Recent developments on ion-exchange membranes and electro-membrane processes

Design Strategies for High-Performance Aqueous Zn/Organic Batteries

Organic electroactive compounds are attractive to serve as the cathode materials of aqueous zinc-ion batteries (ZIBs) because of their resource renewability, environmentally friendliness and structural diversity. Up to now, various organic electrode materials have been developed and different redox mechanisms are observed in aqueous Zn/organic battery systems. In this Minireview, we present the recent developments in the energy storage mechanisms and design of the organic electrode materials of aqueous ZIBs, including carbonyl compounds, imine compounds, conductive polymers, nitronyl nitroxides, organosulfur polymers and triphenylamine derivatives. Furthermore, we highlight the design strategies to improve their electrochemical performance in the aspects of specific capacity, output voltage, cycle life and rate capability. Finally, we discuss the challenges and future perspectives of aqueous Zn/organic batteries.

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement

Nowadays, ion-exchange membranes have numerous applications in water desalination, electrolysis, chemistry, food, health, energy, environment and other fields. All of these applications require high selectivity of ion transfer, i.e., high membrane permselectivity. The transport properties of ion-exchange membranes are determined by their structure, composition and preparation method. For various applications, the selectivity of transfer processes can be characterized by different parameters, for example, by the transport number of counterions (permselectivity in electrodialysis) or by the ratio of ionic conductivity to the permeability of some gases (crossover in fuel cells). However, in most cases there is a correlation: the higher the flux density of the target component through the membrane, the lower the selectivity of the process. This correlation has two aspects: first, it follows from the membrane material properties, often expressed as the trade-off between membrane permeability and permselectivity; and, second, it is due to the concentration polarization phenomenon, which increases with an increase in the applied driving force. In this review, both aspects are considered. Recent research and progress in the membrane selectivity improvement, mainly including a number of approaches as crosslinking, nanoparticle doping, surface modification, and the use of special synthetic methods (e.g., synthesis of grafted membranes or membranes with a fairly rigid three-dimensional matrix) are summarized. These approaches are promising for the ion-exchange membranes synthesis for electrodialysis, alternative energy, and the valuable component extraction from natural or waste-water. Perspectives on future development in this research field are also discussed.

Transport and Electrochemical Characteristics of CJMCED Homogeneous Cation Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions

Recently developed and produced by Hefei Chemjoy Polymer Material Co. Ltd., homogeneous CJMC-3 and CJMC-5 cation-exchange membranes (CJMCED) are characterized. The membrane conductivity in NaCl, Na2SO4, and CaCl2 solutions, permeability in respect to the NaCl and CaCl2 diffusion, transport numbers, current-voltage curves (CVC), and the difference in the pH (DpH) of the NaCl solution at the desalination compartment output and input are examined for these membranes in comparison with a well-studied commercial Neosepta CMX cation-exchange membrane produced by Astom Corporation, Japan. It is found that the conductivity, CVC (at relatively low voltages), and water splitting rate (characterized by DpH) for both CJMCED membranes are rather close to these characteristics for the CMX membrane. However, the diffusion permeability of the CJMCED membranes is significantly higher than that of the CMX membrane. This is due to the essentially more porous structure of the CJMCED membranes; the latter reduces the counterion permselectivity of these membranes, while allowing much easier transport of large ions, such as anthocyanins present in natural dyes of fruit and berry juices. The new membranes are promising for use in electrodialysis demineralization of brackish water and natural food solutions.

Electrodialysis Applications in Wastewater Treatment for Environmental Protection and Resources Recovery: A Systematic Review on Progress and Perspectives

This paper presents a comprehensive review of studies on electrodialysis (ED) applications in wastewater treatment, outlining the current status and the future prospect. ED is a membrane process of separation under the action of an electric field, where ions are selectively transported across ion-exchange membranes. ED of both conventional or unconventional fashion has been tested to treat several waste or spent aqueous solutions, including effluents from various industrial processes, municipal wastewater or salt water treatment plants, and animal farms. Properties such as selectivity, high separation efficiency, and chemical-free treatment make ED methods adequate for desalination and other treatments with significant environmental benefits. ED technologies can be used in operations of concentration, dilution, desalination, regeneration, and valorisation to reclaim wastewater and recover water and/or other products, e.g., heavy metal ions, salts, acids/bases, nutrients, and organics, or electrical energy. Intense research activity has been directed towards developing enhanced or novel systems, showing that zero or minimal liquid discharge approaches can be techno-economically affordable and competitive. Despite few real plants having been installed, recent developments are opening new routes for the large-scale use of ED techniques in a plethora of treatment processes for wastewater.

