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Showing papers on "Membrane published in 2010"


Journal ArticleDOI
01 Jan 2010-Science
TL;DR: The evidence for how this principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to selectively focus membrane bioactivity is reviewed.
Abstract: Cell membranes display a tremendous complexity of lipids and proteins designed to perform the functions cells require. To coordinate these functions, the membrane is able to laterally segregate its constituents. This capability is based on dynamic liquid-liquid immiscibility and underlies the raft concept of membrane subcompartmentalization. Lipid rafts are fluctuating nanoscale assemblies of sphingolipid, cholesterol, and proteins that can be stabilized to coalesce, forming platforms that function in membrane signaling and trafficking. Here we review the evidence for how this principle combines the potential for sphingolipid-cholesterol self-assembly with protein specificity to selectively focus membrane bioactivity.

3,811 citations


Journal ArticleDOI
TL;DR: In this article, the authors present an overview of the key requirements for the proton exchange membranes (PEM) used in fuel cell applications, along with a description of the membrane materials currently being used and their ability to meet these requirements.

1,715 citations


Journal ArticleDOI
09 Sep 2010-Nature
TL;DR: It is shown that when immersed in an ionic solution, a layer of graphene becomes a new electrochemical structure that is called a trans-electrode, which is an ideal substrate for very high resolution, high throughput nanopore-based single-molecule detectors.
Abstract: Isolated, atomically thin conducting membranes of graphite, called graphene, have recently been the subject of intense research with the hope that practical applications in fields ranging from electronics to energy science will emerge. The atomic thinness, stability and electrical sensitivity of graphene motivated us to investigate the potential use of graphene membranes and graphene nanopores to characterize single molecules of DNA in ionic solution. Here we show that when immersed in an ionic solution, a layer of graphene becomes a new electrochemical structure that we call a trans-electrode. The trans-electrode's unique properties are the consequence of the atomic-scale proximity of its two opposing liquid-solid interfaces together with graphene's well known in-plane conductivity. We show that several trans-electrode properties are revealed by ionic conductance measurements on a graphene membrane that separates two aqueous ionic solutions. Although our membranes are only one to two atomic layers thick, we find they are remarkable ionic insulators with a very small stable conductance that depends on the ion species in solution. Electrical measurements on graphene membranes in which a single nanopore has been drilled show that the membrane's effective insulating thickness is less than one nanometre. This small effective thickness makes graphene an ideal substrate for very high resolution, high throughput nanopore-based single-molecule detectors. The sensitivity of graphene's in-plane electronic conductivity to its immediate surface environment and trans-membrane solution potentials will offer new insights into atomic surface processes and sensor development opportunities.

1,327 citations


Journal ArticleDOI
13 Oct 2010-ACS Nano
TL;DR: The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.
Abstract: Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young’s modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for “pristine” graphene. The prestress (39.7−76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.

975 citations


Journal ArticleDOI
TL;DR: The development of a high performance thin-film composite membrane for forward osmosis applications with high water flux was directly related to the thickness, porosity, tortuosity, and pore structure of the polysulfone support layer.
Abstract: Recent studies show that osmotically driven membrane processes may be a viable technology for desalination, water and wastewater treatment, and power generation. However, the absence of a membrane designed for such processes is a significant obstacle hindering further advancements of this technology. This work presents the development of a high performance thin-film composite membrane for forward osmosis applications. The membrane consists of a selective polyamide active layer formed by interfacial polymerization on top of a polysulfone support layer fabricated by phase separation onto a thin (40 μm) polyester nonwoven fabric. By careful selection of the polysulfone casting solution (i.e., polymer concentration and solvent composition) and tailoring the casting process, we produced a support layer with a mix of finger-like and sponge-like morphologies that give significantly enhanced membrane performance. The structure and performance of the new thin-film composite forward osmosis membrane are compared wi...

870 citations


Journal ArticleDOI
TL;DR: The synthesized novel ZIF-8 membranes displayed unprecedented high CO( 2) permeances and relatively high separation indexes for equimolar mixtures of CO(2) and CH(4) and the presence of small, highly crystalline, microporous crystals led to continuous thin membranes.
Abstract: ZIF-8 membranes, a type of zeolite imidazolate framework, were synthesized by secondary seeded growth on tubular α-Al2O3 porous supports. The presence of small, highly crystalline, microporous crystals with narrow particle size distribution led to continuous thin membranes. The synthesized novel ZIF-8 membranes displayed unprecedented high CO2 permeances and relatively high separation indexes for equimolar mixtures of CO2 and CH4.

