Membranes

4 pages, 161 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Membranes in 2018

by Membranes Editorial Office

Membranes 2019, 9(1), 17; https://doi.org/10.3390/membranes9010017 - 17 Jan 2019

Viewed by 2375

Abstract

Rigorous peer-review is the corner-stone of high-quality academic publishing [...] Full article

14 pages, 5618 KiB

Open AccessArticle

Dye Degrading and Fouling-Resistant Membranes Formed by Deposition with Ternary Nanocomposites of N-Doped Graphene/TiO₂/Activated Carbon

by Tao Wu, Zongman Zhang, Ding Zhai, Yang Liu, Qingguo Liu, Lixin Xue and Congjie Gao

Membranes 2019, 9(1), 16; https://doi.org/10.3390/membranes9010016 - 15 Jan 2019

Cited by 19 | Viewed by 4135

Abstract

A ternary nanocomposite consisting of N-doped graphene (NGR)/TiO₂/activated carbon (NGRT@AC) was prepared, and the components’ synergetic effect on dye degradation was investigated after deposition on the surface of a polysulfone membrane (PSF). As far as we know, this ternary composite catalyst [...] Read more.

A ternary nanocomposite consisting of N-doped graphene (NGR)/TiO₂/activated carbon (NGRT@AC) was prepared, and the components’ synergetic effect on dye degradation was investigated after deposition on the surface of a polysulfone membrane (PSF). As far as we know, this ternary composite catalyst has never previously been used to degrade dyes nor been used as a functional layer for separation membranes. The surface morphology and structure of the as-prepared membranes were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The NGRT@AC-modified PSF membrane (NGRT@AC-PSF) presents excellent photodegradation efficiency to methyl orange (MO) under both UV (95.2%) and sunlight (78.1%) irradiation, much higher than those values of PSF, TiO₂- modified PSF (TiO₂-PSF), and N-doped graphene/TiO₂ (NGRT)-modified PSF membranes (NGRT-PSF) under the same conditions. The high flux recovery ratio (95.5%) demonstrates that the NGRT@AC-PSF membrane shows improved antifouling performance. The photocatalytic results prove that surface deposition method (95.2%) was better than the blending method (31.1%) for forming high-performance membranes. Therefore, the NGRT@AC-PSF membrane has the potential for broad applications in dye degradation to treat waste water from textile industries. Full article

(This article belongs to the Section Inorganic Membranes)

► Show Figures

Graphical abstract

19 pages, 7220 KiB

Open AccessFeature PaperArticle

Glucose Can Protect Membranes against Dehydration Damage by Inducing a Glassy Membrane State at Low Hydrations

by Alexander Dhaliwal, Adree Khondker, Richard Alsop and Maikel C. Rheinstädter

Membranes 2019, 9(1), 15; https://doi.org/10.3390/membranes9010015 - 15 Jan 2019

Cited by 21 | Viewed by 5803

Abstract

The physical effects of small sugars on membranes have been studied for decades, primarily because of their membrane stabilization in cold or dehydrated environments. We studied the effects of up to 20 mol% glucose in bilayers made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at [...] Read more.

The physical effects of small sugars on membranes have been studied for decades, primarily because of their membrane stabilization in cold or dehydrated environments. We studied the effects of up to 20 mol% glucose in bilayers made of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at low hydration by combining X-ray diffraction and Molecular Dynamics (MD) simulations. In agreement with previous studies, we observe membrane thinning at low and membrane thickening at high sugar concentrations. Glucose was found to preferentially localize to the outer head region of phospholipid bilayers at all concentrations, and partitioning of sugar in the membranes was found to monotonically increase with increasing sugar concentration. While the number of gauche defects in the lipid acyl tails and the lipid packing in the presence of sugar resembled values of a fluid lipid bilayer, tail dynamics, as assessed by autocorrelation of the carbon atoms in the phospholipid tails, were slowed down significantly with increasing glucose content. Thus, our findings suggest that sugar leads to a a disordered, glassy state of the hydrophobic membrane core. The non-monotonic effect of glucose on membrane thickness was found to be an effect of fluidification at low concentrations and decreased interdigitation in the higher sugar concentration regime. Full article

