Ion-selective Properties Research Articles

Modeling of nanochannels in synthetic membranes

The behavior of a diluted electrolyte in a system of joint microchannel and nanochannel with charged dielectric walls under the action of external potential difference and external pressure is investigated numerically. The surface charge on the nanochannel walls prevents the ions of corresponding polarity from passing through it. Consequently, the system in question acquires ion-selective properties and can, under certain assumptions, be viewed as a fragment of an ion-selective membrane, including one synthesized by creating nanopores in a dielectric material. Such systems are used in experiments to control the movement of charged particles through concentration polarization. The objective of the work is to investigate the influence of a single pore on electrolyte flow and the possibilities to control that flow by changing the geometric and physical properties of the pore. The investigation relies on the specially developed simplified models based on cross-section-averaged Nernst-Planck, Poisson and Stokes equations that are subsequently reduced to a single nonlinear differential equation. The simplified models allow identifying the impact of different physical mechanisms of electrolyte movement: pressure-based (generated by the external mechanical action) and electroosmotic (generated by the electric field). A finite-difference method with semi-implicit time integration is used for the numerical solution of equations. It has been found that the behavior of the system qualitatively matches the behavior of a cell based on a non-ideally-selective ion-exchange membrane. In particular, the model correctly predicts the underlimiting and limiting electric current regimes, as well as vortex formation near the nanochannel inlet due to concurrency between electrolyte movement mechanisms. The proposed models can be extended to describe a channel with arbitrary geometry and an electrolyte with arbitrary number of charged species.

Prussian blue analogue based integrated membrane electrodes for desalination and selective removal of ammonium ions in a rocking-chair capacitive deionization

Capacitive deionization (CDI) technology has shown significant promise in selective removal of nutrients from wastewater. In this study, a novel inorganic integrated membrane electrodes (i-IMEs) were developed with Prussian blue analogues (PBAs), cation insertion materials, as a coating on activated carbon (AC) electrode to replace cation exchange membrane. When the i-IMEs were operated in a rocking-chair CDI (RCDI) system for continuous desalination, a high specific adsorption capacity (SAC) of 42.7 mg/g and an impressive charge efficiency of 71.6 % were obtained. Moreover, taking advantage of PBAs' ion-selective properties for monovalent cations especially NH4+, this IME-RCDI achieved highly selective removal of cations compared to a RCDI with bare AC electrodes. The selectivity coefficients (Si/j) of NH4+ to divalent cations (such as Ca2+) and monovalent cations (such as Na+) were determined to be 2.15 and 1.95, respectively. These values are much higher than those obtained for AC electrodes, which were 0.3 and 1.07, respectively. Overall, this work demonstrates that the incorporation of PBAs in the i-IME-RCDI configuration offers superior desalination performance and selective removal capabilities for specific ions such as NH4+.

Effect of the stability of 1,3-bis(diphenylphosphoryl)-2-oxapropane complexes on the separation of lanthanide ions and their detection.

Phosphoryl podands of neutral type with a flexible ethylene glycol chain and diphenylphosphorylmethyl end groups are known for their complexation properties towards various cations. In this work, the complexation process between 1,3-bis(diphenylphosphoryl)-2-oxapropane (L) and lanthanide ions was studied. Namely, the stability constants of lanthanide complexes with L in acetonitrile were estimated by the method of spectrophotometric titration. It was found that the stability constants of Ln3+ complexes with L increase in the lanthanide series, which is consistent with the extraction and ion-selective properties of L. The extraction ability of L and this ligand in the presence of ionic liquids (ILs) such as methyltrioctylammonium nitrate (MTOAN) and bis[(trifluoromethyl)sulfonyl]imide 1-butyl-3-methylimidazolium (C4mimTf2N) was studied. It was found that in the presence of ILs, L extracts the elements of the yttrium subgroup of lanthanides much better than those of the cerium subgroup: SFLu/Ce(L-MTOAN) = 2.29; SFLu/Ce(L-C4mimTf2N) = 110.38. The use of the L-C4mimTf2N mixture in the processes of lanthanide separation into subgroups is much more efficient than the use of L without the addition of ILs or the use of the L-MTOAN mixture. The ion-selective properties of L towards Ln3+ ions were studied. Podand L exhibits potentiometric selectivity to Lu3+ ions.

