belongs to the Special Issue Seawater Reverse Osmosis Desalination)
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<p>The trend in plant capacity for seawater desalination, created by Toray from GWI/DesalData in December 2020 [<a href="#B2-membranes-11-00138" class="html-bibr">2</a>,<a href="#B3-membranes-11-00138" class="html-bibr">3</a>].</p> Full article ">Figure 2
<p>The schematic apparatus and method for the measurement of mBFR.</p> Full article ">Figure 3
<p>The basic configuration of the RO process. (<b>a</b>) Typical configuration of the RO element (spiral-wound type), (<b>b</b>) configuration of pressure vessels containing the RO elements, and (<b>c</b>) basic flow of single pass and single stage system.</p> Full article ">Figure 4
<p>The schematic flow of the typical ERDs (Pelton wheel, Francis Turbines, Hydraulic turbocharger and Pressure exchanger (PX and DWEER).</p> Full article ">Figure 5
<p>The basic flow configuration of the two-pass system. Alkaline is usually dosed into SWRO permeate at the first pass (i.e., feed water of the second pass) to enhance boron removal.</p> Full article ">Figure 6
<p>The boron dissociative equilibrium. Higher pH raises the ratio of B(OH)<sub>4</sub><sup>−</sup>, which enhances rejection due to the electric repulsion effect of the RO membrane surface.</p> Full article ">Figure 7
<p>The schematic flow configuration of the brine conversion two stage RO system (BCS) with an example of flow balance [<a href="#B67-membranes-11-00138" class="html-bibr">67</a>].</p> Full article ">Figure 8
<p>The schematic flow configuration of the integrated system of sewage reclamation and seawater desalination at “Water Plaza” in Kitakyushu, Japan. RO brine of sewage reclamation system, which is normally wasted, is reused for seawater dilution to reduce the osmotic pressure of feed water of the SWRO desalination system. It is expected that a more than 30% reduction of energy consumption is achieved in seawater desalination systems.</p> Full article ">Figure 9
<p>The sequential operation of CCD. At the first step, RO treatment is carried out with brine recirculation to feed water. The concentration of RO feed water gradually increases, then the brine stored in the side tank is discharged by pushing new seawater (second step). Then, the side tank is connected with the recirculation line to increase the pressure in the side tank (third step). Finally, the line is switched to push the seawater stored in the side tank to use feed water by replacing the condensed brine in the side tank (4th step), going back to the first step.</p> Full article ">
13 pages, 2590 KiB  
Article
Comparison between Lipase Performance Distributed at the O/W Interface by Membrane Emulsification and by Mechanical Stirring
by Emma Piacentini, Rosalinda Mazzei and Lidietta Giorno
Membranes 2021, 11(2), 137; https://doi.org/10.3390/membranes11020137 - 16 Feb 2021
Cited by 13 | Viewed by 2855
Abstract
Multiphase bioreactors using interfacial biocatalysts are unique tools in life sciences such as pharmaceutical and biotechnology. In such systems, the formation of microdroplets promotes the mass transfer of reagents between two different phases, and the reaction occurs at the liquid–liquid interface. Membrane emulsification [...] Read more.
Multiphase bioreactors using interfacial biocatalysts are unique tools in life sciences such as pharmaceutical and biotechnology. In such systems, the formation of microdroplets promotes the mass transfer of reagents between two different phases, and the reaction occurs at the liquid–liquid interface. Membrane emulsification is a technique with unique properties in terms of precise manufacturing of emulsion droplets in mild operative conditions suitable to preserve the stability of bioactive labile components. In the present work, membrane emulsification technology was used for the production of a microstructured emulsion bioreactor using lipase as a catalyst and as a surfactant at the same time. An emulsion bioreaction system was also prepared by the stirring method. The kinetic resolution of (S,R)-naproxen methyl ester catalyzed by the lipase from Candida rugosa to obtain (S)-naproxen acid was used as a model reaction. The catalytic performance of the enzyme in the emulsion systems formulated with the two methods was evaluated in a stirred tank reactor and compared. Lipase showed maximum enantioselectivity (100%) and conversion in the hydrolysis of (S)-naproxen methyl ester when the membrane emulsification technique was used for biocatalytic microdroplets production. Moreover, the controlled formulation of uniform and stable droplets permitted the evaluation of lipase amount distributed at the interface and therefore the evaluation of enzyme specific activity as well as the estimation of the hydrodynamic radius of the enzyme at the oil/water (o/w) interface in its maximum enantioselectivity. Full article
(This article belongs to the Special Issue Membrane and Membrane Bioreactors Applied to Health and Life Sciences)
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<p>Crossflow membrane emulsification equipment and schematic representation of emulsion droplet formation at the membrane pore.</p> Full article ">Figure 2
<p>Schematic representation of stirred tank reactor geometry (impeller blade width (L), impeller blade height (W), diameter of impeller (Da), distance between middle of impeller blade and bottom of reactor (E), diameter of baffles (Db), diameter of tank (Dt), height of liquid in reactor (Hl), height of reactor (Ht)).</p> Full article ">Figure 3
<p>Schematic representation of lipase approximated to spherical macromolecules distributed at the oil (yellow)/water (light blue) interface of a spherical oil drop. The circle area occupied by a single lipase macromolecule is also highlighted. (To simplify the scheme, only some macromolecules from various perspectives were drawn).</p> Full article ">Figure 4
<p>Size distribution of oil/water (o/w) emulsion produced by membrane emulsification.</p> Full article ">Figure 5
<p>Time course of conversion and enantiomeric excess of the emulsion bioreaction carried out using the lipase distributed at the oil/water interface by membrane emulsification (ME) and mechanical stirring in a stirred tank reactor (STR).</p> Full article ">Figure 6
<p>Time course of specific activity and catalytic activity of lipase distributed at the oil/water interface by membrane emulsification (ME) and stirring tank reactor (STR).</p> Full article ">Figure 7
<p>SDS-PAGE of lipase initial solution and filtered aqueous phase after emulsion preparation by membrane emulsification. Line 1: Standard solution; Line 2 represents the initial lipase solution at 2 g/L; Lines 3 represents the uncomplexed lipase present in the filtered aqueous phase of emulsion prepared using lipase solution of 2 g/L.</p> Full article ">
24 pages, 4338 KiB  
Article
Understanding of Adsorption and Desorption Mechanisms of Anthocyanins and Proanthocyanidins on Heterogeneous and Homogeneous Cation-Exchange Membranes
by Véronique Perreault, Veronika Sarapulova, Ksenia Tsygurina, Natalia Pismenskaya and Laurent Bazinet
Membranes 2021, 11(2), 136; https://doi.org/10.3390/membranes11020136 - 16 Feb 2021
Cited by 13 | Viewed by 2605
Abstract
The presence of membrane fouling is the main drawback in membrane processes, and it is related to the premature use and high cost for the replacement of membranes. Polyphenols in cranberry juice are associated with ion-exchange membrane fouling, and it results in a [...] Read more.