► Show Figures

Graphical abstract

21 pages, 2372 KiB

Open AccessArticle

Integrated Design and Control of Various Hydrogen Production Flowsheet Configurations via Membrane Based Methane Steam Reforming

by Alexios-Spyridon Kyriakides, Spyros Voutetakis, Simira Papadopoulou and Panos Seferlis

Membranes 2019, 9(1), 14; https://doi.org/10.3390/membranes9010014 - 15 Jan 2019

Cited by 10 | Viewed by 4132

Abstract

This work focuses on the development and implementation of an integrated process design and control framework for a membrane-based hydrogen production system based on low temperature methane steam reforming. Several alternative flowsheet configurations consisted of either integrated membrane reactor modules or successive reactor [...] Read more.

This work focuses on the development and implementation of an integrated process design and control framework for a membrane-based hydrogen production system based on low temperature methane steam reforming. Several alternative flowsheet configurations consisted of either integrated membrane reactor modules or successive reactor and membrane separation modules are designed and assessed by considering economic and controller dynamic performance criteria simultaneously. The design problem is expressed as a non-linear dynamic optimization problem incorporating a nonlinear dynamic model for the process system and a linear model predictive controller aiming to maintain the process targets despite the effect of disturbances. The large dimensionality of the disturbance space is effectively addressed by focusing on disturbances along the direction that causes the maximum process variability revealed by the analysis of local sensitivity information for the process system. Design results from a multi-objective optimization study, where only the annualized equipment and operational costs are minimized, are used as reference case in order to evaluate the proposed design framework. Optimization results demonstrate the controller’s ability to track the imposed setpoint changes and alleviate the effects of multiple simultaneous disturbances. Also, significant economic improvements are observed by the implementation of the integrated design and control framework compared to the traditional design methodology, where process and controller design are performed sequentially. Full article

(This article belongs to the Special Issue Modeling and Design of Membrane Reactors)

► Show Figures

Figure 1

13 pages, 2331 KiB

Open AccessArticle

Electrochemical Properties of Homogeneous and Heterogeneous Anion Exchange Membranes Coated with Cation Exchange Polyelectrolyte

by Xenia Nebavskaya, Veronika Sarapulova, Dmitrii Butylskii, Christian Larchet and Natalia Pismenskaya

Membranes 2019, 9(1), 13; https://doi.org/10.3390/membranes9010013 - 11 Jan 2019

Cited by 16 | Viewed by 4539

Abstract

Coating ion exchange membranes with polyelectrolyte has been proven to be a cheap way to reduce concentration polarization and increase limiting current (for polyelectrolytes carrying fixed groups of the same sign of charge with respect to the membrane bulk), to create high monovalent [...] Read more.

Coating ion exchange membranes with polyelectrolyte has been proven to be a cheap way to reduce concentration polarization and increase limiting current (for polyelectrolytes carrying fixed groups of the same sign of charge with respect to the membrane bulk), to create high monovalent selectivity, and to add the function of H⁺/OH⁻ ions generation (for polyelectrolytes bearing fixed groups of the opposite sign of charge with respect to the membrane bulk). In the latter case, the balance between the counterion transport and the H⁺/OH⁻ ions generation is affected by parameters of the substrate and the modifying layer. In this study we investigated the electrochemical characteristics of homogeneous Neosepta AMX-Sb and heterogeneous MA-41P membranes coated with one, two, or three layers of oppositely charged polyelectrolyte (the maximum thickness of each layer was 5 µm). It was found that the limiting current decreased earlier and the generation of H⁺/OH⁻ ions was stronger in the case of the heterogeneous membrane. The shift in the pH of the solution depended more on the generation of H⁺/OH⁻ ions at the modifying layer/solution interface than on the generation at the membrane/modifying layer interface, and in all cases water splitting started in the same range of potential drops over the membrane. Full article

(This article belongs to the Section Polymeric Membranes)

