Removal of aromatic compounds in the aqueous solution via micellar enhanced ultrafiltration: Part 1. Behavior of nonionic surfactants

The effects of nonionic surfactants having different hydrophilicity and membranes having different hydrophobicity and molecular weight cut-off on the performance of micellar-enhanced ultrafiltration (MEUF) process were examined. A homologous series of polyethyleneglycol (PEG) alkylether having different numbers of methylene groups and ethylene oxide groups was used for nonionic surfactants. Polysulfone membranes and cellulose acetate membranes having different molecular cut-off were used for hydrophobic membranes and hydrophilic membranes, respectively. The concentration of surfactant added to pure water was fixed at the value of 100 times of critical micelle concentration (CMC). The flux through polysulfone membranes decreased remarkably due to adsorption mainly caused by hydrophobic interactions between surfactant and membrane material. The decline of solution flux for cellulose acetate membranes was not as serious as that for polysulfone membranes because of hydrophilic properties of cellulose acetate membranes. The surfactant rejections for the cellulose acetate membranes increased with decreasing membrane pore size and with increasing the hydrophobicity of surfactant. On the other hand the surfactant rejections for polysulfone membranes showed totally different rejection trends with those for cellulose acetate membranes. The surfactant rejections for the polysulfone membranes depend on the strength of hydrophobic interactions between surfactant and membrane material and molecular weight of surfactants.     

Effect of treatment of synthetic zeolite-polymer membranes on their electrochemical-potential response characteristics

Summary The performance of synthetic-polymer membrane-electrodes for cation sensing is investigated by obtaining E versus pM graphs and E versus time curves of the same membrane type under different treatments or of membranes constructed by modified procedures. The slopes of E versus pM curves for the salts of monovalent cations show different values for the same membrane type as well as for the different membrane types and are found within the range of 43 to 57 mV per pM. The response time of the membrane is found to be slower when the membranes are plastic phase deficient. Generally, the detection limit is only slightly dependent on the composition of the membrane and the best value is obtained with the polished membranes which is close to the value of pM=5 while for the other membranes the values are within the range of pM 4 to 5. The range of linearity is also slightly dependent on the method of membrane construction and in general is shorter when the membranes are plastic phase deficient. The selectivity coefficients are found to depend significantly on the method of construction of the membrane but in general the selectivity of all the membranes studied in this report is poor. The asymmetry potential is found to be related to an ion exchange process and is developed slowly in 5A-type membranes. However, when the value of asymmetry potential is high, a longer time is needed to reach the final value of e.m.f. in measurements among different concentrations of the same metal ion and much longer is needed where there is switching of measurement from a monovalent cation to a divalent cation.     

Physico-chemical characterization of nanofiltration membranes.

This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.     

Molecular polyimide brushes as a novel membrane material for pervaporation processes

Samples of molecular polyimide brushes with poly(methyl methacrylate) side chains with substantially different grafting densities and lengths of side chains are obtained by the atom-transfer radical polymerization of methyl methacrylate using samples of polyimide multicenter macroinitiators with different contents of initiation groups. Strong homogeneous films suitable for use as diffusion membranes for pervaporation separations of liquid mixtures are cast from solutions of polyimide brushes in dimethylformamide. Investigations are performed for films of polyimide brushes with loosely grafted short side chains or densely grafted long side chains as well as for films of a polyimide identical in its chemical structure to the backbone of polyimide brushes. It is shown that all film membranes sorb water moderately and do not sorb isopropanol. For membranes made of the polyimide and the loosely grafted brush, which is close to the polyimide in its properties, the active sorption of acetonitrile is demonstrated. It is found that all membranes exhibit high selectivities for water upon pervaporation of water–isopropanol mixtures. In addition, membranes made of the brush with densely grafted side chains show high productivity.     

Formation of porous bilayer hollow fibre membranes

Support membranes in bioartificial organs contact blood or plasma on one-side and adhesion dependent cells on the other side. Since membranes for biomedical applications, such as for haemodialysis, are optimised for blood contact and membranes for biotechnological applications for cell contact, there are no membranes available addressing the requirements of artificial organ technology. One approach is the preparation of porous bilayer membranes with a wall consisting of two chemical different polymer layers. Results of the preparation of such membrane types using triple spinnerets and a wet phase inversion process are shown here. It is demonstrated that one of the most important parameter is the structural integrity of the membrane wall at the interface between both layers. A new spinneret construction is presented where the membrane forming polymer solutions are layered in the spinneret before extrusion. As a result porous bilayer hollow fibre membranes with a high structural integrity could be manufactured using different composed polysulfone (PSu) polymer solutions for model investigation.     

