Cation Permselective Membrane Research Articles

Cation-permselective membranes enabled by synergistic ion channels of crown ethers and anionic sites

The specific interaction existing between crown ethers (CEs) and alkali metal ions serves a dual purpose in both facilitating the selective ion transport across polymeric membranes and exerting a significant influence on the microstructure by means of non-covalent interactions among the CEs. In this study, synergistic ion channels featuring a bi-periodic structure are constructed using both CEs and sulfonate (−SO3−) groups. It is observed that the membranes with reduced water uptake demonstrate enhanced ion permselectivity, attributable to the partial dehydration of ions during binding behavior. The bi-functional membranes exhibit excellent permselectivity for alkali metal ions, particularly K+, Na+ and Li+ ions, over Mg2+ ions. The permselectivity sequence of K+>Na+>Li+ and the notably superior K+/Mg2+ permselectivity, reaching up to 244.43, is attributed to the relatively stable CE-K+ complex within the channels, as supported by molecular dynamics simulations. Specifically, the fabricated membrane is successfully utilized in a 4-stage “ion-distillation” process, achieving an impressive separation factor for K+/Mg2+ over 40,000. The investigation of the synergy between CEs and anionic sites provides valuable insights for the development of cation-permselective membranes.

Waste acid recovery utilizing monovalent cation permselective membranes through selective electrodialysis

Waste acid recovery utilizing monovalent cation permselective membranes through selective electrodialysis

Precise regulating the hierarchical structure of MCPMs for mono/multivalent ions separation

Surface modification is a promising strategy to prepare monovalent cation perm-selective membranes (MCPMs) that can offer improved perm-selectivity with a slight increase in membrane resistance. Herein, we have developed MCPMs by precisely regulating the hierarchical structure through the auto-mixing of two different polymers (chloromethylated polyethersulfone (CMPES) and sulfonated polyphenylsulfone (SPPSU)) and controlling the electrochemical properties of the top modified layer. In analogy to the penetrating glue, a semi-permeable selective functional layer can be drawn between the supporting membrane and the functional layer in terms of the spreading and solvent evaporation process. With further cross-linking and quaternization, the excess aldehyde groups (CHO) in the functional layer of the membrane can be transformed into -COO- groups in the presence of an alkaline medium. Thus, an electric-double structure was formed. The synergy of the semi-permeable and electric-double hierarchical structure in the MCPMs enables accurate mono/multivalent ion separation during ED-based separation processes.

Effect of [Na+]/[Li+] concentration ratios in brines on lithium carbonate production through membrane electrolysis.

Lithium is a fundamental raw material for the production of rechargeable batteries. The technology currently in use for lithium salts recovery from continental brines entails the evaporation of huge water volumes in desert environments. It also requires that the native brines reside for not less than a year in open air ponds, and is only applicable to selected compositions, not allowing its application to more diluted brines such as those geothermally sourced or waters produced from the oil industry. We have proposed an alternative technology based on membrane electrolysis. In three consecutive water electrolyzers, fitted alternately with anion and cation permselective membranes, we have shown, at proof-of-concept level, that it is possible to sequentially recover lithium carbonate and several by-products, including magnesium and calcium hydroxide, sodium bicarbonate, H2 and HCl. The big challenge is to bring this technology closer to practical implementation. Thus, the issue is how to apply relatively well-known electrochemical technology principles to large volumes and to a highly complex and saline broth. We have studied the application of this new methodology to ternary mixtures (NaCl, LiCl and KCl) with constant LiCl and KCl composition and increasing NaCl content. Results showed very similar behaviour for systems containing [Na+]/[Li+] concentration ratios ranging from 1.24 to 4.80. The voltage developed between the anode and cathode is almost the same in all systems at roughly 3.5 V when a constant current density of 50 A m-2 is applied. The three monovalent cations migrate with different rates across the cation exchange membrane, with Li+ being the most sluggish and thus crystallization of Li2CO3 only occurs close to completion of the electrolysis. The dimensionless concentration profiles are almost indistinguishable despite the changes in total salinity. The solids crystallized from different feeds showed higher Na+ and K+ contents as the initial Na+ concentration was increased. However, solids with over 99.9% purity in Li2CO3 could be obtained after a simple re-suspension treatment in hot water. The electrochemical energy consumption greatly increases with higher Na+ concentrations, and the amount of fresh water that can be recovered is diminished.