► Show Figures

Graphical abstract

14 pages, 5105 KiB

Open AccessArticle

Electrospun Polycaprolactone Fibrous Membranes Containing Ag, TiO₂ and Na₂Ti₆O₁₃ Particles for Potential Use in Bone Regeneration

by Erick Ramírez-Cedillo, Wendy Ortega-Lara, María R. Rocha-Pizaña, Janet A. Gutierrez-Uribe, Alex Elías-Zúñiga and Ciro A. Rodríguez

Membranes 2019, 9(1), 12; https://doi.org/10.3390/membranes9010012 - 10 Jan 2019

Cited by 31 | Viewed by 4987

Abstract

Biocompatible and biodegradable membrane treatments for regeneration of bone are nowadays a promising solution in the medical field. Bioresorbable polymers are extensively used in membrane elaboration, where polycaprolactone (PCL) is used as base polymer. The goal of this work was to improve electrospun [...] Read more.

Biocompatible and biodegradable membrane treatments for regeneration of bone are nowadays a promising solution in the medical field. Bioresorbable polymers are extensively used in membrane elaboration, where polycaprolactone (PCL) is used as base polymer. The goal of this work was to improve electrospun membranes’ biocompatibility and antibacterial properties by adding micro- and nanoparticles such as Ag, TiO₂ and Na₂Ti₆O₁₃. Micro/nanofiber morphologies of the obtained membranes were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy and a tensile test. Also, for this study optical microscopy was used to observe DAPI-stained cells. Membranes of the different systems were electrospun to an average diameter of 1.02–1.76 μm. To evaluate the biological properties, cell viability was studied by growing NIH/3T3 cells on the microfibers. PCL/TiO₂ strength was enhanced from 0.6 MPa to 6.3 MPa in comparison with PCL without particles. Antibacterial activity was observed in PCL/TiO₂ and PCL/Na₂Ti₆O₁₃ electrospun membranes using Staphylococcus aureus bacteria. Bioactivity of the membranes was confirmed with simulated body fluid (SBF) treatment. From this study, the ceramic particles TiO₂ and Na₂Ti₆O₁₃, combined with a PCL matrix with micro/nanoparticles, enhanced cell proliferation, adhesion and antibacterial properties. The electrospun composite with Na₂Ti₆O₁₃ can be considered viable for tissue regenerative processes. Full article

(This article belongs to the Special Issue Electrospun Nanofiber Membranes: Advances and Applications)

► Show Figures

Graphical abstract

8 pages, 1741 KiB

Open AccessArticle

Preparation and Properties of Carboxymethyl Chitosan/Alginate/Tranexamic Acid Composite Films

by Qing-Kun Zhong, Ze-Yin Wu, Ya-Qi Qin, Zhang Hu, Si-Dong Li, Zi-Ming Yang and Pu-Wang Li

Membranes 2019, 9(1), 11; https://doi.org/10.3390/membranes9010011 - 8 Jan 2019

Cited by 30 | Viewed by 4971

Abstract

In this study, the porous composite films of carboxymethyl chitosan/alginate/tranexamic acid were fabricated, with calcium chloride as the crosslinking agent and glycerin as a plasticizer. The composite films were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The properties [...] Read more.

In this study, the porous composite films of carboxymethyl chitosan/alginate/tranexamic acid were fabricated, with calcium chloride as the crosslinking agent and glycerin as a plasticizer. The composite films were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The properties of the composite films, including water absorption, air permeability, and cumulative release rate, were tested. In addition, their hemostatic performance was evaluated. The results showed that the appearance of the films with good adhesion was smooth and porous. FTIR showed that chemical crosslinking between carboxymethyl chitosan and sodium alginate was successful. The excellent cumulative release of tranexamic acid in the composite films (60–80%) gives the films a significant procoagulant effect. This has good prospects for the development of medical hemostasis materials. Full article

(This article belongs to the Section Membrane Chemistry)

► Show Figures

Figure 1

14 pages, 2504 KiB

Open AccessEditor’s ChoiceArticle

Experimental Mixed-Gas Permeability, Sorption and Diffusion of CO₂-CH₄ Mixtures in 6FDA-mPDA Polyimide Membrane: Unveiling the Effect of Competitive Sorption on Permeability Selectivity

by Giuseppe Genduso, Bader S. Ghanem and Ingo Pinnau

Membranes 2019, 9(1), 10; https://doi.org/10.3390/membranes9010010 - 8 Jan 2019

Cited by 54 | Viewed by 7588

Abstract

The nonideal behavior of polymeric membranes during separation of gas mixtures can be quantified via the solution-diffusion theory from experimental mixed-gas solubility and permeability coefficients. In this study, CO₂-CH₄ mixtures were sorbed at 35 °C in 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA)-m-phenylenediamine (mPDA)—a [...] Read more.