离子液体支撑液膜分离CO2

支撑液膜是一种在湿法冶金、生物技术以及气体分离等多个领域都有应用的重要膜分离技术。本文回顾了支撑液膜技术分离CO2的研究进展,按照液膜相的不同,分类介绍了常规载体支撑液膜和离子液体支撑液膜,指出了常规载体支撑液膜分离CO2的局限性,重点介绍了离子液体支撑液膜分离CO2的发展,分析了气体在离子液体支撑液膜中的传质机理以及常规离子液体结构、含量和支撑膜材料等对分离效果的影响;讨论了离子液体的功能化方法以及功能化离子液体支撑液膜分离CO2的渗透率、选择性和液膜稳定性;介绍了两种新的离子液体支撑液膜改进方法:聚离子液体膜与凝胶化离子液体支撑液膜。最后指出了今后用于CO2分离的离子液体支撑液膜的发展方向。     

A comparative study on the chitosan membranes prepared from acetic acid and glycine hydrochloride for removal of copper

Application of chitosan-based materials as adsorbents in wastewater treatment has received considerable attention in recent years. This study is concerned with the influence of various parameters of the reaction medium with a metal and a biosorbant on the kinetics of copper biosorption from synthetic solutions. Initially, we prepared pure chitosan-based membranes and those modified in two different ways: chitosan membrane prepared from traditional acetic acid and the membrane prepared from glycine hydrochloride, chitosan membranes modified such as chitosan/polyvinyl alcohol (PVA) blends membrane with different compositions (100/0, 80/20, 50/50, 20/80 and 0/100%) and chitosan membranes cross-linked with glutaraldehyde. The membranes were characterized by FTIR spectroscopy, DSC, and rheological measurements. Then, we studied the kinetics of copper biosorption by the membranes. The results suggest that adding PVA to a chitosan membrane can greatly improve the flexibility and wettability of chitosan membranes. The values attained in equilibrium for the chitosan membranes prepared from glycine hydrochloride (95.5 mg g^?1 for chitosan/PVA 50/50%) exceed those for chitosan membranes prepared from acetic acid (61.5 mg/g for chitosan/PVA 50/50%).     

Large influence of cholesterol on solute partitioning into lipid membranes

Cholesterol plays an important role in maintaining the correct fluidity and rigidity of the plasma membrane of all animal cells, and hence, it is present in concentrations ranging from 20 to 50 mol %. Whereas the effect of cholesterol on such mechanical properties has been studied exhaustively over the last decades, the structural basis for cholesterol effects on membrane permeability is still unclear. Here we apply systematic molecular dynamics simulations to study the partitioning of solutes between water and membranes. We derive potentials of mean force for six different solutes permeating across 20 different lipid membranes containing one out of four types of phospholipids plus a cholesterol content varying from 0 to 50 mol %. Surprisingly, cholesterol decreases solute partitioning into the lipid tail region of the membranes much more strongly than expected from experiments on macroscopic membranes, suggesting that a laterally inhomogeneous cholesterol concentration and permeability may be required to explain experimental findings. The simulations indicate that the cost of breaking van der Waals interactions between the lipid tails of cholesterol-containing membranes account for the reduced partitioning rather than the surface area per phospholipid, which has been frequently suggested as a determinant for solute partitioning. The simulations further show that the partitioning is more sensitive to cholesterol (i) for larger solutes, (ii) in membranes with saturated as compared to membranes with unsaturated lipid tails, and (iii) in membranes with smaller lipid head groups.     

A review on the latest development of carbon membranes for gas separation

Inorganic membranes have been developed before 1945. The earlier application of inorganic membranes was primarily concentrate on military purpose. Carbon membrane is one type of porous inorganic membrane. Although the concept of carbon membrane for gas separation has been found in the early 1970, the interest to develop carbon membrane only increased, since Koresh and Soffer successfully prepared apparently crack-free molecular sieving hollow fiber carbon membranes. Nowadays, plenty of researchers have used different polymeric materials; including polyimides, to prepare carbon membranes by using pyrolysis. In general, carbon membranes can be divided into four major configurations: flat sheet, membrane supported on tube, capillary, and hollow fiber. Permeation properties of carbon membranes have been improved greatly in these 20 years. Carbon membranes offer advantages over polymeric membranes especially in terms of selectivity as well as thermal and chemical stability. More attention will be paid to carbon membranes in this century. This paper will review the development of carbon membranes in the last 30 years and give a clear future direction in research for carbon membrane.     