847 citations


Journal ArticleDOI
TL;DR: In this article, the authors used alginate as a model organic foulant to examine forward osmosis (FO) membrane fouling and cleaning behavior with the ultimate goal of determining the underlying FO fouling/cleaning mechanisms.

808 citations


Journal ArticleDOI
TL;DR: The determinants and functional implications of the subcellular distribution and membrane topology of the most abundant negatively charged phospholipid in eukaryotic membranes are discussed.
Abstract: Phosphatidylserine (PS) is the most abundant negatively charged phospholipid in eukaryotic membranes. PS directs the binding of proteins that bear C2 or gamma-carboxyglutamic domains and contributes to the electrostatic association of polycationic ligands with cellular membranes. Rather than being evenly distributed, PS is found preferentially in the inner leaflet of the plasma membrane and in endocytic membranes. The loss of PS asymmetry is an early indicator of apoptosis and serves as a signal to initiate blood clotting. This review discusses the determinants and functional implications of the subcellular distribution and membrane topology of PS.

793 citations


Journal ArticleDOI
TL;DR: In this paper, the performance studies of mixed matrix membrane (MMM) for gas separation were critically reviewed, and the materials selection and the preparation techniques of MMM were also discussed.

735 citations


Journal ArticleDOI
TL;DR: The role of engineered nanomaterials in (pressure driven) membrane technology for water treatment, to be applied in drinking water production and wastewater recycling, is reviewed.

719 citations


Journal ArticleDOI
TL;DR: In this article, DNA translocations through nanopores created in graphene membranes are reported. But, the nanopores are made from 1-5 nm thick graphene membranes with electron-beam sculpted nanopores from 5 to 10 nm in diameter.
Abstract: We report on DNA translocations through nanopores created in graphene membranes. Devices consist of 1-5 nm thick graphene membranes with electron-beam sculpted nanopores from 5 to 10 nm in diameter. Due to the thin nature of the graphene membranes, we observe larger blocked currents than for traditional solid-state nanopores. However, ionic current noise levels are several orders of magnitude larger than those for silicon nitride nanopores. These fluctuations are reduced with the atomic-layer deposition of 5 nm of titanium dioxide over the device. Unlike traditional solid-state nanopore materials that are insulating, graphene is an excellent electrical conductor. Use of graphene as a membrane material opens the door to a new class of nanopore devices in which electronic sensing and control are performed directly at the pore.

