Heterogeneous Cation Exchange Membranes Research Articles

Electrochemical properties and structure of ion-exchange membranes upon thermochemical treatment

The effect of temperature-induced morphological changes on the electrochemical and physicochemical properties of the heterogeneous sulfo cation-exchange membrane MK-40 in aqueous, alkaline, and acidic media is subjected to comparative analysis. The deviation between the surface and volume microstructure of swollen membrane samples after their chemical conditioning and thermochemical treatment are visualized by a scanning electron microscope. The porosity and the fraction of the ion-exchange component in membranes subjected to heating in water and aggressive media are observed to increase more noticeably in their surface layer as compared with their volume. The maximum effect thus modified structural characteristics on the transport (conductivity, diffusion permeability, selectivity) and physicochemical (exchange capacity, water content, density, linear sizes) properties is observed for MK-40 membrane samples when heated in a sulfuric acid solution. The effect of thermal destruction of inert polymers (divinylbenzene, caprone) involved in the membrane composition on the transport characteristics is revealed.

Sulfonation Process and Desalination Effect of Polystyrene/PVDF Semi-Interpenetrating Polymer Network Cation Exchange Membrane

With the classical sulfonation method of polystyrene-based strongly acidic cation exchange resins, polystyrene/polyvinylidene fluoride (PVDF) alloy particles were sulfonated to obtain a cation exchange resin, which was then directly thermoformed to prepare a semi-interpenetrating polymer network (semi-IPN) cation exchange membrane. The effects of the swelling agent, sulfonation time and temperature and the relative contents of polystyrene and divinylbenzene (DVB) in the alloy particles on the feasibility of the membrane formation are discussed. The results indicate that a favorable sulfonation degree above 80% and a suitable ion exchange capacity of 1.5–2.4 mmol/g can be gained, with concentrated sulfuric acid as the sulfonation agent and 1,2-dichloroethane as the swelling agent. The running electrical resistance and desalination effect of the prepared cation exchange membrane were measured in a pilot-scale electrodialyser and not only obviously exceeded a commercial heterogeneous cation exchange membrane, but was also very close to a commercial homogenous membrane. In this way, the authors have combined the classical sulfonation method of polystyrene-based cation exchange resins with the traditional thermoforming manufacturing process of heterogeneous cation exchange membranes, to successfully develop a novel, low-price, but relatively high-performance polystyrene/PVDF cation exchange membrane with the semi-IPN structure.

Fabrication of novel mixed matrix electrodialysis heterogeneous ion-exchange membranes modified by ilmenite (FeTiO3): electrochemical and ionic transport characteristics

Novel mixed matrix polyvinylchloride-based electrodialysis heterogeneous cation-exchange membranes were prepared by casting technique. Ilmenite (FeTiO3) was employed as additive in membrane fabrication. The effect of additive concentration on electrochemical properties of membranes was studied. Water content was decreased slightly by increase of FeTiO3 concentration. Ion-exchange capacity was improved initially by increase in additive content to 16 wt.% and then showed decreasing trend by more additive loading. Membrane potential, transport number and selectivity were enhanced initially in NaCl solution by increase of FeTiO3 content up to 16 wt.% and then decreased by more additive loading. Increment of FeTiO3 concentration led to decrease of selectivity and transport number in BaCl2 solution. Permeability and flux were declined slightly by increase in additive content up to 8 wt.% and then began to increase sharply by more additive content from 8 to 16 wt.%. Permeability and flux were decreased again by more additive concentration from 16 to 32 wt.%. Electrodialysis experiment results in laboratory scale showed higher dialytic rate for modified membrane compared to pristine one. Membrane areal electrical resistance was declined by increase of additive concentration. Membranes exhibited higher selectivity and flux for monovalent ions compared to bivalent ones.

