Porosity of microporous polyethylene membranes modified with polypyrrole and their diffusion permeability to low-molecular weight substances (original) (raw)
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Electrochimica Acta, 2011
A mechanism for the macroscopic charge balance during the transport of anions and cations across polypyrrole based composite membranes is proposed. For the mechanism to be studied, anions and cations were monitored simultaneously across PPy based composite membranes, which are known to have cation exchange (PPy(PSS)), anion exchange (PPy(ClO 4 )) and mixed ion exchange properties (PPy(pTS)). Even though none of the membranes were found to be completely permselective, the flux of cations was higher than that of anions across the PPy(PSS) composite membrane, while the flux of anions was higher than that of cations across the PPy(ClO 4 ) composite membrane. Distinct changes in pH of the receiving solution were also observed. These were a decrease in pH when a predominantly anion exchanging polypyrrole composite membrane was used, and an increase in pH when a membrane that maintains charge balance principally by cation exchange was used. When membranes which display approximately equal permeability towards anions and cations were used the pH of the receiving solution was ca. 6-8. There was only a negligible flux of Ca 2+ across the PPy(PSS) membrane in the transport experiments carried out with the source solution consisting of either Ca(NO 3 ) 2 or an equimolar mixture of KNO 3 and Ca(NO 3 ) 2 . The PPy(PSS) composite membrane was impermeable towards NO 3 − ions when the source solution was Ca(NO 3 ) 2 but permeability towards NO 3 − was observed when the source solution was either KNO 3 or an equimolar mixture of KNO 3 and Ca(NO 3 ) 2 .
Preparation and transport properties of PPy/PVDF composite membrane
Polymers for Advanced Technologies, 2011
In this work, composite cation-exchange membrane was prepared by chemical polymerization of pyrrole on the surface of the poly(vinylidene fluoride) (PVDF) membrane using ferric ions. The changes in the surface morphologies of non-modified and polymer-modified PVDF membrane were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and atomic force microscopy. The ion-exchange capacity, water uptake, and fixed group concentration of the composite membrane were investigated. The polypyrrole/PVDF composite membrane was used for the removal of copper (II), chromium (III), iron (III), and aluminum (III) ions from aqueous solution with Donnan dialysis experiments. The flux values (J) and recovery factors (RF) of Cu(II), Cr(III), Fe(III), and Al(III) were obtained. Because of the smaller ion charge and hydration volume, the transport of the Cu(II) ion is higher than that of the other metals.
Protonation and diffusion phenomena in poly(4-vinylpyridine)-based weak anion-exchange membranes
Journal of Membrane Science, 2009
Purification and concentration of mineral acids can be carried through dialysis processes with anionexchange membranes. Weak anion-exchange membranes are active only for sufficient acid concentrations in their structure, however too high concentrations result in significant proton leakage, i.e. reduction in the transport selectivity. The present paper deals with the kinetics of acid diffusion through two commercial poly(4-vinylpyridine)-based weak anion-exchange membranes which comprises protonation of the exchanging groups. The electrical conductivity and the water content of the membranes were shown to be linear function of the protonation degree of poly(4-vinylpyridine) groups. Kinetics of protonation and diffusion of acids have been investigated using dialysis cells. First diffusion kinetics has been studied in a conventional dialysis cell, by observation of the transient acid transport through the membrane (macroscopic studies). Besides, protonation kinetics was investigated using a miniaturised dialysis cell coupled to confocal Raman microspectrometer. Profiles of non-protonated and protonated sites in the membrane were recorded along time, depending on the membrane grade and the nature of the acid transported. Interpretation of the two sources of data yielded permeability coefficient and diffusion coefficient, whose meaning is discussed. A mechanism for protonation/diffusion in this type of weak anion exchangers in acidic media was proposed.
Desalination, 2017
Herein, we report the galvanostatic modification of a commercial cation exchange membrane CMX by polypyrrole (Ppy). The presence of Ppy in the cation exchange membrane (CEM) was confirmed by cyclic voltammetry, stereo microscopy, fourier transform infrared spectroscopy, scanning electron microscopy, and energy dispersive X-ray. Ppy was present both on the membrane surface and inside the pores. The quantity of Ppy in CEM, compactness of Ppy, and the charges on Ppy (negative or positive) were controlled effectively by changing the electrosynthesis conditions. The permeability and water content of the modified membranes obtained under different conditions were investigated. The transport properties of the modified CEMs were evaluated qualitatively using polarization curves and quantitatively by chronopotentiometry. NaCl and MgCl 2 solutions ranging in concentrations from 5 mM to 0.1 M were used for testing the selectivity. The presence of Ppy in the membranes decreased the transport number of Na and Mg, and the reduction in transport number was more significant for Mg.