Multicomponent membranes on solid substrates: Interfaces for protein binding

Even though lipid membranes deposited on a solid support are now used for more than 20 years as a model system for cellular membranes, their potential has, as yet, not been fully exploited. Only in recent years, the composition of solid supported membranes became more and more complex, which is a prerequisite for the elucidation of biologically relevant protein adsorption processes. Multicomponent bilayers resemble the heterogeneity of the biological membrane, which is composed of hundreds of different lipids varying in their headgroup and acyl chain composition. The development of a multitude of elaborated surface sensitive techniques allows to study the phase behavior of these membranes and their interaction with proteins, some of which will be highlighted in this review.     

Electrochemical characterization of ionically conductive polymer membranes

Cation conductive membranes, especially highly proton conductive membranes, are of interest not only for chlor-alkali electrolysis but for polymer electrolyte fuel cells as well. The very challenge for electrochemical characterization in this case is the low specific resistance of the polymer required for such applications, which in turn makes resistance measurements a non-trivial problem. We investigate the different possibilities to characterize such membranes. The present part of our work deals with the adequate conditioning and equilibration of membranes designed especially for direct methanol fuel cell applications, with the measurement of the conductivity and with the determination of apparent transport numbers in the membrane. The usefulness of the respective leaching investigations, impedance spectroscopy measurements and concentration potential measurements for the case of membranes made from sulfonated poly(phenylene oxide) is discussed.     

Effect of hydration of polyamide membranes on the surface electrokinetic parameters: surface characterization by x-ray photoelectronic spectroscopy and atomic force microscopy

The surface and the solid/liquid interface of two polyamide membranes, one experimental (B0) and one commercial (NF45), have been characterized by X-ray photoelectronic spectroscopy (XPS), atomic force microscopy (AFM), and zeta potential, respectively. The surface roughness, determined by AFM data analysis, is different for the two membranes, and results show that the commercial NF45 membrane presents a much lower roughness than the experimental B0 membrane. XPS data indicate that the surface of membrane NF45 is similar to that of pure polyamide, while membrane B0 contains a considerable amount of impurities. The homogeneity in depth of both membranes was also studied by determining the composition profile at different analysis angles. Streaming potential along the membrane surface or tangential streaming potential (TSP) measurements with NaCl solutions at different concentrations were carried out with both membranes to determine the zeta potential and the electrokinetic surface charge density, and a correlation between membrane surface and interface parameters is made. Some differences in atomic concentrations of membrane surface elements and X-ray photoelectronic spectra of the samples used in TSP measurements and after a drying process at 90 degrees C for 24 h can be observed when they are compared with those for fresh membranes. Electrokinetic parameters for membrane NF45 (TSP, zeta potential, and surface electrokinetic charge density) obtained from three different series of measurements strongly decrease as a result of membrane use, but for membrane B0 they are practically independent of the number of measurements. This difference in the electrokinetic behavior of the two membranes has been related to the hydration process of the surface for each sample studied by XPS and AFM.     

Ultrafiltration of hydrosoluble polymers. : Effect of operating conditions on the performance of the membrane

Two sulfonated polyvinylidene fluoride membranes of different porosity, prepared by the casting and gelation technique, were tested in an ultrafiltration laboratory-scale pilot plant with hydrosoluble polymer feed solutions. Polyethyleneglycols and dextrans of different average molecular weight were used as solutes for the feed solutions. Flux and rejection of the membranes were determined as functions of operating conditions (pressure, temperature and recirculation rate). The effect of properties of feed solutions (solute, concentration and molecular weight) on the performance of the membranes was also investigated.     