The presence of membrane fouling is the main drawback in membrane processes, and it is related to the premature use and high cost for the replacement of membranes. Polyphenols in cranberry juice are associated with ion-exchange membrane fouling, and it results in a loss of these beneficial compounds in the juice when treated by membrane processes such as electrodialysis. In the present work, four heterogeneous or pseudohomogeneous cation-exchange membranes (CSE-fg, MK-40, CEM Type-II, and CJMC-5), different in terms of the polymer matrix (aromatic, aliphatic), exchange capacity, size, and location of meso and macropores, were studied to understand the impact of the membrane structure and physico-chemical properties on adsorption and desorption of phenolic compounds (anthocyanins and proanthocyanidins) from cranberry juice. It appeared from these results that MK-40, CEM Type-II, and CSE-fg were more prone to fouling due to their high ion-exchange capacity, their thickness, and the presence of meso and macropores in their structure. Indeed, electrostatic interactions occurred between fixed groups of membranes and polyphenolic ions. Desorption of the entire membrane and cryogenic grinding with pH adjusted to 10 allowed a better recovery of anthocyanins and proanthocyanidins (PACs), respectively, since hydroxide ions competed with polyphenols and membrane that induced desorption of polyphenols. In the future, this new knowledge will become the basis for a more sensible choice of membranes and for the development of protocols for extending their life cycle. Full article
(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume II))
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<p>Design of the two desorption protocols.</p> Full article ">Figure 2
<p>Coupon preparation for optical visualization of membrane fouling with cranberry juice.</p> Full article ">Figure 3
<p>Optical images of the surface and cross-sections of pristine membranes CSE-fg (<b>a</b>), MK-40 (<b>b</b>), CEM Type-II (<b>c</b>), and CJMC-5 (<b>d</b>) in a 1.0 M NaCl solution.</p> Full article ">Figure 4
<p>Concentration dependencies of (<b>a</b>) specific electric conductivity of the studied membranes, κ<sub>membrane</sub> (mS/cm), and (<b>b</b>) the same dependencies presented in logarithmic coordinates.</p> Full article ">Figure 5
<p>Ratios of the specific electrical conductivities of pristine membranes and membranes soaked in cranberry juice for 168 h.</p> Full article ">Figure 6
<p>Optical images of the surfaces (left) and sections (right) of CJMC-5 membrane coupons that were in contact with cranberry juice for 3, 17, 72, and 168 h. Before obtaining images, these coupons were placed for 2 h in buffer solutions at pH 3.6, 6.9, and 9.3. The dependence of cranberry juice pH (diluted 10 times) on its color is shown below the figure. The scale is 200 μm.</p> Full article ">Figure 7
<p>Optical images of the surfacesthe total concentration of anthocyanins and PACs in these solutions increased in the same sequence (left) and cross-sections (right) of MK-40 membrane coupons that were in contact with cranberry juice for 3, 17, 72, and 168 h. Before obtaining images, these coupons were placed for 2 h in a buffer solution at pH 3.6, 6.9, and 9.3. The dependence of cranberry juice pH (diluted 10 times) on its color is shown below the figure. The scale is 300 μm.</p> Full article ">Figure 8
<p>Optical images of the surface (left) and cross-sections (right) of CSE-fg membrane coupons that were in contact with cranberry juice for 3, 17, 72, and 168 h. Before obtaining images, these coupons were placed for 2 h in a buffer solution at pH 3.6, 6.9, and 9.3. The dependence of cranberry juice pH (diluted 10 times) on its color is shown below the figure. The scale is 300 μm for membrane surface and 150 µm for cross-section.</p> Full article ">Figure 9
<p>Photos of entire membranes before (<b>a1</b>–<b>a4</b>) and after (<b>b1</b>–<b>b4</b>) treatment in 25% acetonitrile/25% methanol/25% isopropanol/25% water at pH 6.</p> Full article ">Figure 10
<p>Photos of desorption solutions after the treatment of (<b>a</b>) entire coupons and (<b>b</b>) ground (cryogenic grinding) coupons.</p> Full article ">Figure 11
<p>Schematic structure of individual anthocyanins (<b>a</b>) and proanthocyanidins (PACs) (<b>b</b>) [<a href="#B42-membranes-11-00136" class="html-bibr">42</a>,<a href="#B43-membranes-11-00136" class="html-bibr">43</a>].</p> Full article ">Figure 12
<p>Photos of the grinded membranes (<b>a1</b>–<b>a4</b>) before and (<b>b1</b>–<b>b4</b>) after treatment in 25% acetonitrile/25% methanol/25% isopropanol/25% water at pH 6.</p> Full article ">
22 pages, 7308 KiB  
Article
The Influence of Concentration and Temperature on the Membrane Resistance of Ion Exchange Membranes and the Levelised Cost of Hydrogen from Reverse Electrodialysis with Ammonium Bicarbonate
by Yash Dharmendra Raka, Robert Bock, Håvard Karoliussen, Øivind Wilhelmsen and Odne Stokke Burheim
Membranes 2021, 11(2), 135; https://doi.org/10.3390/membranes11020135 - 16 Feb 2021
Cited by 19 | Viewed by 4248
Abstract
The ohmic resistances of the anion and cation ion-exchange membranes (IEMs) that constitute a reverse electrodialysis system (RED) are of crucial importance for its performance. In this work, we study the influence of concentration (0.1 M, 0.5 M, 1 M and 2 M) [...] Read more.
The ohmic resistances of the anion and cation ion-exchange membranes (IEMs) that constitute a reverse electrodialysis system (RED) are of crucial importance for its performance. In this work, we study the influence of concentration (0.1 M, 0.5 M, 1 M and 2 M) of ammonium bicarbonate solutions on the ohmic resistances of ten commercial IEMs. We also studied the ohmic resistance at elevated temperature 313 K. Measurements have been performed with a direct two-electrode electrochemical impedance spectroscopy (EIS) method. As the ohmic resistance of the IEMs depends linearly on the membrane thickness, we measured the impedance for three different layered thicknesses, and the results were normalised. To gauge the role of the membrane resistances in the use of RED for production of hydrogen by use of waste heat, we used a thermodynamic and an economic model to study the impact of the ohmic resistance of the IEMs on hydrogen production rate, waste heat required, thermochemical conversion efficiency and the levelised cost of hydrogen. The highest performance was achieved with a stack made of FAS30 and CSO Type IEMs, producing hydrogen at 8.48× 10?7 kg mmem?2s?1 with a waste heat requirement of 344 kWh kg?1 hydrogen. This yielded an operating efficiency of 9.7% and a levelised cost of 7.80 € kgH2?1. Full article
(This article belongs to the Special Issue Advanced Membrane Technology on Desalination and Concentration)
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<p>Schematic of an ammonium bicarbonate reverse electrodialysis cell with a thermally regenerative system. Here, C is the cathode where the hydrogen evolution reaction (HER) occurs, A is the anode where water is produced. Both of these electrodes are in contact with electrode rinse solution made of 1 M sodium bicarbonate. The “+” marked symbol denotes anion exchange membrane and “−” marked symbol denotes cation exchange membrane. The concentrate and dilute feed solutions are described as HC and LC, respectively.</p> Full article ">Figure 2