Fabrication of novel heterogeneous cation exchange membrane by use of synthesized carbon nanotubes-co-copper nanolayer composite nanoparticles: Characterization, performance in desalination

In this research polyvinyl chloride/multi walled carbon nanotube–co-copper nanolayer composite nanoparticles heterogeneous cation exchange membranes were prepared by solution casting techniques. The MWCNT–co-Cu nanolayer composite nanoparticles were prepared by magnetron sputtering method. The effect of composite nanoparticle concentration on physico-chemical properties of membranes was studied. The SEM, TEM and XRD results showed uniform distribution and crystalline structure for the deposited Cu nanolayer on the MWCNTs' surface. SOM images also showed relatively uniform particle distribution for the membranes. The membrane potential, transport number, selectivity and electrical conductivity were improved by an increase of additive content in prepared membranes. Membrane average roughness was decreased slightly by an increase of additive concentration. Membrane ionic permeability and flux were decreased initially by an increase of additive ratio up to 0.5wt.% and then showed an increasing trend by more additive concentration. Furthermore, mechanical stability of prepared membranes was improved by an increase of MWCNT–co-Cu nanolayer composite nanoparticle content in membrane matrix. Also, modified membrane containing 4wt.% composite nanoparticles showed better electrochemical properties compared to other modified membranes, membrane containing pure MWCNTs and unmodified ones.

Fabrication and modification of mixed matrix polyvinylchloride based heterogeneous cation exchange membrane by Ag nanolayer/plasma treatment: investigation of nanolayer deposition rate effect

Abstract In this research, mixed matrix cation exchange membranes were prepared by the solution casting technique using polyvinylchloride (PVC) as base binder, resin powder as functional groups agent, iron-nickel oxide nanoparticles as adsorptive filler and silver (Ag) nanolayers as surface modifier. Ag nanolayer was deposited on the membrane surface by the magnetron sputtering method. The effects of nanolayer deposition rate (low, medium and high) on physicochemical and antibacterial characteristics of the membranes were studied. X-ray diffraction (XRD) results revealed that membrane crystallinity was improved with increase in deposition rate. In addition, atomic force microscopy (AFM) results showed that membrane roughness was decreased by increase in deposition rate. Membrane selectivity was slightly enhanced by increase in Ag nanolayer deposition rate in modified membranes. Ionic fluxes were also increased by increase in Ag nanolayer deposition rate in membranes. Moreover, membranes containing Ag nanolayers showed good ability in Escherichia coli removal. The Ag nanolayer-modified membranes at a high deposition rate showed better performance compared to others.

Surface modification of heterogeneous cation exchange membranes by simultaneous using polymerization of (acrylic acid-co-methyl methacrylate): Membrane characterization in desalination process

In the current research poly(vinyl chloride) based composite heterogeneous cation exchange membranes were prepared by solution casting technique. Poly(acrylic acid)-co-poly(methyl methacrylate) was used as membrane surface modifier by emulsion/graft polymerization technique to improve the membrane electrochemical properties. Also the effect of used emulsifier content ratio in modifier emulsion on properties of membranes was studied. The FT-IR spectrum analysis decisively proved the graft polymerization of poly(acrylic acid)-co-poly(methyl methacrylate). SOM images showed uniform particle distribution and relatively uniform surfaces for the membranes. Results revealed that surface modification of membrane led to increase in membrane potential, transport number, selectivity, surface charge density, ion exchange capacity and ionic permeability in modified membranes. Also, results showed that increase of emulsifier (SDBS) ratio in used emulsion led to increase in membrane transport number, selectivity and ionic flux for the modified composite membranes. Conversely, opposite trends were found for membrane electrical resistance by AA-co-MMA polymerization.

Ion transport through homogeneous and heterogeneous ion-exchange membranes in single salt and multicomponent electrolyte solutions

The increasing demand for clean industrial processes has intensified the use of electrodialysis in the treatment of metal containing effluents and encourages the investigation of the different phenomena involved in the transport of metal ions through cation-exchange membranes. Ion sorption, chronopotentiometric and current–voltage characteristics have been obtained to characterize the transport of sodium and iron through homogeneous and heterogeneous cation-exchange membranes. The heterogeneous membranes having a broader pore size distribution showed increased electrical resistances with solutions of trivalent iron, which may be caused by the blockage of the smallest pores by multivalent ions. However, for both types of membranes an unexpected decrease of the electrical resistance with increasing current densities was verified with concentrated solutions of Fe2(SO4)3. This behavior was explained to be a consequence of the dissociation of FeSO4+ ions into more conductive Fe3+ and SO42− ions as the depleting solution layer becomes diluted. When tested with multicomponent mixtures, the homogeneous perfluorosulfonic membranes show an increased preference for Na+ ions at low current densities and, once Na+ ions are depleted from the membrane surface Fe3+ ions are transported preferentially at higher current densities. On the contrary, both Na+ ions and Fe(III) species are responsible for the ion transport through the heterogeneous membranes within the ohmic regime of currents.