Preparation and electrochemical characterization of cation- and anion-exchange/polyaniline composite membranes

Composite membranes were prepared by chemical polymerization of a thin layer of polyaniline (PANI) in the presence of a high oxidant concentration on a single face of a sulfonated cation-exchange membrane (CEM) and quaternary aminated anion-exchange membrane (AEM). IR and SEM studies for both types of membranes confirmed PANI loading on the ion-exchange membranes. PANI composite ion-exchange membranes were characterized as a function of the polymerization time by ion-exchange capacity, coating density, and membrane conductance measurements. Membrane potential measurements were performed in various electrolyte solutions in order to observe the selectivity of these membranes for different types of counterions. Membrane potential data in conjunction with membrane conductance data was interpreted on the basis of frictional considerations between membrane matrix and solute. Electrodialysis experiments, using PANI composite ion-exchange membranes with 4 h polymerization time, were performed in single and mixed electrolyte solutions for observing electromigration of solute across PANI composite ion-exchange membranes. Relative dialytic rates of Na(2)SO(4), CaCl(2), and CuCl(2) were estimated with reference to NaCl on the basis of electrodialysis experiments and it was concluded that it is possible to separate different electrolytes using PANI composite ion-exchange membranes.     

Pervaporation from a dense membrane: roles of permeant-membrane interactions, Kelvin effect, and membrane swelling

Dense polymeric membranes with extremely small pores in the form of free volume are used widely in the pervaporative separation of liquid mixtures. The membrane permeation of a component followed by its vaporization on the opposite face is governed by the solubility and downstream pressure. We measured the evaporative flux of pure methanol and 2-propanol using dense membranes with different free volumes and different affinities (wettabilities and solubilities) for the permeant. Interestingly, the evaporative flux for different membranes vanished substantially (10-75%) below the equilibrium vapor pressure in the bulk. The discrepancy was larger for a smaller pore size and for more wettable membranes (higher positive spreading coefficients). This observation, which cannot be explained by the existing (mostly solution-diffusion type) models ofpervaporation, suggests an important role for the membrane-permeant interactions in nanopores that can lower the equilibrium vapor pressure. The pore sizes, as estimated from the positron annihilation, ranged from 0.2 to 0.6 nm for the dry membranes. Solubilities of methanol in different composite membranes were estimated from the Flory-Huggins theory. The interaction parameter was obtained from the surface properties measured by the contact angle goniometry in conjunction with the acid-base theory of polar surface interactions. For the membranes examined, the increase in the "wet" pore volume due to membrane swelling correlates almost linearly with the solubility of methanol in these membranes. Indeed, the observations are found to be consistent with the lowering of the equilibrium vapor pressure on the basis of the Kelvin equation. Thus, a higher solubility or selectivity of a membrane also implies stronger permeant-membrane interactions and a greater retention of the permeant by the membrane, thus decreasing its evaporative flux. This observation has important implications for the interpretation of existing experiments and in the separation of liquid mixtures by pervaporation.     

The gram-negative outer membrane modeler: Automated building of lipopolysaccharide-rich bacterial outer membranes in four force fields

Outer membranes are a crucial component of Gram-negative bacteria, containing standard lipids in their inner leaflet, lipopolysaccharides (LPSs) in their outer leaflet, and transmembrane β-barrels known as outer membrane proteins (OMPs). OMPs regulate functions such as substrate transport and cell movement, while LPSs act as a protective barrier for bacteria and can cause toxic reactions in humans. However, the experimental study of outer membranes is challenging. Molecular dynamics simulations are often used for the computational study of membrane systems, but the preparation of complex, LPS-rich outer membranes is not straightforward. The Gram-Negative Outer Membrane Modeler (GNOMM) is an automated pipeline for preparing simulation systems of OMPs embedded in LPS-containing membranes in four different force fields. Given the physiological and clinical importance of outer membranes and their components, GNOMM can be a useful tool in the study of their structure, function, and implications in diseases. GNOMM is available at http://bioinformatics.biol.uoa.gr/GNOMM . © 2019 Wiley Periodicals, Inc.     