<p>A flow cell configuration measuring membrane resistance using electrochemical impedance spectroscopy (<b>left</b>). Diffusion boundary layer (DBL) near the surface of a cation-exchange membrane and the salt concentration distribution in different layers at steady state (<b>right</b>). The current direction is to the right.</p> Full article ">Figure 3
<p>Equivalent circuit used for the fitting of electrochemical impedance spectroscopy (EIS) measurements. The resistance (R<math display="inline"><semantics> <msub> <mrow/> <mrow> <mi>i</mi> <mi>n</mi> <mi>t</mi> </mrow> </msub> </semantics></math>) and constant phase element (C<math display="inline"><semantics> <msub> <mrow/> <mrow> <mi>i</mi> <mi>n</mi> <mi>t</mi> </mrow> </msub> </semantics></math>) represent the interface between electrode and solution layer on the ion-exchange membrane (IEM) (i.e., solution–electrode interface). The ohmic resistance of the IEM and the electrode is represented by R<math display="inline"><semantics> <msub> <mrow/> <mrow> <mi>m</mi> <mo>+</mo> <mi>e</mi> <mi>l</mi> <mi>e</mi> </mrow> </msub> </semantics></math>.</p> Full article ">Figure 4
<p>Experimental setup for direct membrane resistance measurement using two electrodes and electrochemical impedance spectroscopy. A. Platinum wire, B. Platinum disc electrode, C. Ceramic casing, D. Stopper, E. Tightening screw, F. Metal casing, G. IEM, H. Solution thin film, I. K-type thermocouple, J. Heating coil, K. Cables.</p> Full article ">Figure 5
<p>Anion exchange membrane (AEM) resistance as a function of thickness for different concentrations at 298 K.</p> Full article ">Figure 6
<p>AEM resistance as a function of thickness for different concentrations at 313 K.</p> Full article ">Figure 7
<p>Cation exchange membrane (CEM) resistance as a function of thickness for different concentrations at 298 K.</p> Full article ">Figure 8
<p>CEM resistance as a function of thickness for different concentrations at 313 K.</p> Full article ">Figure 9
<p>Effect of the solution concentration on the IEM conductivity.</p> Full article ">Figure 10
<p>Levelised cost of hydrogen (LCH) as a function of membrane resistance for different membrane cost. Here, we assume the membrane resistances R<math display="inline"><semantics> <msub> <mrow/> <mrow> <mi>a</mi> <mi>e</mi> <mi>m</mi> </mrow> </msub> </semantics></math> = R<math display="inline"><semantics> <msub> <mrow/> <mrow> <mi>c</mi> <mi>e</mi> <mi>m</mi> </mrow> </msub> </semantics></math>. CSO and FAS30 permselectivities were measured and used as input. The membrane cost range assumed for lab, pilot and commercial scale is 130–150, 50–80 and less than 30 € m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </semantics></math>, respectively. The cost of heating is assumed to be 0.005 € kWh<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>[<a href="#B26-membranes-11-00135" class="html-bibr">26</a>]. We assume for the pilot scale, that the material development will lead to cheaper and less resistive membranes, i.e., SPEEK or carbon-based membranes, and that for the commercial scale these membranes will be produced at large scale (60 × 10<math display="inline"><semantics> <msup> <mrow/> <mn>8</mn> </msup> </semantics></math> m<math display="inline"><semantics> <msup> <mrow/> <mn>2</mn> </msup> </semantics></math> per year) and reduced thickness (25 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m and maintaining the mechanical strength) which will in turn reduce the cost and resistance further [<a href="#B26-membranes-11-00135" class="html-bibr">26</a>,<a href="#B31-membranes-11-00135" class="html-bibr">31</a>,<a href="#B32-membranes-11-00135" class="html-bibr">32</a>].</p> Full article ">
9 pages, 2788 KiB  
Article
Preparation and Properties of Crystalline IGZO Thin Films
by Xiao Wang, Zhihua Shen, Jie Li and Shengli Wu
Membranes 2021, 11(2), 134; https://doi.org/10.3390/membranes11020134 - 14 Feb 2021
Cited by 12 | Viewed by 5292
Abstract
IGZO thin films can be used as active layers of thin-film transistors and have been widely studied. However, amorphous indium gallium zinc oxide (IGZO) fabricated at room temperature is vulnerable in subsequent manufacturing processes, such as etching and sputtering; this limits IGZO thin [...] Read more.
IGZO thin films can be used as active layers of thin-film transistors and have been widely studied. However, amorphous indium gallium zinc oxide (IGZO) fabricated at room temperature is vulnerable in subsequent manufacturing processes, such as etching and sputtering; this limits IGZO thin film transistors’ (TFTs) use in commercial products. In this paper, we prepared a c-axis crystallized IGZO thin film by Radio Frequency (RF) sputtering at 180 °C, with a 50% O2 ratio and 110 W power. XRD images show that the crystallized film has an obvious diffraction peak near 31°, and the spacing between the crystal surfaces was calculated to be ?0.29 nm. The HRTEM map confirmed the above results. The stability of IGZO thin films was investigated by etching them with an acid solution. The crystalline IGZO films exhibited better acid corrosion resistance, and their anticorrosion performance was 74% higher than that of amorphous IGZO (a-IGZO) films, indicating the crystalline IGZO film can provide more stable performance in applications. Full article
(This article belongs to the Special Issue Application of Ferroelectric-Polymer Composites)
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<p>A main effects plot of the deposition rate.</p> Full article ">Figure 2
<p>XRD spectrum of prepared IGZO thin films and the standard spectrum diagram of IGZO.</p> Full article ">Figure 3
<p>HRTEM image and FFT diffractogram (inset) of S9-1.</p> Full article ">Figure 4
<p>The interplanar spacing was obtained from the HRTEM image: (<b>a</b>) calibrated crystallographic orientation on an FFT diffractogram and (<b>b</b>) the corresponding interplanar spacing on an HRTEM image of five layers.</p> Full article ">Figure 5
<p>The cross-sectional SEM images of (<b>a</b>) S1-2 (a-IGZO film) and (<b>b</b>) S9-2 (crystallized IGZO film) after etching.</p> Full article ">
18 pages, 3599 KiB  
Article
Higher Acid Recovery Efficiency of Novel Functionalized Inorganic/Organic Composite Anion Exchange Membranes from Acidic Wastewater
by Muhammad Imran Khan, Abdallah Shanableh, Noureddine Elboughdiri, Karim Kriaa, Djamel Ghernaout, Saad Ghareba, Majeda Khraisheh and Mushtaq Hussain Lashari
Membranes 2021, 11(2), 133; https://doi.org/10.3390/membranes11020133 - 14 Feb 2021
Cited by 14 | Viewed by 3369
Abstract
In this work, the synthesis of a series of the functionalized inorganic/organic composite anion exchange membranes (AEMs) was carried out by employing the varying amount of inorganic filler consist of N-(trimethoxysilylpropyl)-N,N,N-trimethylammonium chloride (TMSP-TMA+Cl? [...] Read more.