The nonideal behavior of polymeric membranes during separation of gas mixtures can be quantified via the solution-diffusion theory from experimental mixed-gas solubility and permeability coefficients. In this study, CO₂-CH₄ mixtures were sorbed at 35 °C in 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA)-m-phenylenediamine (mPDA)—a polyimide of remarkable performance. The existence of a linear trend for all data of mixed-gas CO₂ versus CH₄ solubility coefficients—regardless of mixture concentration—was observed for 6FDA-mPDA and other polymeric films; the slope of this trend was identified as the ratio of gas solubilities at infinite dilution. The CO₂/CH₄ mixed-gas solubility selectivity of 6FDA-mPDA and previously reported polymers was higher than the equimolar pure-gas value and increased with pressure from the infinite dilution value. The analysis of CO₂-CH₄ mixed-gas concentration-averaged effective diffusion coefficients of equimolar feeds showed that CO₂ diffusivity was not affected by CH₄. Our data indicate that the decrease of CO₂/CH₄ mixed-gas diffusion, and permeability selectivity from the pure-gas values, resulted from an increase in the methane diffusion coefficient in mixtures. This effect was the result of an alteration of the size sieving properties of 6FDA-mPDA as a consequence of CO₂ presence in the 6FDA-mPDA film matrix. Full article

(This article belongs to the Special Issue Gas Transport in Glassy Polymers)

► Show Figures

Graphical abstract

14 pages, 2585 KiB

Open AccessEditor’s ChoiceArticle

Acidic Gases Separation from Gas Mixtures on the Supported Ionic Liquid Membranes Providing the Facilitated and Solution-Diffusion Transport Mechanisms

by Alsu I. Akhmetshina, Nail R. Yanbikov, Artem A. Atlaskin, Maxim M. Trubyanov, Amal Mechergui, Ksenia V. Otvagina, Evgeny N. Razov, Alla E. Mochalova and Ilya V. Vorotyntsev

Membranes 2019, 9(1), 9; https://doi.org/10.3390/membranes9010009 - 5 Jan 2019

Cited by 48 | Viewed by 5861

Abstract

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO₂ carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such [...] Read more.

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO₂ carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such membranes may be appropriate for better understanding of various factors affecting the separation performance and the selection of the optimal operating conditions. In this work, we have tested CH₄, CO₂ and H₂S permeability across the supported ionic liquid membranes impregnated by 1-butyl-3-methylimidazolium acetate (bmim[OAc]) with the following determination of the ideal selectivity in order to compare the facilitated transport membrane performance with the supported ionic liquid membrane (SILM) that provides solution-diffusion mechanism, namely, containing 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF₄]). Both SILMs have showed modest individual gases permeability and ideal selectivity of CO₂/CH₄ and H₂S/CH₄ separation that achieves values up to 15 and 32, respectively. The effect of the feed gas mixture composition on the permeability of acidic gases and permeselectivity of the gas pair was investigated. It turned out that the permeation behavior for the bmim[OAc]-based SILM toward the binary CO₂/CH₄, H₂S/CH₄ and ternary CO₂/H₂S/CH₄ mixtures was featured with high acidic gases selectivity due to the relatively low methane penetration through the liquid phase saturated by acidic gases. Full article

(This article belongs to the Special Issue Ionic Liquid and Polymerized Ionic Liquids as Membranes for Clean Energy Generation and Industrial Gas Separations)

► Show Figures

Figure 1

26 pages, 3967 KiB

Open AccessEditor’s ChoiceArticle

Modelling Mixed-Gas Sorption in Glassy Polymers for CO₂ Removal: A Sensitivity Analysis of the Dual Mode Sorption Model

by Eleonora Ricci and Maria Grazia De Angelis

Membranes 2019, 9(1), 8; https://doi.org/10.3390/membranes9010008 - 4 Jan 2019

Cited by 45 | Viewed by 6472

Abstract

In an effort to reduce the experimental tests required to characterize the mixed-gas solubility and solubility-selectivity of materials for membrane separation processes, there is a need for reliable models which involve a minimum number of adjustable parameters. In this work, the ability of [...] Read more.