Preparation and characterization of nanocomposite heterogeneous cation exchange membranes modified by silver nanoparticles

We prepared polyvinylchloride based nanocomposite heterogeneous cation exchange membranes by solution casting technique using cation exchange resin powder as functional groups agent and tetrahydrofuran as solvent. Silver nanoparticles were also used as fillers in membrane fabrication. The effect of silver nanoparticles concentration in casting solution on membrane physico/chemical and antibacterial characteristics was studied. The SEM images showed compact structure for the modified membranes. X-ray diffraction results also revealed that membrane crystallinity was clearly changed by increase of nanoparticle concentration. Membrane selectivity and transport number were enhanced initially by increase in nanoparticle content up to 4%wt in prepared membrane, and then showed decreasing trend by more increase in additive concentration from 4 to 8%wt. Selectivity and transport number were enhanced another time by further increase in nanoparticle loading ratio from 8 to 16%wt. Opposite trend was found for the membranes’ average grain size by variation in additive content. Ionic flux was also clearly enhanced by using Ag nanoparticles in membrane matrix. Moreover, modified membranes showed good ability in decrease of Escherichia coli growth rate.

Electrochemical characterization of mixed matrix heterogeneous cation exchange membrane modified by aluminum oxide nanoparticles: Mono/bivalent ionic transportation

Polyvinylchloride/aluminum oxide nanoparticles mixed matrix heterogeneous cation exchange membranes were prepared by solution casting technique. The effect of Al2O3 nanoparticles concentration on membrane electrochemical properties was studied. It was found that membrane water content was enhanced by increase of additive concentration in prepared membrane. Increase of aluminum oxide nanoparticles loading ratio in casting solution also caused to decrease in ion exchange capacity. Obtained results revealed that membrane permselectivity and transport number were improved initially in sodium chloride and barium chloride ionic solutions by increase of aluminum oxide nanoparticles concentration up to 2wt% in prepared membranes and then showed decreasing trend by more increase in additive content. Also membranes exhibited lower selectivity and transport number for bivalent ions in comparison with monovalent ones. Furthermore, membrane ionic permeability and flux were decreased initially by increase in aluminum oxide nanoparticles loading ratio up to 2wt% and then increased again by more additives concentration. Opposite trend was found for membrane areal electrical resistance. Results showed that modified membranes in this study are comparable with that of other commercial ones.

Surface modification of heterogeneous cation exchange membrane through simultaneous using polymerization of PAA and multi walled carbon nano tubes

Polyvinylchloride based heterogeneous cation exchange membrane was modified by using in situ polymerization of polyacrylic acid and multi walled carbon nano tubes simultaneously. Spectra analysis confirmed graft polymerization decisively. SEM images illustrated that grafted-PAA/MWCNTs filled the cracks in membrane by simple gel network entanglement. Ion exchange capacity was improved by PAA/MWCNTs grafting in modified membranes. Membrane water content was decreased by PAA grafting and then showed increasing trend by using MWCNTs in modifier solution up to 0.1%wt. Water content was decreased again by more MWCNTs loading ratio. Grafted-PAA membranes showed lower membrane potential, transport number, selectivity and flux compared to pristine membrane in sodium chloride ionic solution. These parameters were decreased more by using MWCNTs up to 0.1%wt in modifier solution and then showed increasing trend by more MWCNTs concentration from 0.1 to 0.3%wt. All mentioned parameters were declined again by more increase in MWCNTs content from 0.3 to 1.0%wt. Results exhibited lower membrane selectivity for the modified membranes compared to pristine ones in bivalent ionic solution. The grafted-PAA/MWCNTs modified membranes also showed lower electrical resistance compared to unmodified ones. Obtained results showed different behavior for permeability in bivalent ionic solution compared to monovalent type.