In this work, the synthesis of a series of the functionalized inorganic/organic composite anion exchange membranes (AEMs) was carried out by employing the varying amount of inorganic filler consist of N-(trimethoxysilylpropyl)-N,N,N-trimethylammonium chloride (TMSP-TMA+Cl?) into the quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (QPPO) matrix for acid recovery via diffusion dialysis (DD) process. Fourier transform infrared (FTIR) spectroscopy clearly demonstrated the fabrication of the functionalized inorganic/organic composite AEMs and the subsequent membrane characteristic measurements such as ion exchange capacity (IEC), linear swelling ratio (LSR), and water uptake (WR) gave us the optimum loading condition of the filler without undesirable filler particle aggregation. These composite AEMs exhibited IEC of 2.18 to 2.29 meq/g, LSR of 13.33 to 18.52%, and WR of 46.11 to 81.66% with sufficient thermal, chemical, and mechanical stability. The diffusion dialysis (DD) test for acid recovery from artificial acid wastewater of HCl/FeCl2 showed high acid DD coefficient (UH+) (0.022 to 0.025 m/h) and high separation factor (S) (139-260) compared with the commercial membrane. Furthermore, the developed AEMs was acceptably stable (weight loss < 20%) in the acid wastewater at 60 °C as an accelerated severe condition for 2 weeks. These results clearly indicated that the developed AEMs have sufficient potential for acid recovery application by DD process. Full article
(This article belongs to the Special Issue Ion-Exchange Membranes and Processes (Volume II))
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Graphical abstract
Full article ">Figure 1
<p>Fabrication of the quaternized poly (2,6-dimethyl-1,4-phenylene oxide) (QPPO) anion exchange membrane (AEM).</p> Full article ">Figure 2
<p>Schematic principle of the diffusion dialysis (DD) process for acid recovery from the simulated mixture of HCl/FeCl<sub>2</sub>.</p> Full article ">Figure 3
<p>FTIR spectra of the pure BPPO membrane, QPPO membrane, and functionalized inorganic/organic composite AEMs QPPO-2.5 to QPPO-10.</p> Full article ">Figure 4
<p>SEM micrographs of surfaces and cross-sections of the prepared functionalized inorganic/organic composite AEMs.</p> Full article ">Figure 5
<p>(<b>a</b>) Ion exchange capacity, (<b>b</b>) water uptake, (<b>c</b>) linear swelling ratio of the prepared functionalized inorganic/organic composite AEMs at room temperature.</p> Full article ">Figure 6
<p>TGA thermograms as well as onset differential thermogravimetric analysis (DrTGA) of the QPPO and prepared functionalized inorganic/organic composite AEMs QPPO-2.5 to QPPO-10.</p> Full article ">Figure 7
<p>(<b>a</b>) The DD coefficient of acid (U<sub>H</sub><sup>+</sup>), (<b>b</b>) separation factor (S) of the prepared functionalized inorganic/organic composite AEMs at room temperature.</p> Full article ">Figure 8
<p>Comparison of the DD efficiency (diffusion dialysis coefficient of acid (U<sub>H</sub><sup>+</sup>) and separation factor (S)) of the prepared functionalized inorganic/organic composite AEM (This work) with the reported AEMs in literature at room temperature [<a href="#B9-membranes-11-00133" class="html-bibr">9</a>,<a href="#B32-membranes-11-00133" class="html-bibr">32</a>,<a href="#B42-membranes-11-00133" class="html-bibr">42</a>,<a href="#B44-membranes-11-00133" class="html-bibr">44</a>,<a href="#B52-membranes-11-00133" class="html-bibr">52</a>,<a href="#B53-membranes-11-00133" class="html-bibr">53</a>,<a href="#B54-membranes-11-00133" class="html-bibr">54</a>].</p> Full article ">Figure 9
<p>Weight loss of the prepared functionalized inorganic/organic composite AEMs measured after soaking into the mixture of HCl/FeCl<sub>2</sub> feed solution for 2 weeks at 60 °C, indicating excellent acid stability.</p> Full article ">
17 pages, 1681 KiB  
Article
Study of Resveratrol’s Interaction with Planar Lipid Models: Insights into Its Location in Lipid Bilayers
by Daniela Meleleo
Membranes 2021, 11(2), 132; https://doi.org/10.3390/membranes11020132 - 14 Feb 2021
Cited by 18 | Viewed by 2939
Abstract
Resveratrol, a polyphenolic molecule found in edible fruits and vegetables, shows a wide range of beneficial effects on human health, including anti-microbial, anti-inflammatory, anti-cancer, and anti-aging properties. Due to its poor water solubility and high liposome-water partition coefficient, the biomembrane seems to be [...] Read more.
Resveratrol, a polyphenolic molecule found in edible fruits and vegetables, shows a wide range of beneficial effects on human health, including anti-microbial, anti-inflammatory, anti-cancer, and anti-aging properties. Due to its poor water solubility and high liposome-water partition coefficient, the biomembrane seems to be the main target of resveratrol, although the mode of interaction with membrane lipids and its location within the cell membrane are still unclear. In this study, using electrophysiological measurements, we study the interaction of resveratrol with planar lipid membranes (PLMs) of different composition. We found that resveratrol incorporates into palmitoyl-oleoyl-phosphatidylcholine (POPC) and POPC:Ch PLMs and forms conductive units unlike those found in dioleoyl-phosphatidylserine (DOPS):dioleoyl-phosphatidylethanolamine (DOPE) PLMs. The variation of the biophysical parameters of PLMs in the presence of resveratrol provides information on its location within a lipid double layer, thus contributing to an understanding of its mechanism of action. Full article
(This article belongs to the Special Issue Electrical Properties of Model Lipid Membranes)
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Graphical abstract
Full article ">Figure 1
<p>Structure of <span class="html-italic">Trans</span>-resveratrol.</p> Full article ">Figure 2
<p>Molecular structures of (<b>a</b>) palmitoyl-oleoyl-phosphatidylcholine (POPC), (<b>b</b>) dioleoyl-phosphatidylethanolamine (DOPE), (<b>c</b>) dioleoyl-phosphatidylserine (DOPS), (<b>d</b>) and Cholesterol (Ch).</p> Full article ">Figure 3
<p>Experimental set-up during investigations into resveratrol channel-like incorporation.</p> Full article ">Figure 4
<p>Resveratrol channel-like activity in POPC planar lipid membranes (PLMs). Representative traces illustrating channel activity of resveratrol in membranes made up of POPC with associated histograms of the conductance fluctuations. The histograms of the probability, P(Λ), for the frequency of a given conductivity unit were fitted by a Gaussian which is shown as a solid curve. Experiments were performed in the presence of 10 μM (top trace) and 20 μM (bottom trace) of resveratrol added to the <span class="html-italic">cis</span> side, while the aqueous phase contained 0.1 M KCl (pH 7) and T = 23 ± 1 °C. Applied voltage was set to 60 mV (top trace) and 40 mV (bottom trace).</p> Full article ">Figure 5
<p>Resveratrol channel-like activity in POPC:Ch PLMs. Representative traces illustrating channel activity of resveratrol in membranes made up of POPC:Ch (65:35, w:w) with associated histograms of the conductance fluctuations. The histograms of the probability, P(Λ), for the frequency of a given conductivity unit were fitted by a Gaussian which is shown as a solid curve. Experiments were performed in the presence of 10 μM (top trace) and 20 μM (bottom trace) of resveratrol added to the <span class="html-italic">cis</span> side, while the aqueous phase contained 0.1 M KCl (pH 7) and T = 23 ± 1 °C. Applied voltage was set to 80 mV (top trace) and 40 mV (bottom trace).</p> Full article ">Figure 6
<p>Schematic model of the resveratrol interaction with PLM at different lipid composition. Resveratrol adsorbs onto the membrane surface, regardless to the PLM composition. In POPC or POPC:Ch PLMs (top), resveratrol inserts and assembles into membrane forming conductive units, once an appropriate resveratrol/lipid ratio has been reached. In DOPE:DOPS PLMs (bottom), resveratrol inducing negative curvature of membrane is unable to insert into it.</p> Full article ">
15 pages, 890 KiB  
Review
Cleaning Methods for Ceramic Ultrafiltration Membranes Affected by Organic Fouling
by Kamila Gruskevica and Linda Mezule
Membranes 2021, 11(2), 131; https://doi.org/10.3390/membranes11020131 - 14 Feb 2021
Cited by 42 | Viewed by 7976
Abstract
The use of ceramic membranes in the treatment and processing of various liquids, including those of organic origin, has increased tremendously at the industrial level. Apart from the selection of the most appropriate membrane materials and operational conditions, suitable membrane cleaning procedures are [...] Read more.
