Liquid Membrane Transport of Heavier Rare Earth Metal Ions Based on CPC Results with Di(2-Ethylhexyl) Phosphoric Acid

Abstract

The behaviors of heavier rare earth metal ions in bulk liquid membrane transport systems were examined for Gd³⁺, Tb³⁺, Dy³, Ho³⁺, Er³⁺, Tm³, Yb³⁺ and Lu³⁺ ions. The liquid membrane transport system was constructed by aq. HCl/CHCl₃ containing Di (2-ethylhexyl) phosphoric acid/aq. HCl. The optimum concentration of HCl in the aqueous phase with respect to the rate of transport for these ions increased with the atomic number of the rare earth elements. This trend of transport behaviors was on the same line observed for lighter rare earth ions in the preceding work. Difference in the rate of transport can be used for selective liquid membrane transport of several sets of combination with these ions.     

Polyaniline decorated graphene oxide on sulfonated poly(ether ether ketone) membrane for direct methanol fuel cells application

In direct methanol fuel cells (DMFC), methanol crossover is a major issue which has reduced the performance of polymer electrolyte membrane (PEM) for energy generation. In this study, graphene oxide (GO) and conductive polyaniline decorated GO (PANI-GO) were used as additives in fabrication of sulfonated poly(ether ether ketone) (SPEEK) nanocomposite PEM membrane to reduce methanol crossover. PANI-GO was synthesized by in situ polymerization method and the formation of PANI coated GO nanostructures was confirmed by surface morphology and crystallinity analysis. The membrane morphology and topography analysis confirmed that GO and PANI-GO were well dispersed on the surface of SPEEK membrane. 0.1 wt% PANI-GO modified SPEEK nanocomposite membrane exhibited the highest water uptake and ion exchange capacity of 40% and 1.74 meq g^?1, respectively. The oxidative stability of the nanocomposite membranes also improved. Lower methanol permeability of 4.33 × 10^?7 cm^?2S^?1 was noticed for 0.1 wt% PANI-GO modified SPEEK membrane. PANI-GO modified SPEEK membrane enhanced the proton conductivity, which was due to the existence of acidic and hydrophilic group present in PANI and GO. PANI-GO modified SPEEK membrane held higher selectivity of 1.94 × 10⁴ S cm^?3 s^?1. Overall, these studies revealed that PANI-GO modified SPEEK membrane is a potential material for DMFC applications.     

Adsorption of phenyltin compounds onto phosphatidylcholine / cholesterol bilayers

Phenyltin compounds are known to be biologically active and, whan widely spread, are potentially hazardous. As their chemical structure suggests, they interact with the lipid fraction of the cell membrane. Their effect on the model phosphatidylcholine/cholesterol bilayer has been studied using fluorescence and ¹H NMR techniques. The change in the fluorescein‐PE fluorescence intensity indicates the amount of charge added by phenyltin compounds to the membrane surface. Although the presence of cholesterol alone does not alter membrane interface properties measured with fluorescein‐PE, ¹H NMR measurements show that lipid mobility is altered throughout the hydrophobic core of the membrane. Cholesterol in the phosphatidylcholine bilayer does not alter tetraphenyltin interaction with the membrane, though the effect of diphenyltin dichloride, penetrating deeply into the hydrophobic core of the membrane, is reduced when the amount of cholesterol in the membrane is increased, suggesting decreased compound adsorption. Triphenyltin chloride has a qualitatively different effect on the lipid bilayer, when observed using this fluorescence technique. The adsorption of triphenyltin onto the phosphatidylcholine/cholesterol membrane induces a lateral phase separation of membrane components. Since triphenyltin chloride is known to be adsorbed onto the interface of the lipid bilayer, this separation mechanism must originate in this region and does not seem to be electrostatic in origin. ¹H NMR measurements have confirmed the observation that these two active phenyltin compounds interact with the phosphatidylcholine/cholesterol membrane differently, disrupting different regions of the bilayer to a different degree. Copyright © 2000 John Wiley & Sons, Ltd.     

The development of fluoride-sensitive membrane electrodes : Part I. Membranes containing thorium,lanthanum or calcium fluoride

Fluoride-sensitivc membrane electrodes of the Pungor type are described. In these electrodes, a fluoride precipitate is incorporated in a silicone rubber membrane; fluorides of thorium, lanthanum and other rare earths, and calcium have been examined. The method of preparing the precipitate is important; an excess of metal is vital for correct functioning of the final electrode. The most reliable results were obtained with calcium fluoride electrodes, though their sensitivity was less than that of the best lanthanum fluoride electrodes. With these electrodes, linear responses are obtained in the l0^-2–10^-4M fluoride range.     

