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.

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 Long-lasting, monovalent-selective capacitive deionization electrodes

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Eric N. Guyes ◽  
Amit N. Shocron ◽  
Yinke Chen ◽  
Charles E. Diesendruck ◽  
Matthew E. Suss
Keyword(s):  
Water Treatment ◽  
Ionic Conductivity ◽  
Ion Selectivity ◽  
Single Step ◽  
Carbon Electrodes ◽  
Capacitive Deionization ◽  
Treatment Technologies ◽  
Porous Carbon Electrodes ◽  
Monovalent Ion ◽  
Direct Use

AbstractEmerging water purification applications often require tunable and ion-selective technologies. For example, when treating water for direct use in irrigation, often monovalent Na+ must be removed preferentially over divalent minerals, such as Ca2+, to reduce both ionic conductivity and sodium adsorption ratio (SAR). Conventional membrane-based water treatment technologies are either largely non-selective or not dynamically tunable. Capacitive deionization (CDI) is an emerging membraneless technology that employs inexpensive and widely available activated carbon electrodes as the active element. We here show that a CDI cell leveraging sulfonated cathodes can deliver long-lasting, tunable monovalent ion selectivity. For feedwaters containing Na+ and Ca2+, our cell achieves a Na+/Ca2+ separation factor of up to 1.6. To demonstrate the cell longevity, we show that monovalent selectivity is retained over 1000 charge–discharge cycles, the highest cycle life achieved for a membraneless CDI cell with porous carbon electrodes to our knowledge, while requiring an energy consumption of ~0.38 kWh/m3 of treated water. Furthermore, we show substantial and simultaneous reductions of ionic conductivity and SAR, such as from 1.75 to 0.69 mS/cm and 19.8 to 13.3, respectively, demonstrating the potential of such a system towards single-step water treatment of brackish and wastewaters for direct use in irrigation.

Zoospore Germination in Blastocladiella Emersonii

1972 ◽  
Vol 10 (2) ◽  
pp. 315-333
Author(s):  
D. R. SOLL ◽  
D. R. SONNEBORN
Keyword(s):  
Osmotic Shock ◽  
Cell Structure ◽  
Ion Selectivity ◽  
Choline Chloride ◽  
Exposure Period ◽  
Monovalent Cation ◽  
Continuous Exposure ◽  
Initial Exposure ◽  
Cell Conversion ◽  
High Concentrations

Zoospore germination in B. emersonii is accompanied by a series of abrupt, dramatic changes in cell structure. Membranes appear to be variously involved in many of these changes. Germination is subject to simple manipulations of the ionic environment: swimming zoospores can be maintained for long periods in the buffered CaCl2 solution into which they are initially released, whereas dilution into a solution containing KCl and MgCl2 in addition to CaCl2 results in rapid, semisynchronous germination of entire zoospore populations. The control of germination by ionic means has been characterized in the following ways: (a) Very brief (40 S to 2 min) exposure to GS, followed by replacement with buffered CaCl2 is as effective as continuous exposure in eliciting rapid germination of the entire zoospore population. (b) The effective component of GS is KCl: GS lacking KCl does not elicit rapid germination; conversely, buffered KCl alone is as effective as complete GS in eliciting germination. (c) Zoospore populations are sensitive to KCl concentration; as the KCl concentration is reduced, the proportion of cells which undergo rapid germination is also reduced. (d) At optimal concentration (5 x 10-2 M), the following salts are equally as effective as KCl in eliciting germination: KI, KBr, NaCl, CsCl, RbCl, and choline chloride. (e) At high concentrations (2.5-5 x 10-2 M), CaCl2 and MgCl2 elicit semi-synchronous conversion of zoospores to round cells, but only after sizeable delays (v. KCl). Conversion of round cells to germlings does not occur in MgCl2 and is enormously delayed in CaCl2; when formed, the germ tubes appear abnormal. (f) Monovalent cation salts of complex divalent anions (sulphate, tartrate, molybdate, tungstate) also exhibit decreased effectiveness (v. KCl) in eliciting germination. (g) The monovalent cation salts NH4Cl and LiCl, the divalent cation salt MnCl2, and the non-ionic compound sucrose are all ineffective in eliciting rapid germination. When in combination with an effective elicitor (KCl), LiCl totally blocks germination, MnCl2 and sucrose lead to significant delays in zoospore to round cell conversion, while NH4Cl has no effect on the population kinetics. (h) LiCl can block germination even when added after the completion of the otherwise sufficient early exposure period to GS (see (a) above). The blocking effect of LiCl can be almost completely reversed by replacement with KCl. On the basis of this characterization it is concluded that (1) rapid germination is not elicited simply by osmotic shock; rather, the cells are capable of responding to other (especially ionic) properties of their chemical environment; and (2) while brief exposure to KCl is sufficient to elicit germination, there are evidently other ion-sensitive steps occurring after the completion of this initial exposure period. Implications of the results in relation to the regular ion selectivity patterns found in other ion-dependent systems, the possible site(s) of action of the eliciting compounds, and the newly discovered ‘zoospore maintenance factor’ are discussed.

