A new method for estimating counter-ion selectivity of a cationic association colloid: Trapping of interfacial chloride and bromide counter-ions by reaction with micellar bound aryldiazonium salts

1990 ◽  
Vol 48 ◽  
pp. 123-137 ◽  
Author(s):  
John A. Loughlin ◽  
Laurence S. Romsted
Keyword(s):  
Ion Selectivity ◽  
New Method ◽  
Counter Ion ◽  
Counter Ions

scholarly journals Ion mobility and partition determine the counter-ion selectivity of ion exchange membranes

2020 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Ion Exchange ◽  
Ion Mobility ◽  
Ion Selectivity ◽  
Quantitative Relation ◽  
Ion Exchange Membranes ◽  
Membrane Conductivity ◽  
Counter Ion ◽  
Counter Ions ◽  
New Perspective ◽  
Two Parameters

Ion (perm)selectivity and conductivity are the two most essential properties of an ion exchange membrane, yet no quantitative relation between them has been suggested. In this work, the selectivity between two different counter-ions is correlated to the membrane conductivity. We show that the counter-ion selectivity measured by conventional electrodialysis (ED) can be expressed by the product of two parameters: (a) the mobility ratio between these two different counter-ions in the membrane and (b) their partition coefficient between the solution and the membrane. This is reminiscent of the classical solution-diffusion model. Via the counter-ion mobility in the membrane, the selectivity could be simply expressed with the membrane conductivity and dimensional swelling degree at pure counter-ion forms and at mixed counter-ion form when the membrane has been equilibrated with 1:1 equivalence ratio of the two counter-ions in the solution. This correlation is validated experimentally for the ion selectivity of K+/Na+ in two commercial hydrocarbon-based cation exchange membranes (CEMs). For K+/Na+ in a commercial perfluorosulfonic CEM, and for Mg2+/Na+ in all the three types of CEMs, the correlation could predict the counter-ion partition very well; but there is an underestimation of the K+/Na+ and Mg2+/Na+ mobility ratios afforded by this correlation, which might be due to simplification of the cation activity coefficients in CEMs. This work offers a convenient method to decouple experimentally the effect of partition and mobility in controlling the membrane selectivity, and also proposes a new perspective to study the selectivity as well as conductivity of ion exchange membranes.

scholarly journals Noise spectra of K+ and NH4+ ions at over-limiting current in an electrochemical system with a cation exchange membrane

2013 ◽  
Vol 3 (3) ◽  
pp. 291-296
Author(s):  
K. Oulmi ◽  
K. E. Bouhidel ◽  
G. M. Andreadis
Keyword(s):  
Limiting Current ◽  
Electrical Noise ◽  
Singular Behaviour ◽  
Counter Ion ◽  
Power Spectral ◽  
Counter Ions ◽  
Voltage Curve ◽  
Current Voltage ◽  
Current Voltage Curve ◽  
Exchange Membrane

The present work investigates the effect of the counter ion nature on the noise of the over-limiting current (Iov). Moreover, the electrochemical methods, current voltage curve (I–V) and the chronopotentiometry (V–t) measurements are applied. The over-limiting current is always accompanied by a neat electrical noise. It is a well accepted experimental phenomenon. The study of this noise may contribute to a better understanding of the Iov and the feasibility of electrodialysis operation at this current in terms of energy consumption. The electrical noise depends directly on the counter ion nature. The power spectral density of the membrane's potential fluctuation was obtained via Fourier analysis of the time series recorded during the transport of counter ions (K+ and NH4+). The spectra are evaluated above the limiting current indicating the differences between the K+ and the NH4+. It is found that the cation NH4+ presents a singular behaviour and the noise is minimal.

Counter-Ion Effects and Interfacial Properties of Aqueous Tetrabutylammonium Halide Solutions

2004 ◽  
Vol 57 (12) ◽  
pp. 1211 ◽  
Author(s):  
Luboš Vrbka ◽  
Pavel Jungwirth
Keyword(s):  
Slab Geometry ◽  
Ion Interactions ◽  
Counter Ion ◽  
Counter Ions ◽  
Aqueous Solvation ◽  
Ionic Size ◽  
Surface Active ◽  
Ion Effects ◽  
Dynamics Simulations ◽  
The Individual

Aqueous solvation of tetrabutylammonium fluoride and iodide was investigated by means of molecular dynamics simulations in extended slab geometry. The varying propensities of the individual ions for the air/water interface were quantified and analyzed in terms of hydrophobic, polarization, and ion–ion interactions. While the cations behave as standard ionic surfactants, the surface behaviour of the halide counter ions strongly depends on the ionic size and polarizability—iodide is surface active, while fluoride is repelled from the interface. The counter-ion effects at different concentrations on the density and charge profiles across the aqueous slab are discussed in detail.

THE DIFFUSE LAYER CORRECTION TO THE DISCRETE-ION EFFECT IN ELECTRIC DOUBLE LAYER THEORY

1965 ◽  
Vol 43 (10) ◽  
pp. 2834-2866 ◽  
Author(s):  
S. Levine ◽  
J. Mingins ◽  
G. M. Bell
Keyword(s):  
Aqueous Electrolyte ◽  
Canonical Ensemble ◽  
Hexagonal Lattice ◽  
The Self ◽  
Diffuse Layer ◽  
Charge Densities ◽  
Counter Ion ◽  
Counter Ions ◽  
Inner Region ◽  
Upper Estimate