Differences in permeability of dioleoylphosphatidylcholine model membranes containing saturated or unsaturated phosphatidic acids

At low millimolar Ca²⁺ concentrations, large unilamellar dioleoylphosphatidylcholine vesicles containing dimyristoylphosphatidate (20 mol%) release enclosed solutes like sulphate, but influx of Ca²⁺ is not demonstrable. Coincident with the permeability change, vesicle aggregation and membrane fusion are observed. These results contrast with those for dioleoylphosphatidate-containing vesicles under the same conditions, which show Ca²⁺ influx and Ca²⁺ chelator efflux, but no sulphate efflux, vesicle aggregation or membrane fusion. The observed differences in permeability behaviour of membranes containing these two phosphatidate molecular species are discussed with respect to the differences in their phase behaviour.     

Transport properties of vanadium ions in cation exchange membranes:: Determination of diffusion coefficients using a dialysis cell

Diffusion coefficients of vanadium ions in cation exchange membranes are of interest because they allow to calculate the ion exchange across the membrane in an all vanadium redox flow battery which leads to undesired cross contamination and energy losses in the battery system. Diffusion coefficients of V²⁺, V³⁺, VO²⁺ and VO⁺₂ ions in CMS, CMV and CMX cation exchange membranes have been determined by measuring the ion exchange fluxes of these ions with H₃O⁺ ions using a dialysis cell. The experimental data are evaluated on the basis of integrated flux equations which require also ion exchange sorption equilibria obtained already in previous work. The lowest diffusion coefficients are observed in the CMS membrane for all vanadium ions. This membrane turns out to be the most suitable one for being applied in a vanadium battery since it is expected to prevent most effectively cross contamination of vanadium ions.     

Physicochemical characterization of ion-exchange membranes in water-methanol mixtures

A complete physicochemical characterization of two ion-exchange membranes—CM2 and Nafion^®117—used in electrodialysis and in direct methanol fuel cells (DMFC) has been carried out. For each membrane, in different methanol-water mixtures—0%, 20%, 40%, 60%, 80% and 100%—and at different temperatures (25.0; 40.0 et 55.0 °C), we have measured the variations of the geometrical dimensions, the proton electrical conductivity, the swelling rate and the amount of methanol in the membrane. The FTIR analysis of Nafion^®117 was performed at different methanol contents of the external solution.The results show that the CM2 membrane presents the best geometrical stability, and the lowest conductivity at any methanol content. At high methanol contents, Nafion^®117 is 10 times more conductive than the CM2 membrane. It was found that the methanol is absorbed more by Nafion^®117, and its effect is more noticeable on the microstructure of this membrane, under standard conditions. The high methanol permeability of these membranes, particularly of the Nafion^®117, induces bad cell efficiencies and lifetimes.     

Development of Poly(Vinyl Alcohol)-Based Polymers as Proton Exchange Membranes and Challenges in Fuel Cell Application: A Review

Abstract

Poly(vinyl alcohol) (PVA) is a biodegradable, water-soluble membrane that has low methanol permeation and reactive chemical functionalities. Modification of these features makes PVA an attractive proton exchange membrane (PEM) alternative to Nafion^TM. However, the pristine PVA membrane is a poorer proton conductor than the Nafion^TM membrane due to the absence of negatively charged ions. Hence, modification of PVA matrixes whilst complying with the requirements of projected applications has been examined extensively. Generally, three modification methods of PVA membranes have been highlighted in previous reports, and these are (1) grafting copolymerization, (2) physical and chemical crosslinking, and (3) blending of polymers. The use of each modification method in different applications is reviewed in this study. Although the three modification methods can improve PVA membranes, the mixed method of modification provides another attractive approach. This review covers recent studies on PVA-based PEM in different fuel cell applications, including (1) proton-exchange membrane fuel cells and (2) direct-methanol fuel cells. The challenges involved in the use of PVA-based PEM are also presented, and several approaches are proposed for further study.     