In an effort to reduce the experimental tests required to characterize the mixed-gas solubility and solubility-selectivity of materials for membrane separation processes, there is a need for reliable models which involve a minimum number of adjustable parameters. In this work, the ability of the Dual Mode Sorption (DMS) model to represent the sorption of CO₂/CH₄ mixtures in three high free volume glassy polymers, poly(trimethylsilyl propyne) (PTMSP), the first reported polymer of intrinsic microporosity (PIM-1) and tetrazole-modified PIM-1 (TZ-PIM), was tested. The sorption of gas mixtures in these materials suitable for CO₂ separation has been characterized experimentally in previous works, which showed that these systems exhibit rather marked deviations from the ideal pure-gas behavior, especially due to competitive effects. The accuracy of the DMS model in representing the non-idealities that arise during mixed-gas sorption was assessed in a wide range of temperatures, pressures and compositions, by comparing with the experimental results available. Using the parameters obtained from the best fit of pure-gas sorption isotherms, the agreement between the mixed-gas calculations and the experimental data varied greatly in the different cases inspected, especially in the case of CH₄ absorbed in mixed-gas conditions. A sensitivity analysis revealed that pure-gas data can be represented with the same accuracy by several different parameter sets, which, however, yield markedly different mixed-gas predictions, that, in some cases, agree with the experimental data only qualitatively. However, the multicomponent calculations with the DMS model yield more reliable results than the use of pure-gas data in the estimation of the solubility-selectivity of the material. Full article

(This article belongs to the Special Issue Gas Transport in Glassy Polymers)

► Show Figures

Graphical abstract

22 pages, 7191 KiB

Open AccessArticle

Performance of Void-Free Electrospun SPEEK/Cloisite as a Function of Degree of Dispersion State on Nanocomposite Proton Exchange Membrane for Direct Methanol Fuel Cell Application

by Nuha Awang, Juhana Jaafar, Ahmad Fauzi Ismail, Mohd Hafiz Dzarfan Othman and Mukhlis A. Rahman

Membranes 2019, 9(1), 7; https://doi.org/10.3390/membranes9010007 - 2 Jan 2019

Cited by 12 | Viewed by 3980

Abstract

One of the main problems in direct methanol fuel cell (DMFC) application is methanol crossover. In order to solve the problem, an exfoliated void-free electrospun Sulfonated Poly(Ether Ether Ketone) (SPEEK)/cloisite nanocomposite membrane was developed. The membrane was prepared by immersing electrospun SPEEK/cloisite fiber [...] Read more.

One of the main problems in direct methanol fuel cell (DMFC) application is methanol crossover. In order to solve the problem, an exfoliated void-free electrospun Sulfonated Poly(Ether Ether Ketone) (SPEEK)/cloisite nanocomposite membrane was developed. The membrane was prepared by immersing electrospun SPEEK/cloisite fiber mats onto incomplete solidified SPEEK polymer matrix. A well dispersed and reduction size of cloisite particles that ranges from 0.29–0.39 µm was observed by using Scanning Electron Microscopy Analysis (SEM) and Atomic Force Microscope (AFM). The effect of the morphology of the composite membrane in terms of degree of dispersion state of the Cloisite on the membrane performance was discussed. SP/e-spunCL15 with fully exfoliated structure exhibited the highest performance as compared to other tested membranes and Nafion^® 115 with current density of 1042.2 mAcm⁻² and power density of 1.18 mWcm⁻². Improved morphological, dimensional change properties, and performance assigned to well-dispersed cloisite15A induced by the electrospinning technique make the membranes more efficient for direct methanol fuel cell applications. Full article