Journal ArticleDOI
TL;DR: The control of MOF/ polymer interface morphology is easier than that of the zeolite/polymer interface, since the organic linkers in MOFs have better affinity with polymer chains than the inorganic zeolites do, and the surface properties of MOFs can be easily tuned by functionalization with various organic molecules if necessary.
Abstract: Metal–organic frameworks (MOFs) are an emerging class of nanoporous materials comprising metal centers connected by various organic linkers to create one-, two-, and threedimensional porous structures with tunable pore volumes, surface areas, and chemical properties. Several thousand MOF materials have been synthesized and their numbers continue to grow rapidly. MOFs are predicted to be highly attractive for application in gas-separation membranes and also have a range of other potential applications, for example in selective gas adsorption, hydrogen storage, catalysis, and sensing. Recently, thin continuous MOFmembranes for gas separation have been reported by several authors using MOFs such as MOF-5, HKUST-1 (Cu3(BTC)2), [8] Cu(hfipbb)(H2hfipbb)0.5, [9] and ZIF-8. However, the gas-permeation properties (permeability and selectivity) have so far not been found to be technologically attractive. This may have several reasons, such as membrane defects and related processing issues, use of MOFs with low selectivity, and unfavorable orientation of crystals in the membrane. An alternative route to high-performance MOF membranes is to incorporate them into polymers to obtain nanocomposite (mixed-matrix) membranes. The incorporation of nanoporous molecular sieves such as zeolites into polymeric membranes has attracted much attention, since one can in principle combine the size/shape selectivity of nanoporous materials with the processibility and mechanical stability of polymers. However, zeolite/polymer composite membranes often have defective morphologies characterized by void spaces between the zeolite particles and the polymeric matrix, leading to poor gas-separation performance since the gas molecules bypass the zeolite particles. Recent approaches to address the issue of interface compatibilization are emerging. On the other hand, the use of MOFs in mixed-matrix membranes provides several potential advantages over zeolites. The control of MOF/polymer interface morphology is easier than that of the zeolite/polymer interface, since the organic linkers in MOFs have better affinity with polymer chains than the inorganic zeolites do, and the surface properties of MOFs can be easily tuned by functionalization with various organic molecules if necessary. In general, MOFs also have higher pore volumes and lower density than zeolites, and hence their effect on the membrane properties can be greater for a given mass loading. Recently, several MOFmixed-matrix membranes such as Cu-BPY-HFS (Cu-4,40-bipyridine hexafluorosilicate) in Matrimid, HKUST-1 in poly(sulfone), MOF-5 in Matrimid, and Cu-TPA (terephthalic acid) in poly(vinyl acetate) have been reported. Although a high degree of MOF/polymer adhesion (as characterized by scanning electron microscopy) was found, the gas-separation performance of these membranes was not high. In addition to the control of interface morphology, the selection of appropriate MOF/polymer pairs is indispensable for high-performance mixed-matrix membranes, a fact emphasized in theoretical predictions. ZIF-90 (zeolitic imidazolate framework-90) is an attractive MOF for application in CO2-selective mixed-matrix membranes. ZIF-90 has a sodalite cagelike structure with 0.35 nm pore windows, through which size exclusion of CH4 from CO2/CH4 mixtures is possible. [20] Furthermore, the imidazole linker in ZIF-90 contains a carbonyl group, which has a favorable chemical noncovalent interaction with CO2. [21] Submicrometer-sized crystals of a related MOF material, ZIF-8, have recently been reported. So far, ZIF-90 crystals have been synthesized by the conventional solvothermal method. However, their size (ca. 100 mm) is too large for use in thin mixed-matrix membranes (which require submicrometer-sized crystals). Herein, we describe the synthesis of submicrometer-sized ZIF-90 crystals by a novel method, namely nonsolvent-induced crystallization. The ZIF-90 crystals were thoroughly characterized, and we compare them with solvothermally synthesized ZIF-90. Mixed-matrix membranes were then fabricated using three poly(imide)s as polymer matrices, and their CO2/CH4 separation properties were investigated. In particular, we demonstrate the first MOF-containing gas-separation membranes with technologically attractive properties. The morphology of our ZIF-90 crystals is shown in Figure 1. In general, the synthesis of smaller crystals requires reaction conditions that favor nucleation over crystal growth. Particle-size control proved difficult in conventional solvothermal synthesis. We crystallized small ZIF-90 particles at room temperature by the rapid addition of a nonsolvent to the reagent solution (see the Supporting Information), leading to supersaturation of the solution. The nucleation rate can be [*] Dr. T.-H. Bae, J. S. Lee, Dr. W. Qiu, Prof. Dr. W. J. Koros, Prof. Dr. C. W. Jones, Prof. Dr. S. Nair School of Chemical & Biomolecular Engineering Georgia Institute of Technology 311 Ferst Drive NW, Atlanta, GA 30332-0100 (USA) Fax: (+1)404-894-4200 E-mail: christopher.jones@chbe.gatech.edu sankar.nair@chbe.gatech.edu

Journal ArticleDOI
TL;DR: Different hybrid materials based on polybenzimidazoles and several inorganic proton conductors such as heteropoly acids, as well as sulfonated derivatives of the polymers, all of which contribute to a quickly-developing field with many blooming results and useful potential are reviewed.
Abstract: The development of high-temperature PEM fuel cells (working at 150–200 °C) is pursued worldwide in order to solve some of the problems of current cells based on Nafion® (CO tolerance, improved kinetics, water management, etc.). Polybenzimidazole membranes nanoimpregnated with phosphoric acid have been studied as electrolytes in PEMFCs for more than a decade. Commercially available polybenzimidazole (PBI) has been the most extensively studied and used for this application in membranes doped with all sorts of strong inorganic acids. In addition to this well-known polymer we also review here studies on ABPBI and other polybenzimidazole type membranes. More recently, several copolymers and related derivatives have attracted many researchers' attention, adding variety to the field. Furthermore, besides phosphoric acid, many other strong inorganic acids, as well as alkaline electrolytes have been used to impregnate benzimidazole membranes and are analyzed here. Finally, we also review different hybrid materials based on polybenzimidazoles and several inorganic proton conductors such as heteropoly acids, as well as sulfonated derivatives of the polymers, all of which contribute to a quickly-developing field with many blooming results and useful potential which are the subject of this critical review (317 references).