scholarly journals Counterion condensation or lack of solvation? Understanding the activity of ions in thin film block copolymer electrolytes

2020 ◽  
Vol 8 (31) ◽  
pp. 15962-15975
Author(s):  
Qi Lei ◽  
Ke Li ◽  
Deepra Bhattacharya ◽  
Jingya Xiao ◽  
Subarna Kole ◽  
...  
Keyword(s):  
Thin Film ◽  
Block Copolymer ◽  
Ionic Conductivity ◽  
Activity Coefficients ◽  
Counterion Condensation ◽  
Block Copolymer Electrolytes

Dissociation of ion charge pairs in block copolymer electrolytes and its relation to activity coefficients and normalized ionic conductivity.

Effect of Charge-balancing Species on Sm3+ Incorporation in Calcium Vanadinite

2015 ◽  
Vol 1744 ◽  
pp. 119-124
Author(s):  
M. R. Gilbert
Keyword(s):  
Experimental Approach ◽  
Secondary Phase ◽  
Monovalent Cation ◽  
Phase System ◽  
Secondary Phases ◽  
Good Potential ◽  
Phase Systems ◽  
Multi Phase ◽  
Charge Balancing ◽  
Static Lattice

ABSTRACTApatites are often seen as good potential candidates for the immobilization of halide-rich wastes. In particular, phosphate apatites have received much attention in recent years, however, their synthesis often produces complicated multi-phase systems, with a number of secondary phases forming [1.2]. Calcium vanadinite (Ca5(VO4)3Cl) demonstrates a much simpler phase system, with only a single Ca2V2O7 secondary phase which can easily be retarded by the addition of excess CaCl2. However, when doping with SmCl3 (as an inactive analogue for AnCl3) the Sm forms a wakefieldite (SmVO4) phase rather than being immobilized within the vanadinite, a result of having to form an energetically unfavourable Ca vacancy in order for the lattice to remain neutral overall. It has been postulated that charge-balancing the lattice via co-substitution of a monovalent cation will be less disfavoured and therefore help stabilise formation of a (Ca5-2xSmxAx)(VO4)3Cl solid solution (A = monovalent cation). This has been investigated using a combined modelling and experimental approach. Static lattice calculations performed using Li+, Na+ and K+ as charge-balancing species have shown the energy cost to be less than half that of charge-balancing via formation of a Ca vacancy. As a result, solid state synthesis of (Ca5-2xSmxLix)(VO4)3Cl, (Ca5−2xSmxNax)(VO4)3Cl and (Ca5-2xSmxKx)(VO4)3Cl solid solutions have been trialled, and analysis of the resulting products has shown a significant reduction in both the SmVO4 and Ca2V2O7 secondary phases across all dopant levels.

scholarly journals Monovalent Cation Permeation through the Connexin40 Gap Junction Channel

1997 ◽  
Vol 109 (4) ◽  
pp. 509-522 ◽  
Author(s):  
Dolores A. Beblo ◽  
Richard D. Veenstra
Keyword(s):  
Gap Junction ◽  
Single Channel ◽  
Ion Selectivity ◽  
Ion Pairs ◽  
Monovalent Cation ◽  
Chloride Salt ◽  
Monovalent Cations ◽  
Gap Junction Channels ◽  
Gap Junction Channel ◽  
Cation Radius

The unitary conductances and permeability sequences of the rat connexin40 (rCx40) gap junction channels to seven monovalent cations and anions were studied in rCx40-transfected neuroblastoma 2A (N2A) cell pairs using the dual whole cell recording technique. Chloride salt cation substitutions (115 mM principal salt) resulted in the following junctional maximal single channel current-voltage relationship slope conductances (γj in pS): CsCl (153), RbCl (148), KCl (142), NaCl (115), LiCl (86), TMACl (71), TEACl (63). Reversible block of the rCx40 channel was observed with TBA. Potassium anion salt γj are: Kglutamate (160), Kacetate (160), Kaspartate (158), KNO3 (157), KF (148), KCl (142), and KBr (132). Ion selectivity was verified by measuring reversal potentials for current in rCx40 gap junction channels with asymmetric salt solutions in the two electrodes and using the Goldman-Hodgkin-Katz equation to calculate relative permeabilities. The permeabilities relative to Li+ are: Cs+ (1.38), Rb+ (1.32), K+ (1.31), Na+ (1.16), TMA+ (0.53), TEA+ (0.45), TBA+ (0.03), Cl− (0.19), glutamate− (0.04), and NO3− (0.14), assuming that the monovalent anions permeate the channel by forming ion pairs with permeant monovalent cations within the pore thereby causing proportionate decreases in the channel conductance. This hypothesis can account for why the predicted increasing conductances with increasing ion mobilities in an essentially aqueous channel were not observed for anions in the rCx40 channel. The rCx40 effective channel radius is estimated to be 6.6 Å from a theoretical fit of the relationship of relative permeability and cation radius.

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