(This article belongs to the Special Issue Mass Transfer in Membranes)

► Show Figures

Figure 1

12 pages, 2355 KiB

Open AccessArticle

Effect of Chemical Structure on the Performance of Sulfonated Poly(aryl ether sulfone) Composite Nanofiltration Membranes

by Shouhai Zhang, Shanshan Guan, Chengde Liu, Zhenlin Wang, Danhui Wang and Xigao Jian

Membranes 2019, 9(1), 6; https://doi.org/10.3390/membranes9010006 - 2 Jan 2019

Cited by 12 | Viewed by 3814

Abstract

This paper discusses the effect of the chemical structure of sulfonated poly(aryl ether sulfone) on the performance of composite nanofiltration membranes. The composite nanofiltration membranes were fabricated by coating sulfonated poly(aryl ether sulfone) solution onto the top surface of poly(phthalazinone ether sulfone ketone) [...] Read more.

This paper discusses the effect of the chemical structure of sulfonated poly(aryl ether sulfone) on the performance of composite nanofiltration membranes. The composite nanofiltration membranes were fabricated by coating sulfonated poly(aryl ether sulfone) solution onto the top surface of poly(phthalazinone ether sulfone ketone) support membranes. Three kinds of sulfonated poly(aryl ether sulfone)s with different amounts of phthalazinone moieties, namely, sulfonated poly(phthalazinone ether sulfone) (SPPES), sulfonated poly(phthalazinone biphenyl ether sulfone) (SPPBES), and sulfonated poly(phthalazinone hydroquinone ether sulfone)s (SPPHES), were used as coating materials. The solvents used in preparing the coating solution were investigated and optimized. The separation properties, thermal stability, and chlorine resistance of composite membranes were determined. The structures and morphologies of membranes were characterized with FTIR and SEM, respectively. The membrane prepared from SPPES with more phthalazinone moiety groups showed high water flux and salt rejection. The salt rejection of composite membranes followed the order SPPES > SPPHES > SPPBES. The rejection of the three composite membranes decreased slightly with the solution temperature rising from 20 to 90 °C, while the composite membrane with SPPES as the active layer showed a higher increase in flux than others. The results indicate that SPPES composite membranes show better thermal stability than others. Full article

(This article belongs to the Special Issue Novel Membrane Materials)

► Show Figures

Figure 1

12 pages, 4287 KiB

Open AccessFeature PaperArticle

Ceramic-Based Composite Membrane with a Porous Network Surface Featuring a Highly Stable Flux for Drinking Water Purification

by Li Zhu, Kadalipura Puttaswamy Rakesh, Man Xu and Yingchao Dong

Membranes 2019, 9(1), 5; https://doi.org/10.3390/membranes9010005 - 2 Jan 2019

Cited by 18 | Viewed by 4224

Abstract

Highly efficient drinking water purification is still an important challenge for membrane techniques where high flux, high rejection, and low fouling are highly emphasized. In the present work, a porous network surface with carbon nanotubes (CNTs) was in situ constructed on hierarchically-structured mullite [...] Read more.

Highly efficient drinking water purification is still an important challenge for membrane techniques where high flux, high rejection, and low fouling are highly emphasized. In the present work, a porous network surface with carbon nanotubes (CNTs) was in situ constructed on hierarchically-structured mullite ceramic membranes. Interestingly, such a composite structure was demonstrated to effectively remove bacteria from drinking water with a highly stable long-term flux. After membrane structure characterizations, separation performance, such as flux and rejection, was assessed by the purification of bacteria-contaminated drinking water. The results confirmed that the mullite-CNT composite membrane claimed a complete removal of two model bacteria (100% rejection of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus)), driven by a trans-membrane pressure of 0.1 MPa, where a surface sieving mechanism was dominant. A highly stable long-term flux for the 24 h filtration process was achieved, which can be attributed to the porous membrane surface with a special randomly-oriented CNTs network structure, featuring very high three-dimensional open porosity, allowing water to rapidly transport. The bacteria were only trapped on the CNTs network surface via surface filtration, without pore plugging, endowing the mullite-CNT membrane with unprecedentedly low fouling propensity to keep high flux with long-term operation time. Full article