Numerical investigation of electroconvection transport of polymer electrolyte solutions on a perfectly selective membrane

Ion-selective properties are widely used in desalination, energy storage in batteries, electroplating, etc. This paper presents a direct numerical simulation of electroconvective flow (ECF) in electrolyte solutions on a perfectly selective membrane surface (PSMS), considering fluid viscoelasticity and Joule heating. Different polymer elasticities on PSMS mass transfer are investigated in detail, including the instantaneous evolution, morphology structure, ion transport mechanism, and global assessment. The results reveal that polymer electrolytes promote the formation of small vortices (low flux) and merge into a reduced number of large vortex structures (high flux). The crown and spike morphology of charge density and the mushroom-like morphology of salt concentration tend to be cloudier in the polymer electrolytes, with a marked decrease in injection height compared to that of Newtonian fluid. The streaks of strong polymer stretching reduce fluctuations with increased interface impedance in the extended space charge layer (ESCL), described by the first normal stress difference (N1) and the local Weissenberg number (Wil). The cumulative distribution function (CDF) and power spectral density (PSD) are characterized by an effective enhancement of the system stability, reducing the ion mass transfer and reaching a maximum of 45 %. The relevant results also facilitate an improved understanding of the complex nature of polymeric fluids in electroosmotic flow.

Asymmetry and Ion Selectivity Properties of Bacterial Channel NaK Mutants Derived from Ionotropic Glutamate Receptors

Ionotropic glutamate receptors are ligand-gated cation channels that play essential roles in the excitatory synaptic transmission throughout the central nervous system. A number of open-pore structures of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic-acid (AMPA)-type glutamate receptors became available recently by cryo-electron microscopy (cryo-EM). These structures provide valuable insights into the conformation of the selectivity filter (SF), the part of the ion channel that determines the ion selectivity. Nonetheless, due to the moderate resolution of the cryo-EM structures, detailed information such as ion occupancy of monovalent and divalent cations as well as positioning of the side-chains in the SF is still missing. Here, in an attempt to obtain high-resolution information about glutamate receptor SFs, we incorporated partial SF sequences of the AMPA and kainate receptors into the bacterial tetrameric cation channel NaK, which served as a structural scaffold. We determined a series of X-ray structures of NaK-CDI, NaK-SDI and NaK-SELM mutants at 1.42–2.10 Å resolution, showing distinct ion occupation of different monovalent cations. Molecular dynamics (MD) simulations of NaK-CDI indicated the channel to be conductive to monovalent cations, which agrees well with our electrophysiology recordings. Moreover, previously unobserved structural asymmetry of the SF was revealed by the X-ray structures and MD simulations, implying its importance in ion non-selectivity of tetrameric cation channels.

Complexing and Ion-Selective Properties of Some Phosphoryl Podands towards Cadmium Cation

Complexing and Ion-Selective Properties of Some Phosphoryl Podands towards Cadmium Cation

Hierarchical MXene/Polypyrrole-Decorated Carbon Nanofibers for Asymmetrical Capacitive Deionization

Membrane capacitive deionization (MCDI) has emerged as a promising electric-field-driven technology for brackish water desalination and specific salt or charged ion separation. The use of carbon-based or pseudocapacitive materials alone for MCDI usually suffers from the drawbacks of low desalination capacity and poor cycling stability due to their limited accessible adsorption sites and obstructed charge-carrier diffusion pathways. Therefore, developing a hybrid electrode material with multiple charge storage mechanisms and continuous electron/ion transport pathways that can synergistically improve its specific capacitance and cycling durability has currently become one of the most critical technical demands. Herein, we developed a novel hierarchically architectured hybrid electrode by first spinning MXene into polyacrylonitrile (PAN)-based carbon nanofibers (MCNFs) to obtain a highly conductive carbon nanocomposite framework. The excellent spatial support structure can effectively prevent the dense packing of Cl-- and DBS--doped polypyrrole (PPy) molecular chains during the following electrodeposition process, which not only ensures the efficient transport of electrons in the continuous hybrid carbon nanofibrous skeleton but also provides abundant accessible sites for ion adsorption and insertion. The obtained self-supporting membrane electrodes (MCNF@PPy+Cl- and MCNF@PPy+DBS-) have the advantages of outstanding specific capacitance (318.4 and 153.9 F/g, respectively), low charge transfer resistance (10.0 and 5.3 Ω, respectively), and excellent cycling performance (78% and 90% capacitance retention ratios, respectively, after 250 electrochemical cycles). Furthermore, the asymmetrical membrane electrodes showed a superior desalination capacity of 91.2 mg g-1 in 500 mg/L NaCl aqueous solution and obvious divalent ion (Ca2+, Mg2+) selective adsorption properties in high-salt water from the cooling towers of thermal power plants.

