Search Results (73)

Today, the development of ion exchange membranes has increased considerably in various applications, such as water treatment, energy conversion and storage, as well as environmental applications. In this study, several ion exchange membranes based on cellulose acetate propionate (CAP) and ionic liquids (ILs) were fabricated using the phase inversion method, aiming to develop more sustainable membrane materials for environmental and energy applications. Three different ILs with a similar cation and different anions (1-(4-sulfobutyl)-3-methylimidazolium trifluoromethanesulfonate [SMIM][TFS], 1-(4-sulfobutyl)-3-methylimidazolium hydrogen sulfate [SMIM][HS], and 1-(4-sulfobutyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [SMIM][TFSI]) were used in three concentrations (i.e., 9, 17, and 23 wt.%). The main objective of this work is to evaluate the influence of the anion structure on the membrane’s physical, morphological, hydrophilic, thermal, mechanical, and electrochemical properties. Water contact angle measurements demonstrated the weaker hydrophilicity of composite membranes containing [SMIM][TFS] (81–106°) and [SMIM][TFSI] (87–94°) in comparison with pure CAP (~79°) and CAP/[SMIM][HS] (79–83°) membranes. The CAP/[SMIM][HS] membrane showed higher elongation at break (~36%) compared with the pure CAP membrane (~24%), confirming the plasticization behavior of [SMIM][HS]. The CAP/[SMIM][TFS] membrane containing 23 wt.% of IL showed promising membrane potential, permselectivity, transport number and ion flux ratio values of 53.2 mV, 74.7%, 0.85, and 5.5, respectively, indicating its potential as a candidate for further evaluation in electrochemical membrane processes such as electrodialysis and fuel cells. Full article

This work provides a systematic experimental study for the electrochemical desalination of saline water using an electrospun permselective polyvinylidene difluoride (PVDF) membrane. Several nano additives were initially screened during membrane development; however, only the materials that demonstrated stable dispersion, reproducible membrane formation, and consistent electrochemical behaviour, namely graphene oxide (GO) and carbon nanotubes (CNTs) were selected for full analysis in this study. Accordingly, the study focuses on pure PVDF, PVDF/GO, and PVDF/CNTs membranes integrated with an alternating Ag/AgCl electrode system. The silver electrode is prepared by spray-coating of silver nanoparticles on high surface carbon cloth, whereas the AgCl electrode was prepared electrochemically from the Ag electrode using a three-electrode electrochemical cell. The electrochemical behaviour of various modified electrodes (bare carbon cloth, Ag/carbon cloth, Ag/nafion/carbon black/PVDF, and Ag/nafion/carbon cloth) was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and X-Ray Diffraction (XRD). The electrode prepared using Nafion and PVDF as binders with carbon black as conductive additive exhibited the highest current response and lowest charge-transfer resistance. When coupled with this optimized electrode, the PVDF/GO membrane delivered the best desalination performance, achieving an ion removal efficiency of 68%, a salt adsorption capacity (SAC) of 775.40 mg/g, and a specific energy consumption (SEC) of 16.17 kJ/mole values superior to those reported in the literature. Full article

Phenomena associated with an ion-exchange membrane (IEM) in contact with an ionic solution, such as its selectivity and ionic transport, commonly occur when an ion approaches the membrane surface. Because of this, if a change occurs in the IEM/Solution interfacial region, then it is expected that these processes will be affected. For example, if the IEM surface is modified with an electronic conducting polymer (ECP), then its selectivity and the phenomena associated with ionic transport will change. These changes can be quantified by parameters such as the permselectivity, the contact angle, and others, and are associated with the hydrophilic/hydrophobic balance of its surface. This work reports the characterization of commercial anion-exchange membrane samples modified voltammetrically with polyaniline (PAni) obtained at different temperatures (10, 15, and 20 °C). Among the main results obtained, it was found that with an increase in synthesis temperature of the PAni, the membrane’s permselectivity will increase from 0.757 to 0.782 to 0.808. While contrary behavior is observed in the case of the contact angle, since an increase in the synthesis temperature will cause a greater hydrophilic character when going from 67° to 53° to 50°. According to this work, these trends in the properties of the modified membranes are related to the morphological characteristics of PAni deposits conferred by the variation in the synthesis temperature. Full article