(This article belongs to the Special Issue Novel Membrane Materials)

► Show Figures

Figure 1

16 pages, 3292 KiB

Open AccessArticle

Preparation of PVA-Based Hollow Fiber Ion-Exchange Membranes and Their Performance for Donnan Dialysis

by Mitsuru Higa, Yuriko Kakihana, Takehiro Sugimoto and Kakuya Toyota

Membranes 2019, 9(1), 4; https://doi.org/10.3390/membranes9010004 - 2 Jan 2019

Cited by 7 | Viewed by 5561

Abstract

Hollow fiber type cation-exchange (C-HF) membranes and hollow fiber type anion-exchange (A-HF) membranes were prepared from poly (vinyl alcohol) (PVA)-based copolymer with cation-exchange groups and by blending PVA and polycation, respectively, by a gel fiber spinning method. In order to control the water [...] Read more.

Hollow fiber type cation-exchange (C-HF) membranes and hollow fiber type anion-exchange (A-HF) membranes were prepared from poly (vinyl alcohol) (PVA)-based copolymer with cation-exchange groups and by blending PVA and polycation, respectively, by a gel fiber spinning method. In order to control the water content of the hollow fiber membranes, the membranes were cross-linked physically by annealing, and then cross-linked chemically by using glutaraldehyde (GA) solutions at various GA concentrations. The outer diameter of C-HF and A-HF membranes were ca. 1000 μm and ca. 1500 μm, respectively, and the thickness of the membranes were ca. 170 μm and 290 μm, respectively. Permeation experiments were carried out in two Donnan dialysis systems, which included mixed 0.1 M NaCl and 0.1 M CaCl₂/C-HF /3 × 10⁻⁴ M CaCl₂ and mixed 0.1 M NaCl and 0.1 M NaNO₃/A-HF/3 × 10⁻⁴ M NaNO₃ to examine ionic perm selectivity of the membranes. In the Donnan dialysis experiments using C-HF membranes, uphill transport of the divalent cations occurred, and, in the case of A-HF membranes, uphill transport of NO₃⁻ ions occurred. C-HF and A-HF membranes had about half of the flux in the uphill transported ions and also about half of the selectivity between the uphill transport ions and driven ions in comparison with those of the commercial flat sheet cation-exchange membrane (Neosepta^® CMX) and anion-exchange membrane (Neosepta^® AMX). Yet, IEC of C-HF and A-HF membranes were about one fifth of CMX and less than half of AMX, respectively. Since hollow fiber membrane module will have higher packing density than a flat membrane stack, the hollow fiber type ion-exchange membranes (IEMs) prepared in this study will have a potential application to a Donnan dialysis process. Full article

(This article belongs to the Special Issue Mass Transfer in Membranes)

► Show Figures

Graphical abstract

28 pages, 11105 KiB

Open AccessReview

Membranes with Intrinsic Micro-Porosity: Structure, Solubility, and Applications

by Haoli Zhou and Wanqin Jin

Membranes 2019, 9(1), 3; https://doi.org/10.3390/membranes9010003 - 26 Dec 2018

Cited by 38 | Viewed by 7430

Abstract

Microporous polymer membranes have been widely studied because of their excellent separation performance. Among them, polymers of intrinsic micro-porosity (PIMs) have been regarded as a potential next-generation membrane material for their ultra-permeable characteristics and their solution-processing ability. Therefore, many reviews have been reported [...] Read more.

Microporous polymer membranes have been widely studied because of their excellent separation performance. Among them, polymers of intrinsic micro-porosity (PIMs) have been regarded as a potential next-generation membrane material for their ultra-permeable characteristics and their solution-processing ability. Therefore, many reviews have been reported on gas separation and monomers for the preparation of PIMs. This review aims to provide an overview of the structure-solubility property. Different structures such as non-network and network macromolecular structure made of different monomers have been reviewed. Then their solubility with different structures and different separation applications such as nanofiltration, pervaporation, and gas/vapor separation are summarized. Lastly, we also provide our perspectives on the challenges and future directions of the microporous polymer membrane for the structure-property relationship, anti-physical aging, and more. Full article