Intensification of nickel recovery from water using an electrically driven hybrid process: continuous electropermutation

Process intensification through the combined use of electrodialysis (ED) and ion-exchange resin (IER) hybrid process, called continuous electropermutation (CEP), was employed to remove Ni(II) cations from water. To carry out this process, Amberjet 1200 H cation-exchange resin was introduced into the feed compartment of the ED cell. The applied electrical field improves the mobility of species and ensures a continuous resin activation which is a main drawback in IER process. Furthermore, the IER incorporated in the ED cell enhances the conductivity of the feed water, therefore it extends the range of ED which could be applied for the recovery of ions from very low concentration wastewaters. The effects of some factors such as the type of regenerating electrolyte, current density, quantity of resin incorporated in the conducting space and concentration of Ni(II) at the inlet were investigated. The efficiency of CEP and ED for Ni(II) removal was expressed in terms of recovery rate and concentration factor. In CEP process, recovery rates of 99% were found with a 40 ppm Ni(II) concentration and an applied current density of 2 mA.cm^-2 resulting in an outlet Ni(II) concentration lower than 1 ppm, against 73.69% in conventional ED. Moreover, in CEP Ni(II) cation was recovered in receiver compartment more than the feed solution with concentration factor more than 10 against 0.39 in ED. On the other hand, the voltage of ED cell was found to increase due to the lower conductivity in the feed compartment compared with that of CEP. In CEP, the highest concentration factor was found at an applied current density of 2.7 mA.cm^-2 which reached 41.26. Finally, with increasing Ni(II) feed inlet concentration, there was a trade-off between obtaining a high Ni(II) concentration in the receiver compartment and a low Ni(II) concentration at the outlet of feed compartment.

Heterogeneous ion exchange membranes based on thermoplastic polyurethane (TPU): effect of PSS/DVB resin on morphology and electrodialysis

In this research, novel heterogeneous cation exchange membranes based on thermoplastic polyurethane (TPU) have been prepared by the solution casting technique. The effects of incorporation level of sulfonated polystyrene divinyl-benzene (PSS/DVB) resin on water uptake, ion exchange capacity, membrane potential and salt extraction have been elucidated. Morphological and water uptake studies suggested a two-phase heterogeneous membrane morphology owing to the presence of hard and soft segments in the TPU backbone and swelling of PSS/DVB particles. This morphology was shifted to a semi-gelled morphology throughout the membrane bulk when resin loading exceeded 50 wt%. The physically cross-linked hard segments in the TPU backbone ensured a compact membrane morphology and prevented the formation of water channels. The membrane potential showed that increasing the resin content increased the membrane transport number (max. 0.95) up to 50 wt% resin loading and beyond this, the transport number started decreasing showing a pronounced effect of voids and water flow channels developing on excessive swelling. The permselectivity reached a maximum (up to 0.92) and salt extraction values also increased (by varying voltage) up to 50 wt% loading and started decreasing beyond this optimum content. This study shows successful development of low-cost heterogeneous cation exchange membranes based on TPU with acceptable electrochemical properties.