Fine-tuning of carbon nanostructures/alginate nanofiltration performance: Towards electrically-conductive and self-cleaning properties

Electrically-conductive membranes became the center of attention owing to their enhanced ion selectivity and self-cleaning properties. Carbon nanostructures (CNS) attain high electrical conductivity, and fast water transport. Herein, we adopt a water-based, simple method to entrap CNS within Alginate network to fabricate self-cleaning nanofiltration membranes. CNS are embedded into membranes to improve the swelling/shrinkage resistivity, and to achieve electrical-conductivity. The CaAlg PEG-formed pores are tuned by organic-inorganic network via silane crosslinking. Flux/rejection profiles of Na2SO4 are studied/optimized in reference to fabrication parameters. 90% Na2SO4 rejection (7 LMH) is achieved for silane-CaAlg200-10% CNS membranes. Membranes exhibit outstanding electrical conductivity (∼2858 S m−1), which is attractive for fouling control. CaAlg/CNS membranes are tested to treat dye/saline water via two-stage filtration, namely, dye/salt separation and desalination. A successful dye/salt separation is achieved at the first stage with a rejection of 100%-RB and only 3.1% Na2SO4, and 54% Na2SO4 rejection in the second stage.

Thermodynamic and Kinetic Analyses of Ion Intercalation/Deintercalation Using Different Temperatures on NiHCF Electrodes for Battery Electrode Deionization.

Prussian blue analogues are used in electrochemical deionization due to their cation sorption capabilities and ion selectivity properties. Elucidating the fundamental mechanisms underlying intercalation/deintercalation is important for the development of ion-selective electrodes. We examined the thermodynamic and kinetic properties of nickel hexacyanoferrate electrodes by studying different temperatures effects on intercalation/deintercalation with monovalent ions (Li+, Na+, K+, and NH4+) relevant to battery electrode deionization applications. Higher temperatures reduced the interfacial charge transfer resistance and increased the diffusion coefficient of cations in the solid material. Ion transport in the solid material, rather than interfacial charge transfer, was found to be the rate-controlling step, as shown by higher activation energies for ion transport (e.g., 31 ± 3 kJ/mol for K+) than for interfacial charge transfer (5 ± 1 kJ/mol for K+). The largest increase in cation adsorption capacity with temperature was observed for NH4+ (28.1% from 15 to 75 °C) due to its smallest activation energy. These results indicate that ion hydration energy determines the intercalation potential and activation energies of ion transport in solid material control intercalation/deintercalation rate. Together with the endothermic behavior of deintercalation and exothermic behavior of intercalation, the higher operating temperature results in improvement of ion adsorption capacity depending on specific cations.

Ion behavior in the selectivity filter of HCN1 channels

Hyperpolarization-activated cyclic-nucleotide gated channels (HCNs) are responsible for the generation of pacemaker currents (If or Ih) in cardiac and neuronal cells. Despite the overall structural similarity to voltage-gated potassium (Kv) channels, HCNs show much lower selectivity for K+ over Na+ ions. This increased permeability to Na+ is critical to their role in membrane depolarization. HCNs can also select between Na+ and Li+ ions. Here, we investigate the unique ion selectivity properties of HCNs using molecular-dynamics simulations. Our simulations suggest that the HCN1 pore is flexible and dilated compared with Kv channels with only one stable ion binding site within the selectivity filter. We also observe that ion coordination and hydration differ within the HCN1 selectivity filter compared with those in Kv and cyclic-nucleotide gated channels. Additionally, the C358T mutation further stabilizes the symmetry of the binding site and provides a more fit space for ion coordination, particularly for Li+.