Fabrication and electrochemical characterization of PVC based electrodialysis heterogeneous ion exchange membranes filled with Fe3O4 nanoparticles

In this research, novel polyvinylchloride based electrodialysis heterogeneous cation exchange membranes were prepared by casting technique. Iron oxide nanoparticle was also employed as additive in membrane fabrication. The effect of additive concentration on electrochemical properties of homemade membranes was studied. SOM images showed uniform particles distribution and relatively uniform surfaces for the membranes. Membrane water content and ion exchange capacity were increased initially by increase in additive loading ratio to 2%wt and then showed decreasing trend by higher additive content to 8%wt. Membrane potential, permselectivity and transport number all were enhanced with increase of additive content in sodium and barium chloride ionic solutions. They showed different behaviors for the membranes in lead nitrate ionic solution. Membranes exhibited lower potential, selectivity and transport number for bivalent ions compared to monovalent ones. Permeability and flux were enhanced initially in sodium and barium chloride ionic solutions by increase in additive content up to 2%wt and then began to decrease by more additive loading. The electrodialysis experiment results showed that dialytic rate of lead ions removal was increased obviously by increase of additive concentration. Modified membranes showed better electrochemical properties compared to pristine one.

Electrochemical, morphological and antibacterial characterization of PVC based cation exchange membrane modified by zinc oxide nanoparticles

In the current research, mixed matrix polyvinylchloride based heterogeneous cation exchange membranes were prepared by solution casting technique. Zinc oxide nanoparticle was also utilized as additive in membrane fabrication. The effect of ZnO nanoparticles concentration in casting solution on physico-chemical and antibacterial characteristics of membranes was studied. SEM images showed compressed structure for the modified membranes. Images also exhibited relatively uniform surfaces for the membranes. 3D SEM images showed smooth surface for membranes at high ZnO loading ratio content. X-ray diffraction results revealed that membrane crystalinity was improved by increase of nanoparticles’ concentration. The membrane selectivity and transport number were increased initially by increase of additive content up to 8 %wt in casting solution and then showed decreasing trend by more ZnO concentration to 16 %wt. The membrane ionic flux also enhanced initially by increase of zinc oxide nanoparticles content up to 4 %wt and then began to decrease. The modified membrane containing 4 %wt zinc oxide nanoparticles showed superior characteristics compared to other modified membranes and pristine/unmodified ones. The modified membranes also showed good ability in E.coli removal.

Fabrication of mixed matrix heterogeneous ion exchange membrane by multiwalled carbon nanotubes: Electrochemical characterization and transport properties of mono and bivalent cations

In this research, polyvinylchloride/multiwalled carbon nanotubes (MWCNTs) mixed matrix heterogeneous cation exchange membranes were prepared by solution casting technique. The effect of MWCNT concentration on membrane electrochemical characteristics was studied. Membrane water content was increased initially by increase of additive concentration up to 4wt.% and then showed decreasing trend by more additive content. Increase of MWCNTs' loading ratio in casting solution also caused to decrease in ion exchange capacity. Membrane permselectivity and transport number were declined initially for monovalent ionic solution by increase of additive loading up to 4wt.% and then increased by more additive concentration. Results revealed that membrane selectivity and transport number were improved slightly in bivalent ionic solution by increase of MWCNT concentration up to 8wt.% and then decreased sharply by more additive concentration. The monovalent ionic flux was enhanced by increase of additive content. Also ionic flux was improved initially for bivalent ions by increase of additive concentration up to 2wt.% and then decreased by more additive concentration from 2 to 8wt.%. The bivalent ionic flux showed increasing trend with further increase in additive concentration. Membrane areal electrical resistance was decreased by increase of additive concentration.