Journal of Membrane Biology, 1996
The rates at which ions (86 Rb + , [ 3 H]-choline, 36 Cl), 3 H 2 O and nonelectrolytes ([ 14 C]-urea, [ 14 C]glycerol, and [ 14 C]-sugars) equilibrate across tracketched polyethyleneterephthalate (PETP) membranes (isotopic diffusion) have been measured by a 'static' and a 'dynamic' technique under conditions where no net flow takes place; the two techniques give essentially the same results. All tracers diffuse faster the longer the membranes are etched, consistent with an increase in pore size. Water and neutral solutes diffuse at rates that are relatively independent of ionic strength, pH or the presence of divalent cations. Diffusion of cations is decreased by high ionic strength, by reducing pH or by addition of divalent catons; diffusion of chloride is increased by these procedures. Treatment of the membrane with diazomethane to reduce the negative fixed charge decreases diffusion of cations and increases that of anions; diffusion of water and neutral solutes is unaffected by methylation except in the membranes with the narrowest pores (i.e., those etched for the shortest time), in which case diffusion is reduced. We conclude (1) that the special features of flow near a charged surface apply to ions but not to water or nonelectrolytes and (2) that calculation of absolute rates of diffusion leads to values for the radii of pores through track-etched PETP membranes that are in remarkably good agreement with measured values.
Ion transport in the polyamide layer of RO membranes: Composite membranes and free-standing films
Journal of Membrane Science, 2011
The permeability of the composite ESPA1 membrane to ferro-and ferricyanide ions without and with an excess of supporting buffer was analyzed by three different methods: filtration followed by phenomenological analysis, and electrochemical impedance spectroscopy and chronoamperometry using free polyamide films isolated from the membrane. Appropriate relations were developed that relate the observed permeability to actual permeability of the trace redox ions and correct for concentration polarization of the trace ion in presence of a more concentrated (dominant) electrolyte. Within the uncertainties associated with polarization correction, coupling of ionic fluxes, and ion association in solution and within the membrane, consistent values of permeabilities, of about 0.03-0.05 m/s, were obtained by all methods. The results validate that (a) the contribution of convection to salt permeation through the active layer of thin-film composite membranes is small; (b) the procedures used to isolate the active polyamide layer from commercial membranes has a minimal impact on the transport properties of the polyamide films; the isolated free films may then adequately represent the properties of the original active layer in characterization studies. This information may have important implications for studying transport, modeling and characterization of thin-film composite membranes.
Synthetic Metals, 2011
Polypyrrole (PPy) films doped with acid-treated multi-walled carbon nanotubes (CNTs) were prepared by galvanostatic polymerisation of pyrrole (Py) dissolved in aqueous dispersions of CNTs, which served as the background electrolyte. Morphological characterization of PPy(CNT) films showed a random deposition of the polymer on the surface of the support material, with the former creating a porous, interconnecting three-dimensional network structure. The porous nature of PPy(CNT) films favours movement of large amounts of water in and out of the films during redox cycling, which also causes extensive volume changes. Raman spectroscopy, the electrochemical quartz crystal microbalance method and scanning electron microscopy were used to explore the properties of PPy(CNT) films. In addition, the factors influencing the electrochemically controlled transport of metal ions across composite membranes composed of polypyrrole doped with acid-treated multi-walled carbon nanotubes (PPy(CNT)) were studied. The factors examined were: The polymerization conditions (current density and time), the type of support material on which the polypyrrole films were deposited, and the use of single layer or bilayer type polypyrrole films. The flux of metal ions across the composite membranes was able to be electrochemically controlled when Nucleopore ® track-etched membranes were used as the support material, while the flux was controlled by the concentration gradient present when polyvinylidene difluoride (PVDF) was used as the support material for PPy(CNT) films. However, electrochemically controlled movement of metal ions across PVDF-supported membranes was achieved when a bilayer type PPy film (PPy(pTS)/PPy(CNT)) was used (pTS = toluene-4-sulfonic acid). Increasing the thickness of the PPy(CNT) layer in the composite membrane was found to enhance the membranes permeability towards K + . .fi (A. Ivaska). incorporated are expelled or, alternatively, anions present in the surrounding solution (either the original dopant or other anions present in the electrolyte) are incorporated. Thus, during electrochemical switching of PPy between the oxidised and reduced states (redox cycling), ions move in and out of the film for charge compensation to occur. In the case of membranes composed of PPy, electrochemical switching enables the movement of ions from a solution on one side of the membrane across to a solution on the other side.
Transport of Ions and Solvent Through a Nafion Membrane Modified with Polypyrrole
Journal of Membrane and Separation Technology, 2012
The Nafion ® 117 membrane was modified chemically, using a conducting polymer pyrrole. The oxidants ferric chloride (PPy-Fe), hydrogen peroxide (PPy-O) and ammonium persulfate (PPy-S) were used to carry out the polymerization in the membrane both in aqueous and organic media. The Nafion ® modified in the presence of the Nméthylformamide increases the transport of alkali and heavy metal cations and reduces considerably the transport of methanol both in diffusion and electro-osmosis. Therefore, the modified Nafion ® membrane can be used successfully in electrodialysis of electrolyte solutions in both aqueous and hydro-organic media and may be regarded as a good material to use in Direct Methanol Fuel Cells.
Journal of Applied Polymer Science, 1995
The reverse osmosis performance of thin-film composite membranes prepared from sulfonated polyphenylene oxide polymer with different ion-exchange capacities was studied using various electrolyte solutes. The effect of the solvent used for the preparation of the polymer solution for surface coating was also studied. It was found that the preparation of thin-film composite membranes with high selectivities and high fluxes was possible by adjusting properly the ion-exchange capacity and the solvent. It was also found that the membrane performance was governed primarily by the ion-exchange reaction between the solute cation and the proton in SO3H and the Donnan equilibrium. © 1995 John Wiley & Sons, Inc.