Anion exchange membranes (AEMs) serve as critical components in diffusion dialysis (DD) systems due to their unique permselectivity. This study developed a series of triethanolamine (TEA)-functionalized chloromethylated polysulfone (CMPSF) AEMs via solution casting. The physical and chemical structural characterization through ¹H NMR, XPS, FTIR, and SEM proved successful membrane synthesis. The performances of the membranes, such as ion exchange capacity (IEC), water contact angle (WCA), water uptake (WU), chemical stability, and mechanical stability, were systematically evaluated. For HCl/FeCl₂ acid recovery (1 mol L⁻¹ HCl + 0.25 mol L⁻¹ FeCl₂), the optimal membrane (TEA-CMPSF-M50) demonstrated exceptional DD performance, with an acid dialysis coefficient (U_H⁺) of 47.9 × 10⁻³ m h⁻¹ and separation factor (S) of 3.87. Crucially, after 7-day immersion in acidic solution at 65 °C, the membrane maintained U_H⁺ and S values of CMPSF-M50 AEM of 45.4 × 10⁻³ m h⁻¹ and 4.02, respectively, confirming the outstanding acid resistance and thermal stability of TEA-CMPSF-M50 AEM. These results indicated that the TEA-functionalized AEMs developed in this work hold great promise for industrial acid recovery applications. Full article

Ion-exchange membranes (IEMs) are widely used in reverse-electrodialysis (RED) technology, which can collect the salinity gradient energy between concentrated and diluted solutions and convert it into electromotive force (EMF) to drive power generation and hydrogen production. Recent studies have indicated that the permselectivity of IEMs is vital to determining the performance of an RED stack. In this study, the influences of solution concentration, ion species, and solution temperature on the permselectivity of IEMs were experimentally investigated. The results demonstrate that the permselectivity of IEMs decreases with increasing concentrations of KAc, LiCl, and LiBr solutions for both concentrated solutions (3–5 M) and dilute solutions (0.02–0.2 M). Further, through comparing the LiBr and KBr solutions as well as the LiCl, KCl, and NH₄Cl solutions, respectively, K⁺ demonstrates a higher permselectivity than Li⁺, and both of which are smaller than NH₄⁺ under the same cation and concentration conditions. Moreover, another test was conducted using three potassium salt solutions with different anions, and the experimental permselectivity order is Ac⁻ > Br⁻ > Cl⁻. A slight increase in solution temperature enhances the permselectivity of IEMs due to the increase in ionic mobility. However, an excessive temperature is detrimental to membrane stability and thus reduces permselectivity. It can be seen that ions with low hydration energy, a small hydration radius, and high mobility show a higher permselectivity. Full article

Anion exchange membranes are utilised in cutting-edge energy technologies including electrolysers and fuel cells. Recently, these membranes have also emerged as a promising tool in CO₂ capture techniques, such as moisture-driven direct air capture and the separation of CO₂ from other gases, leveraging the moisture-induced sorption/desorption and diffusion of CO₂ in its ionic forms. In this study, we examine the absorption and permeation of CO₂ and CH₄ in two commercially available anion exchange membranes, Fumasep^® and Sustainion^®, under dry conditions. With the exception of CO₂ sorption in Fumasep^®, these measurements have not been previously reported. These new data points are crucial for evaluating the fundamental separation capabilities of these materials and for devising innovative CO₂ capture strategies, as well as for the simulation of novel combined processes. In a dry state, both materials demonstrate similar CO₂ absorption levels, with a higher value for Sustainion^®. The CO₂ solubility coefficient decreases with pressure, as is typical for glassy polymers. Fumasep^® exhibits higher CO₂/CH₄ ideal solubility selectivity, equal to ~10 at sub-ambient pressures, and higher diffusivity. The CO₂ diffusion coefficient increases with the CO₂ concentration in both membranes due to swelling of the matrix, varying between 0.7 and 2.2 × 10⁻⁸ cm²/s for Fumasep^® and between 1.6 and 9.0 × 10⁻⁹ cm²/s for Sustainion^®. CO₂ permeability exhibits a minimum at a pressure of approximately 2–3 bar. The CO₂ permeability in the dry state is higher in Fumasep^® than in Sustainion^®: 3.43 and 0.72 Barrer at a 2-bar transmembrane pressure, respectively. The estimated perm-selectivity was found to reach values of up to 40 at sub-ambient pressures. The CO₂ permeability and CO₂/CH₄ estimated perm-selectivity in both polymers are of a similar order of magnitude to those measured in fluorinated ion exchange membranes such as Nafion^®. Full article