The use of ceramic membranes in the treatment and processing of various liquids, including those of organic origin, has increased tremendously at the industrial level. Apart from the selection of the most appropriate membrane materials and operational conditions, suitable membrane cleaning procedures are a must to minimize fouling and increase membrane lifespan. The review summarizes currently available and practiced non-reagent and cleaning-in-place methods for ceramic membranes that are used in the treatment of organic liquids, thus causing organic fouling. Backflushing, backwashing, and ultrasound represent the most often used physical methods for reversible fouling treatment. At the same time, the use of alkalis, e.g, sodium hydroxide, acids, or strong oxidants are recommended for cleaning of irreversible fouling treatment. Full article
(This article belongs to the Section Inorganic Membranes)
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<p>Membrane fouling progression: no changes in flux (<b>a</b>), permeate flux is affected (<b>b</b>), hydraulic resistance increased (<b>c</b>), and cake layer formation (<b>d</b>).</p> Full article ">Figure 2
<p>Typical membrane cleaning-in-place (CIP) procedure sequence including cake layer before treatment (<b>a</b>), draining (<b>b</b>) rinsing (<b>c</b>), chemical cleaning (<b>d</b>), and final rinsing (<b>e</b>).</p> Full article ">
21 pages, 8050 KiB  
Article
Runge–Kutta Numerical Method Followed by Richardson’s Extrapolation for Efficient Ion Rejection Reassessment of a Novel Defect-Free Synthesized Nanofiltration Membrane
by Chabi Noël Worou, Jing Kang, Jimin Shen, Pengwei Yan, Weiqiang Wang, Yingxu Gong and Zhonglin Chen
Membranes 2021, 11(2), 130; https://doi.org/10.3390/membranes11020130 - 14 Feb 2021
Cited by 7 | Viewed by 2670
Abstract
A defect-free, loose, and strong layer consisting of zirconium (Zr) nanoparticles (NPs) has been successfully established on a polyacrylonitrile (PAN) ultrafiltration substrate by an in-situ formation process. The resulting organic–inorganic nanofiltration (NF) membrane, NF-PANZr, has been accurately characterized not only with regard to [...] Read more.
A defect-free, loose, and strong layer consisting of zirconium (Zr) nanoparticles (NPs) has been successfully established on a polyacrylonitrile (PAN) ultrafiltration substrate by an in-situ formation process. The resulting organic–inorganic nanofiltration (NF) membrane, NF-PANZr, has been accurately characterized not only with regard to its properties but also its structure by the atomic force microscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy. A sophisticated computing model consisting of the Runge–Kutta method followed by Richardson extrapolation was applied in this investigation to solve the extended Nernst–Planck equations, which govern the solute particles’ transport across the active layer of NF-PANZr. A smart, adaptive step-size routine is chosen for this simple and robust method, also known as RK4 (fourth-order Runge–Kutta). The NF-PANZr membrane was less performant toward monovalent ions, and its rejection rate for multivalent ions reached 99.3%. The water flux of the NF-PANZr membrane was as high as 58 L · m?2 · h?1. Richardson’s extrapolation was then used to get a better approximation of Cl? and Mg2+ rejection, the relative errors were, respectively, 0.09% and 0.01% for Cl? and Mg2+. While waiting for the rise and expansion of machine learning in the prediction of rejection performance, we strongly recommend the development of better NF models and further validation of existing ones. Full article
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Figure 1

Figure 1
<p>Flowchart describing the Runge–Kutta modeling of nanofiltration (NF) membrane transport equation.</p> Full article ">Figure 2
<p>Solute particles transport across the novel synthesized NF-PANZr membrane active layer.</p> Full article ">Figure 3
<p>Procedure for novel thin-film composite membrane NF-PANZr synthesis.</p> Full article ">Figure 4
<p>H-PAN (<b>a</b>,<b>d</b>); BG-PAN (<b>b</b>,<b>e</b>); and NF-PANZr (<b>c</b>,<b>f</b>) membranes’ field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images, respectively.</p> Full article ">Figure 5
<p>Polyacrylonitrile (PAN), hydrolyzed-PAN (H-PAN), BG-PAN, and NF-PANZr membranes (<b>a</b>) water contact angle and (<b>b</b>) zeta potential.</p> Full article ">Figure 6
<p>(<b>a</b>) Energy spectrum analysis results of the NF-PANZr and the sample table surface elements containing (<b>b</b>) carbon, (<b>c</b>) oxygen, (<b>d</b>) zirconium, and (<b>e</b>) nitrogen.</p> Full article ">Figure 7
<p>Probability density function curves of the PAN substrate, H-PAN, BG-PAN, and NF-PANZr membranes.</p> Full article ">Figure 8
<p>Water flux and salt rejection of NF-PANZr as a function of transmembrane pressure under conditions, <math display="inline"><semantics> <mrow> <mfenced close="]" open="["> <mrow> <mi>P</mi> <mi>r</mi> <mi>e</mi> <mi>s</mi> <mi>s</mi> <mi>u</mi> <mi>r</mi> <mi>e</mi> </mrow> </mfenced> <mo> </mo> <mo>=</mo> <mo> </mo> <mn>0.6</mn> <mrow> <mo> </mo> <mi>MPa</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mfenced close="]" open="["> <mrow> <mi>T</mi> <mi>e</mi> <mi>m</mi> <mi>p</mi> <mi>e</mi> <mi>r</mi> <mi>a</mi> <mi>t</mi> <mi>u</mi> <mi>r</mi> <mi>e</mi> </mrow> </mfenced> <mo> </mo> <mo>=</mo> <mo> </mo> <mn>25</mn> <mo> </mo> <mo>°</mo> <mi mathvariant="normal">C</mi> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mo stretchy="false">[</mo> <mi>S</mi> <mi>a</mi> <mi>l</mi> <mi>t</mi> <mi>s</mi> <mo stretchy="false">]</mo> <mo> </mo> <mo>=</mo> <mo> </mo> <mn>1000</mn> <mi>mg</mi> <mo>·</mo> <msup> <mi mathvariant="normal">L</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>H</mi> <mo> </mo> <mo>=</mo> <mo> </mo> <mn>6</mn> <mo>±</mo> <mn>0.5</mn> </mrow> </semantics></math>.</p> Full article ">Figure 9
<p>Concentration of the ion <math display="inline"><semantics> <mrow> <msup> <mrow> <mi>Mg</mi> </mrow> <mrow> <mn>2</mn> <mo>+</mo> </mrow> </msup> </mrow> </semantics></math> inside the novel synthesized nanofiltration membrane (NFM), NF-PANZr, active layer for different volumetric flux (<math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>v</mi> </msub> </mrow> </semantics></math> ) as a function of step size: (<b>a</b>) number of steps equals 200, (<b>b</b>) number of steps equals 100.</p> Full article ">Figure 10
<p>Concentration of the ion <math display="inline"><semantics> <mrow> <msup> <mrow> <mi>Cl</mi> </mrow> <mo>−</mo> </msup> </mrow> </semantics></math> inside the novel synthesized NFM, NF-PANZr active layer for different volumetric fluxes (<math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi>v</mi> </msub> </mrow> </semantics></math>) as a function of step size: (<b>a</b>) number of steps equals 200, (<b>b</b>) number of steps equals 100.</p> Full article ">Figure 11
<p>Test of long-term stability carried out on the synthesized organic-inorganic NF-PANZr membrane under test conditions: <math display="inline"><semantics> <mrow> <mi>cross</mi> <mo>−</mo> <mrow> <mi>flow</mi> <mo> </mo> <mi>rate</mi> <mo> </mo> </mrow> <mo>=</mo> <mo> </mo> <mn>30</mn> <mrow> <mo> </mo> <mi mathvariant="normal">L</mi> </mrow> <mo>·</mo> <msup> <mi mathvariant="normal">h</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </semantics></math>; <math display="inline"><semantics> <mrow> <mrow> <mi>pH</mi> </mrow> <mo>=</mo> <mn>6</mn> </mrow> </semantics></math>; [<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>MgCl</mi> </mrow> <mn>2</mn> </msub> <mo stretchy="false">]</mo> <mo> </mo> <mo>=</mo> <mo> </mo> <mn>1000</mn> <mrow> <mo> </mo> <mi>mg</mi> </mrow> <mo>/</mo> <mi mathvariant="normal">L</mi> </mrow> </semantics></math>, 168 h test; pressure = <math display="inline"><semantics> <mrow> <mn>0.6</mn> <mrow> <mo> </mo> <mi>MPa</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">
13 pages, 433 KiB  
Article
Debye-Hückel Free Energy of an Electric Double Layer with Discrete Charges Located at a Dielectric Interface
by Guilherme Volpe Bossa and Sylvio May
Membranes 2021, 11(2), 129; https://doi.org/10.3390/membranes11020129 - 14 Feb 2021
Cited by 8 | Viewed by 2932
Abstract
Poisson–Boltzmann theory provides an established framework to calculate properties and free energies of an electric double layer, especially for simple geometries and interfaces that carry continuous charge densities. At sufficiently small length scales, however, the discreteness of the surface charges cannot be neglected. [...] Read more.