Sorption and conducting properties of perfluorinated MF-4SC membranes in aqueous solutions containing phenylammonium ions

A comparative study of the sorption effect is performed for nitrogen-containing ammonium, phenylammonium (PhA⁺), and tetrabutylammonium (TBA⁺) cations on conducting and hydrophilic properties of protonic form of perfluorinated sulfocationite MF-4SC membrane. Conductometric method was used to study thermodynamic equilibria in the systems of perfluorinated MF-4SC membrane—aniline in the acid solutions of variable composition (PhA⁺/HCl and PhA⁺/H₂SO₄). Concentration constants of ion-exchange equilibrium are calculated for a MF-4SC membrane on the basis of these data. These constants in the solutions of aniline with HCl and H₂SO₄ are 10.3 and 27.0, accordingly. The choice of sulfuric acid as background electrolyte for matrix polyaniline synthesis is substantiated.     

Swollen polymeric complex membranes for olefin/paraffin separation

Swollen complex membrane of linear low density polyethylene-graft-poly(acrylic acid)-Ag⁺ (LLDPE-g-AA-Ag⁺) were studied and compared with the corresponding membranes based on silicone rubber (SR) and poly[1-(trimethylsilyl)-1-propyne] (PTMSP), such as SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺. The polymeric matrix was first grafted with acrylic acid (AA) and then incorporated with silver ions (Ag⁺) in glycerol solution for forming the swollen complex membrane. Various metal ions and swollen agents in membranes for isobutene/isobutane separation were presented. The swelling of the complex membrane containing Ag⁺ with glycerol shows a higher olefin/paraffin selectivity than those membranes containing Cu⁺ or Cu²⁺ ions and/or other swelling agents. The gas permeability coefficients and the isobutene/isobutane selectivity of LLDPE-g-AA-Ag⁺ membrane were compared with those of SR-g-AA-Ag⁺ and PTMSP-g-AA-Ag⁺ membranes. The PTMSP-g-AA-Ag⁺ complex membrane was found to reach high gas permeability and high olefin/paraffin selectivity. The effects of solubility and diffusivity in membranes are compared with the corresponding non-Ag membranes. The sorption properties in these complex membranes were also included.     

Composite Nafion membrane embedded with hybrid nanofillers for promoting direct methanol fuel cell performance

A special type of hybrid nano-particles was incorporated into the Nafion^® matrix to form a composite membrane. These nano-particles possessed a core–shell structure consisting of silica core (<10 nm) and a densely grafted oligomeric ionmer layer, which was synthesized via atom transfer radical polymerization (ATRP) on the particles’ surface. Besides considerable improvement in the proton conductivity of the membrane, the presence of these hybrid nano-particles in the Nafion^® matrix also repressed its methanol permeability by almost four times. The composite membrane also demonstrated superior performance when tested in a single cell membrane-electrolyte assembly (MEA) under direct methanol fuel cell (DMFC) operating condition. It was found that the composite membrane enabled a power density output that was 1.5 times greater than that of pristine Nafion^®.     

125I-Labeled Peptide Mapping and High-Performance Liquid Chromatography I-Peptide Separation of Protein I of Four Strains of Neisseria Gonorrhoeae

Abstract

¹²⁵I-labeled α-chymotryptic peptides of the principal outer membrane proteins (P.Is) of four strains of Neisseria gonorrhoeae were separated and visualized by two-dimensional (2-D) ¹²⁵I-peptide mapping and by high-performance liquid chromatography (HPLC) coupled with a Beckman Biogamma counter. In addition, ¹²⁵I-peptides were recovered from the HPLC separation and re-separated by the 2-D ¹²⁵I-peptide mapping system. The results indicated that the 2-D ¹²⁵I-peptide mapping procedure was best suited for comparative analyses of α-chymotryptic digests whereas the HPLC system, which is able to detect many more peptides than the 2-D system, is ideally suited for preparative separation of the ¹²⁵I-peptides. ¹²⁵I-peptides separated by HPLC could be recovered, rerun on the 2-D system, and the location of each peptide ascertained. The coupling of these two procedures allows for the isolation of specific ¹²⁵I-labeled peptides for further immunological and structural analyses of these outer membrane proteins.     