Journal ArticleDOI
TL;DR: Microporous membranes with pore apertures below the nanolevel can exhibit size selectivity by serving as a molecular sieve, which is promising for overcoming Robeson s “upperbound” limits in membrane-based gas separation.
Abstract: Microporous membranes with pore apertures below the nanolevel can exhibit size selectivity by serving as a molecular sieve, which is promising for overcoming Robeson s “upperbound” limits in membrane-based gas separation. Zeolites, polymers of intrinsic microporosity (PIMs), metal oxides, and active carbon are the typical materials used for this purpose. Metal–organic frameworks (MOFs) have attracted much research interest in recent years, and are emerging as a new family of molecular sieves. MOFs are novel porous crystalline materials consisting of metal ions or clusters interconnected by a variety of organic linkers. In addition to promising applications in adsorptive gas separation and storage or in catalysis, their unique properties, such as their highly diversified structures, large range in pore sizes, very high surface areas, and specific adsorption affinities, make MOFs excellent candidates for use in the construction of molecular sieve membranes with superior performance. The preparation of MOF membranes for gas separation is rapidly becoming a research focus. A number of attempts have been made to prepare supported-MOF membranes; however, progress is very limited and so far there are only very few reports of continuous MOF films on porous supports being used as separating membranes. Recently, Guo et al. reported a copper-net-supported HKUST-1 (Cu3(BTC)2; BTC= benzene-1,3,5-tricarboxylate) membrane exhibiting a H2/N2 selectivity of 7 [13] (separation factor of H2 over N2 is calculated as the permeate-to-retentate composition ratio of H2, divided by the same ratio for N2 as proposed by IUPAC) ; this is the first MOF membrane to show gasseparation performance beyond Knudsen diffusion behavior. Very recently, Ranjan and Tsapatsis prepared a microporous metal–organic framework [MMOF, Cu(hfipbb)(H2hfipbb)0.5; hfipbb= 4,4’-(hexafluoroisopropylidene)bis(benzoic acid)] membrane by seeded growth on an alumina support. The ideal selectivity for H2/N2, based on single permeation tests, was 23 at 190 8C. This higher selectivity, compared to the report from Guo et al., might be a result of the smaller effective pore size (ca. 0.32 nm of MMOF versus 0.9 nm of HKUTS-1), which results in a relatively low H2 permeance of this MMOF membrane (10 9 molm 2 s Pa 1 at 190 8C). The authors attributed this finding to the blockage of the onedimensional (1D) straight-pore channels in the membrane. Therefore, with regard to H2 separation, small-pore MOFs having three-dimensional (3D) channel structures are considered to be ideal membrane materials. Zeolitic imidazolate frameworks (ZIFs), a subfamily of MOFs, consist of transition metals (Zn, Co) and imidazolate linkers which form 3D tetrahedral frameworks and frequently resemble zeolite topologies. A number of ZIFs exhibit exceptional thermal and chemical stability. Another important feature of ZIFs is their hydrophobic surfaces, which give ZIF membranes certain advantages over zeolite membranes and sol–gel-derived silica membranes in the separation of H2 in the presence of steam. Very recently we reported the first result from permeation measurements on a ZIF-8 membrane. The ZIF-8 membrane showed a H2/CH4 separation factor greater than 10. Whereas the ZIF-8 pores (0.34 nm) are slightly larger than the kinetic diameter of CO2 (0.33 nm), and are very flexible, the H2/CO2 separation on this ZIF-8 membrane showed Knudsen selectivity. In the current work, we therefore chose ZIF-7 as a promising candidate for the development of a H2-selective membrane to satisfy the above requirements. ZIF-7 (Zn(bim)2) is formed by bridging benzimidazolate (bim) anions and zinc cations with soladite (SOD) topology. The pore size of ZIF-7 (the hexagonal window size in the SOD cage) estimated from crystallographic data is about 0.3 nm, which is just in between the size of H2 (0.29 nm) and CO2 (0.33 nm). We could therefore expect a ZIF-7 membrane to achieve a high selectivity of H2 over CO2 and other gases through a molecular sieving effect. In many cases, it was reported that the heterogeneous nucleation density of MOF crystals on ceramic supports is very low, 14] which makes it extremely difficult to prepare supported-MOF membranes by an in situ synthesis route. Chemical modifications of substrate surfaces have been proposed to direct the nucleation and orientation of the deposited MOF layers. Based on our knowledge in the development of zeolite membranes, we adopted a seeded secondary growth method for the ZIF-7 membrane prepara[*] Prof. Dr. Y.-S. Li, F.-Y. Liang, H. Bux, A. Feldhoff, Prof. Dr. J. Caro Institute of Physical Chemistry and Electrochemistry and the Laboratory for Nano and Quantum Engineering (LNQE) in cooperation with the Center for Solid State Research and New Materials, Leibniz Universit t Hannover Callinstrasse 3A, 30167 Hannover (Germany) Fax: (+49)511-762-19121 E-mail: yanshuo.li@pci.uni-hannover.de juergen.caro@pci.uni-hannover.de