Numerical simulation of ion transport across monovalent ion perm-selective membranes

The separation of specific ions is common in chemical processes, including lithium mining, hydrometallurgy, and biochemical engineering. The monovalent cation perm-selective membrane is a vital material for ion classification. Although many advanced membranes with sufficient permeability and selectivity were developed, the systematical relationships between membrane function and ion transport character are still unclear. In this work, we successfully developed a two-dimensional model based on Navier-Stokes and Nernst-Planck-Poisson equations asserted through numerical simulation. The impact of modified layer's thickness, fixed charge concentration, as well as base membrane fixed charge density on ion flux and selectivity were thoroughly investigated. The combined contribution of membrane properties on the trade-off between ion selectivity and permeability was thus established using this innovative simulation and modeling strategy. This is the first systematic research to provide a substantial reference for the development of advanced cation perm-selective membranes for monovalent ions isolation.

Highly efficient monovalent ion transport enabled by ionic crosslinking‐induced nanochannels

AbstractCharge‐governed ion transport is of significant importance to industrial development, and advanced membrane materials with fast and selective ionic transport are essential components. In cell membranes, ionic transport is mainly determined by the charge‐governed protein channels, representing an architecture with functional differentiation. Inspired by this, a novel class of membranes was developed by ionically crosslinking sulfonated (poly[ether ether ketone]) and quaternized poly(2,6‐dimethyl‐1,4‐phenylene oxide) to construct the cationic conductive biomimetic nanochannels. Ionic crosslinking was tailored to realize nanophase separation and efficient ion transport mainly based on surface chemistry without altering the scaffold feature of polymeric pore channels. The best‐performing ionic crosslinking membrane exhibited a high ionic permeation (2.23 mol·m−2·h−1 for K+) and high cationic selectivity (7.91 for K+/Mg2+), which were comparable with the commercial monovalent cation permselective CIMS membrane, owing to the negligent surface resistance toward monovalent cations but strong positively charged repulsion against divalent cations.

Highly efficient Li+/Mg2+ separation of monovalent cation permselective membrane enhanced by 2D metal organic framework nanosheets

Monovalent cation permselective membranes (MCPMs) manifest remarkable effectiveness and potential in lithium extraction whereas facing the challenge to achieve high permselectivity and high Li+ permeability simultaneously. In this work, Zn-TCPP, a kind of two-dimensional nanosheet with abundant negative charges, was successfully synthesized via surfactant-assisted method and introduced into surface cross-linked SPES membrane to fabricate MCPMs. The physicochemical properties, electrochemical properties and Li+/Mg2+ separation performance of resulted MCPMs were systematically estimated. As ions passing through the membrane, dense PVA/GA crosslinked layer separated Li+ and Mg2+ by pore-size sieving effect. Afterwards, uniformly distributed Zn-TCPP nanosheets with rich negative charges and physically adsorbed water molecules elevated the charge density and water content in the membrane and thus expedited Li+ transporting. Therefore, high Li+/Mg2+ permselectivity (PMg2+Li+= 8.99) and Li+ permeation flux (JLi+= 9.12 × 10−9 mol cm−2∙s−1) were obtained. Furthermore, membrane surface resistance was reduced from 108.99 Ω cm2 to 24.12 Ω∙cm2. This study points out the feasibility of the new method for accelerating monovalent ion transport and alleviating the restriction between ion permeation and permselectivity in selective ion exchange membranes.

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.

Optimizing functional layer of cation exchange membrane by three-dimensional cross-linking quaternization for enhancing monovalent selectivity

Monovalent cation perm-selective membrane (MCPMs) allow fast and selective transport of monovalent cations, and they are promisingly required for extraction of special ions, such as lithium extraction, acid recovery and sea salt production. Herein, we report a novel strategy to design the critical functional layers of MCPMs with both space charge repulsion and cross-linked dense screenability. The in-situ deposition polymerization of pyrrole was carried out on the surface of sulfonated polyphenyl sulfone (SPPSU) substrate membrane followed by cross-linking quaternization of the polypyrrole (PPy) layer with diiodinated functional molecules, thus, the membrane obtained more excellent selective permeability and stable transport properties of monovalent cations. It confirms that the designed PPy layers with charged surface and cross-linking structure improved the hydrophilicity, facilitated cation transport and increased ion flux. Meanwhile, for the dense PPy layer, the charged cross-linked structure endowed the functional layer with the synergistic characteristics of Donnan exclusion and pore size sieving for positively charged ions, which improved the monovalent cation perm-selectivity of the membranes. At a constant current density of 5.1 mA/cm2, the optimal membrane exhibited superior perm-selectivity (PMgNa=2.07) and monovalent cation flux (JNa+ = 2.80 × 10 −8 mol cm−2 s−1) during electrodialysis.

