Heterogeneous Cation Exchange Membranes Research Articles

The effect of electrostatically enhanced adsorption of polylysine on a heterogeneous cation-exchange membrane

Electrostatics influences the interactions between charged biopolymers and ion-exchange membranes. When carrying a charge opposite to that bound in the membrane, the biopolymers readily adsorb on the membrane surface, altering local conditions and, thus, affecting the desalination processes that proceed. To provide a coherent description of the consequences of such adsorption, we experimentally investigate the effects of polylysine as a model cationic polymer on the behavior of a heterogenous cation-exchange membrane. We show that even short exposure to polylysine changes the membrane behavior dramatically. Such a change reflects the influence of the adsorbed polylysine on natural convection, electroconvection, and water splitting. By directly observing the membrane-electrolyte interface, we find polylysine suppresses the beneficial electrical-field-induced convective transport at the membrane-electrolyte interface. Specifically, it diminishes electroconvection dominating at the membrane surface for polylysine-free solutions and attenuates natural convection, dictating the developed flow patterns. At the same time, it provides conditions enhancing a water-splitting reaction, significantly affecting the pH of the solutions adjacent to the membrane. All these effects are dependent on the polylysine concentration. Our study emphasizes the potentially harmful impact of biomolecular adsorption mediated by electrostatic interactions.

Electrodeposition modification of heterogeneous cation exchange membrane using expanded polystyrene waste: Enhanced electrochemical properties and electrodialytic performance

In this study, surface modification of a cation exchange membrane based on polyvinyl chloride was accomplished via electrochemical deposition of post-sulfonated waste-expanded polystyrene aiming to enhance its electrochemical properties and electrodialytic performance. The membrane was synthesized by the phase inversion method, modified with different concentrations of polyelectrolyte, characterized by FTIR and SEM analyses, and applied for electrodialytic desalination of NaCl solution. Deposition of sulfonated polystyrene with polyelectrolyte concentration of 2 g/l, current of 8 mA/cm2, and period time of 30 min caused a reduction in electrical resistance up to 52 %. Furthermore, the sodium ionic flux through electrodialytic desalination was improved by 58 % as a result of the promotion of the electrochemical properties of the membrane.

Preparation of heterogeneous cation exchange membrane and its contributions in enhancing the removal of Ni2+ by capacitive deionization system

Capacitive deionization (CDI), an emerging method to eliminate ions from water at a low cost, has garnered significant interest in recent years. This study evaluates the implication of cation exchange resin loading on the membrane via the nonsolvent-induced phase inversion method. After determining the quantity of resins efficiently loaded on the membrane, it was subsequently utilized as a cation exchange membrane in the membrane capacitive deionization (MCDI) unit to examine the performance removal of Ni2+. The results show that the amount of resins influenced the membrane structure and significantly improved the efficiency of Ni2+ removal. The sulfonic acid group show a strong intensity directly proportional to the quantity of resins based on the FTIR measurement. In conjunction with the enhanced resin amount, ion exchange capacity and water content were increased. Simultaneously, there was an observed elevation in the water contact angle and the roughness of the membrane surface with increased resin amount. In the MCDI unit, membrane M20 (20% by weight resin) was employed to elucidate its roles in the CDI unit, encompassing an examination of various concentrations and flow rates, with Ni2+ utilized as a test contaminant. The results demonstrated that using membrane M20 in the MCDI (MCDI-M20) unit consistently exhibited higher adsorption levels than the CDI unit, reaching 19.80 mg g−1 ACC in the MCDI-M20 unit, while CDI unit achieved 10.27 mg g−1 ACC at 200 mg L−1 Ni2+ concentration and a flow rate of 10 mL min−1 at 1.2 V. Additionally, Ni2+ concentrations and flow rates in CDI system had an evident impact on the duration of adsorption due to the mechanisms of ions transport on the membrane. This study suggests that employing the prepared membrane in the MCDI unit enhanced the removal of Ni2+ from the solution, contributing to sustainable development goals.

Bilayer Heterogeneous Cation Exchange Membrane with Polyaniline Modified Homogeneous Layer: Preparation and Electrotransport Properties.