Voltammetry at Hexamethyl-P-Terphenyl Poly(Benzimidazolium) (HMT-PMBI)-Coated Glassy Carbon Electrodes: Charge Transport Properties and Detection of Uric and Ascorbic Acid

We describe the voltammetric behavior of an anion-exchange membrane, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI). The anion-exchange properties of HMT-PMBI chemically modified electrodes were investigated using K4Fe(CN)6 and K2IrCl6 as redox probes. The permselectivity properties of HMT-PMBI chemically modified electrodes were ascertained using tris(2-2')bipyridyl-ruthenium(II) chloride Ru(bpy)32+. Cyclic voltammetry and chronoamperometry were utilized to extract parameters such as the concentration of the redox mediators inside the films and the apparent diffusion coefficients. We found the concentration of K4Fe(CN)6 and K2IrCl6 redox species within HMT-PMBI-coated films to be on the order of 0.04-0.1 mol·dm-3, and values of Dapp ca. 10-10-10-9 cm2·s-1. To evaluate the possibility of using such a polymer coating in electroanalysis, HMT-PMBI-modified electrodes were utilized for the voltammetric detection of uric acid in artificial urine, Surine® and ascorbic acid in Vitamin C samples. The results showed that HMT-PMBI-coated electrodes can detect uric acid in Surine® with a limit of detection (LoD) of 7.7 µM, sensitivity of 0.14 µA·µM-1·cm-2, and linear range between 5 μM and 200 μM, whereas for Vitamin C tablets, the LoD is 41.4 µM, the sensitivity is 0.08 µA·µM-1·cm-2, and the linear range is between 25 μM and 450 μM.

Alkaline all iron redox flow battery with a polyethylene/poly(styrene-co-divinylbenzene) interpolymer cation-exchange membrane

This work describes the suitability of a polyethylene styrene–DVB based interpolymer cation exchange membrane for use in a highly alkaline redox flow battery (RFB) with a [Fe(TEA)OH]²⁻/[Fe(TEA)OH]⁻ and Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox couple. The alkaline stability of the membrane for 1440 h was evaluated in 5 N NaOH containing a 200 mM Fe(CN)₆³⁻/Fe(CN)₆⁴⁻ redox couple. It was assessed according to the changes in the electrochemical and physicochemical properties. The performance of the membrane was evaluated over 40 charge–discharge cycles at a current density of 5 mA cm⁻² current in a designed RFB cell. The obtained average coulombic efficiency (CE) was 92%, energy efficiency (EE) was 75%, voltage efficiency (VE) was 82% and volumetric efficiency was 34%. Under identical experimental conditions, the values of CE, EE, and VE for Nafion®-112 were 99%, 75%, and 76%, respectively. These results indicate the suitability of the polyethylene styrene–DVB based interpolymer cation exchange membrane for use in an alkaline RFB.

A polyethylene styrene–DVB interpolymer cation exchange membrane is reported for use in a highly alkaline all iron redox flow battery.

Concentration Dependencies of Diffusion Permeability of Anion-Exchange Membranes in Sodium Hydrogen Carbonate, Monosodium Phosphate, and Potassium Hydrogen Tartrate Solutions

The concentration dependencies of diffusion permeability of homogeneous (AMX-Sb and AX) and heterogeneous (MA-41 and FTAM-EDI) anion-exchange membranes (AEMs) is obtained in solutions of ampholytes (sodium bicarbonate, NaHCO₃; monosodium phosphate, NaH₂PO₄; and potassium hydrogen tartrate, KHT) and a strong electrolyte (sodium chloride, NaCl). It is established that the diffusion permeability of AEMs increases with dilution of the ampholyte solutions, while it decreases in the case of the strong electrolyte solution. The factors causing the unusual form of concentration dependencies of AEMs in the ampholyte solutions are considered: (1) the enrichment of the internal AEM solution with multiply charged counterions and (2) the increase in the pore size of AEMs with dilution of the external solution. The enrichment of the internal solution of AEMs with multiply charged counterions is caused by the Donnan exclusion of protons, which are the products of protolysis reactions. The increase in the pore size is conditioned by the stretching of the elastic polymer matrix due to the penetration of strongly hydrated anions of carbonic, phosphoric, and tartaric acids into the AEMs.