Journal ArticleDOI
27 Jul 2010-ACS Nano
TL;DR: This work illustrates how block copolymers can be employed in the preparation of membranes for use in controlled, long-term, protein-delivery devices and demonstrates that highly efficient and tunable separations are possible with blockCopolymers.
Abstract: With nanoscale pores, high porosity, narrow pore size distributions, and tunable chemical and mechanical properties, block copolymers hold tremendous potential as robust, efficient, and highly selective separation membranes. Recent work by Yang et al. illustrates how block copolymers can be employed in the preparation of membranes for use in controlled, long-term, protein-delivery devices. Their work demonstrates that highly efficient and tunable separations are possible with block copolymer membranes. Although significant progress over the past 10 years has advanced the quality, efficacy, and applicability of such membranes, more work is required before benefits are realized for other demanding applications such as water purification.

Journal ArticleDOI
27 Aug 2010-ACS Nano
TL;DR: A coarse-grained model for gold nanoparticles (AuNPs) is developed to simulate their interactions with model lipid membranes and suggests a way of controlling the AuNP-cell interactions by manipulating surface charge densities of AuNPs to achieve designated goals in their biomedical applications.
Abstract: Nanoparticle penetration into cell membranes is an interesting phenomenon that may have crucial implications on the nanoparticles’ biomedical applications. In this paper, a coarse-grained model for gold nanoparticles (AuNPs) is developed (verified against experimental data available) to simulate their interactions with model lipid membranes. Simulations reveal that AuNPs with different signs and densities of surface charges spontaneously adhere to the bilayer surface or penetrate into the bilayer interior. The potential of mean force calculations show that the energy gains upon adhesion or penetration is significant. In the case of penetration, it is found that defective areas are induced across the entire surface of the upper leaflet of the bilayer and a hydrophilic pore that transports water molecules was formed with its surrounding lipids highly disordered. Penetration and its concomitant membrane disruptions can be a possible mechanism of the two observed phenomena in experiments: AuNPs bypass endocyt...

Journal ArticleDOI
TL;DR: In this article, two types of thin-film composite FO hollow fibers with an ultra-thin polyamide-based RO-like skin layer on either the outer surface or inner surface of a porous hollow fiber substrate have been successfully fabricated.

