Irreversible thermodynamics of transport across charged membranes : Part II-ion-water interactions in permeation of alkali

The detailed analysis of membrane phenomena in the system Nafion 120 membrane/NaOH_aq at 298, 313 and 3n33 K has been performed, taking for discussion the phenomenological transport coefficients r_ii, f_ik and diffusion indices D̄_i^r. Comparing the numerical values found here with the corresponding data determined for the system with NaCl solutions it is shown that cation-anion frictional force, which is usually assumed zero, cannot be neglected for the Na⁺-OH⁻ pair of ions. These interactions influence diffusional and osmotic transport of a solute and water across the membrane. Another specific effect of OH⁻ ions important for membrane permeation is the very low friction of OH⁻ ions with water.     

Preparation,properties, andin vitro thrombogenic characterization of urokinase-collagen membrane

Urokinase (EC 3.4.4.a) was immobilized on collagen membrane. The urokinase-collagen membrane gave a flat pH profile from 7.5 to 9.5. It was more stable against heat than native urokinase. Furthermore, the stability of urokinase in the pH range of 7.0-8.8 was increased with immobilization. The collagen fibril network might stabilize urokinase. The diffusion coefficients of urea, uric acid, and creatinine through the urokinase-collagen membrane were in the range of 2.5-4.5 x 10^-7 cm³/sec. The diffusion coefficients decreased to the range of 6.9-8.2 x 10^-8 cm²/sec when fibrin clot was formed on the membranein vitro. Immobilized urokinase activates plasmin which lyzes fibrin clot. Therefore, fibrin clot formed on the membrane could be lyzed during prolonged incubation at 37°C and the diffusion coefficients restored to the initial values. The fibrin clot formedin vivo may be lyzed with immobilized urokinase.     

Strategies to improve the surface plasmon resonance-based immmunodetection of bacterial cells

We have made a comparison of (a) different surface chemistries of SPR sensor chips (such as carboxymethylated dextran and carboxymethylated C1) and (b) of different assay formats (direct, sandwich and subtractive immunoassay) in order to improve the sensitivity of the determination of the model bacteria Acidovorax avenae subsp. citrulli (Aac). The use of the carboxymethylated sensor chip C1 resulted in a better sensitivity than that of carboxymethylated dextran CM5 in all the assay formats. The direct assay format, in turn, exhibits the best sensitivity. Thus, the combination of a carboxymethylated sensor chip C1 with the direct assay format resulted in the highest sensitivity for Aac, with a limit of detection of 1.6?×?10⁶ CFU mL^-1. This SPR immunosensor was applied to the detection of Aac in watermelon leaf extracts spiked with the bacteria, and the lower LOD is 2.2?×?10⁷ CFU mL^?1.

Diffusion coefficients of ions through ion excange membrane in Donnan dialysis using ions of different valence

Donnan dialysis with an ion exchange membrane was investigated for ions of different valence. The effective diffusion coefficients (D_e) of various kinds of ions in the membrane were obtained by fitting of the equation derived from the Nernst–Planck equation to three or more sets of experimental data for Donnan dialysis. It became apparent that the value of D_e/D_s of monovalent ions (e.g., K⁺ or Na⁺ ions) at z_A=1 and z_B=2 (feed ions are monovalent ones and driving ions are bivalent ones) remained constant at ca. 1/210 and that of bivalent ions (e.g., Ca²⁺, Cu²⁺, or Mg²⁺ ions) remained constant at ca. 1/526 where D_s denotes the diffusion coefficient of ions at infinite dilution in water calculated from the Nernst–Einstein equation, and z_A and z_B represent the valences of the feed and driving ions, respectively. D_e/D_s of monovalent ions (e.g., H⁺, K⁺, or Na⁺ ions) at z_A=2 and z_B=1 (feed ions are bivalent ones and driving ions are monovalent ones) was constant at ca. 1/23.3 and that of bivalent ions remained constant at ca. 1/58.4. It was proved that D_e/D using D_e at z_A=1 and z_B=2 was constant at 1/3.0 and that at z_A=2 and z_B=1 remained constant at 3.0 where D represents the diffusion coefficient of ions in the membrane at z_A=z_B (the valences of both feed and driving ions are equal). Therefore, it was found that a large flux of ions could be obtained using the monovalent driving ions in Donnan dialysis. On the other hand, the small flux can be obtained using bi- or higher-valent driving ions.     