A bilayer membrane based on a heterogenous cation exchange membrane with a homogeneous cation exchange layer and a polyaniline on its surface is prepared. The intercalation of polyaniline into the membrane with a homogeneous cation exchange layer is performed by oxidative polymerization of aniline. The influence of the homogeneous cation exchange layer and the polyaniline on the structure, conductivity, diffusion permeability, selectivity, and current-voltage curve of the heterogeneous cation exchange membrane is established. Membrane properties are studied in the HCl, NaCl, and CaCl2 solutions. The homogeneous cation exchange layer has a negligible effect on the transport properties of the initial heterogeneous membrane. The polyaniline synthesis leads to a decrease in the macropore volume in the membrane structure, conductivity, and diffusion permeability. The counterion transport number in the bilayer membrane is significantly reduced in a solution of calcium chloride and practically does not change in sodium chloride and hydrochloric acid. In addition, the asymmetry of the diffusion permeability and shape of current-voltage curve depending on the orientation of the membrane surface to the flux of electrolyte or counterion are found.

3D printed heterogeneous cation exchange membrane processed using stereolithography

AbstractMembrane chemistry belongs to the field in which 3D printing can advantageously also be used because of enabling the production of prototypes with precisely defined dimensions. The presented work aimed to develop new polymeric compositions for heterogeneous cation exchange membranes manufactured using stereolithography (SLA) from commercially available materials. Three types of photo‐curable thermoset resins (acrylic resin and two types of epoxy resins) were used as polymer matrixes in combination with strong acid cation exchange resin (CER) powder. The membrane production consisted of several stages, namely mixing the photo‐curable resin with finely ground CER powder, processing using SLA, and appropriate post‐curing using UV light and elevated temperature. The work aimed to monitor the influence of the photo‐curable resin type and post‐curing on the microstructural, electrochemical, and mechanical properties of resulting membrane objects. The results revealed that heterogeneous cation exchange membranes could be processed using SLA from the mixture of the acrylic photo‐curable resin and CER powder (weight ratio of 60/40) without the need for post‐curing. These products exhibited high permselectivity (93%), high ion exchange capacity (2.23 meq⋅g−1), and sufficiently low electrical resistance (2200 Ω⋅cm), which predetermines them for efficient electrophoretic separation.

Elecrtochemical Investigation of Heterogeneous Cation-Exchange Membranes Modified by Polyanilin in Solutions of Monovalent and Divalent Cations

A series of composite ion-exchange membranes based on a heterogeneous cation-exchange MK-40 membrane and polyaniline was obtained under the conditions of electrodiffusion of a monomer and an oxidizing agent. The process of polyaniline synthesis on the membrane surface was accompanied by the registration of chronopotentiograms and the pH of the solution leaving the desalination compartment. The initial MK-40 cation-exchange membrane and the composites based on it were studied by voltammetry and chronopotentiometry in NaCl, CaCl2, and MgCl2 solutions in the same electrodialysis flow cell in which the composites were obtained. To calculate the transport numbers of counterions in membranes in CaCl2 and MgCl2 solutions by the chronopotentiometric method, the apparent fraction of the conducting membrane surface in the NaCl solution was calculated based on experimental data on the potentiometric transport numbers of counterions in the membrane. The conditions for the synthesis of polyaniline on the surface of a heterogeneous MK-40 membrane, leading to the preparation of samples with selectivity to singly charged ions, are revealed.

Comparative Study of Different Ion-Exchange Membrane Types in Diffusion Dialysis for the Separation of Sulfuric Acid and Nickel Sulfate

The possibility of using various types of ion-exchange membranes in diffusion dialysis for the separation of sulfuric acid and nickel sulfate has been evaluated. The process of the dialysis separation of a real waste solution from an electroplating facility containing 252.3 g/L of sulfuric acid, 20.9 g/L of nickel ions and small amounts of zinc, iron, copper ions, etc. has been studied. Heterogeneous cation-exchange membrane containing sulfonic groups and heterogeneous anion-exchange membranes with different thicknesses (from 145 μm to 550 μm) and types of fixed groups (four samples with quaternary ammonium base and one sample with secondary and tertiary amines) have been used. The diffusion fluxes of sulfuric acid, nickel sulfate, and the total and osmotic fluxes of the solvent have been determined. The use of a cation-exchange membrane does not allow the separation of the components, since the fluxes of both components are low and comparable in magnitude. The use of anion-exchange membranes makes it possible to efficiently separate sulfuric acid and nickel sulfate. Anion-exchange membranes with quaternary ammonium groups are more effective in the diffusion dialysis process, while the thin membrane turns out to be the most effective.