The enrichment of ⁶Li isotopes from a natural stage of 7.6% to above 59% is required for the development of next-generation green technologies capable of sustaining climate change mitigation and energy-mix targets. In this study, we developed two categories of custom laboratory-made organic membranes, membranes that were non-impregnated before electromigration (AI-1) and membranes impregnated with LiNTf₂ (AI-2), to evaluate their performance in lithium isotope separation. Both types of membranes were exposed in synthesis to ionic liquid and crown ether. The objective of the study was to test the performance of membranes in separating lithium isotopes from a lithium-loaded organic phase in an aqueous solution with variable potentials and time intervals. The results show that the impregnated AI-2 membranes increased the enrichment of ⁶Li in the early stages, and the effect decreased after 25 h. The efficiency of lithium isotope enrichment was positively related to the potential profile applied, migration time, and concentration of organic solution in the anode chamber. The 0.5 mol/L Bis-(trifluoromethane) sulfonimide lithium salt (Li[NTf₂]) with 0.1 M tetra butyl ammonium perchlorate (TBAP) in acetonitrile (CH₃CN) ionic solution significantly improved Li isotope separation compared with an aqueous environment with higher salt concentrations. The maximum isotopic separation coefficient (α) for AI-1.2 (15-crown-5 ether and 1 mol/L LiNTf₂ in TBAP solution after 48 h of electromigration) gradually increased to 1.0317. Our results demonstrated that in the laboratory-made setup described, the migration efficiency and Li isotope separation in the catholyte environment needed a minimum of 9 V and a migration time of 6 h, respectively; these values varied with the concentration of the organic solution in the anode chamber. The ability of laboratory-engineered membranes to impart isotope selectivity and enhance permselectivity or selectivity towards singly charged ions was demonstrated through the functionality of single-collector inductively coupled plasma mass spectrometry (ICP-MS). This technology is particularly valuable and commercially feasible for future lithium isotope research in nuclear technology. Full article

Innovations for separation via membranes are extremely energy-efficient, and through the previous decade, attention to this technology has spiked tremendously. Biopolymers are becoming widely recognized as membrane materials since they are sustainable. Furthermore, the second most common biopolymer, chitin, is the source of chitosan, which has several benefits that make it ideal for the construction of membranes. This review article presents an evaluation of current developments in the utilization of chitosan membranes. The applications of interest in this review are nanofiltration, pervaporation and ion exchange. The chitosan based nanofiltration membranes are comprehensively reviewed with respect to various factors (e.g., solvent, pH resistant, etc.). The development of water permselective, organic permselective, and organic-organic separation films, as well as its permeability and segregation properties, are addressed in pervaporation (PV) section. Full article

Electroosmosis reduces the available energy from ion transport arising due to concentration gradients across ion-exchange membranes. This work builds on previous efforts to describe the electroosmosis, the permselectivity and the apparent transport number of a membrane, and we show new measurements of concentration cells with the Selemion CMVN cation-exchange membrane and single-salt solutions of HCl, LiCl, NaCl, MgCl₂, CaCl₂ and NH₄Cl. Ionic transport numbers and electroosmotic water transport relative to the membrane are efficiently obtained from a relatively new permselectivity analysis method. We find that the membrane can be described as perfectly selective towards the migration of the cation, and that ${\mathrm{Cl}}^{-}$ does not contribute to the net electric current. For the investigated salts, we obtained water transference coefficients, $t_w$, of 1.1 ± 0.8 for HCl, 9.2 ± 0.8 for LiCl, 4.9 ± 0.2 for NaCl, 3.7 ± 0.4 for KCl, 8.5 ± 0.5 for MgCl₂, 6.2 ± 0.6 for CaCl₂ and 3.8 ± 0.5 for NH₄Cl. However, as the test compartment concentrations of LiCl, MgCl₂ and CaCl₂ increased past 3.5, 1.3 and 1.4 mol kg⁻¹, respectively, the water transference coefficients appeared to decrease. The presented methods are generally useful for characterising concentration polarisation phenomena in electrochemistry, and may aid in the design of more efficient electrochemical cells. Full article