Ionizing Radiation for Preparation and Functionalization of Membranes and Their Biomedical and Environmental Applications

The use of ionizing radiation processing technologies has proven to be one of the most versatile ways to prepare a wide range of membranes with specific tailored functionalities, thus enabling them to be used in a variety of industrial, environmental, and biological applications. The general principle of this clean and environmental friendly technique is the use of various types of commercially available high-energy radiation sources, like ⁶⁰Co, X-ray, and electron beam to initiate energy-controlled processes of free-radical polymerization or copolymerization, leading to the production of functionalized, flexible, structured membranes or to the incorporation of functional groups within a matrix composed by a low-cost polymer film. The present manuscript describes the state of the art of using ionizing radiation for the preparation and functionalization of polymer-based membranes for biomedical and environmental applications.

Modular Fabrication of Intelligent Material-Tissue Interfaces for Bioinspired and Biomimetic Devices

One of the goals of biomaterials science is to reverse engineer aspects of human and nonhuman physiology. Similar to the body's regulatory mechanisms, such devices must transduce changes in the physiological environment or the presence of an external stimulus into a detectable or therapeutic response. This review is a comprehensive evaluation and critical analysis of the design and fabrication of environmentally responsive cell-material constructs for bioinspired machinery and biomimetic devices. In a bottom-up analysis, we begin by reviewing fundamental principles that explain materials' responses to chemical gradients, biomarkers, electromagnetic fields, light, and temperature. Strategies for fabricating highly ordered assemblies of material components at the nano to macro-scales via directed assembly, lithography, 3D printing and 4D printing are also presented. We conclude with an account of contemporary material-tissue interfaces within bioinspired and biomimetic devices for peptide delivery, cancer theranostics, biomonitoring, neuroprosthetics, soft robotics, and biological machines.

A review on functional polymer-clay based nanocomposite membranes for treatment of water

Water is essential for every living being. Increasing population, mismanagement of water sources, urbanization, industrialization, globalization, and global warming have all contributed to the scarcity of fresh water sources and the growing demand of such resources. Securing and allocating sufficient water resources has thus become one of the current major global challenges. Membrane technology has dominated the field of water purification due to its ease of usage and fabrication with high efficiency. The development of novel membrane materials can hence play a central role in advancing the field of membrane technology. It is noted that polymer-clay nanocomposites have been used widely for treatment of waste water. Nonetheless, not much efforts have been put to functionalize their membranes to be selective for specific targets. This review was organized to offer better insights into various types of functional polymer and clays composite membranes developed for efficient treatment and purification of water/wastewater. Our discussion was extended further to evaluate the efficacy of membrane techniques employed in the water industry against major chemical (e.g., heavy metal, dye, and phenol) and biological contaminants (e.g., biofouling).

Preparation and Electrochemical Characterization of Organic-Inorganic Hybrid Poly(Vinylidene Fluoride)-SiO2 Cation-Exchange Membranes by the Sol-Gel Method Using 3-Mercapto-Propyl-Triethoxyl-Silane

A new synthesis method for organic–inorganic hybrid Poly(vinylidene fluoride)-SiO₂ cation-change membranes (CEMs) is proposed. This method involves mixing tetraethyl orthosilicate (TEOS) and 3-mercapto-propyl-triethoxy-silane (MPTES) into a polyvinylidene fluoride (PVDF) sol-gel solution. The resulting slurry was used to prepare films, which were immersed in 0.01 M HCl, which caused hydrolysis and polycondensation between the MPTES and TEOS. The resulting Si-O-Si polymers chains intertwined and/or penetrated the PVDF skeleton, significantly improving the mechanical strength of the resulting hybrid PVDF-SiO₂ CEMs. The -SH functional groups of MPTES oxidized to-SO₃H, which contributed to the excellent permeability of these CEMs. The surface morphology, hybrid structure, oxidative stability, and physicochemical properties (IEC, water uptake, membrane resistance, membrane potential, transport number, and selective permittivity) of the CEMs obtained in this work were characterized using scanning electron microscope and Fourier transform infrared spectroscopy, as well as electrochemical testing. Tests to analyze the oxidative stability, water uptake, membrane potential, and selective permeability were also performed. Our organic–inorganic hybrid PVDF-SiO₂ CEMs demonstrated higher oxidative stability and lower resistance than commercial Ionsep-HC-C membranes with a hydrocarbon structure. Thus, the synthesis method described in this work is very promising for the production of very efficient CEMs. In addition, the physical and electrochemical properties of the PVDF-SiO₂ CEMs are comparable to the Ionsep-HC-C membranes. The electrolysis of the concentrated CoCl₂ solution performed using PVDF-SiO₂-6 and Ionsep-HC-C CEMs showed that at the same current density, Co²⁺ production, and current efficiency of the PVDF-SiO₂-6 CEM membrane were slightly higher than those obtained using the Ionsep-HC-C membrane. Therefore, our novel membrane might be suitable for the recovery of cobalt from concentrated CoCl₂ solutions.