Fabrication of layer-by-layer ion exchange membrane by applying PDA-POSS nanocomposite onto heterogeneous cationic substrate for water treatment

Double layer Cation Exchange Membranes (DLCEMs) have been prepared by surface polymerization of dopamine-co-POSS nanoparticles on a PVC based heterogeneous cation exchange membrane. FTIR and FESEM images proved relatively uniform forming of intended DLCEMs. The FESEM images illustrated almost integrity dispensation of nanoparticles through the surface layer. Results represented that developing nanocomposite layer resulted in surface hydrophilicity enhancement. The obtained data for Cu2+ and Cr2+ removal percentage for the prepared membranes represents higher capacity for DLCEMs to remove heavy metals compared to pristine cationic membrane. Also membranes showed higher Cr2+ removal capacity rather than Cu2+. The membrane surface modification by introducing PDA nanocomposite also caused to improving sodium permeability and flux. Furthermore, transport number and permselectivity of the prepared CEMs generally follow an increasing procedure nearly. It should be noticed that incorporation of POSS nanoparticles into the surface layer resulted in electrical resistance reduction obviously.

Fabrication of Thin Film Heterogeneous Cation Exchange Membrane in Chitosan Nanocomposite Layer with Copper Oxide Nanoparticles

Fabrication of Thin Film Heterogeneous Cation Exchange Membrane in Chitosan Nanocomposite Layer with Copper Oxide Nanoparticles

Functional stability of novel homogeneous and heterogeneous cation exchange membranes for abiotic and microbial electrochemical technologies

Two novel cation exchange membranes (CEM) denoted as PSEBS SU and CF22R14 were examined for two electrochemical applications, and compared to a commercial membrane (Fumasep FKE). Application in microbial electrolysis cells (MEC) and abiotic electrochemical cells (EC) were selected as low and high current density systems (∼1 A m−2 and 50 A m−2, respectively). Hydration number (λ), ion exchange capacity (IEC) and ionic conductivity (σ), as well as changes in these parameters during 10 days of operation were studied. λ was stable after MEC operation, however EC mode caused remarkable changes and a decrease of λ (by −8.2 ± 0.3, −13.8 ± 0.8 and −39.3 ± 8.8% for FKE, PSEBS SU and CF22R14, respectively). The decrease of IEC was significant for each membrane regardless of the operation mode. However, only MEC operation led to reversible functionality losses, whereas EC mode caused permanent decrease of IEC (87.9 ± 2.8, 85.3 ± 3.8 and 46.6 ± 4.4% re-activation efficiency for FKE, PSEBS SU and CF22R14, respectively). The EC operation resulted in more severe loss of σ for each CEM, among which PSEBS SU showed the best re-activation efficiency (74.9 ± 8.1%). In general, the membrane properties were much more impaired during EC operation due to higher current densities.

Monovalent selective membrane for electrodialysis desalination of water for agriculture

Agriculture is the world’s largest consumer of water accounting for about 70% of freshwater withdrawals. Faced with scarcity of pure water, it results in need in desalination to produce water for agricultural needs from brackish water, seawater or polluted sources. Widely used technologies reduce total salinity decreasing also the levels of calcium, magnesium, sulphates and phosphates required for normal growth of plants. Recently a layer-by-layer adsorption of charged polymers was proposed for creation of functional materials that would preferentially remove monovalent ions such as Na+ and Cl−. Our previous studies demonstrated the creation of cation selective membrane basing on affordable heterogeneous cation exchange membrane that specifically separated Na+ from Na+/Ca2+ mixed solution during electrodialysis. Further characterization showed that, in addition to the expected increase in specific selectivity with respect to singly charged counterions, there was an increase in the overall selectivity with respect to counterions. We provide data from measurements of electrical conductivity, diffusion permeability, and the results of calculating the transport numbers of counterions, demonstrating an increase in selectivity.

Functional Stability of Novel Homogeneous and Heterogeneous Cation Exchange Membranes for Abiotic and Microbial Electrochemical Technologies

Functional Stability of Novel Homogeneous and Heterogeneous Cation Exchange Membranes for Abiotic and Microbial Electrochemical Technologies

Silane functionalized graphene oxide-bound polyelectrolyte layers for producing monovalent cation permselective membranes