Membrane capacitive deionization (MCDI) is an electrochemical ion separation process that combines ion-exchange membranes (IEMs) with porous carbon electrodes to enhance desalination efficiency and address the limitations of conventional capacitive deionization (CDI). In this study, a cation-exchange membrane (CEM) embedded with a metal–organic framework (MOF) was developed to effectively separate monovalent and multivalent cations in influent solutions via MCDI. To fabricate CEMs with high monovalent ion selectivity, ZIF-8 was incorporated into sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) at various weight ratios. The resulting membranes were systematically characterized using diverse electrochemical methods. The ZIF-8-embedded CEMs demonstrated a sieving effect based on differences in ion size and hydration energy, achieving excellent permselectivity for monovalent ions. MCDI tests using the prepared CEMs showed a Na⁺ ion removal rate exceeding 99% in Na⁺/Mg²⁺ and Na⁺/Ca²⁺ mixed feed solutions, outperforming a commercial membrane (CSE, Astom Corp., Tokyo, Japan), which achieved a removal rate of 94.1%. These findings are expected to provide valuable insights for advancing not only MCDI but also other electro-membrane processes capable of selectively separating specific ions. Full article

New homogeneous bilayer membranes with a thin anion-exchange layer have been developed based on the copolymer of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and ethyl methacrylate (EMA) on the surface of a membrane substrate made from polyfluorosulfonic acid (PFSA). The overall and partial current–voltage characteristics, as well as external and internal diffusion-limiting currents, were theoretically and experimentally investigated. Parameters such as specific conductivity, sorption, and diffusion permeability of individual membrane layers were determined, along with effective transport numbers and specific permselectivity of the bilayer homogeneous membranes in mixed solutions of calcium chloride and sodium chloride. It was found that applying a thin anion-exchange layer of DADMAC and EMA to the homogeneous membrane allows for the creation of a charge-selective bilayer membrane with enhanced selectivity toward monovalent metal cations. The specific selectivity of the bilayer membrane for sodium cations increases more than 6-fold (from 0.8 to 4.8). Verification of the obtained experimental data was performed within a four-layer mathematical model with quasi-equilibrium boundary conditions for the diffusion layer (I)/modifying layer (II)/membrane substrate (III)/diffusion layer (IV) in ternary NaCl+CaCl₂ solutions. Full article

This work is an effort to mitigate the existing environmental issues caused by brine discharge from Kuwait’s desalination plants and to find an economical and efficient way of managing reject brine from local desalination plants. Low- and high-resistance membranes (LRMs and HRMs, respectively) were used to produce salt and low-salinity water from brine effluent utilizing an electrodialysis (ED)–evaporator hybrid system. The effect of high current densities of 300, 400, and 500 A/m² and brine flowrates of 450 and 500 L/h on the quality of produced salt and diluate were investigated for LRM and HRM. The recovered salt purity for LRM is up to 90.58%. Results show that the low-resistance membrane (LRM) achieved higher water recovery, energy consumption, desalination rate, operation time and ion removal rate than those of the high-resistance membrane (HRM) under the same operating conditions. The difference in concentration for 300 A/m² between LRM and HRM increased from 0.93% at 10 min to 8.28% at 140 min. The difference in diluate concentration effluent is negligible for both membranes, whereas LRM produced higher concentrate effluent than HRM for all current densities and low flowrate (400 L/h). The maximum difference between LRM and HRM (with LRM achieving higher concentrations) is 10.7% for 400 A/m². The permselectivity of LRM for monovalent cations decreased with current density, whereas the effect on permselectivity for HRM was insignificant for the current density values. The addition of a neutral cell was effective in reducing the buildup of divalent ions on the inner membrane of the cathode side. Full article