Conductance behaviour of a microporous membrane and the application of absolute reaction rate theory

The membrane conductance of a microporous membrane prepared by the hydrogen peroxide (5%) treatment of ion-exchange membranes of the ‘Neosepta’ family has been studied at different temperatures. The membranes were bathed in some common uni-univalent chloride solutions at different concentrations. In general, the membrane conductance, in the temperature range studied, shows values increasing more or less linearly with increases in concentration, but tends towards limiting values at higher concentrations. The magnitudes follow the order K⁺ > NH₄⁺ ≥ Na⁺ > Li⁺, which is the reverse order of the hydrated sizes of these ions. The temperature variations of the conductance have been utilised to calculate the activation parameters, E_a, ΔH3, ΔG3 and ΔS3, assuming the applicability of the theory of absolute reaction rate. The activation energies for conduction increase in the order K⁺ < NH₄⁺ ≤ Na⁺ < Li⁺, which is the reverse of the order of conductances but the same as the sequence of the hydrated sizes of the cations. For a particular electrolyte solution, the energy values decrease with increasing concentrations of the bathing electrolyte. The ΔS3 values are found to be mostly very small positive quantities, indicating that virtually neither any bond formation nor any loss of membrane structure takes place during the permeation process.     

The influence of an anionic additive on the properties of cation-exchanger based calcium-selective electrodes

Potentiometric and electrochemical impedance spectroscopic investigations of calcium-selective membranes containing poly(vinylchloride), dioctylphenylphosphonate, calcium (bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate) and different amounts of the lipophilic anionic additive tridodecylmethylammonium chloride were carried out. The addition of the lipophilic additive changes the properties of calcium-selective electrodes, e.g. slope and calcium selectivity. The selectivity for calcium in presence of H⁺, Na⁺, K⁺, NH₄ ⁺, Mg²⁺, Ba²⁺, Sr²⁺ and (C₂H₅)₄N⁺ was measured by three different methods, namely separate solution method, fixed interference method and matched potential method. Membranes with different concentration ratios between the calcium-exchanger and tridodecylmethylammonium chloride were investigated within half a year. The tendency of changing from cationic into anionic response for membranes containing nearly equivalent concentrations of cation- and anion-exchanger was shown. This inversion of the electrode response depends not only upon the concentration ratio of both ion-exchangers but also upon the total concentration of calcium-exchanger. Electrochemical impedance spectroscopy was used for monitoring the development of membrane resistances during a soaking period of one month. Based on these results dielectric constants for the calcium-selective membranes depending on the membrane composition were determined. Furthermore, the dependence of the membrane resistance on the membrane thickness and the concentration of tridodecylmethylammonium chloride was evaluated.     

Dye-ligand immobilized IPNs membrane for removal heavy metal ions

We have developed a novel approach to obtain high metal sorption capacity utilizing a membrane containing chitosan and an immobilized reactive dye (i.e. Reactive Yellow-2). The composite membrane was characterized by SEM, FT-IR, swelling test, and elemental analysis. The membrane has uniform small pores distribution and the pore dimensions are between 5 and 10 μm, and the HEMA:chitosan ratio was 50:1. The reactive dye immobilized composite membrane was used in the removal of heavy metal ions [i.e., Pb(II), Hg(II) and Cd(II)] from aqueous medium containing different amounts of these ions (5-600 mg l⁻¹) and at different pH values (2.0-7.0). The maximum adsorption capacities of heavy metal ions onto the composite membrane under non-competitive conditions were 64.3 mmol m⁻² for Pb(II), 52.7 mmol m⁻² for Hg(II), 39.6 mmol m⁻² for Cd(II) and the affinity order was Pb(II) > Hg(II)>Cd(II).     

Probing of ferrocenylanilines on model micelle/reverse micelle membrane and their enhanced reactivity for reactive oxidants

Reactive oxygen species are formed in the human body but can be removed by suitable antioxidants. In this study we synthesized and characterized three ferrocene derivatives, 4‐ferrocenylaniline (pFA), 3‐ferrocenylaniline (mFA) and 3‐methyl‐4‐ferrocenylaniline (MeFA), having significant potential to be used as antioxidants. The synthesized compounds are insoluble in water, with the solubility of these compounds increasing in micelle solution. The micelle and reverse micelle solutions were considered as model membranes. The synthesized compounds were probed on the model membranes, made by sodium dioctylsulfosuccinate reverse micelle and tetradecyltrimethylammonium bromide micelle, using ¹H NMR spectroscopy. The ¹H NMR results indicated that these compounds are present in the polar region of the model membrane interface. Quantitative measurements showed that mFA has the greatest ability to penetrate into the micelle membrane among these compounds, and pFA is least penetrating in this respect. Solubilization of these compounds in aqueous micelle solution facilitates crystallization (of mFA) and enhances the antioxidant potential of these compounds. X‐ray crystal structure analysis revealed that mFA captures water molecules during crystallization in micelle solution. Their ability to act as antioxidants was evaluated, in dimethylsulfoxide (DMSO) and in micelle solution, using standard 1,1‐ diphenyl‐2‐picrylhydrazyl (DPPH) assay. It was found that their antioxidant potential is good in DMSO and that potential increases on the interface of the model membrane. The highest increase (by 19.6%) in the antioxidant potential, on the model membrane interface, was observed for mFA.     