Synthesis and Ion-Selective Properties of the MoO2/C Composite

Synthesis and Ion-Selective Properties of the MoO2/C Composite

Investigation of Some Ion Selective and Water Repellent Properties of Carbazole Based Polymers

A polymer derived from poly-9-bis[4-(thiophen-3,4-yloxy)biphenyl)]-9H-carbazole containing a carbazole and thiophene group, abbreviated as B2, was synthesized via the oxidation method by using FeCl3 as an oxidant. Additionally, P(B2) was synthesized and coated onto an ITO–glass surface via electrochemical oxidative polymerization. UV spectra of these polymers and their metal complexes (like Fe2+, Cd2+, Hg2+, Pb2+) were recorded in DMSO solutions, and then their UV spectra depending on the concentration were recorded. According to the results, when the concentration was rising, the absorbance peak intensity increased gradually for B2. Also, for P(B2), the absorbance peak followed a fluctuating course. The photo images of its some metal complexes were recorded under UV light. Resultantly, B2 polymer was determined to be selective against Fe2+ ion and it can be said that B2 could be used as fluorescence Fe2+ ion probe. Finally, contact angle (CA) measurements of B2 and P(B2) were realized and, according to the recorded photo images it can be said that B2 had more hydrophobic property than P(B2).

Influence of Microdefect Size on Corrosion Behavior of Epoxy-Coated Rebar for Application in Seawater-Mixed Concrete

Corrosion behavior of epoxy-coated rebar with different size of microdefects in uncarbonated/carbonated simulated pore solution (U/CSPS) of seawater concrete was investigated. Specimens in both solutions underwent two stages of corrosion, according to the electrochemical impedance spectroscopy (EIS) response. The initial stage was the extension of corrosion. The second stage was dominated by the diffusion process, due to the corrosion products blocking the defects and hindering the transportation of the reaction matter. Local electrochemical impedance spectroscopy (LEIS), scanning vibrating electrode technique (SVET) measurements and the observation of corrosion products indicated that 50 μm might be the threshold, because the corrosion of specimens with defects bigger than 50 μm in diameter was significantly more severe. Crevice corrosion was identified to occur in the experiments. The corrosion products of specimens in USPS and CSPS were mainly Fe3O4 and FeOOH, respectively. α-FeOOH and β-FeOOH exhibited an anion ion-selective property in the corrosion process, which induced crevice corrosion in CSPS. In particular, it is contended herein that Fe3O4 has the cation ion-selective property to protect the substrate in USPS.

Solubilization, purification, and functional reconstitution of human ROMK potassium channel in copolymer styrene-maleic acid (SMA) nanodiscs

Expression, purification, and functional reconstitution of mammalian ion channels are often challenging. Heterologous expression of mammalian channels in bacteria can be advantageous due to unrelated protein environment and the lack of risk of copurification of endogenous proteins, e.g., accessory channel subunits that can influence the channel activity. Also, direct recording of channel activity could be challenging due to their intracellular localization like in the case of mitochondrial channels. The activity of purified channels can be characterized at the single-molecule level by electrophysiological techniques, such as planar lipid bilayers (PLB). In this work, we describe a simple approach to accomplish PLB recording of the activity of single renal outer medullary potassium channels ROMK expressed in E. coli. We focused on the ROMK2 isoform that is present at low levels in the mitochondria and can be responsible for mitoKATP activity. We screened for the best construct to express the codon-optimized ROMK proteins with a 6xHis tag for protein purification. The strategy involved the use of optimal styrene-maleic acid (SMA) copolymer, which forms so-called polymer nanodiscs, to solubilize and purify ROMK-containing SMA lipid particles (SMALPs), which were amenable for fusion with PLB. Reconstituted ROMK channels exhibited ion selectivity, rectification, and pharmacological properties, which are in agreement with previous work on ROMK channels.

Quantification of the ion transport mechanism in protective polymer coatings on lithium metal anodes.

Protective Polymer Coatings (PPCs) have been proposed to protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology. However, the ion transport mechanism in PPCs remains unclear. Specifically, the degree of polymer swelling in the electrolyte and the influence of polymer/solvent/ion interactions are never quantified. Here we use poly(acrylonitrile-co-butadiene) (PAN–PBD) with controlled cross-link densities to quantify how the swelling ratio of the PPC affects conductivity, Li+ ion selectivity, activation energy, and rheological properties. The large difference in polarities between PAN (polar) and PBD (non-polar) segments allows the comparison of PPC properties when swollen in carbonate (high polarity) and ether (low polarity) electrolytes, which are the two most common classes of electrolytes. We find that a low swelling ratio of the PPC increases the transference number of Li+ ions while decreasing the conductivity. The activation energy only increases when the PPC is swollen in the carbonate electrolyte because of the strong ion–dipole interaction in the PAN phase, which is absent in the non-polar PBD phase. Theoretical models using Hansen solubility parameters and a percolation model have been shown to be effective in predicting the swelling behavior of PPCs in organic solvents and to estimate the conductivity. The trade-off between conductivity and the transference number is the primary challenge for PPCs. Our study provides general guidelines for PPC design, which favors the use of non-polar polymers with low polarity organic electrolytes.