The screening effect of the diffuse layer on the self-atmosphere (or discrete-ion) potential of a counter-ion adsorbed from aqueous electrolyte on to a plane charged interface is investigated. A theory based on Fourier–Bessel integrals and the approximate method of Loeb and Williams for treating the potential distribution in the diffuse layer is presented. The distribution of counter-ions in the adsorption plane surrounding a specified ion adsorbed in the plane is expressed in terms of a two-dimensional grand canonical ensemble and this is approximated by a 'revised cut-off model'. The 'Grahame cut-off model' is an approximation to the adsorbed counter-ion distribution based on a canonical ensemble and we present arguments to show that this interpretation is incorrect. We also show that the radius of the revised disc is, in general, smaller than that of the Grahame disc but approaches it at large charge densities (σβ) of counter-ions in the Stern inner region. Comparison is made with an alternative approach to this discrete-ion effect by Buff and Stillinger, who also applied a Fourier–Bessel technique to the mercury – aqueous electrolyte system. Their results provide a lower estimate to the magnitude of the self-atmosphere potential, whereas our revised cut-off model gives an upper estimate. A third method, which assumes the adsorbed ions to be situated on a hexagonal lattice, is also discussed and is found to give a potential larger than the upper estimate of the revised cut-off approach.It is shown that the effect of the diffuse layer is to diminish the discrete-ion potential at the adsorbed ion. When the electrolyte concentration tends to zero the results with the Grahame model reduce to those derived in an earlier paper from the method of multiple electrostatic images. Calculations on the discrete-ion potential at an adsorbed counter-ion are given for metallic and dielectric surfaces in contact with an aqueous 1–1 electrolyte solution and the parameters of the inner region are chosen to be consistent with known data on mercury and silver iodide systems. It is shown in both cases that on dilute salt solutions [Formula: see text] the diffuse layer screening is small compared to the unscreened term except at small charge densities of counter-ions in the inner region.

Power Generation From Concentration Gradient by Reverse Electrodialysis in Ion Selective Nanochannel

2009 ◽  
Author(s):  
Dong-Kwon Kim ◽  
Chuanhua Duan ◽  
Yu-Feng Chen ◽  
Arun Majumdar
Keyword(s):  
Power Generation ◽  
Concentration Gradient ◽  
Ion Selectivity ◽  
Electrical Energy ◽  
Anodic Bonding ◽  
Channel Height ◽  
Cmos Process ◽  
Surface Charges ◽  
Reverse Electrodialysis ◽  
Counter Ions

In this article, ion selective nanochannels are studied to generate electric power from concentration gradient by reverse electrodialysis. When nanochannels bring into contact with aqueous solution, the surface of nanochannels acquires charges from ionization, ion adsorption, and ion dissolution. These surface charges draw counter-ions toward the surface and repel co-ions away. Therefore, when an electrolyte concentration gradient is applied to nanochannels, counter-ions are transported through nanochannels much more easily than co-ions, which results in a net charge migration of ions. Gibbs free energy of mixing, which forces ion diffusion, thus can be converted into electrical energy by using ion-selective nanochannels. Silica nanochannels with heights of 26 nm and 80 nm fabricated by glass-silicon anodic bonding were used in this study. We experimentally investigated the power generation from these nanochannels placed between two potassium chloride solutions with various combinations of concentrations. The power generation per unit channel volume increases when the concentration gradient increases, while it decreases as channel height decreases. The highest power density measured is 26 kW/m3. Our data also indicates that the efficiency of energy conversion and the ion selectivity increase with a decrease of concentrations and channel height. The best efficiency obtained is 24%. Compared with ion-selective membranes, nanochannels promise more reliable operation since they are readily compatible with standard CMOS process and do not shrink and swell in response to their environment. Power generation from concentration gradient in ion selective nanochannels could be used in a variety of applications, including micro batteries and micro power generators.

scholarly journals Application of counter-ion condensation in calculating the ion activity coefficients for interpreting the membrane selectivity

2021 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Ionic Conductivity ◽  
Activity Coefficients ◽  
Experimental Approach ◽  
Average Distance ◽  
Ion Selectivity ◽  
Monovalent Cation ◽  
Homogeneous Distribution ◽  
Linear Charge Density ◽  
Membrane Conductivity ◽  
Counter Ion

The transport selectivity of different cations through cation exchange membranes (CEMs) could be estimated with the partition coefficient (K_j^i) and the cation mobility ratio in the membrane ((u_m^i)⁄(u_m^j )), which in turn can be related to corresponding membrane conductivity and dimensional swelling degree data [Journal of Membrane Science, 2020, 597, 117645]. This method has been validated in two hydrocarbon-based CEMs, and the obtained K+/Na+ selectivity equals to the one obtained with conventional electrodialysis (ED) method. However, the K+/Na+ selectivity of perfluorosulfonic acid (PFSA) membranes, and the bi-/monovalent cation (Mg2+/Na+) selectivity of all three types of CEMs estimated with this ionic conductivity experimental approach deviate noticeably from corresponding values obtained with ED. In this work, it is proved that this deviation is mostly due to the simplification of cation activity coefficients in the membrane. Here, the cation activity coefficients in three types of CEMs are calculated according to Manning`s counter-ion condensation model. In this model, the Manning parameter (ξ) characterizing the dimensionless linear charge density is determined by the average distance between two adjacent fixed sulfonate groups (b) and the permittivity of hydrated membranes (ε). In hydrocarbon-based CEMs, the average distance between fixed sulfonate groups can be estimated by assuming homogeneous distribution of the fixed groups, while in PFSA membranes three representative structure models are employed to estimate this average distance. After accounting for the cation activity coefficients in the membrane, the cation transport selectivity obtained with the ionic conductivity experimental approach agrees well with the selectivity obtained with the ED method. This work shows the importance of cation activity coefficients in the membrane phase in interpreting the membrane transport properties, and complements the proposed conductivity approach to characterize the counter-ion selectivity of ion exchange membranes.

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