Electrical pumping in carrier-mediated membrane transport

A model of carrier-mediated pumping induced by electrochemical (redox) reactions is presented. The model is compared with published data for the facilitated transport of nitric oxide in a formamide membrane containing dissolved ferrous and ferric chlorides wherein the flux of nitric oxide is augmented by diffusion of the reversible complex, (NO—Fe²⁺. Passing a current through the membrane drives the reduction of ferric ions at the cathode and the oxidation of ferrous ions at the anode, coupling the charge and mass fluxes within the membrane. Our results indicate that this electrically powered, carrier-mediated membrane can pump permeant up to a concentration 0(10) times greater than that in the feed.     

Irreversible thermodynamics of transport across charged membranes : Part I — Macroscopic resistance coefficients for a system with nafion 120 membrane

The transport of aqueous NaCl solutions across the perfluorinated Nafion 120 membrane is studied on the base of irreversible thermodynamics. The straight resistance coefficients r_ii, partial frictions f_ik^p and diffusion indices RT/c?_ir_ii are presented and discussed. The results suggest that the main force, which impedes the flow of chloride ions across the membrane is not the friction of these ions with the negatively charged polymer network, but the friction with water. The diffusion indices RT/c?_ir_ii exceed self-diffusion coefficients found by some authors while using tracer technique. Following Meares' suggestion such results point out to the convective flow contribution to the transport of ions and water.     

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.     

Transport of Na+, K+ ions in a bubbling pseudo-emulsion liquid membrane system with p-tert-butylcalixarenes as carriers

The liquid membrane transport of Na⁺ ions by p-tert-butylcalix[6]arene and that of K⁺ ions by p-tert-butylcalix[8]arene were investigated by means of a bubbling pseudo-emulsion liquid membrane system. This system represents a proton-coupled transport with a flow of protons in the opposite direction. The driving force for the transport is the pH gradient between the source and receiving phases. When the pH difference between the two phases is sufficient, the carriers calix[6]arene(or calix[8]arene) can successfully transport Na⁺ (or K⁺) ions from the source phase with a lower Na⁺ (or K⁺) concentration into the receiving phase with a higher Na⁺ (or K⁺) concentration, like a Na⁺ (or K⁺) ion pump.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.     

Role of Ion exchange in permeation processes

The single ion transport of transition metal ions like Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺ were carried out through the H⁺ and alkali metal ion forms of Nafion membrane. These studies showed that the ion exchange selectivity coefficient of the permeating ion had an effect on its transport process. It was found that the diffusion coefficient values (D) were directly proportional to the selectivity coefficient (K). This shows that the initial stage of permeation is governed by ion exchange process (effect of K on D).     

Separation of Cr ions from Co and mn ions by poly (bis(phenoxy) phosphazene) membranes

Poly(bis (phenoxy)phosphazene) was synthesized and cast by knife techniques into membranes supported on porous Inconel plates for separation testing. A solution of Cr³⁺, Co²⁺ and Mn^2/t+ nitrates was used as the feed solution in diffusion experiments conducted from 25 to 180°C. It was discovered that Co²⁺ and Mn²⁺ ions had much higher diffusion coefficients than Cr³⁺ ions through the membrane, with a maximum difference occurring near 100°C. The lower diffusion associated with Cr³⁺ ions is believed to be due to formation of polymerized hydrated Cr³⁺ ions that are too large to penetrate the membranes. Diffusion activation energies are reported.     

Diffusion current at microdisk electrodes—application to accurate measurement of diffusion coefficients

Stationary electrodes (platinum and glassy carbon) were used for accurate measurement of diffusion coefficients. The theoretical diffusion current-time profile was calculated by digital simulation, by means of which the diffusion coefficient and the product of the charge number of electrode reaction n and the reactant concentration c^o were determined simultaneously from a single chronoamperogram. The feasibility of the method was demonstrated by measuring the diffusion coefficients of Tl(I) ions. When the nc^o value agreed with the corresponding known value, the diffusion coefficients were in good agreement with the standard values determined by the thin-walled hanging mercury drop electrode method. The diffusion coefficient of hexacyanoferrate(III) ions in 1 mol dm^?3 KCl at, 25°C was also determined.     