Fabrication and modification of polyvinylchloride based heterogeneous cation exchange membranes by simultaneously using Fe-Ni oxide nanoparticles and Ag nanolayer: Physico-chemical and antibacterial characteristics

Polyvinylchloride-blend-styrene butadiene rubber based nanocomposite cation exchange membranes were prepared by solution casting technique. Iron-oxide nanoparticles and Ag-nanolayer were simultaneously utilized as filler and surface modifier in membrane fabrication. The effects of Ag-nanolayer film thickness on membrane physicochemical and antibacterial characteristics of nanocomposite PVC-blend-SBR/Iron-oxide nanoparticles were studied. SEM images showed membrane roughness decreasing by Ag nanolayer thickness increasing. Membrane charge density and selectivity declined by Ag nanolayer coating up to 5 nm in membranes and then showed increasing trend by more nanolayer thickness. Ionic flux also showed increasing trend. Membranes showed good ability in E-Coli removal. 20 nm Ag-nanolayer coated membrane showed better performance compared to others.

Preparation and characterization of semi‐interpenetrating network polystyrene/PVDF cation exchange alloy membranes

AbstractThe polystyrene‐DVB/PVDF alloy particles were prepared by pulverizing the polymerization product of styrene/DVB/PVDF in DMF, and then sulfonated with concentrated sulfuric acid to gain the cation exchange alloy powder, which was directly thermoformed by a hot‐press machine to form the titled cation exchange alloy membranes with the structure of semi‐interpenetrating polymer network. The effects of the polystyrene‐DVB to PVDF mass ratio and the DVB content in the monomers on the physical and electrochemical properties of the prepared alloy membranes were investigated. While the Fourier transform infrared spectroscopy (FTIR) confirms the components of membranes, the scanning electron microscopy (SEM) reveals that the alloy membranes possess a uniform distribution of functional groups, and a more dense structure with the increases of DVB content and PVDF content. The optimal prepared membranes have the area electrical resistance values within 3.0–6.6 Ω·cm2, obviously superior to the commercial heterogeneous cation exchange membrane, as well as the moderate water contents of 35–40% and the desirable permselectivity with a transport number more than 0.95. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1220‐1227, 2013

Improving the Electrochemical Properties of Electro-Dialysis Heterogeneous Cation Exchange Membrane by Surface Modification

In this research, the surface modification of heterogeneous cation exchange membrane was carried out to achieve efficient electrochemical properties which are useful in applications such as electro-dialysis processes related to water recovery and water treatment. For the purpose, styrene butadiene rubber (SBR), multi walled carbon nano tube (MWCNT), activated carbon (AC), and sodium dodecyl sulphate (SDS) were used. A thin film of (SBR), (SBR-blend-MWCNTs), (SBR-blend-AC), and (SBR-blend-SDS) was applied as surface modifier on the virgin membrane surface using the casting technique. Scanning electron microscope (SEM) images indicated that the membrane surface modification results in filling of cracks and fissures with the modifier. Besides surface coating, the diffusion of the modifier into the membrane matrix occupies the voids, cavities, and fissures in the membrane matrix. The results revealed that the membrane potential, transport number, and selectivity, all are improved by the surface modification. (SBR-blend-SDS) coated membrane exhibited lower potential, transport number, and selectivity compared to other modified membranes. The SBR coating of the virgin membrane decreased the ionic permeability and flux which increased again by additive loading in the modifier solution. Conversely, membrane real electrical resistance showed an opposite trend. The (SBR-blend-AC) coated membrane showed better performance compared to the virgin type and other modified membranes.

Use of electrochemical impedance spectroscopy for determining the diffusion layer thickness at the surface of ion-exchange membranes

Three ion-exchange membranes (an AMX homogeneous anion-exchange membrane, a MK-40 heterogeneous cation-exchange membrane, and a Nafion-117 homogeneous cation-exchange membrane) have been studied by electrochemical impedance spectroscopy. Processing of the experimental impedance spectra according to the model developed previously has made it possible to find the Nernst diffusion boundary layer (DBL) thickness δ as a function of current density. The behavior of the AMX membrane has been shown to be close to the “ideal” one described by the model: the impedance spectrum of the membrane is close to the theoretical spectrum and the value of δ is only slightly smaller than the quantity δLev calculated by the Leveque equation derived in terms of classical convective diffusion theory. The behavior of the MK-40 and Nafion membranes markedly differs from the “ideal” behavior: the reactive component of the impedance in the region of medium frequencies corresponding to the maximum point in the low-frequency range of a Warburg type finite-length impedance spectrum is significantly lower than its theoretically predicted value. The value of δ is less than δLev even for underlimiting currents, and the deviation increases with the increasing current density. This specific behavior of the membranes correlate well with the voltammetry data. The behavior of the studied membranes is associated with the surface properties: the heterogeneity (case of MK-40) and, especially, high hydrophobicity of the (Nafion-117) surface facilitate the development of electroconvection. Homogeneity and high hydrophilicity of the surface of the AMX membrane determine its behavior, which is close to the ideal.