This study reports a novel layer-by-layer (LbL) strategy for producing a monovalent cation perm-selective membrane with an improved antifouling property. LbL architectures were fabricated by using the polyvinyl chloride (PVC) based heterogeneous cation exchange membrane as the substrate and chitosan (CS) and polyacrylic acid (PAA) as the polycation and polyanion, respectively. The coating layers on the substrate consist of 1.5 bilayers with CS as the initiating and terminating layer and PAA blended with silane functionalized graphene oxide (S-f-GO) as the middle layer. Molecular electrostatic potential (MEP) of the utilized materials proved the availability of appropriate reactive sites in their structures. FTIR spectra, EDX analysis, zeta-potential measurement, and FESEM images verified successful LbL assembly of CS and PAA blended with S-f-GO. The presence of S-f-GO in the anionic layer of the LbL architectures caused more compactness of the terminating cationic layer and increased the porosity of the anionic layer. LbL membranes containing S-f-GO possessed lower surface roughness and more hydrophilic surface and provided higher antifouling property, monovalent selectivity, and electrical conductivity than LbL architecture without additive. Results showed that utilizing 2 wt% S-f-GO in the anionic layer led to increasing permselectivity (PMg2+Na+)from 1.03 to 6. Also, the incorporation of S-f-GO was found to enhance the regeneration ability of the LbL membranes. This novel strategy for producing the MCPM can open up a new insight into designing advanced monovalent selective ion exchange membranes.

Overlimiting convection at a heterogeneous cation-exchange membrane studied by particle image velocimetry

Electroconvection and gravitational convection are recognized as the primary mechanisms driving overlimiting currents in ion-exchange systems. Here, we use particle image velocimetry (PIV) to characterize the convection on a small piece of a commercially available heterogeneous cation-exchange membrane. We perform chronoamperometric measurements under various experimental conditions and simultaneously record the developed convection at the membrane-electrolyte solution interface using tracking particles. The convection is observed independently in horizontal and vertical planes, capturing flow fields pertinent to electroconvection and gravitational convection. PIV analysis computes velocity vector fields we employ to calculate the volumetric flow rate through a virtual semi-cylindrical wall around the membrane. The volumetric flow rate represents a way how to quantify the intensity of electroconvection. The electroconvection recorded on the horizontal plane manifests itself as a local short-range chaotic whirring localized at the membrane surface superimposed by two long-range counter-current vortices. The volumetric flow rate associated with the two counter-current vortices almost linearly increases with voltage and decreases with increasing concentration. The stagnant points of the vortices localize from 100 to 450 μm away from the membrane. The convection observed on the vertical plane occurs as a result of electroconvection and gravitational convection. We show that gravitational convection eventually dominates and produces an upward-directed intensive flow with similar values of characteristic velocities as the electroconvection. The development of the gravitational convections is approximately one order of magnitude slower (on the order of seconds) than that of electroconvection (on the order of hundreds of milliseconds).

The effect of 3D printing parameters on electrochemical properties of heterogeneous cation exchange membrane

PurposeThe study aims to focus on the preparation of a heterogeneous cation exchange membrane by a three-dimensional (3D) method – fused filament fabrication using a series of nozzles of various diameters (0.4–1.0 mm). Polypropylene random copolymer (PPR) as a polymeric binder was mixed with 50 Wt.% of the selected conventional cation exchange resin, and a filament was prepared using a single screw mini extruder. Then filament was processed by FFF into the membranes with a defined 3D structure.Design/methodology/approachElectrochemical properties, morphology, mechanical properties and water absorption properties were tested.FindingsDependence of the tested properties on the used nozzle diameter was found. Both areal and specific resistances increased with increasing nozzle diameter. The same trend was also found for permselectivity. The optimal membrane with permselectivity above 90%, areal resistance of 8 O.cm2 and specific resistance of 124 O.cm2 was created using a nozzle diameter of 0.4 mm.Originality/valueUsing new materials for 3D print of cation exchange membrane with production without waste. The possibility of producing 3D membranes with a precisely defined structure and using a cheap 3D printing method. New direction of membrane structure formation. 3D-printed heterogeneous cation exchange membranes were prepared, which can compete with commercial membranes produced by conventional technologies. 3D-printed heterogeneous cation exchange membranes were prepared, which can compete with commercial membranes produced by conventional technologies.

Modification of a heterogeneous cation-exchange membrane by Ti-Si based particles to enhance electroconvection and mitigate scaling during electrodialysis