Under ideal conditions, nanotubes with a fixed negative tube-wall charge will reject anions and transport-only cations. Because many proposed nanofluidic devices are optimized in this ideally cation-permselective state, it is important to know the experimental conditions that produce ideal responses. A parameter called C_crit, the highest salt concentration in a contacting solution that still produces ideal cation permselectivity, is of particular importance. Pioneering potentiometric studies on gold nanotubes were interpreted using an electrostatic model that states that C_crit should occur when the Debye length in the contacting salt solution becomes equivalent to the tube radius. Since this “double-layer overlap model” (DLOM), treats all same-charge ions as identical point charges, it predicts that all same-charged cations should produce the same C_crit. However, the effect of cation on C_crit in gold nanotubes was never investigated. This knowledge gap has become important because recent studies with a polymeric cation-permselective nanopore membrane showed that DLOM failed for every cation studied. To resolve this issue, we conducted potentiometric studies on the effect of salt cation on C_crit for a 10 nm diameter gold nanotube membrane. C_crit for all cations studied were, within experimental error, the same and identical, with values predicted by DLOM. The reason DLOM prevailed for the gold nanotubes but failed for the polymeric nanopores stems from the chemical difference between the fixed negative charges of these two membranes. Full article

Limitations in existing anion exchange membranes deter their use in the efficient treatment of industrial wastewater effluent. This work presents an approach to fabricating novel anion-conducting membranes using epoxy resin monomers like hydrophobic or hydrophilic diglycidyl ether and quaternized polyethyleneimine (PEI). Manipulating the diglycidyl ether nature, the quantitative composition of the copolymer and the conditions of quaternization allows control of the physicochemical properties of the membranes, including water uptake (20.0–330%), ion exchange capacity (1.5–3.7 mmol/g), ionic conductivity (0.2–17 mS/cm in the Cl form at 20 °C), potentiostatic transport numbers (75–97%), as well as mechanical properties. A relationship was established between copolymer structure and conductivity/selectivity trade-off. The higher the quaternized polyethyleneimine, diluent fraction, and hydrophilicity of diglycidyl ether, the higher the conductivity and the lower the permselectivity. Hydrophobic diglycidyl ether gives a much better conductivity/selectivity ratio since it provides a lower degree of hydration than hydrophilic diglycidyl ether. Different mesh and non-woven reinforcing materials were also examined. The developed membranes demonstrate good stability in both neutral and acidic environments, and their benchmark characteristics in laboratory electrodialysis cells and batch-mode dialysis experiments are similar to or superior to, commercial membranes such as Neosepta© AMX, FujiFilm© Type1, and Fumasep FAD-PET. Full article

The high concentration of chloride ions in desulphurization wastewater is the primary limiting factor for its reusability. Monovalent anion selective electrodialysis (S-ED) enables the selective removal of chloride ions, thereby facilitating the reuse of desulfurization wastewater. In this study, different concentrations of NaCl and Na₂SO₄ were used to simulate different softened desulfurization wastewater. The effects of current density and NaCl and Na₂SO₄ concentration on ion flux, permselectivity ($P_{{\mathrm{SO}}_4^{2-}}^{{\mathrm{Cl}}^{-}}$) and specific energy consumption were studied. The results show that Selemion ASA membrane exhibits excellent permselectivity for Cl⁻ and SO₄²⁻, with a significantly lower flux observed for SO₄²⁻ compared to Cl⁻. Current density exerts a significant influence on ion flux; as the current density increases, the flux of SO₄²⁻ also increases but at a lower rate than that of Cl⁻, resulting in an increase in permselectivity. When the current density reaches 25 mA/cm², the permselectivity reaches a maximum of 50.4. The increase in NaCl concentration leads to a decrease in the SO₄²⁻ flux; however, the permselectivity is reduced due to the elevated Cl⁻/SO₄²⁻ ratio. The SO₄²⁻ flux increases with the increase in Na₂SO₄ concentration, while the permselectivity increases with the decrease in Cl⁻/SO₄²⁻ ratio. Full article