Poisson–Boltzmann theory provides an established framework to calculate properties and free energies of an electric double layer, especially for simple geometries and interfaces that carry continuous charge densities. At sufficiently small length scales, however, the discreteness of the surface charges cannot be neglected. We consider a planar dielectric interface that separates a salt-containing aqueous phase from a medium of low dielectric constant and carries discrete surface charges of fixed density. Within the linear Debye-Hückel limit of Poisson–Boltzmann theory, we calculate the surface potential inside a Wigner–Seitz cell that is produced by all surface charges outside the cell using a Fourier-Bessel series and a Hankel transformation. From the surface potential, we obtain the Debye-Hückel free energy of the electric double layer, which we compare with the corresponding expression in the continuum limit. Differences arise for sufficiently small charge densities, where we show that the dominating interaction is dipolar, arising from the dipoles formed by the surface charges and associated counterions. This interaction propagates through the medium of a low dielectric constant and alters the continuum power of two dependence of the free energy on the surface charge density to a power of 2.5 law. Full article
(This article belongs to the Special Issue Electrostatics in Cell Membranes and in Artificial Membrane Models)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Left side: Charged circular regions (blue disks), each carrying a uniform surface charge density <math display="inline"><semantics> <mover accent="true"> <mi>σ</mi> <mo>¯</mo> </mover> </semantics></math>, located at an interface (the red plane) that separates two media with dielectric constants <math display="inline"><semantics> <msub> <mi>ε</mi> <mi>w</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>ε</mi> <mi>l</mi> </msub> </semantics></math> from each other. The medium with <math display="inline"><semantics> <msub> <mi>ε</mi> <mi>w</mi> </msub> </semantics></math> contains a symmetric 1:1 salt solution of bulk concentration <math display="inline"><semantics> <msub> <mi>n</mi> <mn>0</mn> </msub> </semantics></math>. The blue transparent cylinder of radius <span class="html-italic">R</span> represents a unit cell (the Wigner–Seitz cell). Right side: The unit cell is fully characterized by the <span class="html-italic">r</span> and <span class="html-italic">z</span> directions of cylindrical coordinates with <math display="inline"><semantics> <mrow> <mn>0</mn> <mo>≤</mo> <mi>r</mi> <mo>≤</mo> <mi>R</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>−</mo> <mo>∞</mo> <mo>&lt;</mo> <mi>z</mi> <mo>&lt;</mo> <mo>∞</mo> </mrow> </semantics></math>. We denote the electrostatic potential for <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>≥</mo> <mn>0</mn> </mrow> </semantics></math> by <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>,</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> and for <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>≤</mo> <mn>0</mn> </mrow> </semantics></math> by <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>,</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 2
<p>The Bessel function of the first kind and first order <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>y</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> and the Bessel function of the first kind and zeroth order <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mi>y</mi> <mo>)</mo> </mrow> </mrow> </semantics></math>. The <math display="inline"><semantics> <msub> <mi>y</mi> <mi>n</mi> </msub> </semantics></math>’s indicate the solutions of <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>y</mi> <mi>n</mi> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> in increasing order starting with <math display="inline"><semantics> <mrow> <msub> <mi>y</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math>.</p> Full article ">Figure 3
<p>Scaled surface charge density <math display="inline"><semantics> <mrow> <mi>σ</mi> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi>σ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> (left diagram) and scaled surface potential <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> (right diagram) according to Equation (<a href="#FD9-membranes-11-00129" class="html-disp-formula">9</a>), with <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mi>R</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>=</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> </mrow> </semantics></math>. In both diagrams, the different curves correspond to <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.4</mn> </mrow> </semantics></math> (blue), <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.2</mn> </mrow> </semantics></math> (orange), <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math> (green), <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.05</mn> </mrow> </semantics></math> (red), and <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> <mo>=</mo> <mn>0.025</mn> </mrow> </semantics></math> (purple).</p> Full article ">Figure 4
<p>Left diagram: The scaled potential <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> for a charged disk of radius <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> and surface charge density <math display="inline"><semantics> <msub> <mi>σ</mi> <mn>0</mn> </msub> </semantics></math> that resides in a unit cell of radius <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> (blue curve), <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>1.2</mn> </mrow> </semantics></math> (orange), <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>1.5</mn> </mrow> </semantics></math> (green), <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> (red), <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>4</mn> </mrow> </semantics></math> (purple), and <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>→</mo> <mo>∞</mo> </mrow> </semantics></math> (black). The black curve is calculated using <math display="inline"><semantics> <mrow> <msubsup> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> <mrow> <mi>s</mi> <mi>e</mi> <mi>l</mi> <mi>f</mi> </mrow> </msubsup> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> in Equation (<a href="#FD14-membranes-11-00129" class="html-disp-formula">14</a>), and all others are based on <math display="inline"><semantics> <mrow> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> in Equation (<a href="#FD9-membranes-11-00129" class="html-disp-formula">9</a>), with <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>=</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> </mrow> </semantics></math> in each case. Right diagram: The difference <math display="inline"><semantics> <mrow> <mo>▵</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>/</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mn>0</mn> </msub> </mrow> </semantics></math> between each colored curve and the black curve on the left diagram. The legend on the left diagram also applies to the right diagram. Note that <math display="inline"><semantics> <mrow> <mo>▵</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> </msub> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> <mo>−</mo> <msubsup> <mi mathvariant="sans-serif">Φ</mi> <mi>s</mi> <mrow> <mi>s</mi> <mi>e</mi> <mi>l</mi> <mi>f</mi> </mrow> </msubsup> <mrow> <mo>(</mo> <mi>r</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> corresponds to the surface potential in the unit cell produced by all charged disks other than that in the considered unit cell.</p> Full article ">Figure 5