Journal ArticleDOI
TL;DR: Recent studies with artificial model membranes have highlighted the striking resemblance of the mechanisms of membrane permeabilization of amyloid-forming proteins to those of pore-forming toxins and antimicrobial peptides.
Abstract: The toxicity of amyloid-forming proteins is correlated with their interactions with cell membranes. Binding events between amyloidogenic proteins and membranes result in mutually disruptive structural perturbations, which are associated with toxicity. Membrane surfaces promote the conversion of amyloid-forming proteins into toxic aggregates, and amyloidogenic proteins, in turn, compromise the structural integrity of the cell membrane. Recent studies with artificial model membranes have highlighted the striking resemblance of the mechanisms of membrane permeabilization of amyloid-forming proteins to those of pore-forming toxins and antimicrobial peptides.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate water transport through a porous graphene membrane and compare the results with thin (less than 10 nm in thickness/length) carbon nanotube (CNT) membranes.
Abstract: Graphene can be considered as an ideal membrane since its thickness is only one carbon diameter. In this study, using molecular dynamics simulations, we investigate water transport through a porous graphene membrane and compare the results with water transport through thin (less than 10 nm in thickness/length) carbon nanotube (CNT) membranes. For smaller diameter pores, where a single-file water structure is obtained, CNT membranes provide higher water flux compared to graphene membranes. For larger diameter pores, where the water structure is not single-file, graphene membranes provide higher water flux compared to CNT membranes. Furthermore, in thin CNT membranes, the water flux did not vary significantly with the thickness of the membrane. We explain the results through a detailed analysis considering pressure distribution, velocity profiles, and potential of mean force. This work opens up opportunities for graphene-based membranes in molecular sieving, water filtration, fuel cells, and so forth.

Journal ArticleDOI
TL;DR: A novel covalent functionalization strategy was developed to prepare reproducible ZIF-90 molecular sieve membranes by using 3-aminopropyltriethoxysilane as a covalently linked linker between the Zif-90 layer and Al(2)O(3) support via imines condensation.
Abstract: A novel covalent functionalization strategy was developed to prepare reproducible ZIF-90 molecular sieve membranes by using 3-aminopropyltriethoxysilane as a covalent linker between the ZIF-90 layer and Al(2)O(3) support via imines condensation. The ZIF-90 membranes show high thermal and hydrothermal stabilities, and they allow the separation of hydrogen from larger gases by molecular sieving.

Journal ArticleDOI
TL;DR: In this paper, a review of the development of RO membranes with improved flux and salt rejection, chlorine tolerance, fouling resistance and thermal stability is presented, focusing on the modification of current polymeric membrane materials, and synthesis and separation performance of new polymer membranes, inorganic membranes, and mixed matrix membranes.
Abstract: Reverse osmosis (RO) desalination is one of the main technologies for producing fresh water from seawater and other saline water sources. The membrane properties greatly affect the water productivity and energy costs in the reverse osmosis desalinatin processes. Recent years have seen significant research efforts devoted to developing high-performance RO membranes. This article reviews recent activities in the development of RO membranes with improved flux and salt rejection, chlorine tolerance, fouling resistance and thermal stability. In particular, this review mainly focuses on the modification of current polymeric membrane materials, and synthesis and separation performance of new polymer membranes, inorganic membranes and mixed matrix membranes.

Journal ArticleDOI
TL;DR: A theoretical process model for MCDI is presented which describes the time-dependent electric current and effluent ion concentration, both during the deionization stage and during the subsequent stage of ion release.

Journal ArticleDOI
TL;DR: This critical review primarily focuses on the various aspects of membrane processes related to the separation of biogas, more in specific CO(2) and H(2S)S removal from CH(4) andH(3) streams.
Abstract: Over the past two decades, membrane processes have gained a lot of attention for the separation of gases. They have been found to be very suitable for wide scale applications owing to their reasonable cost, good selectivity and easily engineered modules. This critical review primarily focuses on the various aspects of membrane processes related to the separation of biogas, more in specific CO2 and H2S removal from CH4 and H2 streams. Considering the limitations of inorganic materials for membranes, the present review will only focus on work done with polymeric materials. An overview on the performance of commercial membranes and lab-made membranes highlighting the problems associated with their applications will be given first. The development studies carried out to enhance the performance of membranes for gas separation will be discussed in the subsequent section. This review has been broadly divided into three sections (i) performance of commercial polymeric membranes (ii) performance of lab-made polymeric membranes and (iii) performance of mixed matrix membranes (MMMs) for gas separations. It will include structural modifications at polymer level, polymer blending, as well as synthesis of mixed matrix membranes, for which addition of silane-coupling agents and selection of suitable fillers will receive special attention. Apart from an overview of the different membrane materials, the study will also highlight the effects of different operating conditions that eventually decide the performance and longevity of membrane applications in gas separations. The discussion will be largely restricted to the studies carried out on polyimide (PI), cellulose acetate (CA), polysulfone (PSf) and polydimethyl siloxane (PDMS) membranes, as these membrane materials have been most widely used for commercial applications. Finally, the most important strategies that would ensure new commercial applications will be discussed (156 references).