Cation Exchange Membranes Coated with Polyethyleneimine and Crown Ether to Improve Monovalent Cation Electrodialytic Selectivity.

Developing monovalent cation permselective membranes (MCPMs) with high-efficient permselectivity is the core concern in specific industrial applications. In this work, we have fabricated a series of novel cation exchange membranes (CEMs) based on sulfonated polysulfone (SPSF) surface modification by polyethyleneimine (PEI) and 4′-aminobenzo-12-crown-4 (12C4) codeposited with dopamine (DA) successively, which was followed by the cross-linking of glutaraldehyde (GA). The as-prepared membranes before and after modification were systematically characterized with regard to their structures as well as their physicochemical and electrochemical properties. Particularly, the codeposition sequence of modified ingredients was investigated on galvanostatic permselectivity to cations. The modified membrane (M-12C4-0.50-PEI) exhibits significantly prominent selectivity to Li+ ions ( = 5.23) and K+ ions ( = 13.56) in Li+/Mg2+ and K+/Mg2+ systems in electrodialysis (ED), which is far superior to the pristine membrane (M-0, = 0.46, = 1.23) at a constant current density of 5.0 mA·cm−2. It possibly arises from the synergistic effects of electrostatic repulsion (positively charged PEI), pore-size sieving (distribution of modified ingredients), and specific interaction effect (12C4 ~Li+). This facile strategy may provide new insights into developing selective CEMs in the separation of specific cations by ED.

Preparation of monovalent cation perm-selective membranes by controlling surface hydration energy barrier

Cationic separating the with different valence states is greatly desirable but technically challenging. Achieving such a precise separation using membranes requires accurately distinguishing tiny differences of cations on physico-chemical properties. Here, inspired by the ion dehydration effect, a series of cation exchange membrane with adjustable surface hydrophobicity based on quaternized polypyrrole were prepared. We demonstrate that improving hydrophobicity of modified layer substantially hinder cations with higher hydration energy to enter the modified layer due to their stronger binding ability with water molecules. When applied in electro-driven cation separation, the optimal membrane exhibited an outstanding perm-selectivity between monovalent and divalent cations (PNaMg = 12.95, PLiMg = 1.28) than commercial monovalent cation perm-selective membrane (PNaMg = 2.46, PLiMg = 1.07). Overall, our results indicate that the hydrophobicity of the modified layer governs the cations dehydration behavior through the polymeric pores due to ion-pore wall interactions, providing the scientific basis for the construction of membranes with high monovalent cation perm-selectivity.

Ti-exchanged UiO-66-NH2–containing polyamide membranes with remarkable cation permselectivity

Monovalent cation permselective membranes (MCPMs) are highly desirable for the extraction of Li+ and Na+ ions from earth-abundant sources, such as salt lakes and seawater. Metal–organic frameworks (MOFs) are promising functional nanomaterials with excellent potential for ion separation technologies owing to their regular structure and tunable pore sizes. However, the successful use of MOFs in ion separation membranes is still challenging owing to the numerous difficulties in preparing ultrathin and defect-free MOF membranes. Here, we proposed a facile post-synthetic method for the preparation of UiO-66(Zr/Ti)–NH2 and subsequently immobilized UiO-66(Zr/Ti)–NH2 in an ultrathin polyamide layer (~100 nm). The resulting thin-film nanocomposite membranes presented high monovalent cation flux and excellent selectivity for mono-/di-valent cations. The PNa+/Mg2+ and PLi+/Mg2+ permselectivities of the best-performing thin-film nanocomposite membrane were 13.44 and 11.38, respectively, which were 3.8 and 5.1 times higher, respectively, than those of the commercial state-of-art CSO membrane.