Relatively low counterion fluxes and scaling on the ion-exchange membranes are the major factors limiting commercial applications of electrodialysis. A strategy for simultaneous mass transfer increase and scaling mitigation is realized by adjusting the membrane surface charge. The strategy involves modification of a heterogeneous cation-exchange membrane МК-40 by coating its surface with a thin film of a perfluorosulfonic acid polymer containing metal oxide particles. A series of samples with the particles, which differ in the composition and functional groups grafted to their surface, is studied. The best performance is demonstrated by the sample containing TiO2 and the sample containing Ti-Si based particles grafted with –(CH2)3Cl functional groups. These samples possess an optimal combination of surface properties with respect to the development of electroconvection, namely, a high surface charge while maintaining a sufficiently low degree of its hydrophilicity along with the “better” distribution of current lines at the membrane surface. This results in an increase in mass transfer (an increase in the limiting current density reached 50 % in comparison with the initial membrane) and a decrease in water splitting. These samples are characterized by a significant decrease in scaling during electrodialysis treatment of a model solution containing ions capable of forming sparingly soluble and insoluble compounds at elevated pH. Thus, the enhancement of electroconvection of the depleted solution at the surface of the modified membranes increases mass transfer rate and reduces scaling due to the suppression of water splitting (pH shift) and inducing hydrodynamic factor that can flush away scale deposits from the membrane surface.

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.

Effect of current-induced coion transfer on the shape of chronopotentiograms of cation-exchange membranes

Chronopotentiometry using pulses of a constant current of density j is a powerful method for characterizing ion-exchange membranes (IEMs). We report on the influence of coion transport on the shape of chronopotentiogram (ChP) and the consequent new possibility of quantifying coion transport based on ChP analysis. We show that in the case where the bathing solution contains Ca2+ or Mg2+ ions, the ChPs of the homogeneous (CMX) and heterogeneous (MK-40) cation-exchange membranes at overlimiting current densities have a maximum (a peak), which appears a few seconds after the transition time. The time required to reach a stationary state is of the order of d2/D‾2 (where d is the membrane thickness and D‾2 is the coion diffusion coefficient in the membrane); this time under our experiment conditions is about 300–400 s. We show that the cause of the maximum is the increase in coion transfer caused by the current-induced concentration polarization of the bathing solution. This increase in coion transfer results in increasing the limiting current density jlim, which at j = const leads to a reduction in the resistance of the depleted diffusion layer over time and the appearance of a maximum on the ChP. 1D mathematical modeling is based on the Nernst-Planck-Poisson equations. The main assumption inspired by the works of Levich and Amatore is that the apparent electrolyte diffusion coefficient in the depleted solution increases with increasing electroconvection. The stationary value of this diffusion coefficient is found from the I–V curve. The only fitting parameter is the critical potential difference, which refers to the onset of intensive electroconvection.

The Development of Electroconvection at the Surface of a Heterogeneous Cation-Exchange Membrane Modified with Perfluorosulfonic Acid Polymer Film Containing Titanium Oxide

One way to enhance mass transfer and reduce fouling in wastewater electrodialysis is stimulation of electroconvective mixing of the solution adjoining membranes by modifying their surfaces. Several samples were prepared by casting the perfluorosulfonic acid (PFSA) polymer film doped with TiO2 nanoparticles onto the surface of the heterogeneous cation-exchange membrane MK-40. It is found that changes in surface characteristics conditioned by such modification lead to an increase in the limiting current density due to the stimulation of electroconvection, which develops according to the mechanism of electroosmosis of the first kind. The greatest increase in the current compared to the pristine membrane can be obtained by modification with the film being 20 μm thick and containing 3 wt% of TiO2. The sample containing 6 wt% of TiO2 provides higher mass transfer in overlimiting current modes due to the development of nonequilibrium electroconvection. A 1.5-fold increase in the thickness of the modifying film reduces the positive effect of introducing TiO2 nanoparticles due to (1) partial shielding of the nanoparticles on the surface of the modified membrane; (2) a decrease in the tangential component of the electric force, which affects the development of electroconvection.

Structure and transport properties of polyvinyl chloride-based heterogeneous cation-exchange membrane modified by additive blending and sulfonation

In this work, the structure-performance relationship of modified heterogeneous ion-exchange membranes (IEMs) was investigated by the microheterogeneous model. Polyvinyl chloride (PVC)-based IEM has been modified by introducing hydrophilic additive and immersing in sulfuric acid solution. The modified membrane has displayed a high degree of structural heterogeneity with inter-gel phase fractions (f2) of 0.28 to 0.43. The α value isaround 0.20–0.31 which indicates that the prepared membranes have a randomly distributed conductive phase. In general, the inter-gel phase fraction (f2) has a positive effect on membrane conductivity. However, membrane permselectivity decreases at higher inter-gel phase fraction. The addition of hydrophilic polymer increases the fraction of inter-gel phase while the sulfuric acid immersion increases the gel-phase conductivity (kg). Moreover, it has been found that the permselectivity is linearly correlated to kg/f2.