<p>Scaled Debye-Hückel free energy <math display="inline"><semantics> <mrow> <mi>F</mi> <mo>/</mo> <msub> <mi>F</mi> <mn>0</mn> </msub> </mrow> </semantics></math> according to Equation (<a href="#FD19-membranes-11-00129" class="html-disp-formula">19</a>) as a function of relative disk size <math display="inline"><semantics> <mrow> <msub> <mi>r</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>R</mi> </mrow> </semantics></math> for fixed <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>/</mo> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>=</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> </mrow> </semantics></math>. Different curves correspond to <math display="inline"><semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> </mrow> </semantics></math> (blue), <math display="inline"><semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mn>33</mn> </mrow> </semantics></math> (orange), <math display="inline"><semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math> (green), <math display="inline"><semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mn>333</mn> </mrow> </semantics></math> (red), <math display="inline"><semantics> <mrow> <msub> <mi>n</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> <mo>=</mo> <mn>1000</mn> </mrow> </semantics></math> (purple).</p> Full article ">Figure 6
<p>Left diagram: Scaled Debye-Hückel free energy <math display="inline"><semantics> <mrow> <mi>F</mi> <mo>/</mo> <msub> <mi>F</mi> <mn>0</mn> </msub> </mrow> </semantics></math> for an ensemble of discrete point charges as a function of the scaled Debye length <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mi>D</mi> </msub> <mo>/</mo> <mi>R</mi> </mrow> </semantics></math>, with <math display="inline"><semantics> <mrow> <mi>R</mi> <mo>=</mo> <msqrt> <mrow> <mi>e</mi> <mo>/</mo> <mo>(</mo> <msub> <mi>σ</mi> <mn>0</mn> </msub> <mi>π</mi> <mo>)</mo> </mrow> </msqrt> </mrow> </semantics></math> being the radius of the Wigner–Seitz cell. Different curves correspond to <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> (blue), <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math> (orange), <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> (green), <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> (red), and <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>2</mn> </mrow> </semantics></math> (purple). Right diagram: The scaled free energy <math display="inline"><semantics> <mrow> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>2</mn> <msubsup> <mi>l</mi> <mi>D</mi> <mn>3</mn> </msubsup> <msub> <mi>ε</mi> <mi>w</mi> </msub> <msub> <mi>ε</mi> <mn>0</mn> </msub> <mi>F</mi> <mo>/</mo> <mrow> <mo>(</mo> <msup> <mi>e</mi> <mn>2</mn> </msup> <mi>A</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> as a function of the scaled surface charge density <math display="inline"><semantics> <mrow> <mi>s</mi> <mo>=</mo> <msubsup> <mi>l</mi> <mi>D</mi> <mn>2</mn> </msubsup> <mo>×</mo> <mrow> <mo>(</mo> <msub> <mi>σ</mi> <mn>0</mn> </msub> <mo>/</mo> <mi>e</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> for <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> (blue), <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0.01</mn> </mrow> </semantics></math> (orange), <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>0.1</mn> </mrow> </semantics></math> (green), and <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> (red). The uppermost straight line (shown in purple) corresponds to the continuum limit <math display="inline"><semantics> <mrow> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>=</mo> <msup> <mi>s</mi> <mn>2</mn> </msup> </mrow> </semantics></math> where the discreteness of the charges is ignored (see also Equation (<a href="#FD1-membranes-11-00129" class="html-disp-formula">1</a>)). The short black line segment close to the red line is a guide to the eye; it has a slope of <math display="inline"><semantics> <mrow> <mn>2.5</mn> </mrow> </semantics></math> and thus indicates a behavior <math display="inline"><semantics> <mrow> <msub> <mi>f</mi> <mi>s</mi> </msub> <mo>∼</mo> <msup> <mi>s</mi> <mrow> <mn>2.5</mn> </mrow> </msup> </mrow> </semantics></math>, as observed for non-vanishing <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mi>l</mi> </msub> <mo>/</mo> <msub> <mi>ε</mi> <mi>w</mi> </msub> </mrow> </semantics></math> in the limit of small <span class="html-italic">s</span>.</p> Full article ">
35 pages, 6419 KiB  
Article
The Need for Accurate Osmotic Pressure and Mass Transfer Resistances in Modeling Osmotically Driven Membrane Processes
by Endre Nagy, Imre Hegedüs, Danyal Rehman, Quantum J. Wei, Yvana D. Ahdab and John H. Lienhard
Membranes 2021, 11(2), 128; https://doi.org/10.3390/membranes11020128 - 14 Feb 2021
Cited by 21 | Viewed by 4410
Abstract
The widely used van ’t Hoff linear relation for predicting the osmotic pressure of NaCl solutions may result in errors in the evaluation of key system parameters, which depend on osmotic pressure, in pressure-retarded osmosis and forward osmosis. In this paper, the linear [...] Read more.
The widely used van ’t Hoff linear relation for predicting the osmotic pressure of NaCl solutions may result in errors in the evaluation of key system parameters, which depend on osmotic pressure, in pressure-retarded osmosis and forward osmosis. In this paper, the linear van ’t Hoff approach is compared to the solutions using OLI Stream Analyzer, which gives the real osmotic pressure values. Various dilutions of NaCl solutions, including the lower solute concentrations typical of river water, are considered. Our results indicate that the disparity in the predicted osmotic pressure of the two considered methods can reach 30%, depending on the solute concentration, while that in the predicted power density can exceed over 50%. New experimental results are obtained for NanoH2O and Porifera membranes, and theoretical equations are also developed. Results show that discrepancies arise when using the van ’t Hoff equation, compared to the OLI method. At higher NaCl concentrations (C > 1.5 M), the deviation between the linear approach and the real values increases gradually, likely indicative of a larger error in van ’t Hoff predictions. The difference in structural parameter values predicted by the two evaluation methods is also significant; it can exceed the typical 50–70% range, depending on the operating conditions. We find that the external mass transfer coefficients should be considered in the evaluation of the structural parameter in order to avoid overestimating its value. Consequently, measured water flux and predicted structural parameter values from our own and literature measurements are recalculated with the OLI software to account for external mass transfer coefficients. Full article
(This article belongs to the Special Issue Numerical Modelling in Membrane Processes)
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Figure 1

Figure 1
<p>SEM images of the surface and cross-section structure of two membranes used in experiments: QuantumFlux (NanoH<sub>2</sub>O) membrane (<b>a</b>–<b>c</b>) and PFO (Porifera) membrane (<b>d</b>–<b>f</b>). (<b>a</b>) Surface structure of the active layer of NanoH<sub>2</sub>O membrane; (<b>b</b>) surface structure of the support, or non-woven fabric, layer of NanoH<sub>2</sub>O membrane with observable circular fibers (15–25 μm thick); (<b>c</b>) the cross-section of NanoH<sub>2</sub>O membrane contains a thin (500–900 nm) active layer and a thick (70–80 μm) porous support layer, which can result in unique separation features; (<b>d</b>) the active surface of PFO membrane; (<b>e</b>) the surface of the support layer of PFO membrane; (<b>f</b>) the cross-section of PFO membrane contains a very thin active layer (<b>f1</b>) and porous sponge-like support layer (<b>f2</b>). PFO membrane fibers of Nomex polymer (50 μm thick) are also well detectable.</p> Full article ">Figure 2