SPPO-based cation exchange membranes with a positively charged layer for cation fractionation

The synthesis of monovalent cation perm-selective membranes (MCPMs) to efficiently discriminate amongst cations from seawater is of great importance for several industrial applications. However, a technical approach is highly desired to construct MCPMs to obtain a high ionic flux and sustain perm-selectivity, simultaneously. In the present work, the thickness of the quaternized poly (2, 6-dimethyl-1, 4-phenylene oxide) (QPPO) layer on the surface of SPPO-PVA (SPVA) composite membrane was adjusted using a facile procedure to achieve high perm-selectivity without scarifying the ionic flux. The thickness of the selective layer was precisely controlled using various concentrations of the QPPO solution. By the introduction of the cationic layer on the SPVA membrane, the monovalent cation can be separated from the divalent cation by their difference in charge density. The influence of the selective barrier (thickness) endows MCPMs with high perm-selectivity up to 12.7 for 0.1 mol L−1 Li+/Mg2+ system, which is very satisfactory for polymeric membranes. The fabricated membranes have low electrical resistance and high limiting current density (ilim). Keeping in view the ED results, the prepared membranes with selective surface layer could be a viable candidate for Li+ selective separation from divalent cation Mg2+.

Electro-nanofiltration membranes with positively charged polyamide layer for cations separation

High performance and low-cost monovalent cation perm-selective membranes (MCPMs) are extremely desirable since the widespread demand for monovalent/multivalent cations separation. Herein, we developed a simple fabrication method for the preparation of electro-nanofiltration membranes (ENFMs), which were used as MCPMs for cations separation. The ultra-thin polyamide layer of ENFMs could offer selective channels for the transport of monovalent cations. Meanwhile, the positive charges in the polyamide layer act as useful barriers to divalent cations via electrostatic repulsion. The results show that the ENF-Q3 membrane with the highest quaternization degree owns outstanding perm-selectivity for Li+/Mg2+ system (PMg2+Li+=11.3), which is 7 times greater than that of the commercial CSO membrane, and high Li+ flux (JLi+=5.79×10-8mol·cm-2·s-1) at the current density of 10 mA cm−2. Moreover, the ENFMs exhibit high limiting current density and excellent long-term stability, indicating that the developed strategy is promising to scale up for industrial applications.

Zwitterion structure membrane provides high monovalent/divalent cation electrodialysis selectivity: Investigating the effect of functional groups and operating parameters

Monovalent cation perm-selective membranes (MCPMs) with enhanced monovalent flux and the capability to reject multivalent cations are critical; however, their realization remains challenging in various industrial applications, such as seawater desalination and wastewater purification. To achieve this criterion, we designed and synthesized a series of MCPMs with a zwitterion structure comprising three quaternary ammonium groups, two carboxylic acids, and one sulfonic acid group. These functional groups act to balance the cation flux and perm-selectivity of the MCPM. The cation fluxes and perm-selectivity of the fabricated MCPMs were investigated for Na+/Mg2+ and Li+/Mg2+ systems. High perm-selectivities of 58.4 and 16.5 were obtained for (PMg2+Na+) and (PMg2+Li+) systems, respectively, using a QPO/DAN-SA-5 membrane. The performance of the MCPMs was compared with the state-of-art commercial monovalent cation selective membrane NeoseptaTM CIMS. The influence of feed concentration and current density on the cation fluxes and perm-selectivity was examined, and the pH was measured to investigate the effect of concentration polarization and water splitting on electrodialysis. Moreover, the presence of various functional groups in the membrane matrix provided additional insights into electrostatic repulsive and interaction effects. The zwitterion structure of the MCPM was capable of tuning the cation flux and perm-selectivity. Our study provides an effective strategy for developing MCPMs with high cation flux and ion perm-selectivity.

Highly Cation Permselective Metal-Organic Framework Membranes with Leaf-Like Morphology.

Highly cation permselective metal-organic framework (MOF) membranes are desirable for the extraction of valuable metal cations. However, fabrication of defect-free and stable permselective MOF membranes is technically challenging, owing to their arduous self-assembly and poor water resistance, respectively. A simple and readily scalable method has been developed for the controlled in situ smart growth of UiO-66-NH2 into leaf-like nanostructures with tunable density of the leaves and the surface layer thickness. The self-assembly approach reproducibly fabricates seamless, ultrathin (<500 nm) UiO-66-NH2 membranes at the surface of anodic aluminum oxide. The membranes contain nanosized interstices among the MOF leaves, which enable maximum admission of ions within the membrane, and angstrom-sized inherent pores in every single UiO-66-NH2 crystal, which efficiently regulate the cation permselectivity. Consequently, the highest ever reported cation separations (Na+ /Mg2+ >200 and Li+ /Mg2+ >60) and excellent membrane stability during five sequential electrodialysis cycles are achieved. These characteristics position the fabricated MOF membranes as potential candidates for efficient extraction of pure lithium and sodium ions from salt lakes and seawater, respectively.