Kinetic studies of cobalt alginate gels

Summary Sodium alginate sol can be converted into ionotropic gels by diffusion of di/or trivalent metal ions. The kinetics of this phase transition is studied by two different methods. It is found that the rate of gel membrane formation at the earlier stages is greater than that of the further gel growth. The kinetic studies of gel formation in the presence of a mixture of Cu²⁺ ions with either Co²⁺ or Ni²⁺ ions show that the exhaust of Co²⁺ and Ni^2- ions is remarkable only at the first stage of gel formation. Meanwhile the Cu²⁺ ions continue exchanging all the time with Na²⁺ ions in the alginate sol. The activation energy of gel formation is found to range between 17–23 kJ mol^–, indicating the diffusion control of the process.With 6 figures and 3 tables     

Kinetics and mechanism of solid-state reaction between cyclooctasulfur and nickel oxide

The mechanism of reaction between sulfur and nickel oxide in the solid state was studied by chemical analysis, TGA, and capillary diffusion methods. Nickel oxide and sulfur react in the molar ratio 3 : 1 to give Ni₃S₅ · 3H₂O. The data for lateral diffusion fit best in the equation ξⁿ = kt. It has been also suggested by thermal analysis that S^?2 ions are formed which are exchanged by 0^?2 ions.     

Diffusion potential is induced by coupled transport of ions through liquid membrane: nonlinear response to pH change in a reverse permeation system

In a cation exchange liquid membrane-aqueous alkali metal chloride system, diffusional flux of alkali metal ion driven by proton was observed. A supported liquid membrane formed on a Teflon filter by impregnating it with stearic acid-doped 1-octanol was used. The internal aqueous phase contained KCl and HCl, and the external aqueous phase also contained KCl. The initial concentrations of K⁺ ions of both phases were 1×10⁻¹ mol dm⁻³ for all the measurements. The concentration of HCl in the internal solution was kept at 1×10⁻² mol dm⁻³. The pH of the external solution was changed successively with HCl, appropriate buffer solution, or KOH. The pH dependence of membrane potential showed hysteresis loop in the range from neutral to alkaline pH, where reverse ion permeation was observed after the flux had been measured in the system with the external solution of an alkaline pH (pH 13). In the acidic range below neutral pH, the hysteresis of the membrane potential as well as reverse ion permeation was not observed. To elucidate the correlation between the appearance of hysteresis loop and the reverse ion permeation driven by proton across the membrane, the time course of the membrane potential in response to pH change was investigated. In the pH range where reverse permeation phenomena appeared, the time dependence of the membrane potential in nonsteady-state showed biphasic behavior. From the time course curve of the membrane potential, the total membrane potential was divided into the Donnan potential and the diffusion potential. From these findings, it was demonstrated that the diffusion potential was generated within the membrane only in the alkaline range where reverse ion permeation occurred. Analyzing the diffusional flux, the diffusion coefficient of potassium ion in the membrane was obtained taking the Donnan potential into account to be much greater than that in the membrane solvent. As a result of comparison of the diffusional fluxes measured by atomic absorption spectrometry and solution conductometry, the flux of the potassium ion was found to be significantly greater than that of the hydrogen ion in the opposite direction, especially at extremely high pH region. This implies the flows of hydroxide ions and neutralization reaction within the membrane facilitate the reverse ion permeation process of potassium ions.     

Kinetic modeling analysis for the removal of cesium ions from aqueous solutions using polyaniline titanotungstate

Polyaniline titanotungstate has been synthesized by incorporation of organic polymer polyaniline into the inorganic precipitate of titanotungstate. This material was characterized using X-ray, IR and TGA studies. The influences of initial concentration of metal ions, particle size and temperature have been reported. The comparison of composite and inorganic materials was studied and indicating that the composite material is better than the inorganic in selectivity of Cs⁺ ions. Thermodynamic parameters, such as changes in Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) have been calculated. The numerical values of ΔG decrease with an increase in temperature, indicating that the sorption reaction of adsorbent was spontaneous and more favorable at higher temperature. The positive values of ΔH correspond to the endothermic nature of sorption processes and suggested that chemisorptions were the predominant mechanism. A comparison of kinetic models applied to the sorption rate data of Cs⁺ ions was evaluated for the pseudo first-order, the pseudo second-order, intraparticle diffusion and homogeneous particle diffusion kinetic models. The results showed that both the pseudo second-order and the homogeneous particle diffusion models were found to best correlate the experimental rate data. Self diffusion coefficient (D_i), Activation energy (Ea) and entropy (ΔS^*) of activation were also computed from the linearized form of Arrhenius equation.     