Mechanisms of activation and desensitization of full-length glycine receptor in lipid nanodiscs

Glycinergic synapses play a central role in motor control and pain processing in the central nervous system. Glycine receptors (GlyRs) are key players in mediating fast inhibitory neurotransmission at these synapses. While previous high-resolution structures have provided insights into the molecular architecture of GlyR, several mechanistic questions pertaining to channel function are still unanswered. Here, we present Cryo-EM structures of the full-length GlyR protein complex reconstituted into lipid nanodiscs that are captured in the unliganded (closed), glycine-bound (open and desensitized), and allosteric modulator-bound conformations. A comparison of these states reveals global conformational changes underlying GlyR channel gating and modulation. The functional state assignments were validated by molecular dynamics simulations, and the observed permeation events are in agreement with the anion selectivity and conductance of GlyR. These studies provide the structural basis for gating, ion selectivity, and single-channel conductance properties of GlyR in a lipid environment.

Monovalent/Divalent salts separation via thin film nanocomposite nanofiltration membrane containing aminated TiO2 nanoparticles

Nanofiltration is widely used in separation of ions with different sizes and charges. However, thin-film composite nanofiltration membrane is hard to reach satisfied selectivity for monovalent ions from divalent ions. In this study, polyamide thin film nanocomposite (TFN) nanofiltration membranes were prepared via interfacial polymerization of piperazine and trimesoyl chloride on a PES substrate by incorporation of aminated titanium dioxide (APTES-TiO2). Surface morphology, roughness of the TFN membranes with varied concentration of aminated TiO2 were tested by SEM, AFM and Zeta analysis. The results showed membrane containing 0.3(w/v%) amino-modified titanium dioxide with ion-selective properties had greatly improved pure water flux while the Na2SO4 rejection keeps at a relative high level (>95%). For the separation of single salt solution, 0.3(w/v%) TFN has a higher rejection for sodium chloride (23.2%) and sodium sulfate (99.7%). For monovalent/divalent mixed salt solution has a separation factor of 477.89 in terms of chloride ion (Cl−) and sulfate (SO42−) in the mixed solution with a salt concentration ratio of 1:19, which was higher than that of the conventional commercial NF membranes, such as Desal-DL, NF 270. This method provides the possibility of recovering concentrated brine and industrial separation of monovalent and divalent ions.

Effect of the [2-(diphenylphosphorylmethoxy)phenyl]diphenylphosphine oxide derivative structures on the extraction and ion-selective properties toward rare-earth elements

The effect of structures of the derivatives of [2-(diphenylphosphorylmethoxy)phenyl]-diphenylphosphine oxide (L1) on the complexation properties toward rare-earth elements (REE) was studied. A new structural analogue of L1, isopropyl 2-(diphenylphosphorylmethoxy)benzoate (L3), was synthesized. The extraction of REE by the carboxylated podand L3 in a 1,1,7-trihydrododecafluoroheptanol—water system with the HNO3 concentration varied in a range from 1 to 6 mol L−1 was studied. The stability constants of the neodymium(iii) and erbium(iii) nitrate complexes with L3 and 1-(methoxydiphenylphosphoryl)-2-diphenylphosphoryl-4-ethylbenzene (L2) and of lutetium(iii) nitrate and chloride complexes with L2 in 1,1,7-trihydrododecafluorheptanol were determined. The properties of the membranes of the ion-selective electrodes based on L1, L2, and L3 toward REE cations were tested. The crystal structures of L3 and [NdL3(NO3)3(DMSO)2] were determined by X-ray diffraction analysis.