Journal ArticleDOI
TL;DR: In this article, a novel zeolitic imidazolate framework (ZIF-7) membrane was tested for its gas separation performance and showed promising H2 separation abilities.

Journal ArticleDOI
TL;DR: The use of ring-opening metathesis polymerization is demonstrated to generate new cross-linked membrane materials exhibiting high hydroxide ion conductivity and good mechanical properties that have the potential to meet the demands of hydrogen-powered fuel cells as well as direct methanol fuel cells.
Abstract: Fuel cells are energy conversion devices that show great potential in numerous applications ranging from automobiles to portable electronics. However, further development of fuel cell components is necessary for them to become commercially viable. One component critical to their performance is the polymer electrolyte membrane, which is an ion conductive medium separating the two electrodes. While proton conducting membranes are well established (e.g., Nafion), hydroxide conducting membranes (alkaline anion exchange membranes, AAEMs) have been relatively unexplored by comparison. Operating under alkaline conditions offers significant efficiency benefits, especially for the oxygen reduction reaction; therefore, effective AAEMs could significantly advance fuel cell technologies. Here we demonstrate the use of ring-opening metathesis polymerization to generate new cross-linked membrane materials exhibiting high hydroxide ion conductivity and good mechanical properties. Cross-linking allows for increased ion incorporation, which, in turn supports high conductivities. This facile synthetic approach enables the preparation of cross-linked materials with the potential to meet the demands of hydrogen-powered fuel cells as well as direct methanol fuel cells.

Journal ArticleDOI
TL;DR: The characterization of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate, as a proton conductor for a fuel cell and the fabrication of a membrane-type fuel cell system using [dema][TfO] under nonhumidified conditions at intermediate temperatures are described in detail.
Abstract: In this paper, the characterization of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), as a proton conductor for a fuel cell and the fabrication of a membrane-type fuel cell system using [dema][TfO] under nonhumidified conditions at intermediate temperatures are described in detail. In terms of physicochemical and electrochemical properties, [dema][TfO] exhibits high activity for fuel cell electrode reactions (i.e., the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR)) at a Pt electrode, and the open circuit voltage (OCV) of a liquid fuel cell is 1.03 V at 150 degrees C, as has reported in ref 27. However, diethylmethylammonium bis(trifluoromethane sulfonyl)amide ([dema][NTf(2)]) has relatively low HOR and ORR activity, and thus, the OCV is ca. 0.7 V, although [dema][NTf(2)] and [dema][TfO] have an identical cation ([dema]) and similar thermal and bulk-transport properties. Proton conduction occurs mainly via the vehicle mechanism in [dema][TfO] and the proton transference number (t(+)) is 0.5-0.6. This relatively low t(+) appears to be more disadvantageous for a proton conductor than for other electrolytes such as hydrated sulfonated polymer electrolyte membranes (t(+) = 1.0). However, fast proton-exchange reactions occur between ammonium cations and amines in a model compound. This indicates that the proton-exchange mechanism contributes to the fuel cell system under operation, where deprotonated amines are continuously generated by the cathodic reaction, and that polarization of the cell is avoided. Six-membered sulfonated polyimides in the diethylmethylammonium form exhibit excellent compatibility with [dema][TfO]. The composite membranes can be obtained up to a [dema][TfO] content of 80 wt % and exhibit good thermal stability, high ionic conductivity, and mechanical strength and gas permeation comparable to those of hydrated Nafion. H(2)/O(2) fuel cells prepared using the composite membranes can successfully operate at temperatures from 30 to 140 degrees C under nonhumidified conditions, and a current density of 250 mA cm(-2) is achieved at 120 degrees C. The protic ionic liquid and its composite membrane are a possible candidate for an electrolyte of a H(2)/O(2) fuel cell that operates under nonhumidified conditions.