Polymeric ionically conductive composite matrices and electrical stimulation strategies for nerve regeneration: In vitro characterization

Stem cell strategies and the use of electrical stimulation (ES) represent promising new frontiers for peripheral nerve regeneration. Composite matrices were fabricated by coating electrospun polycaprolactone/cellulose acetate micro-nanofibers with chitosan and ionically conductive (IC) polymers including, sulfonated polyaniline, and lignin sulfonate. These composite matrices were characterized for surface morphology, coating uniformity, ionic conductivity, and mechanical strength to explore as scaffold materials for nerve regeneration in conjunction with ES. Composite matrices measured conductivity in the range of 0.0049-0.0068 mS/m due to the uniform coating of sulfonated polymers on the micro-nanofibers. Thin films (2D) and composite fiber matrices (3D) of IC polymers seeded with human mesenchymal stem cells (hMSCs) were electrically stimulated at 0.5 V, 20 Hz for 1 h daily for 14 days to study the changes in cell viability, morphology, and expression of the neuronal-like phenotype. In vitro ES lead to changes in hMSCs' fibroblast morphology into elongated neurite-like structures with cell bodies for ES-treated and positive control growth factor-treated groups. Immunofluorescent staining revealed the presence of neuronal markers including β3-tubulin, microtubule-associated protein 2, and nestin in response to ES. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1792-1805, 2019.

Resistance and Permselectivity of 3D-Printed Micropatterned Anion-Exchange Membranes

It has been demonstrated that a micropatterned surface can decrease the resistance of anion-exchange membranes (AEMs) and can induce desirable flow properties in devices, such as mixing. Previously, a model that related the resistance of flat and patterned membranes with the same equivalent thickness was proposed, which used the patterned area and thickness ratio of the features to describe the membrane resistance. Here, we explored the validity of the parallel resistance model for a variety of membrane surface designs and area ratios. We demonstrated that the model can predict the resistance of a wide range of patterned AEMs. We showed that the resistance is independent of the spatial ordering of the design by examining random patterns, which is relevant for applications that require, for example, increased mixing in multilayered devices. Some experimental values of resistance obtained for patterned membranes presented deviations from the model. Scanning electron microscopy (SEM) images of the patterned membranes revealed resolution variations and pattern replication errors due to the stereolithographic process. A geometric correction of the target ratios improved the fit of the modeled data to the experimental values, showing that light bleeding during curing was a source of error. Two additional experimental factors were not accounted for in the model: a distinct interface between the bottom and top layer and overcuring of the bottom layer during successive steps. These sources of error were investigated by examining the resistance of single- and double-layered membranes, as well as single-layer membranes with different curing times. The differences obtained in the resistances for control samples demonstrated that both the interface and the overcuring influenced the resistance of the membrane. The results obtained in this study enlighten the discussion relating membrane-surface morphology and transport properties, as well as the optimization of 3D-printed membranes using a stereolithography process.