Formation of microporous poly(hydroxybutyric acid) membranes for culture of osteoblast and fibroblast

Microporous membranes of a biodegradable polymer, poly(hydroxybutyric acid) (PHB), were prepared by a phase‐inversion process and their cell compatibility was evaluated in vitro. A ternary system, ethanol/chloroform/PHB, was employed to prepare the membranes, wherein ethanol and chloroform were served as the nonsolvent and solvent for PHB, respectively. In the phase‐inversion process, the polymer dissolution temperature was varied from 80 to 120°C to yield membranes with specific morphologies, such as globular particles, porous channels, etc. Moreover, cell viability was examined on the formed membranes. Two cell lines, osteoblast hFOB1.19 and fibroblast L929, were cultured in vitro. It was found that these two types of cells exhibited different responses on different membranes: the hFOB1.19 cells showed significant increase in cell proliferation with increase in surface roughness, whereas the L929 cells demonstrated an opposite trend, preferring to attach and grow on a flat surface. PHB membranes with different morphologies exhibit different cell compatibilities, which may be useful means for the architectural design of materials for tissue engineering. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and Characterization of Novel Sulfonated Hybrid Congo Red Membranes from Chlorofunctionalized Silsesquioxanes for Fuel Cell Application

A new sulfonated copolymers containing congo red groups were synthesized as a potential electrolyte for high temperature PEFCs. The resulting cross-linked sulfonated hybrid congo red membranes showed greatly improved water stability in comparison with the uncrosslinked ones while high proton conductivity was maintained. sulfonated membranes have been tested with respect to fuel cell performance. Short term fuel cell test for 100 hr gave a stable performance. These membranes are less expensive compared to Nafion. New sulfonated proton exchange composites membranes were used biological fuel cells. Molasses which is the waste of sugar factory, was used in anode as fuel and different bacteria species was sowing. Potential change was reported in biological fuel cells.     

Optimization study of polyethylene glycol and solvent system for gas permeation membranes

Cellulose acetate (CA) membranes blended with Polyethylene glycol (PEG) in acetone–water solvent system were synthesized by using solution-casting method that resulted in the formation of flexible, white membranes. Different molecular weight (MW) grades of PEG (including MW 1000, 10,000 and 20,000?g/mol) were used. Cast membranes were tested for tensile strength and permeability at different loading of PEG MW 10,000 and 20,000?g/mol. Excellent flexible membranes were produced in acetone–water solvent system in the presence of PEG, which were otherwise brittle. Surface structure and morphology were analysed using scanning electron microscopy. The presence of different functional groups was confirmed using Fourier transform infra-red spectroscopy and the mechanical characteristics were studied by tensile testing. The introduction of PEG caused an increase in permeability of the membranes. The increase in permeability is due to the opening up of pores as the membrane becomes more flexible, when the plasticizer is added. The permeability continues to increase with the addition of PEG. Moreover, the resulting membranes are not only more flexible, but also have largely improved tensile strength as compared to the CA membranes without PEG. This improved tensile strength can also be attributed to the improved flexibility of the membrane. A trade-off is reached between tensile strength and permeability as increasing amount of PEG improves tensile strength but the resulting membrane becomes too permeable to be used for gas separation. Moreover, using PEG of higher MW resulted in porous membranes, even at low amounts of PEG. Therefore, we concluded that CA membrane with less amount of low-MW PEG (i.e. 5% PEG of MW 1000?g/mol) must be used to optimize both permeability and tensile strength of the membrane.     

Fibrous membranes electrospinning from acrylonitrile-based polymers: specific absorption behaviors and states of water

Fibrous membranes with a fiber diameter ranging from 80 to 800 nm are prepared from polyacrylonitrile and poly[acrylonitrile-co-(N-vinyl-2-pyrrolidone)] by the electrospinning process. The parameters can be controlled to fabricate fibrous membranes with similar fiber diameters (between 600 and 800 nm) for further studies on the swelling behaviors and water states. Water swelling experiments indicate that the fibrous membrane has a great capacity for water sorption, which reaches a maximum in a few minutes because of its extremely high porosity. Furthermore, a remarkable overshoot occurs as a result of polymer chain relaxation and the non-compact structure of the fibrous membranes. Contrary to the dense membrane, the equilibrium water content in the fibrous membrane decreases with the content of hydrophilic NVP though the maximum is almost the same. Results from DSC experiments demonstrate that only non-freezable bound water and free water can be distinguished in the fibrous membrane. On the basis of the results of water swelling and DSC experiments, it is concluded that the specific behaviors of the fibrous membranes are induced by the non-compact and pore-fiber discontinuous structure, which is different from either dense membranes or hydrogels. [GRAPHS: SEE TEXT] DSC curves of fully swollen electrospun fibrous membranes and of fully swollen dense membranes with different NVP contents.