Asymmetric porous monovalent cation perm-selective membranes with an ultrathin polyamide selective layer for cations separation

Highly permeable and selective membranes are desirable for mono/divalent cations separation. Here, we report the fabrication of a novel monovalent cation perm-selective membrane (MCPM) for selective cations separation via electrodialysis. The selective layer was fabricated via interfacial polymerization of ethylenediamine, tetraethylenepentamine and polyethyleneimine with 1,3,5-benzenetricarbonyle trichloride on the hydrolyzed polyacrylonitrile porous substrate. The negatively charged porous substrate and ultrathin polyamide selective layer could offer multidimensional channels for ions transport. In addition, the transport of large-sized Mg2+ was greatly intercepted by the compact polyamide selective layer, thus the perm-selectivity was significantly improved. High perm-selectivity (PMg2+Na+ = 3.3) which is 94% higher than that of a commercial MCPM was obtained, meanwhile it maintained good Na+ flux (JNa+ = 4.27 × 10−8 mol cm−2 s−1) at a current density of 14 mA cm−2. Furthermore, such unique structure also lead to high limiting current density and excellent long-term stability.

In Situ Raman Spectroscopy as a Tool for Structural Insight into Cation Non-Ionomeric Polymer Interactions during Ion Transport.

Low-modified liquid-crystalline polyether (CP36), as a model compound, was synthesised with the purpose of preparing a membrane with columnar ionic channels. A free-standing cation permselective biomimetic membrane was successfully prepared and found to have channels made of polymeric columns homeotropically oriented, which was confirmed in X-ray diffraction (XRD) analysis. A first insight into a real-time interaction between two selected cations: H+ and Na+, and polyether during transport through the polymeric membrane was demonstrated using joined chronoamperometry and Raman spectroscopy techniques. Raman studies unveiled the possibility for smaller protons to bypass the usual ionic pathway via polyetheric chain and use outer part of ionic channel for conduction thanks to ester bonds.

Fouling prevention of peptides from a tryptic whey hydrolysate during electromembrane processes by use of monovalent ion permselective membranes

Peptide adsorption occurring on conventional anion- and cation-exchange membranes is one of the main technological locks in electrodialysis (ED) for hydrolysate demineralization. Hence, the peptide fouling of monovalent anion (MAP) and monovalent cation (MCP) permselective membranes was studied and compared to conventional membranes (AMX-SB and CMX-SB). It appeared that the main peptide sequences responsible for fouling were TPEVDDEALEKFDK, VAGTWY and VLVLDTDYK for both anionic membranes; and ALPMHIR and TKIPAVFK for both cationic membranes. However based on the MS-MS results, the fouling was about 97–100% lower for MAP than AMX-SB and 95–100% lower for MCP than CMX-SB. This was explained by the differences in charge sign distribution at the membrane surface. Consequently, monovalent membranes can represent a very interesting opportunity for treatment of hydrolysate solution in electrodialytic processes by practically eliminating peptide fouling. At our knowledge, it was the first time that such a demonstration was done.

Monovalent cation perm-selective membranes (MCPMs): New developments and perspectives

As one of the most typical and promising membrane processes, electrodialysis (ED) technique plays a more and more significant role in industrial separation. Especially, the separation of monovalent cations and multivalent cations is currently a hot topic, which is not only desirable for many industries but also challenging for academic explorations. The main aim of the present contribution is to view the advances of a wide variety of monovalent cation perm-selective membranes (MCPMs) and their preparation technologies including (1) covalent cross-linking, (2) surface modification, (3) polymer blending, (4) electrospinning, (5) nanofiltration alike membrane, and (6) organic–inorganic hybrid. The relevant advantages and disadvantages with respect to some specific cases have been discussed and compared in detail. Furthermore, we elaborately discuss the opportunities and challenges of MCPMs, the fabricating strategies to take and the future perspectives.