Behavior of Embedded Cation-Exchange Particles in a DC Electric Field

Electrodialysis and electrodeionization are separation processes whose performance depends on the quality and properties of ion-exchange membranes. One of the features that largely affects these properties is heterogeneity of the membranes both on the macroscopic and microscopic level. Macroscopic heterogeneity is an intrinsic property of heterogeneous ion-exchange membranes. In these membranes, the functional ion-exchange component is dispersed in a non-conductive binder. The functional component is finely ground ion-exchange resin particles. The understanding of the effect of structure on the heterogeneous membrane properties and behavior is thus of utmost importance since it does not only affect the actual performance but also the cost and therefore competitiveness of the aforementioned separation processes. Here we study the electrokinetic behavior of cation-exchange resin particle systems with well-defined geometrical structure. This approach can be understood as a bottom up approach regarding the membrane preparation. We prepare a structured cation-exchange membrane by using its fundamental component, which is the ion exchange resin. We then perform an experimental study with four different experimental systems in which the number of used cation-exchange particles changes from 1 to 4. These systems are studied by means of basic electrochemical characterization measurements, such as measurement of current–voltage curves and direct optical observation of phenomena that occur at the interface between the ion-exchange system and the adjacent electrolyte. Our work aims at better understanding of the relation between the structure and the membrane properties and of how structure affects electrokinetic behavior of these systems.

Transport Characteristics of Fujifilm Ion-Exchange Membranes as Compared to Homogeneous Membranes АМХ and СМХ and to Heterogeneous Membranes MK-40 and MA-41

Ion-exchange membranes (IEMs) find more and more applications; the success of an application depends on the properties of the membranes selected for its realization. For the first time, the results of a comprehensive characterization of the transport properties of IEMs from three manufactures (Astom, Japan; Shchekinoazot, Russia; and Fujifilm, The Netherlands) are reported. Our own and literature data are presented and analyzed using the microheterogeneous model. Homogeneous Neosepta AMX and CMX (Astom), heterogeneous MA-41 and MK-40 (Shchekinoazot), and AEM Type-I, AEM Type-II, AEM Type-X, as well as CEM Type-I, CEM Type-II, and CEM Type-X produced by the electrospinning method (Fujifim) were studied. The concentration dependencies of the conductivity, diffusion permeability, as well as the real and apparent ion transport numbers in these membranes were measured. The counterion transport number characterizing the membrane permselectivity increases in the following order: CEM Type-I ≅ MA-41 < AEM Type-I < MK-40 < CMX ≅ CEM Type-II ≅ CEM Type-X ≅ AEM Type-II < AMX < AEM Type-X. It is shown that the properties of the AEM Type-I and CEM Type-I membranes are close to those of the heterogeneous MA-41 and MK-40 membranes, while the properties of Fujifilm Type-II and Type-X membranes are close to those of the homogeneous AMX and CMX membranes. This difference is related to the fact that the Type-I membranes have a relatively high parameter f2, the volume fraction of the electroneutral solution filling the intergel spaces. This high value is apparently due to the open-ended pores, formed by the reinforcing fabric filaments of the Type-I membranes, which protrude above the surface of these membranes.

Polybenzimidazole/BaCe0.85Y0.15O3-δ nanocomposites with enhanced proton conductivity for high-temperature PEMFC application

The present work reports the synthesis of polybenzimidazole (PBI)/BaCe0.85Y0.15O3-δ nanocomposite membrane. The obtained membranes were investigated to use as novel electrolytes in high-temperature proton exchange fuel cells. The PBCYx membranes were prepared with dispersing BaCe0.85Y0.15O3-δ into the polyimidazole membrane by solution casting method. The obtained membranes were used as novel proton conductors. The thermal stability and structural properties were investigated. The conductivity and morphology of the obtained materials were studied using impedance spectroscopy AC (IS) and a scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX). The maximum phosphoric acid adsorption (175%) and protonic conductivity (0.092 S/cm at 180 °C under dry conditions) were observed for all of the PBI nanocomposite membranes containing 5 wt.% of BaCe0.85Y0.15O3-δ in the membrane matrix. The polarization and power density curves were studied at 150 and 180 °C operating temperatures. The power density of about 0.42 W/cm2 and current density of about 0.84 A/cm at 0.5 V and 180 °C were achieved under dry conditions. The data obtained from our studies showed that the physicochemical properties of the novel nanocomposites were enhanced for using in the high-temperature proton transfer fuel cells.