Synthesis and Ion-Selective Properties of (NH4)xV2O5 · nH2O

Formation conditions were studied for compounds of hydrated vanadium oxide $${{\left( {{\text{N}}{{{\text{H}}}_{{\text{4}}}}} \right)}_{x}}{\text{V}}_{y}^{{{\text{4}} + }}{\text{V}}_{{{\text{2}} - y}}^{{{\text{5}} + }}{{{\text{O}}}_{{\text{5}}}} \cdot n{{{\text{H}}}_{{\text{2}}}}{\text{O}}$$ (0.24 ≤ х ≤ 0.36, 0.24 ≤ y ≤ 0.36) prepared by hydrolytic deposition with vanadyl sulfate used as the acidifier. The compound $${{{\text{(N}}{{{\text{H}}}_{{\text{4}}}}{\text{)}}}_{{{\text{0}}{\text{.36}}}}}{\text{V}}_{{{\text{0}}{\text{.36}}}}^{{{\text{4}} + }}{\text{V}}_{{{\text{1}}{\text{.64}}}}^{{{\text{5}} + }}{{{\text{O}}}_{{\text{5}}}} \cdot {\text{0}}.7{{{\text{H}}}_{{\text{2}}}}{\text{O}}$$ with the highest content of tetravalent vanadium was prepared when the molar ratio is 0.1 ≤ NH4VO3/VOSO4 · 3H2O ≤ 1.0. $${{{\text{(N}}{{{\text{H}}}_{{\text{4}}}}{\text{)}}}_{{{\text{0}}{\text{.1}}}}}{\text{V}}_{{{\text{0}}{\text{.1}}}}^{{{\text{4}} + }}{\text{V}}_{{{\text{1}}{\text{.9}}}}^{{{\text{5}} + }}{{{\text{O}}}_{{\text{5}}}} \cdot {\text{1}}.4{{{\text{H}}}_{{\text{2}}}}{\text{O,}}$$ which has the least content of tetravalent vanadium, was prepared by a sol–gel process combined with ion exchange. The prepared ammoniated compounds based on hydrated vanadium oxide show a potential for use as an active material in solid-phase ion-selective electrodes. The electrodes based on $${{{\text{(N}}{{{\text{H}}}_{{\text{4}}}}{\text{)}}}_{{{\text{0}}{\text{.36}}}}}{\text{V}}_{{{\text{0}}{\text{.36}}}}^{{{\text{4}} + }}{\text{V}}_{{{\text{1}}{\text{.64}}}}^{{{\text{5}} + }}{{{\text{O}}}_{{\text{5}}}} \cdot {\text{0}}.7{{{\text{H}}}_{{\text{2}}}}{\text{O}}$$ and $${{{\text{(N}}{{{\text{H}}}_{{\text{4}}}}{\text{)}}}_{{{\text{0}}{\text{.1}}}}}{\text{V}}_{{{\text{0}}{\text{.1}}}}^{{{\text{4}} + }}{\text{V}}_{{{\text{1}}{\text{.9}}}}^{{{\text{5}} + }}{{{\text{O}}}_{{\text{5}}}} \cdot {\text{1}}.4{{{\text{H}}}_{{\text{2}}}}{\text{O}}$$ are selective toward ammonium cations in the range of concentrations 1 ≤ $${\text{p}}{{C}_{{{\text{NH}}_{{\text{4}}}^{ + }}}}$$ ≤ 4 for working solution acidities of 4 ≤ рH ≤ 7 and 5 ≤ рH ≤ 6 with the slope 55 and 50 $${\text{mV/p}}{{C}_{{{\text{NH}}_{{\text{4}}}^{ + }}}},$$ respectively. Selectivity coefficients in the series of singly, doubly, and triply charged cations were determined for (NH4)xV2O5 · nH2O electrodes.

Development of surface-sulfonated graft anion-exchange membranes with monovalent ion selectivity and antifouling properties for electromembrane processes

This communication describes the development of anion-exchange membrane (AEM) with a modified surface possessing monovalent ion selectivity and antifouling properties. Modified AEMs series was obtained by the formation of an oppositely-charged thin layer utilizing the surface sulfonation of the grafted AEMs. The creation of the interface layer leads to a significant increase in the Cl/SO4 selectivity and the appearance of humic acid sorption resistance. The best surface-sulfonated anion-exchange membrane (s-AEM) has a high ionic conductivity of 11.2 mS cm−1 and high Cl/SO4 selectivity up to 6.4 in electrodialysis. The sulfonated layer was characterized by IR spectroscopy and electron microscopy. The relationship between the structure and thickness of the cation-exchange surface layer and the observed changes in membrane transport properties such as diffusion permeability, ionic conductivity, potentiometric transport numbers, and current-voltage characteristics are discussed. It was shown that the Cl/SO4 selectivity of s-AEM in the desalination process depends on the current density. The obtained data were successfully interpreted using a mathematical model based on the concept of the bipolar structure of the s-AEM surface layer and diffusion control of anion transport through it.