Simultaneous monitoring of the transport of anions and cations across polypyrrole based composite membranes (original) (raw)
Related papers
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.
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.
Journal of membrane science & technology, 2017
The composite of poly(vinyl chloride) (PVC) with zirconium aluminophosphate (ZrAlP) employed as additive was prepared by sol-gel method. The physico-chemical properties were elucidated by FT-IR, XRD, TG-DTA and SEM. The influence of polymer ratios on stability of the membrane was investigated; with 25% polymer it shows greater stability. The porosity and water uptake properties were also observed. The membrane potential in different monovalent electrolyte solutions with varying concentrations (1-0.001 M) followed the trend as LiCl > NaCl > KCl > NaNO 3 > KNO 3 attributed to the different sizes of electrolytes. The membrane potential increased with the decrease in cation size. For anions, differences found are according to the size, mobility ratio and strong interaction with the membrane matrix. Small size and higher mobility of Cl À ion shows greater value of membrane potential whereas NO 3 À ion shows lower value because of its large size and strong interaction with the membrane matrix. The potential shows positive values with decrease in electrolyte concentrations confirming the membrane to be cation selective. Membrane potential also gave fixed charge density value of the membrane; evaluated and compared using various theoretical models: (a) Nagasawa, (b) Kobatake and (c) Teorell, Meyer and Sievers. Li + ion shows highest value of fixed charge density in all the methods as the Donnan exclusion is highest for the electrolyte of smaller cation size. The experimental results comparatively agreed with theoretical predictions. Extended form of TMS theory was used to calculate the distribution coefficient, charge effectiveness and transference number of ions. The prepared membrane also shows highest permselectivity for Li + counter-ion while lowest for K + , as potassium counter-ion shows strong interaction with the fixed charge groups on the polymer, thereby, decreasing the value. Co-ion (NO 3 À) with higher hydrated radii and lower charge density also tended to result in low membrane permselectivity. Thus, the composite membrane can be efficiently used in various electro-membrane processes.
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.
Desalination, 2002
The quantity of absorbed electrolyte and the electrical membrane conductivity have been measured and correlated for three cation-exchange membranes (CM2, CMx and MK-40), two electrolytes (KC1 and LiCl), over a large concentration range of the solution (0.1 M 5 C,, 5 3.0 M). The membrane conductivity has been measured according to a French standard. However, because of the lack of standards fixing all the operating conditions, we established an experimental protocol, validated by a statistical study. This method will be proposed to be standardized for this category of measurements. Relationships have been established between the two parameters allowing us to determine both the counter-ion and the co-ion diffusion coefficients in a cation-exchange membrane, considered as homogeneous. The values of these coefficients for the counter-ions are in good agreement with those obtained from other methods. The variations of the computed diffusion coefficients of counter-ions and co-ions for the different studied systems are discussed in terms of internal interactions with the charged polymer matrix and the other diffusing species. The discussion also takes into account the free water content of the polymer.
Chemical Engineering Journal, 2000
Diffusion permeability of the composite polypyrrole/polyethylene (PPy/PE) membranes in relation to various low-molecular weight electrolytes (hydrochloric acid, potassium chloride or sodium hydroxide) was studied. PPy/PE membranes were prepared by oxidative polymerization of pyrrole in the presence of FeCl 3 . They differed in the thickness of PPy layers deposited on both the membrane and pore surfaces and in porosity. It was shown that changes of porous, hydrophilic and ion exchange properties of the membranes affect their diffusion permeability to electrolytes in the same way as was demonstrated earlier for diffusion permeability of microporous ion exchange Neosepta membranes in relation to proteins [M. Bleha, G. Tishchenko, Y. Mizutani, N. Ohmura, in: A. Dyer, M.J. Hudson, P.A. Williams (Eds.), Progress in Ion Exchange. Advances and Applications, Cambridge, 1997, pp. 211-218]. It means that there is an optimum combination of PPy content and membrane porosity ensuring the maximum fluxes of electrolytes through the membranes. At low (<2 h) and high (>6 h) duration of pyrrole polymerization the diffusion permeability of PPy/PE membranes is low. In the first case, PPy covers mainly the outer membrane surfaces; the surface of pores remain hydrophobic because pyrrole has no time for penetrating into them. In the second case, PPy forms thick layers on both the membrane and pore surfaces resulting in their blocking. It was found that the diffusion transport of acid and alkali accompanied with removing of Fe from the PPy/PE membranes. The influence of Fe-containing compounds presenting in the PPy/PE membranes on their diffusion permeability in alkaline or acidic conditions is discussed.
A Study of Osmosis Rate Through Several Proton Conducting Polymer Composite Membranes
Materials Science
Carbon dioxide is typically considered to be a byproduct of various industrial processes that should not be released into the environment due to its nature as a harmful greenhouse gas. One of the more promising ways to dispose of it in an economical and environmentally friendly way is by using it as a raw material in electrochemical synthesis reactors. An important part of such reactors is an ion exchange membrane. In this study the influence of ZrO2 content in SPEEK – ZrO2 composite membranes on rate of osmosis trough them was investigated, with the goal of evaluating ZrO2 as an additive for making ion exchange membranes with fine-tuned osmotic permeability.
Desalination, 2009
Fixed electric charge is believed to play an important role in the transfer of charged solutes in nanofiltration. Electrochemical measurements are useful tools for the determination of electrochemical perm-selectivity, which can be related to the fixed charge density by using a model. In the case of monolayer membranes, the electrochemical perm-selectivity is determined, in particular, through the measurements of stationary membrane potential. With composite/asymmetric NF membranes, the interpretation of this measurement is complicated by the membrane multi-layer structure. In the concentration-step technique, a membrane is equilibrated with an electrolyte solution and left in contact with this solution from the support side alone. The active membrane surface is suddenly touched by a pendant drop of solution of a different concentration, and the electrical response to this is tracked with a pair of reversible electrodes. In the very first moments after the touch, the whole concentration difference is located within the membrane active layer, and the initial electrical response is controlled by its electrochemical perm-selectivity. The characteristic time of relaxation of transient membrane potential is governed by the diffusion permeability of active layer and the porosity of and diffusivity in the membrane support. The concentration-step technique was used to study the electrochemical properties of active layers of a commercial polymer NF membrane (PES10) and a laboratory-made nano-porous ceramic membrane (provided by University of Twente) in KCl solutions of various concentrations. At pH 6, the fixed charge of polymer membrane was found to be negative whereas that of ceramic membrane was positive. The concentration of fixed charges ranged from 0.03 kmol/m 3 to 0.17 kmol/m 3 depending on the salt concentration.
Comparative investigations of ion-exchange membranes
Journal of Membrane Science, 1999
The equilibrium and transport properties (conductivity, transport number, diffusion) of crosslinked ionomer membranes based on sul®nated and sulfonated PSU in aqueous solutions of HCl, NaCl and KCl have been investigated and compared with a Na®on 117 membrane. It has been found that these membranes are more compact and their conducting paths are of smaller dimension than that of the Na®on 117. The in¯uence of length of crosslinking chain, changing from ±(CH 2 ) 4 ± to ±(CH 2 ) 12 ±, is particularly indicated by the diffusion coef®cients; the conductivity and transport numbers of counterions are in¯uenced only slightly. Practically no dependence of this effect on the transport number of H has been found. # 0376-7388/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. P I I : S 0 3 7 6 -7 3 8 8 ( 9 8 ) 0 0 2 4 2 -7