The Effect of Feed Solution Temperature on the Power Output Performance of a Pilot-Scale Reverse Electrodialysis (RED) System with Different Intermediate Distance

Membrane-based reverse electrodialysis (RED) can convert the salinity gradient energy between two solutions into electric power without any environmental impact. Regarding the practical application of the RED process using natural seawater and river water, the RED performance depends on the climate (temperature). In this study, we have evaluated the effect of the feed solution temperature on the resulting RED performance using two types of pilot-scale RED stacks consisting of 200 cell pairs having a total effective membrane area of 40 m² with different intermediate distances (200 µm and 600 µm). The temperature dependence of the resistance of the solution compartment and membrane, open circuit voltage (OCV), maximum gross power output, pumping energy, and subsequent net power output of the system was individually evaluated. Increasing the temperature shows a positive influence on all the factors studied, and interesting linear relationships were obtained in all the cases, which allowed us to provide simple empirical equations to predict the resulting performance. Furthermore, the temperature dependence was strongly affected by the experimental conditions, such as the flow rate and type of stack, especially in the case of the pilot-scale stack.

Codeposition Modification of Cation Exchange Membranes with Dopamine and Crown Ether To Achieve High K+ Electrodialysis Selectivity

Surface modification has been proven to be an effective approach for ion exchange membranes to achieve separation of counterions with different valences by altering interfacial construction of membranes to improve ion transfer performance. In this work, we have fabricated a series of novel cation exchange membranes (CEMs) by modifying sulfonated polysulfone (SPSF) membranes via codeposition of mussel-inspired dopamine (DA) and 4'-aminobenzo-15-crown-5 (ACE), followed by glutaraldehyde cross-linking, aiming at achieving selective separation of specific cations. The as-prepared membranes before and after modification were systematically characterized in terms of their structural, physicochemical, electrochemical, and electrodialytic properties. In the electrodialysis process, the modified membranes exhibit distinct perm selectivity to K⁺ ions in binary (K⁺/Li⁺, K⁺/Na⁺, K⁺/Mg²⁺) and ternary (K⁺/Li⁺/Mg²⁺) systems. In particular, at a constant current density of 5.0 mA·cm^-2, modified membrane M-co-0.50 shows significantly prominent perm selectivity [Formula: see text] in the K⁺/Mg²⁺ system and M-co-0.75 exhibits remarkable performance in the K⁺/Li⁺ system [Formula: see text], superior to commercial monovalent-selective CEM (CIMS, [Formula: see text], [Formula: see text]). Besides, in the K⁺/Li⁺/Mg²⁺ ternary system, K⁺ flux reaches 30.8 nmol·cm^-2·s^-1 for M-co-0.50, while it reaches 25.8 nmol·cm^-2·s^-1 for CIMS. It possibly arises from the effects of pore-size sieving and the synergistic action of electric field driving and host-guest molecular recognition of ACE and K⁺ ions. This study can provide new insights into the separation of specific alkali metal ions, especially on reducing influence of coexisting cations K⁺ and Na⁺ on Li⁺ ion recovery from salt lake and seawater.

Membrane Deformation and Its Effects on Flow and Mass Transfer in the Electromembrane Processes

In the membrane processes, a trans-membrane pressure (TMP) may arise due to design features or operating conditions. In most applications, stacks for electrodialysis (ED) or reverse electrodialysis (RED) operate at low TMP (<0.1 bar); however, large stacks with non-parallel flow patterns and/or asymmetric configurations can exhibit higher TMP values, causing membrane deformations and changes in fluid dynamics and transport phenomena. In this work, integrated mechanical and fluid dynamics simulations were performed to investigate the TMP effects on deformation, flow and mass transfer for a profiled membrane-fluid channel system with geometrical and mechanical features and fluid velocities representative of ED/RED conditions. First, a conservatively high value of TMP was assumed, and mechanical simulations were conducted to identify the geometry with the largest pitch to height ratio still able to bear this load without exhibiting a contact between opposite membranes. The selected geometry was then investigated under expansion and compression conditions in a TMP range encompassing most practical applications. Finally, friction and mass transfer coefficients in the deformed channel were predicted by computational fluid dynamics. Significant effects of membrane deformation were observed: friction and mass transfer coefficients increased in the compressed channel, while they decreased (though to a lesser extent) in the expanded channel.