Gas transport properties of asymmetric polyimide membranes prepared by ion‐beam irradiation

Ion beam irradiation has been widely used to modify the structure and properties of membrane surface layers. In this study, the gas permeability and selectivity of an asymmetric polyimide membrane modified by He ion irradiation were investigated using a high vacuum apparatus equipped with a Baratron absolute pressure gauge at 76 cmHg and 35 °C. Specifically, we estimated the effects of the gas diffusion and solubility on the gas permeation properties of the asymmetric membranes with the carbonized skin layer prepared by ion irradiation. The asymmetric polyimide membranes were prepared by a dry–wet phase inversion process, and the surface skin layer on the membrane was irradiated by He ions at fluences of 1 × 10¹⁵ to 5 × 10¹⁵ ions/cm² at 50 keV. The increase in the gas permeability of the He⁺‐irradiated asymmetric polyimide membrane is entirely due to an increase in the gas diffusion, and the gas selectivity increases of the membranes were responsible for the high gas diffusion selectivities. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 262–269, 2007.     

Diffusion of Cs+ and Zn2+ through Nafion-117 ion exchange membrane

This paper discusses the diffusion of Cs⁺ and Zn²⁺ ions through Nafion-117 cation exchange membrane using radiotracer technique. The validity of the Donnan's equation is checked for these ions using⁶⁵Zn and¹³⁷Cs radiotracers. The paper also discusses the diffusion of Cl^– and I^– anions studied by using³⁶Cl and¹³¹I radiotracers. The probable mechanism of diffusion of these anions in the presence of Zn²⁺ cations is suggested.     

A study of the factors affecting the adsorption of cobalt ions onto Pakistani coal powder from solutions

Large deposits of coal are abundantly available in Pakistan. An attempt has been made to check its efficacy for the cobalt ions from aqueous solutions in order to exploit the locally available naturally occurring cheaper material for the decontamination/removal of metal ions from nuclear and industrial effluents. The adsorption behavior of cobalt ions on coal powder has been studied as a function of various physicochemical parameters i.e., stirring speed, shaking time, pH, concentration of cobalt ions, temperature, etc. Conditions for the uptake of cobalt ions were established. Adsorption dynamics models such as intra-particle diffusion model, pseudo-first order kinetic model (Lagergren’s equation) and pseudo-second order kinetic model were applied to the adsorption data to elucidate the adsorption process and its mechanism. Results reveal that the adsorption mechanism is predominantly diffusion and both intra-particle and boundary layer diffusion seem significant in the rate controlling step. The adsorption process is best accounted for using pseudo second order kinetic model and the overall rate of adsorption process appears to be controlled by more than one step, namely the external mass transfer and intra-particle diffusion mechanism. The existence of two slopes in the Freundlich plot also confirms the surface diffusion and intra-particle diffusion modes of adsorption. The Langmuir isotherm equation was obeyed well in the whole range of cobalt ions concentration with high value of correlation coefficient (r ²  = 0.999). The adsorption energy (E _a) calculated from D–R isotherm was 6.756 kJ/mol indicating physical nature of adsorption. The adsorption of cobalt ions increased with the increase of temperature and thermodynamic parameters such as ΔH, ΔS and ΔG were calculated. Results suggested that the cobalt ions adsorption on coal powder is endothermic (ΔH 33.90 kJ/mol) and spontaneous (negative ΔG values) process. The adsorption of other metal ions on coal powder was studied at optimized condition for cobalt ions to check its selectivity. Consequently, cobalt ions can be removed from Zr, Ru Eu, Er, Sm, Gd, Dy, Ce, U, and Th ions, where as Cs, Cr and Sr ions reduces the adsorption of cobalt ions by co-adsorption and their reducing affect is in the order of Sr > Cr > Cs.     

含低聚醚链共价有机骨架薄膜材料的制备及其离子分离性能

用2,5-二(2-甲氧基-乙氧基)对苯二甲酰肼(BMTH)和1,3,5-三甲氧基-2,4,6-三甲酰基苯(TpOMe)缩聚,基于界面聚合法,在多孔三氧化二铝(AAO)基底上制备出一种二维共价有机骨架(COF)膜TpOMe-BMTH,并研究了所得膜材料对锂、镁离子的分离性能。结果显示,TpOMe-BMTH/AAO膜具有高的结晶性和良好的稳定性,并表现出优异的金属离子选择性,在LiCl(0.1 mol·L^-1)和MgCl₂(0.1 mol·L^-1)组成的二元混合离子体系中,对Li⁺/Mg²⁺的分离因子高达258。基于密度泛函理论的平面波赝势方法计算表明,材料孔道中的富氧低聚醚链对 Li⁺和 Mg²⁺的结合能分别为-282.69和-13.46 kJ·mol^-1,使材料表现出强的亲锂特性,促进了Li⁺沿着COF膜的一维孔道进行吸附扩散,最终实现锂、镁离子的高效分离。