(This article belongs to the Special Issue Nanostructured Membranes)

► Show Figures

Figure 1

10 pages, 830 KiB

Open AccessArticle

Analysis of the Flux Performance of Different RO/NF Membranes in the Treatment of Agroindustrial Wastewater by Means of the Boundary Flux Theory

by Javier M. Ochando-Pulido, Antonio Martínez-Férez and Marco Stoller

Membranes 2019, 9(1), 2; https://doi.org/10.3390/membranes9010002 - 26 Dec 2018

Cited by 12 | Viewed by 4124

Abstract

Dynamic membrane system behaviour must be adequately addressed to avoid process unfeasibility. The lack of proper analysis will mean relying on erroneous permeate flux values in the system design, which will lead to quick and/or steady high fouling rates. In this paper, the [...] Read more.

Dynamic membrane system behaviour must be adequately addressed to avoid process unfeasibility. The lack of proper analysis will mean relying on erroneous permeate flux values in the system design, which will lead to quick and/or steady high fouling rates. In this paper, the authors present additional data supporting the boundary flux theory as a helpful tool for membrane engineers to carefully avoid process failures. By fitting the dynamic permeate flux data to the boundary flux model, it was possible to calculate the β fouling index for the three selected membranes (one nanofiltration (NF) and two reverse osmosis (RO) ones). The dynamic flux given by the low-pressure RO membrane did not follow sub-boundary operating conditions, since a sharp flux loss was measured throughout the whole operating cycle, pinpointing that supra-boundary flux conditions were governing the system. This was supported by the calculated value of the β fouling parameter, which resulted to be in the order of ten times higher for this membrane. However, the values of β→0 for the SC-RO and DK-NF ones, supported by the very low value of the sub-boundary fouling parameter α (0.002 and 0.007 L·h⁻¹·m⁻²·bar⁻², respectively), ensure nearly boundary operating conditions for these membranes. Full article

(This article belongs to the Special Issue Fouling in Liquid Separation Membrane Technologies)

► Show Figures

Figure 1

13 pages, 4614 KiB

Open AccessArticle

Comparative Analysis of Dry and Wet Porometry Methods for Characterization of Regular and Cross-Linked Virus Removal Filter Papers

by Simon Gustafsson, Frank Westermann, Tobias Hanrieder, Laura Jung, Horst Ruppach and Albert Mihranyan

Membranes 2019, 9(1), 1; https://doi.org/10.3390/membranes9010001 - 20 Dec 2018

Cited by 12 | Viewed by 4672

Abstract

Pore-size distribution (PSD) is the most critical parameter for size-exclusion virus removal filters. Yet, different dry- and wet-state porometry methods yield different pore-size values. The goal of this work is to conduct comparative analysis of nitrogen gas sorption (NGSP), liquid-liquid and cryoporometry with [...] Read more.

Pore-size distribution (PSD) is the most critical parameter for size-exclusion virus removal filters. Yet, different dry- and wet-state porometry methods yield different pore-size values. The goal of this work is to conduct comparative analysis of nitrogen gas sorption (NGSP), liquid-liquid and cryoporometry with differential scanning calorimetry (CP-DSC) methods with respect to characterization of regular and cross-linked virus removal filter paper based on cellulose nanofibers, i.e. the mille-feuille filter. The filters were further characterized with atomic force and scanning electron microscopy. Finally, the removal of the worst-case model virus, i.e. minute virus of mice (MVM; 20 nm, nonenveloped parvovirus) was evaluated. The results revealed that there is no difference of the obtained PSDs between the wet methods, i.e. DSC and liquid-liquid porometry (LLP), as well as no difference between the regular and cross-linked filters regardless of method. MVM filtration at different trans membrane pressure (TMP) revealed strong dependence of the virus removal capability on applied pressure. It was further observed that cross-linking filters showed enhanced virus removal, especially at lower TMP. In all, the results of this study highlight the complex nature of virus capture in size-exclusion filters. Full article

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

► Show Figures

Graphical abstract

Journal Menu

Journal Browser

Membranes, Volume 9, Issue 1 (January 2019) – 17 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI