Membranes

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5571 KiB

Open AccessArticle

Polymer Electrolyte Membranes for Water Photo-Electrolysis

by Antonino S. Aricò, Mariarita Girolamo, Stefania Siracusano, David Sebastian, Vincenzo Baglio and Michael Schuster

Membranes 2017, 7(2), 25; https://doi.org/10.3390/membranes7020025 - 29 Apr 2017

Cited by 18 | Viewed by 8200

Abstract

Water-fed photo-electrolysis cells equipped with perfluorosulfonic acid (Nafion^® 115) and quaternary ammonium-based (Fumatech^® FAA3) ion exchange membranes as separator for hydrogen and oxygen evolution reactions were investigated. Protonic or anionic ionomer dispersions were deposited on the electrodes to extend the interface [...] Read more.

Water-fed photo-electrolysis cells equipped with perfluorosulfonic acid (Nafion^® 115) and quaternary ammonium-based (Fumatech^® FAA3) ion exchange membranes as separator for hydrogen and oxygen evolution reactions were investigated. Protonic or anionic ionomer dispersions were deposited on the electrodes to extend the interface with the electrolyte. The photo-anode consisted of a large band-gap Ti-oxide semiconductor. The effect of membrane characteristics on the photo-electrochemical conversion of solar energy was investigated for photo-voltage-driven electrolysis cells. Photo-electrolysis cells were also studied for operation under electrical bias-assisted mode. The pH of the membrane/ionomer had a paramount effect on the photo-electrolytic conversion. The anionic membrane showed enhanced performance compared to the Nafion^®-based cell when just TiO₂ anatase was used as photo-anode. This was associated with better oxygen evolution kinetics in alkaline conditions compared to acidic environment. However, oxygen evolution kinetics in acidic conditions were significantly enhanced by using a Ti sub-oxide as surface promoter in order to facilitate the adsorption of OH species as precursors of oxygen evolution. However, the same surface promoter appeared to inhibit oxygen evolution in an alkaline environment probably as a consequence of the strong adsorption of OH species on the surface under such conditions. These results show that a proper combination of photo-anode and polymer electrolyte membrane is essential to maximize photo-electrolytic conversion. Full article

(This article belongs to the Special Issue Feature Papers)

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2064 KiB

Open AccessFeature PaperArticle

The Effect of Thermal Fluctuation on the Receptor-Mediated Adhesion of a Cell Membrane to an Elastic Substrate

by Bahador Marzban and Hongyan Yuan

Membranes 2017, 7(2), 24; https://doi.org/10.3390/membranes7020024 - 27 Apr 2017

Cited by 9 | Viewed by 5973

Abstract

Mechanics of the bilayer membrane play an important role in many biological and bioengineering problems such as cell–substrate and cell–nanomaterial interactions. In this work, we study the effect of thermal fluctuation and the substrate elasticity on the cell membrane–substrate adhesion. We model the [...] Read more.

Mechanics of the bilayer membrane play an important role in many biological and bioengineering problems such as cell–substrate and cell–nanomaterial interactions. In this work, we study the effect of thermal fluctuation and the substrate elasticity on the cell membrane–substrate adhesion. We model the adhesion of a fluctuating membrane on an elastic substrate as a two-step reaction comprised of the out-of-plane membrane fluctuation and the receptor–ligand binding. The equilibrium closed bond ratio as a function of substrate rigidity was computed by developing a coupled Fourier space Brownian dynamics and Monte Carlo method. The simulation results show that there exists a crossover value of the substrate rigidity at which the closed bond ratio is maximal. Full article

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12849 KiB

Open AccessFeature PaperArticle

Synthesis and Transport Properties of Novel MOF/PIM-1/MOF Sandwich Membranes for Gas Separation

by Alessio Fuoco, Muhanned R. Khdhayyer, Martin P. Attfield, Elisa Esposito, Johannes C. Jansen and Peter M. Budd

Membranes 2017, 7(1), 7; https://doi.org/10.3390/membranes7010007 - 11 Feb 2017

Cited by 28 | Viewed by 10264

Abstract

Metal-organic frameworks (MOFs) were supported on polymer membrane substrates for the fabrication of composite polymer membranes based on unmodified and modified polymer of intrinsic microporosity (PIM-1). Layers of two different MOFs, zeolitic imidazolate framework-8 (ZIF-8) and Copper benzene tricarboxylate ((HKUST-1), were grown onto [...] Read more.

Metal-organic frameworks (MOFs) were supported on polymer membrane substrates for the fabrication of composite polymer membranes based on unmodified and modified polymer of intrinsic microporosity (PIM-1). Layers of two different MOFs, zeolitic imidazolate framework-8 (ZIF-8) and Copper benzene tricarboxylate ((HKUST-1), were grown onto neat PIM-1, amide surface-modified PIM-1 and hexamethylenediamine (HMDA) -modified PIM-1. The surface-grown crystalline MOFs were characterized by a combination of several techniques, including powder X-ray diffraction, infrared spectroscopy and scanning electron microscopy to investigate the film morphology on the neat and modified PIM-1 membranes. The pure gas permeabilities of He, H₂, O₂, N₂, CH₄, CO₂ were studied to understand the effect of the surface modification on the basic transport properties and evaluate the potential use of these membranes for industrially relevant gas separations. The pure gas transport was discussed in terms of permeability and selectivity, highlighting the effect of the MOF growth on the diffusion coefficients of the gas in the new composite polymer membranes. The results confirm that the growth of MOFs on polymer membranes can enhance the selectivity of the appropriately functionalized PIM-1, without a dramatic decrease of the permeability. Full article

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457 KiB

Open AccessArticle

Effect of Sodium and Chloride Binding on a Lecithin Bilayer. A Molecular Dynamics Study

by Maria M. Reif, Christopher Kallies and Volker Knecht

Membranes 2017, 7(1), 5; https://doi.org/10.3390/membranes7010005 - 25 Jan 2017

Cited by 7 | Viewed by 6880

Abstract

The effect of ion binding on the structural, mechanical, dynamic and electrostatic properties of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in a 0.5 M aqueous NaCl solution is investigated using classical atomistic molecular dynamics simulation with different force-field descriptions for ion-ion and ion-lipid [...] Read more.

The effect of ion binding on the structural, mechanical, dynamic and electrostatic properties of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in a 0.5 M aqueous NaCl solution is investigated using classical atomistic molecular dynamics simulation with different force-field descriptions for ion-ion and ion-lipid interactions. Most importantly, the repulsive Lennard–Jones parameters for the latter were modified, such that approximately similar binding of cations and anions to the lipid membrane is achieved. This was done to qualitatively improve the apparent ion-lipid binding constants obtained from simulations with the original force field (Berger lipids and GROMOS87 ions in combination with the SPC water model) in comparison to experimental data. Furthermore, various parameters characterizing membrane structure, elasticity, order and dynamics are analyzed. It is found that ion binding as observed in simulations involving the modified in comparison to the original force-field description leads to: (i) a smaller salt-induced change in the area per lipid, which is in closer agreement with the experiment; (ii) a decrease in the area compressibility and bilayer thickness to values comparable to a bilayer in pure water; (iii) lipid deuterium order parameters and lipid diffusion coefficients on nanosecond timescales that are very similar to the values for a membrane in pure water. In general, salt effects on the structural properties of a POPC bilayer in an aqueous sodium-chloride solution appear to be reproduced reasonably well by the new force-field description. An analysis of membrane-membrane disjoining pressure suggests that the smaller salt-induced change in area per lipid induced by the new force-field description is not due to the alteration of membrane-associated net charge, but must rather be understood as a consequence of ion-specific effects on the arrangement of lipid molecules. Full article

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3132 KiB

Open AccessFeature PaperArticle

Concentration of Tea Extracts by Osmotic Evaporation: Optimisation of Process Parameters and Effect on Antioxidant Activity

by Marisa P. Marques, Vítor D. Alves and Isabel M. Coelhoso

Membranes 2017, 7(1), 1; https://doi.org/10.3390/membranes7010001 - 28 Dec 2016

Cited by 15 | Viewed by 8023

Abstract

In this work, the concentration process of three different tea extracts (medicinal Rosil No. 6, Black, and Forest Fruit teas) using the osmotic evaporation (OE) process, was studied. The effect of the OE process on the content of phenolic compounds and antioxidant activity [...] Read more.

In this work, the concentration process of three different tea extracts (medicinal Rosil No. 6, Black, and Forest Fruit teas) using the osmotic evaporation (OE) process, was studied. The effect of the OE process on the content of phenolic compounds and antioxidant activity was evaluated. The concentration process was carried out in a hollow-fibre membrane contactor with an effective surface area of 0.54 m². The tea extract was circulated through the shell side of the contactor, while a concentrated osmotic solution (CaCl₂ 5 M) was circulated inside the fibres. The flux, the driving force, and the mass transfer coefficient were evaluated. A decrease of the water flux over time was observed and was attributed only to the decrease of the driving force, caused by the dilution of the osmotic solution. Using a surface area/feed volume ratio of 774 m²·m⁻³, it is possible to reach a tea concentration of 40% (w/w) in 5 h, with a constant water flux and without losing the phenolic content and antioxidant potential in most teas. Full article

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2077 KiB

Open AccessFeature PaperArticle

Vitamin E Circular Dichroism Studies: Insights into Conformational Changes Induced by the Solvent’s Polarity

by Drew Marquardt, Brad J. Van Oosten, Mikel Ghelfi, Jeffrey Atkinson and Thad A. Harroun

Membranes 2016, 6(4), 56; https://doi.org/10.3390/membranes6040056 - 14 Dec 2016

Cited by 5 | Viewed by 6319

Abstract

We used circular dichroism (CD) to study differences in CD spectra between α-, δ-, and methylated-α-tocopherol in solvents with different polarities. CD spectra of the different tocopherol structures differ from each other in intensity and peak locations, which can [...] Read more.

We used circular dichroism (CD) to study differences in CD spectra between α-, δ-, and methylated-α-tocopherol in solvents with different polarities. CD spectra of the different tocopherol structures differ from each other in intensity and peak locations, which can be attributed to chromanol substitution and the ability to form hydrogen bonds. In addition, each structure was examined in different polarity solvents using the Reichardt index—a measure of the solvent’s ionizing ability, and a direct measurement of solvent–solute interactions. Differences across solvents indicate that hydrogen bonding is a key contributor to CD spectra at 200 nm. These results are a first step in examining the hydrogen bonding abilities of vitamin E in a lipid bilayer. Full article

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2868 KiB

Open AccessArticle

Investigating Sterol and Redox Regulation of the Ion Channel Activity of CLIC1 Using Tethered Bilayer Membranes

by Heba Al Khamici, Khondker R. Hossain, Bruce A. Cornell and Stella M. Valenzuela

Membranes 2016, 6(4), 51; https://doi.org/10.3390/membranes6040051 - 8 Dec 2016

Cited by 16 | Viewed by 5296

Abstract

The Chloride Intracellular Ion Channel (CLIC) family consists of six conserved proteins in humans. These are a group of enigmatic proteins, which adopt both a soluble and membrane bound form. CLIC1 was found to be a metamorphic protein, where under specific environmental triggers [...] Read more.

The Chloride Intracellular Ion Channel (CLIC) family consists of six conserved proteins in humans. These are a group of enigmatic proteins, which adopt both a soluble and membrane bound form. CLIC1 was found to be a metamorphic protein, where under specific environmental triggers it adopts more than one stable reversible soluble structural conformation. CLIC1 was found to spontaneously insert into cell membranes and form chloride ion channels. However, factors that control the structural transition of CLIC1 from being an aqueous soluble protein into a membrane bound protein have yet to be adequately described. Using tethered bilayer lipid membranes and electrical impedance spectroscopy system, herein we demonstrate that CLIC1 ion channel activity is dependent on the type and concentration of sterols in bilayer membranes. These findings suggest that membrane sterols play an essential role in CLIC1’s acrobatic switching from a globular soluble form to an integral membrane form, promoting greater ion channel conductance in membranes. What remains unclear is the precise nature of this regulation involving membrane sterols and ultimately determining CLIC1’s membrane structure and function as an ion channel. Furthermore, our impedance spectroscopy results obtained using CLIC1 mutants, suggest that the residue Cys24 is not essential for CLIC1’s ion channel function. However Cys24 does appear important for optimal ion channel activity. We also observe differences in conductance between CLIC1 reduced and oxidized forms when added to our tethered membranes. Therefore, we conclude that both membrane sterols and redox play a role in the ion channel activity of CLIC1. Full article

(This article belongs to the Special Issue Feature Papers)

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3267 KiB

Open AccessArticle

A Thin Film Nanocomposite Membrane with MCM-41 Silica Nanoparticles for Brackish Water Purification

by Mohammed Kadhom, Jun Yin and Baolin Deng

Membranes 2016, 6(4), 50; https://doi.org/10.3390/membranes6040050 - 6 Dec 2016

Cited by 47 | Viewed by 7138

Abstract

Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthesized by the interfacial polymerization (IP) process. An m-phenylenediamine (MPD) aqueous solution and an organic phase with trimesoyl chloride (TMC) dissolved in isooctane were used in the IP reaction, occurring on [...] Read more.

Thin film nanocomposite (TFN) membranes containing MCM-41 silica nanoparticles (NPs) were synthesized by the interfacial polymerization (IP) process. An m-phenylenediamine (MPD) aqueous solution and an organic phase with trimesoyl chloride (TMC) dissolved in isooctane were used in the IP reaction, occurring on a nanoporous polysulfone (PSU) support layer. Isooctane was introduced as the organic solvent for TMC in this work due to its intermediate boiling point. MCM-41 silica NPs were loaded in MPD and TMC solutions in separate experiments, in a concentration range from 0 to 0.04 wt %, and the membrane performance was assessed and compared based on salt rejection and water flux. The prepared membranes were characterized via scanning electron microscopy (SEM), transmission electron microscopy (TEM), contact angle measurement, and attenuated total reflection Fourier transform infrared (ATR FT-IR) analysis. The results show that adding MCM-41 silica NPs into an MPD solution yields slightly improved and more stable results than adding them to a TMC solution. With 0.02% MCM-41 silica NPs in the MPD solution, the water flux was increased from 44.0 to 64.1 L/m²·h, while the rejection virtually remained the same at 95% (2000 ppm NaCl saline solution, 25 °C, 2068 kPa (300 psi)). Full article

(This article belongs to the Special Issue Feature Papers)

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4660 KiB

Open AccessArticle

Mass Transport through Nanostructured Membranes: Towards a Predictive Tool

by Siavash Darvishmanesh and Bart Van der Bruggen

Membranes 2016, 6(4), 49; https://doi.org/10.3390/membranes6040049 - 2 Dec 2016

Cited by 10 | Viewed by 5150

Abstract

This study proposes a new mechanism to understand the transport of solvents through nanostructured membranes from a fundamental point of view. The findings are used to develop readily applicable mathematical models to predict solvent fluxes and solute rejections through solvent resistant membranes used [...] Read more.

This study proposes a new mechanism to understand the transport of solvents through nanostructured membranes from a fundamental point of view. The findings are used to develop readily applicable mathematical models to predict solvent fluxes and solute rejections through solvent resistant membranes used for nanofiltration. The new model was developed based on a pore-flow type of transport. New parameters found to be of fundamental importance were introduced to the equation, i.e., the affinity of the solute and the solvent for the membrane expressed as the hydrogen-bonding contribution of the solubility parameter for the solute, solvent and membrane. A graphical map was constructed to predict the solute rejection based on the hydrogen-bonding contribution of the solubility parameter. The model was evaluated with performance data from the literature. Both the solvent flux and the solute rejection calculated with the new approach were similar to values reported in the literature. Full article

(This article belongs to the Special Issue Feature Papers)

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2873 KiB

Open AccessFeature PaperArticle

Hydrogen Induced Abrupt Structural Expansion at High Temperatures of a Ni₃₂Nb₂₈Zr₃₀Cu₁₀ Membrane for H₂ Purification

by Oriele Palumbo, Francesco Trequattrini, Madhura Hulyalkar, Suchismita Sarker, Narendra Pal, Dhanesh Chandra, Ted Flanagan, Michael Dolan and Annalisa Paolone

Membranes 2016, 6(4), 48; https://doi.org/10.3390/membranes6040048 - 21 Nov 2016

Cited by 4 | Viewed by 5201

Abstract

Ni-Nb-Zr amorphous membranes, prepared by melt-spinning, show great potential for replacing crystalline Pd-based materials in the field of hydrogen purification to an ultrapure grade (>99.999%). In this study, we investigate the temperature evolution of the structure of an amorphous ribbon with the composition [...] Read more.

Ni-Nb-Zr amorphous membranes, prepared by melt-spinning, show great potential for replacing crystalline Pd-based materials in the field of hydrogen purification to an ultrapure grade (>99.999%). In this study, we investigate the temperature evolution of the structure of an amorphous ribbon with the composition Ni₃₂Nb₂₈Zr₃₀Cu₁₀ (expressed in atom %) by means of XRD and DTA measurements. An abrupt structural expansion is induced between 240 and 300 °C by hydrogenation. This structural modification deeply modifies the hydrogen sorption properties of the membrane, which indeed shows a strong reduction of the hydrogen capacity above 270 °C. Full article

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5049 KiB

Open AccessArticle

Preparation and Characterization of Hydrophilically Modified PVDF Membranes by a Novel Nonsolvent Thermally Induced Phase Separation Method

by Ningen Hu, Tonghu Xiao, Xinhai Cai, Lining Ding, Yuhua Fu and Xing Yang

Membranes 2016, 6(4), 47; https://doi.org/10.3390/membranes6040047 - 18 Nov 2016

Cited by 32 | Viewed by 9557

Abstract

In this study, a nonsolvent thermally-induced phase separation (NTIPS) method was first proposed to fabricate hydrophilically-modified poly(vinylidene fluoride) (PVDF) membranes to overcome the drawbacks of conventional thermally-induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) methods. Hydrophilically-modified PVDF membranes were successfully prepared by [...] Read more.

In this study, a nonsolvent thermally-induced phase separation (NTIPS) method was first proposed to fabricate hydrophilically-modified poly(vinylidene fluoride) (PVDF) membranes to overcome the drawbacks of conventional thermally-induced phase separation (TIPS) and nonsolvent-induced phase separation (NIPS) methods. Hydrophilically-modified PVDF membranes were successfully prepared by blending in hydrophilic polymer polyvinyl alcohol (PVA) at 140 °C. A series of PVDF/PVA blend membranes was prepared at different total polymer concentrations and blend ratios. The morphological analysis via SEM indicated that the formation mechanism of these hydrophilically-modified membranes was a combined NIPS and TIPS process. As the total polymer concentration increased, the tensile strength of the membranes increased; meanwhile, the membrane pore size, porosity and water flux decreased. With the PVDF/PVA blend ratio increased from 10:0 to 8:2, the membrane pore size and water flux increased. The dynamic water contact angle of these membranes showed that the hydrophilic properties of PVDF/PVA blend membranes were prominently improved. The higher hydrophilicity of the membranes resulted in reduced membrane resistance and, hence, higher permeability. The total resistance R_t of the modified PVDF membranes decreased significantly as the hydrophilicity increased. The irreversible fouling related to pore blocking and adsorption fouling onto the membrane surface was minimal, indicating good antifouling properties. Full article

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Review

Jump to: Research

4283 KiB

Open AccessFeature PaperReview

Membranes with Surface-Enhanced Antifouling Properties for Water Purification

by Nima Shahkaramipour, Thien N. Tran, Sankara Ramanan and Haiqing Lin

Membranes 2017, 7(1), 13; https://doi.org/10.3390/membranes7010013 - 5 Mar 2017

Cited by 169 | Viewed by 16564

Abstract

Membrane technology has emerged as an attractive approach for water purification, while mitigation of fouling is key to lower membrane operating costs. This article reviews various materials with antifouling properties that can be coated or grafted onto the membrane surface to improve the [...] Read more.

Membrane technology has emerged as an attractive approach for water purification, while mitigation of fouling is key to lower membrane operating costs. This article reviews various materials with antifouling properties that can be coated or grafted onto the membrane surface to improve the antifouling properties of the membranes and thus, retain high water permeance. These materials can be separated into three categories, hydrophilic materials, such as poly(ethylene glycol), polydopamine and zwitterions, hydrophobic materials, such as fluoropolymers, and amphiphilic materials. The states of water in these materials and the mechanisms for the antifouling properties are discussed. The corresponding approaches to coat or graft these materials on the membrane surface are reviewed, and the materials with promising performance are highlighted. Full article

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1536 KiB

Open AccessFeature PaperReview

Review of Membranes for Helium Separation and Purification

by Colin A. Scholes and Ujjal K. Ghosh

Membranes 2017, 7(1), 9; https://doi.org/10.3390/membranes7010009 - 17 Feb 2017

Cited by 84 | Viewed by 12155

Abstract

Membrane gas separation has potential for the recovery and purification of helium, because the majority of membranes have selectivity for helium. This review reports on the current state of the research and patent literature for membranes undertaking helium separation. This includes direct recovery [...] Read more.

Membrane gas separation has potential for the recovery and purification of helium, because the majority of membranes have selectivity for helium. This review reports on the current state of the research and patent literature for membranes undertaking helium separation. This includes direct recovery from natural gas, as an ancillary stage in natural gas processing, as well as niche applications where helium recycling has potential. A review of the available polymeric and inorganic membranes for helium separation is provided. Commercial gas separation membranes in comparable gas industries are discussed in terms of their potential in helium separation. Also presented are the various membrane process designs patented for the recovery and purification of helium from various sources, as these demonstrate that it is viable to separate helium through currently available polymeric membranes. This review places a particular focus on those processes where membranes are combined in series with another separation technology, commonly pressure swing adsorption. These combined processes have the most potential for membranes to produce a high purity helium product. The review demonstrates that membrane gas separation is technically feasible for helium recovery and purification, though membranes are currently only applied in niche applications focused on reusing helium rather than separation from natural sources. Full article

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1879 KiB

Open AccessReview

Biological Fuel Cells and Membranes

by Zahra Ghassemi and Gymama Slaughter

Membranes 2017, 7(1), 3; https://doi.org/10.3390/membranes7010003 - 17 Jan 2017

Cited by 44 | Viewed by 8534

Abstract

Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane [...] Read more.

Biofuel cells have been widely used to generate bioelectricity. Early biofuel cells employ a semi-permeable membrane to separate the anodic and cathodic compartments. The impact of different membrane materials and compositions has also been explored. Some membrane materials are employed strictly as membrane separators, while some have gained significant attention in the immobilization of enzymes or microorganisms within or behind the membrane at the electrode surface. The membrane material affects the transfer rate of the chemical species (e.g., fuel, oxygen molecules, and products) involved in the chemical reaction, which in turn has an impact on the performance of the biofuel cell. For enzymatic biofuel cells, Nafion, modified Nafion, and chitosan membranes have been used widely and continue to hold great promise in the long-term stability of enzymes and microorganisms encapsulated within them. This article provides a review of the most widely used membrane materials in the development of enzymatic and microbial biofuel cells. Full article

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3456 KiB

Open AccessFeature PaperReview

Structure and Nanomechanics of Model Membranes by Atomic Force Microscopy and Spectroscopy: Insights into the Role of Cholesterol and Sphingolipids

by Berta Gumí-Audenis, Luca Costa, Francesco Carlá, Fabio Comin, Fausto Sanz and Marina I. Giannotti

Membranes 2016, 6(4), 58; https://doi.org/10.3390/membranes6040058 - 19 Dec 2016

Cited by 37 | Viewed by 12429

Abstract

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the [...] Read more.

Biological membranes mediate several biological processes that are directly associated with their physical properties but sometimes difficult to evaluate. Supported lipid bilayers (SLBs) are model systems widely used to characterize the structure of biological membranes. Cholesterol (Chol) plays an essential role in the modulation of membrane physical properties. It directly influences the order and mechanical stability of the lipid bilayers, and it is known to laterally segregate in rafts in the outer leaflet of the membrane together with sphingolipids (SLs). Atomic force microscope (AFM) is a powerful tool as it is capable to sense and apply forces with high accuracy, with distance and force resolution at the nanoscale, and in a controlled environment. AFM-based force spectroscopy (AFM-FS) has become a crucial technique to study the nanomechanical stability of SLBs by controlling the liquid media and the temperature variations. In this contribution, we review recent AFM and AFM-FS studies on the effect of Chol on the morphology and mechanical properties of model SLBs, including complex bilayers containing SLs. We also introduce a promising combination of AFM and X-ray (XR) techniques that allows for in situ characterization of dynamic processes, providing structural, morphological, and nanomechanical information. Full article

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2071 KiB

Open AccessFeature PaperReview

Incorporation of Graphene-Related Carbon Nanosheets in Membrane Fabrication for Water Treatment: A Review

by Jenny Lawler

Membranes 2016, 6(4), 57; https://doi.org/10.3390/membranes6040057 - 19 Dec 2016

Cited by 20 | Viewed by 9468

Abstract

The minimization of the trade-off between the flux and the selectivity of membranes is a key area that researchers are continually working to optimise, particularly in the area of fabrication of novel membranes. Flux versus selectivity issues apply in many industrial applications of [...] Read more.

The minimization of the trade-off between the flux and the selectivity of membranes is a key area that researchers are continually working to optimise, particularly in the area of fabrication of novel membranes. Flux versus selectivity issues apply in many industrial applications of membranes, for example the unwanted diffusion of methanol in fuel cells, retention of valuable proteins in downstream processing of biopharmaceuticals, rejection of organic matter and micro-organisms in water treatment, or salt permeation in desalination. The incorporation of nanosheets within membrane structures can potentially lead to enhancements in such properties as the antifouling ability, hydrophilicy and permeability of membranes, with concomitant improvements in the flux/selectivity balance. Graphene nanosheets and derivatives such as graphene oxide and reduced graphene oxide have been investigated for this purpose, for example inclusion of nanosheets within the active layer of Reverse Osmosis or Nanofiltration membranes or the blending of nanosheets as fillers within Ultrafiltration membranes. This review summarizes the incorporation of graphene derivatives into polymeric membranes for water treatment with a focus on a number of industrial applications, including desalination and pharmaceutical removal, where enhancement of productivity and reduction in fouling characteristics have been afforded by appropriate incorporation of graphene derived nanosheets during membrane fabrication. Full article

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5370 KiB

Open AccessFeature PaperReview

Application of Semipermeable Membranes in Glucose Biosensing

by Tanmay Kulkarni and Gymama Slaughter

Membranes 2016, 6(4), 55; https://doi.org/10.3390/membranes6040055 - 14 Dec 2016

Cited by 62 | Viewed by 14244

Abstract

Glucose biosensors have received significant attention in recent years due to the escalating mortality rate of diabetes mellitus. Although there is currently no cure for diabetes mellitus, individuals living with diabetes can lead a normal life by maintaining tight control of their blood [...] Read more.

Glucose biosensors have received significant attention in recent years due to the escalating mortality rate of diabetes mellitus. Although there is currently no cure for diabetes mellitus, individuals living with diabetes can lead a normal life by maintaining tight control of their blood glucose levels using glucose biosensors (e.g., glucometers). Current research in the field is focused on the optimization and improvement in the performance of glucose biosensors by employing a variety of glucose selective enzymes, mediators and semipermeable membranes to improve the electron transfer between the active center of the enzyme and the electrode substrate. Herein, we summarize the different semipermeable membranes used in the fabrication of the glucose biosensor, that result in improved biosensor sensitivity, selectivity, dynamic range, response time and stability. Full article

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6334 KiB

Open AccessFeature PaperReview

What Ion Flow along Ion Channels Can Tell us about Their Functional Activity

by Lucia Becucci and Rolando Guidelli

Membranes 2016, 6(4), 53; https://doi.org/10.3390/membranes6040053 - 13 Dec 2016

Cited by 14 | Viewed by 5218

Abstract

The functional activity of channel-forming peptides and proteins is most directly verified by monitoring the flow of physiologically relevant inorganic ions, such as Na⁺, K⁺ and Cl⁻, along the ion channels. Electrical current measurements across bilayer lipid membranes [...] Read more.

The functional activity of channel-forming peptides and proteins is most directly verified by monitoring the flow of physiologically relevant inorganic ions, such as Na⁺, K⁺ and Cl⁻, along the ion channels. Electrical current measurements across bilayer lipid membranes (BLMs) interposed between two aqueous solutions have been widely employed to this end and are still extensively used. However, a major drawback of BLMs is their fragility, high sensitivity toward vibrations and mechanical shocks, and low resistance to electric fields. To overcome this problem, metal-supported tethered BLMs (tBLMs) have been devised, where the BLM is anchored to the metal via a hydrophilic spacer that replaces and mimics the water phase on the metal side. However, only mercury-supported tBLMs can measure and regulate the flow of the above inorganic ions, thanks to mercury liquid state and high hydrogen overpotential. This review summarizes the main results achieved by BLMs incorporating voltage-gated channel-forming peptides, interpreting them on the basis of a kinetic mechanism of nucleation and growth. Hg-supported tBLMs are then described, and their potential for the investigation of voltage-gated and ohmic channels is illustrated by the use of different electrochemical techniques. Full article

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2890 KiB

Open AccessReview

Process-Oriented Review of Bacterial Quorum Quenching for Membrane Biofouling Mitigation in Membrane Bioreactors (MBRs)

by Naila Bouayed, Nicolas Dietrich, Christine Lafforgue, Chung-Hak Lee and Christelle Guigui

Membranes 2016, 6(4), 52; https://doi.org/10.3390/membranes6040052 - 13 Dec 2016

Cited by 25 | Viewed by 7762

Abstract

Quorum Quenching (QQ) has been developed over the last few years to overcome practical issues related to membrane biofouling, which is currently the major difficulty thwarting the extensive development of membrane bioreactors (MBRs). QQ is the disruption of Quorum Sensing (QS), cell-to-cell communication [...] Read more.

Quorum Quenching (QQ) has been developed over the last few years to overcome practical issues related to membrane biofouling, which is currently the major difficulty thwarting the extensive development of membrane bioreactors (MBRs). QQ is the disruption of Quorum Sensing (QS), cell-to-cell communication enabling the bacteria to harmonize their behavior. The production of biofilm, which is recognized as a major part of the biocake formed on a membrane surface, and which leads to biofouling, has been found to be one of the bacterial behaviors controlled by QS. Since the enzymatic disruption of QS was reported to be efficient as a membrane biofouling mitigation technique in MBRs, the application of QQ to lab-scale MBRs has been the subject of much research using different approaches under different operating conditions. This paper gives an overview of the effectiveness of QQ in mitigating membrane biofouling in MBRs. It is based on the results of previous studies, using two microbial strains, Rhodococcus sp. BH4 and Pseudomonas sp. 1A1. The effect of bacterial QQ on the physical phenomena of the MBR process is analyzed, adopting an original multi-scale approach. Finally, the potential influence of the MBR operating conditions on QQ effectiveness is discussed. Full article

(This article belongs to the Special Issue Feature Papers)

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