Coupling of the Polymer Threading a Membrane Transition to the Membrane Adsorption Transition

A polymer molecule threading through a pore in a plane membrane is allowed to adsorb on either or both sides of the membrane. Further, it is confined to the vicinity of the membrane by two plane barriers lying on either side of the membrane. A lattice model of this problem is exactly solvable by matrix techniques. The equilibrium translocation behavior is described as a function of the polymer MW, the membrane adsorption energies, the solution properties, the barrier separations, applied force, and the temperature. The transition is first-order, meaning that small changes in any of these 9 quantities can in the limit of infinite MW, completely translocate the polymer. The work of Park and Sung who used Smoluchowski-like equations to calculate translocation transit times can be generalized by use of the sea-snake model which is relevant to isolated polymer chains in solution. The physics behind the sea-snake model is that if one monomer is pulled into the membrane, the distance the center of mass of the untranslocated portion of the chain moves is MW^−1/2 of the distance between monomer units. This reduces the effective friction coefficient by MW^1/2. It is found for the sea-snake model that the MW dependence of transit times varies as MW^3/2 or MW depending on whether we use a free draining or a non-free draining picture for the polymer.     

The influence of an anionic additive on the properties of cation-exchanger based calcium-selective electrodes

Potentiometric and electrochemical impedance spectroscopic investigations of calcium-selective membranes containing poly(vinylchloride), dioctylphenylphosphonate, calcium (bis[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate) and different amounts of the lipophilic anionic additive tridodecylmethylammonium chloride were carried out. The addition of the lipophilic additive changes the properties of calcium-selective electrodes, e.g. slope and calcium selectivity. The selectivity for calcium in presence of H⁺, Na⁺, K⁺, NH₄ ⁺, Mg²⁺, Ba²⁺, Sr²⁺ and (C₂H₅)₄N⁺ was measured by three different methods, namely separate solution method, fixed interference method and matched potential method. Membranes with different concentration ratios between the calcium-exchanger and tridodecylmethylammonium chloride were investigated within half a year. The tendency of changing from cationic into anionic response for membranes containing nearly equivalent concentrations of cation- and anion-exchanger was shown. This inversion of the electrode response depends not only upon the concentration ratio of both ion-exchangers but also upon the total concentration of calcium-exchanger. Electrochemical impedance spectroscopy was used for monitoring the development of membrane resistances during a soaking period of one month. Based on these results dielectric constants for the calcium-selective membranes depending on the membrane composition were determined. Furthermore, the dependence of the membrane resistance on the membrane thickness and the concentration of tridodecylmethylammonium chloride was evaluated. Received: 21 July 1998 / Revised: 16 October 1998 / Accepted: 23 October 1998     

Transfer of glycols through an MA-41 ion-exchange membrane from aqueous and salt-aqueous solutions

Experiments on the molecular diffusion of glycols through an MA-41 ionite membrane in the SO ₄ ^2? form demonstrated that the flux of the glycols decreases with increasing sodium sulfate concentration in the feed solution and with increasing molecular mass of the glycol. For ethylene glycol, as an example, it was demonstrated that its flux through the membrane nonlinearly depends on its concentration in the feed solution. Based on the observation that the fluxes of the nonelectrolyte and electrolyte differ significantly, we proposed a method for separating these components by means of dialysis through an ionite membrane. Computer simulations of the structure and IR spectra of the ethylene glycol-nine water molecules and ethylene glycol-nine water molecules-M⁺ (M⁺ = Na⁺, K⁺) systems were performed. It was revealed that, for the latter system, the activation energy of self-diffusion of ethylene glycol is lower than that for the former.     

Effect of an acidic treatment on the chemical and charge properties of a nanofiltration membrane

In order to improve the performance of a nanofiltration membrane (DS5 DL from Osmonics^®) several pre-treatments have been tested. Specifically, the membrane has been immersed, for different times, in an aqueous solution of HF or H₃PO₄, or of a mixture of both these acids. The chemical and charge properties of the membranes, both pre-treated and untreated, have been studied.