<p>(<b>a</b>) Osmotic water fluxes of the NanoH<sub>2</sub>O membrane in pressure-retarded osmosis (PRO) and forward osmosis (FO) modes. Experiments were performed at 22 °C and 0.20–0.25 m/s cross-flow velocity with DI water at the feed side and without a hydraulic pressure difference (1 × 10<sup>−6</sup> m/s = 3.6 Lmh). (<b>b</b>) Salt fluxes of the NanoH<sub>2</sub>O membrane in PRO and FO modes. Experiments were performed at 22 °C and 0.20–0.25 m/s cross-flow velocity with DI water at the feed side and without a hydraulic pressure difference.</p> Full article ">Figure 3
<p>Osmotic water flux of the Porifera membrane as a function of the draw NaCl concentration in PRO mode. Experiments were performed at 22 °C and at 0.20–0.25 m/s cross-flow velocity with DI water at the feed side and without a hydraulic pressure difference (the continuous line is a fitted curve to the measured points).</p> Full article ">Figure 4
<p>Predicted power density/water flux as a function of the solute concentration for PRO and FO systems comparing the linear approach and the OLI Stream Analyzer’s data [<a href="#B35-membranes-11-00128" class="html-bibr">35</a>] for the osmotic pressure. (Other parameters are listed in <a href="#membranes-11-00128-t002" class="html-table">Table 2</a>).</p> Full article ">Figure 5
<p>Change of the relative error in percent (<math display="inline"><semantics> <mrow> <mfenced close="" open="|"> <mrow> <msub> <mi>π</mi> <mrow> <mi>l</mi> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>−</mo> <mfenced close="|" open=""> <mrow> <msub> <mi>π</mi> <mrow> <mi>O</mi> <mi>L</mi> <mi>I</mi> </mrow> </msub> </mrow> </mfenced> </mrow> </mfenced> <mo>/</mo> <msub> <mi>π</mi> <mi>x</mi> </msub> </mrow> </semantics></math>, where π<span class="html-italic"><sub>x</sub></span> indicates the higher pressure in each case) as a function of the solute concentration, applying for prediction of the π value by the van ’t Hoff linear approach and the OLI software.</p> Full article ">Figure 6
<p>Power density/water flux as a function of the hydraulic pressure difference applying the van ’t Hoff approach and the OLI software for prediction of the osmotic pressure (other parameters are listed in <a href="#membranes-11-00128-t002" class="html-table">Table 2</a>).</p> Full article ">Figure 7
<p>Water flux as a function of the membrane structural parameter at two different values of the hydraulic pressure (Other parameters are listed in <a href="#membranes-11-00128-t002" class="html-table">Table 2</a>) (1 Lmh = 0.2778 × 10<sup>−6</sup> m/s).</p> Full article ">Figure 8
<p>Power density and concentration of the membrane active layer as a function of the water permeability (constant parameters are given in <a href="#membranes-11-00128-t002" class="html-table">Table 2</a>).</p> Full article ">Figure 9
<p>Power density and concentration of the membrane active layer as a function of the solute permeability (Remained parameter are given in <a href="#membranes-11-00128-t002" class="html-table">Table 2</a>).</p> Full article ">Figure 10
<p>Change of the <span class="html-italic">S/S<sub>∞</sub></span> values as a function of the water flux in a PRO system, taking into account their predicted error of the measured data (±20%), given by Manickam and McCutcheon [<a href="#B40-membranes-11-00128" class="html-bibr">40</a>]. Parameter is the external mass transfer coefficient in the boundary layer facing the active membrane layer, at <span class="html-italic">C<sub>d</sub></span> = 1.0 M, and <span class="html-italic">k<sub>f</sub></span><span class="html-italic">→</span>∞ (<span class="html-italic">A</span> = 1.71 × 10<sup>−7</sup> m/s·bar; <span class="html-italic">B</span> = 1.94 × 10<sup>−7</sup> m/s; <span class="html-italic">C<sub>f</sub></span> = 0; <span class="html-italic">S</span> = 803 × 10<sup>−6</sup> m; Δ<span class="html-italic">P</span> = 0; <span class="html-italic">D</span> = 1.5 × 10<sup>−9</sup> m<sup>2</sup>/s). On the upper horizontal axis, the calculated value of the corresponding structural parameter is given for <span class="html-italic">k<sub>d</sub></span>→∞, <span class="html-italic">k<sub>f</sub></span>→∞.</p> Full article ">Figure 11
<p>Change of the <span class="html-italic">S/S<sub>∞</sub></span> values as a function of the water flux in the FO system, taking into account ±20% error of the measured data, at <span class="html-italic">C<sub>d</sub></span> = 1.5 M, <span class="html-italic">k<sub>f</sub></span>→∞ applied data of Manickam and McCutcheon [<a href="#B40-membranes-11-00128" class="html-bibr">40</a>] (other parameters are given in caption of <a href="#membranes-11-00128-f010" class="html-fig">Figure 10</a>). On the upper horizontal axis, the calculated value of the corresponding structural parameter, <span class="html-italic">S</span><sub>∞</sub>, is given for <span class="html-italic">k<sub>d</sub>→</span>∞, <span class="html-italic">k<sub>f</sub></span>→∞.</p> Full article ">Figure 12
<p>Value of <span class="html-italic">S/S<sub>∞</sub></span> as a function of the draw side mass transfer coefficient with both operating modes, i.e., PRO and FO; <span class="html-italic">C<sub>d</sub></span> = 1.0 M; <span class="html-italic">k<sub>f</sub>→</span>∞; for PRO: <span class="html-italic">J<sub>w</sub>,</span><sub>∞</sub> = 4.92 × 10<sup>−6</sup> m/s; <span class="html-italic">S</span><sub>∞</sub> = 803 μm; for FO: <span class="html-italic">J</span><sub>∞</sub> = 3.0 × 10<sup>−6</sup> m/s; <span class="html-italic">S</span><sub>∞</sub> = 395 μm; other parameters as they are given in caption of <a href="#membranes-11-00128-f010" class="html-fig">Figure 10</a>.</p> Full article ">Figure 13
<p>Effect of the water permeability on the value of <span class="html-italic">S/S</span><sub>∞</sub> and on the water flux, <span class="html-italic">J<sub>w</sub></span><sub>,∞</sub>, as a function of draw side mass transfer coefficient, in a PRO system; <span class="html-italic">C<sub>d</sub></span> = 1.0 M; <span class="html-italic">S<sub>∞</sub></span> = 803 μm; π<span class="html-italic"><sub>d</sub></span> = 43.3 bar; <span class="html-italic">k<sub>f</sub>→</span>∞; other parameters as they are given in caption of <a href="#membranes-11-00128-t005" class="html-table">Table 5</a>.</p> Full article ">Figure 14
<p>Effect of the solute permeability on the value of <span class="html-italic">S/S</span><sub>∞</sub> and on the water flux, <span class="html-italic">J<sub>w</sub></span><sub>,∞</sub>, as a function of draw side mass transfer coefficient, in a PRO system; <span class="html-italic">C<sub>d</sub></span> = 1.0 M; <span class="html-italic">S<sub>∞</sub></span> = 803 μm; <span class="html-italic">k<sub>f</sub></span>→∞; other parameters as in <a href="#membranes-11-00128-t005" class="html-table">Table 5</a>.</p> Full article ">Figure A1
<p>Illustration of the concentration distribution and nomenclature of parameters for PRO (left-hand side figure) and FO (figure on the right-hand side) processes, including external mass transfer resistances. <span class="html-italic">C<sub>m</sub></span> and <span class="html-italic">C<sub>s</sub></span> correspond to the interface concentration of the active layer facing the boundary layer and facing the porous support layer, respectively. Δπ<sub>eff</sub> is the effective osmotic pressure difference on the active layer.</p> Full article ">Figure A2
<p>Osmotic pressure, predicted by the van ’t Hoff linear approach and the OLI Streamline Analyzer software, as a function of the solute concentration for NaCl and MgCl<sub>2</sub>. The vertical axis corresponds to the osmotic pressure.</p> Full article ">
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