Preparation and characterization of PVC based heterogeneous ion exchange membrane coated with Ag nanoparticles by (thermal-plasma) treatment assisted surface modification

PVC based heterogeneous cation exchange membranes were prepared by solution casting technique. Ag nanoparticles were also utilized as surface modifier by plasma treatment. Thermal treatment was used to improve the Ag nanoparticles stability on membrane surface. The effect of treating temperature on separation characteristics of coated membranes was studied. SEM images showed membrane rugosity increasing by the increase of treating temperature. Transport number, selectivity and permeability were enhanced initially by increase of treating temperature up to 80°C and then showed decreasing trend. Conversely membrane resistance showed opposite trend. Modified membrane at 80°C showed better performance compared to others.

Fabrication of (polyvinyl chloride/cellulose acetate) electrodialysis heterogeneous cation exchange membrane: Characterization and performance in desalination process

In this research, polyvinylchloride (PVC)/cellulose acetate (CA) blend heterogeneous cation exchange membranes were prepared by solution casting technique using tetrahydrofuran as solvent and cation exchange resin powder as functional groups agent. CA was employed in membrane fabrication to improve the hydrophilicity of membranes. The effect of blend ratio of polymers binder (PVC to CA) on physico-chemical characteristics of home-made membranes was studied. Scanning optical microscopy (SOM) images showed uniform particles distribution and relatively uniform surfaces for the membranes. Membrane water content and surface hydrophilicity were enhanced with increase of CA blend ratio in casting solution. Membrane ion exchange capacity was also improved slightly with increase of CA ratio in prepared membranes. Membrane fixed ion concentration, membrane potential, charge density, permselectivity, transport number and areal electrical resistance all showed decreasing trends by the increase in CA blend ratio in casting solution. Results revealed that ionic permeability and flux were initially enhanced by the increase of CA concentration up to 20%wt in casting solution and then showed decreasing trend by more CA loading from 20 to 50%wt. These parameters were enhanced again by more increase in CA ratio from 50 to 100%wt in prepared membranes.

Preparation and Electrochemical Characterization of Monovalent Ion Selective Poly (Vinyl Chloride)-Blend-Poly (Styrene-Co-Butadiene) Heterogeneous Cation Exchange Membrane Coated with Poly (Methyl Methacrylate)

In this research, polyvinylchloride/ styrene-butadiene-rubber blend heterogeneous cation exchange membranes were prepared by solution casting technique using tetrahydrofuran as solvent and cation exchange resin powder as functional groups agent. Poly methyl methacrylate (PMMA) was also employed as membrane surface modifier by emulsion polymerization technique to improve the membrane selectivity and anti-fouling property. The effect of used emulsion composition on properties of home-made membranes was studied. SOM images showed uniform particles distribution and relatively uniform surfaces for the membranes. Results revealed that surface modification of membrane led to decrease in water content, ion exchange capacity, and ionic permeability in composite membranes. Membrane potential, transport number, selectivity, ionic concentration, and membrane surface electrical resistance all were increased by the PMMA coating on membrane surface. Also, the results showed that decrease of (Methyl methacrylate (MMA): Sodium dodecyl benzene solfanate (SDBS)) ratio in used emulsion during the modification process led to decrease in water content, IEC and permeability in composite membranes. Conversely, opposite trends were found for membrane potential, transport number, selectivity, and electrical resistance by (MMA: SDBS) ratio decreasing in used emulsion. Composite membranes exhibited higher potential, selectivity, transport number, and permeability for monovalent ions compared to bivalent ones. Modified membranes showed good ability in (monovalent/ bivalent) ions separation.