Journal ArticleDOI
23 Aug 2010-Langmuir
TL;DR: A simple surface modification method results in strong covalent bonds between α-Al(2)O(3) supports and imidazolate ligands, which promote the heterogeneous nucleation and growth of ZIF crystals.
Abstract: Zeolitic imidazolate frameworks (ZIFs) are hybrid organic-inorganic microporous materials that exhibit zeolite-like structures and can be synthesized with a wide range of pore sizes and chemical functionality. ZIFs as thin films and membranes are of interest for their applications in sensors and gas separation. Here, we report a method for ZIF film and membrane fabrication, based on support surface modification and in situ solvothermal growth, which has potential for general application to other ZIF membranes. Our simple surface modification method results in strong covalent bonds between α-Al(2)O(3) supports and imidazolate ligands, which promote the heterogeneous nucleation and growth of ZIF crystals. The microstructure of ZIF-8 films can be controlled by controlling the pH of the growth solution. ZIF-7 films were fabricated to demonstrate the potential for general applicability of our method. Finally, the separation performance of several ZIF-8 membranes was evaluated, revealing molecular sieving behavior with an ideal selectivity for H(2)/CH(4) of 13.

Journal ArticleDOI
TL;DR: In this paper, the quaternized polymers PSGCl-x (where x represents the number of quaternary guanidinium groups/repeat units) were synthesized via chloromethylation of poly(arylene ether sulfone)s, followed by reactions with pentamethylguanidine.
Abstract: Poly(arylene ether sulfone)s were functionalized with quaternary guanidinium groups in order to investigate their properties as novel polymeric hydroxide exchange membrane materials. The quaternized polymers were synthesized via chloromethylation of poly(arylene ether sulfone)s, followed by reactions with pentamethylguanidine. The resulting quaternized polymers PSGCl-x (where x represents the number of the quaternary guanidinium groups/repeat units) presented an elevated molecular weight and exhibited an outstanding solubility in polar aprotic solvents. Consequently flexible and tough membranes of PSGCl-x with varying ionic content could be prepared by casting from the DMSO solution. Novel anion exchange membranes, PSGOH-x, were obtained by an anion exchange of PSGCl-x with 1 M NaOH at room temperature. The membranes displayed a high ionic conductivity and an excellent chemical stability. The obtained alkaline anion exchange membranes (AEMs) showed conductivities almost above 10−2 S cm−1 at room temperatu...

Journal ArticleDOI
TL;DR: In this paper, the authors apply Onsager's symmetry relations to the process of diffusion of a solution through a membrane and show that measured osmotic pressures deviate from those calculated thermodynamically in proportion to the permeability of the membrane to the solute molecules.
Abstract: Application of Onsager's symmetry relations to the process of diffusion of a solution through a membrane shows that measured osmotic pressures deviate from those calculated thermodynamically in proportion to the permeability of the membrane to the solute molecules. Therefore little is learned from one dynamic osmotic measurement but by simultaneous measurements of osmotic pressure and permeation at different membranes the entire molecular weight distribution of the solute can be computed.

Journal ArticleDOI
08 Oct 2010-Science
TL;DR: A gene essential for freezing tolerance in Arabidopsis encodes a galactolipid remodeling enzyme of the outer chloroplast envelope membrane that compensates for changes in organelle volume and stabilizes membranes during freezing.
Abstract: Plants show complex adaptations to freezing that prevent cell damage caused by cellular dehydration. Lipid remodeling of cell membranes during dehydration is one critical mechanism countering loss of membrane integrity and cell death. SENSITIVE TO FREEZING 2 (SFR2), a gene essential for freezing tolerance in Arabidopsis, encodes a galactolipid remodeling enzyme of the outer chloroplast envelope membrane. SFR2 processively transfers galactosyl residues from the abundant monogalactolipid to different galactolipid acceptors, forming oligogalactolipids and diacylglycerol, which is further converted to triacylglycerol. The combined activity of SFR2 and triacylglycerol-biosynthetic enzymes leads to the removal of monogalactolipids from the envelope membrane, changing the ratio of bilayer- to non-bilayer-forming membrane lipids. This SFR2-based mechanism compensates for changes in organelle volume and stabilizes membranes during freezing.