Separation Of Ions Research Articles

Insight Into the Role of Fiber Diameter on Electrospun Polysulfone Mats

ABSTRACTFiber electrospun mats created using cylindrical collectors have been extensively studied as effective membranes for water treatment. However, the relationships between the properties of electrospun mats and the characteristics and performance of membranes are not well‐established. This research examined two samples with average fiber diameters of 1.8 ± 0.49 μm and 0.47 ± 0.26 μm, which were evaluated as supporting substrates for the separation of MgSO4 ions. The variation in fiber diameter resulted from consistent conditions of voltage, distance, and collector rotation speed, while the injection rates were different, set at 2 mL/h and 0.8 mL/h, respectively. The resulting thin‐film composite (TFC) membrane consists of three layers: the first layer is a mesh polyester that underlies a middle hydrophobic electrospun support layer made from a 20 wt.% polysulfone solution. The third layer is a polyamide layer created through interfacial polymerization, involving a reaction between piperazine (PIP) monomers at a concentration of 2% by weight and trimesoyl chloride (TMC) monomers at a concentration of 0.2% by weight. Due to its hydrophobic nature, PSU repels water monomers from its surface during polymerization. Consequently, surface modification using plasma treatment alters the surface characteristics from hydrophobic to hydrophilic, resulting in the formation of a superior polyamide layer. The results indicate that membranes with larger fiber diameters exhibit a rougher texture. Additionally, the increased void space between the fibers in these membranes leads to an increase in pure water flux that is 92% higher compared to membrane samples with smaller fiber diameters; this higher flux is due to larger pore size. Furthermore, membranes with smaller fiber diameters possess a finer pore structure, resulting in a polyamide layer with fewer defects than membranes with larger fibers. This improved structure achieved a separation efficiency of 68% ± 1.02% for MgSO4, while the membrane with an average fiber diameter of 1.80 ± 0.49 μm demonstrated a separation rate of 20% ± 2.26%. These findings provide a step forward in the development of a theoretical framework for engineering TFC membranes with electrospun mats as supports.

Separation of Copper and Nickel Metal Ions from Electroplating Wastewater by Ultrafiltration with Tartaric Acid and Sodium Citrate Reinforced Sodium Polyacrylate Complexation

In this study, sodium polyacrylate (PAAS) and ultrafiltration membranes were used to extract and separate Cu2+ and Ni2+ ions from electroplating wastewater. The effects of pH, the P/M ratio (mass ratio of sodium polyacrylate to metal ions), tartaric acid, and sodium citrate on the complexation of Cu2+ and Ni2+ by sodium polyacrylate were investigated. The retention of Cu2+ and Ni2+ by PAAS in single metal solutions with a P/M ratio = 4 and pH = 5 differed by 45.36%. When the complexation system of PAAS with a single metal contained tartaric acid and sodium citrate, the retention of PAAS for Cu2+ and Ni2+ increased to 80.36% and 58.84%. PAAS retention for Ni2+ decreased, but retention for Cu2+ remained the same. All the results indicated that there was competition between tartaric acid, sodium citrate, and PAAS for the adsorption of Cu2+ and Ni2+. Some of the Ni2+ complexed with PAAS were detached from PAAS complexed by tartaric acid and sodium citrate and permeated through the membrane pores, while the Cu2+ complexed with PAAS was not complexed by tartaric acid and sodium citrate and could not permeate through the membrane pores. Therefore, this study helps to provide a theoretical basis for the separation of Cu2+ and Ni2+ in electroplating wastewater.

Impact of Ion Migration on the Performance and Stability of Perovskite‐Based Tandem Solar Cells

AbstractThe stability of perovskite‐based tandem solar cells (TSCs) is the last major scientific/technical challenge to be overcome before commercialization. Understanding the impact of mobile ions on the TSC performance is key to minimizing degradation. Here, a comprehensive study that combines an experimental analysis of ionic losses in Si/perovskite and all‐perovskite TSCs using scan‐rate‐dependent current–voltage (J–V) measurements with drift‐diffusion simulations is presented. The findings demonstrate that mobile ions have a significant influence on the tandem cell performance lowering the ion‐freeze power conversion efficiency from >31% for Si/perovskite and >30% for all‐perovskite tandems to ≈28% in steady‐state. Moreover, the ions cause a substantial hysteresis in Si/perovskite TSCs at high scan speeds (400 s−1), and significantly influence the performance degradation of both devices through internal field screening. Additionally, for all‐perovskite tandems, subcell‐dominated J–V characterization reveals more pronounced ionic losses in the wide‐bandgap subcell during aging, which is attributed to its tendency for halide segregation. This work provides valuable insights into ionic losses in perovskite‐based TSCs which helps to separate ion migration‐related degradation modes from other degradation mechanisms and guides targeted interventions for enhanced subcell efficiency and stability.

Enrichment of lithium ions for battery application by electrolysis through a nanoporous membrane

In recent years, lithium (Li) has become a valuable commodity widely used in rechargeable batteries. The present study aims to extract battery-grade lithium-ion, as lithium hydroxide (LiOH), from lithium chloride (LiCl) solution by the membrane electrolysis process. Experiments are performed using a commercial cation exchange membrane and an indigenous High flux-Nanofiltration 300 alkali resistant (HF-NF 300 AR) nanoporous membrane. The dual-chamber electrolytic cell incorporates a selective membrane to separate the feed and concentrate chambers containing LiCl solution and deionized water. These two chambers are connected with titanium electrodes through the external circuit. The in-situ design of the compact two-chambered acrylic electrolytic cell helps to separate metal ions from ionizable salts of sodium, lithium, magnesium, potassium, etc. The experiment is conducted on a laboratory scale by varying the LiCl concentration at voltages of 24 V and 36 V. The feed and concentrate solutions are analyzed for pH, conductivity, and total dissolved solids. Inductively coupled plasma-optical emission spectrometry evaluates the presence of metal ions in the solution. The study shows effective metal ion recovery and separation to achieve battery-grade Li.

Engineering Ion Affinity of Zr-MOF Hybrid PDMS Membranes for the Selective Separation of Na+/Ca2+

Ion-selective separation, especially Na+/Ca2+ separation, is of significant importance in the realms of biomimetic research and the fabrication of biomimetic devices, underscoring the pivotal role that sodium and calcium ions play in cellular metabolism. However, the analogous ionic radii and charge densities shared by sodium and calcium ions significantly impede their effective discrimination, presenting formidable challenges for the precise engineering of ion separation materials, such as separation membranes. In this study, a polydimethylsiloxane (PDMS) separation membrane hybridized with zirconium-based metal–organic frameworks (UiO-66, UiO-66-NO2 and UiO-66-NH2) was constructed. Through the meticulous design of the MOF functional groups, the material’s affinity for specific ions was modulated, thereby achieving efficient Na+/Ca2+ separation. Notably, the PDMS integrated with amino-modified Zr-MOF exhibited an efficacious selective separation of Na+ and Ca2+ ions. The interaction between the amino group of UiO-66-NH2 and Ca2+ gave rise to the observed superior selectivity toward Ca2+ cations and enhanced separation efficiencies of up to 64% compared to pristine PDMS for UiO-66-NH2-embedded membranes.

Graphite-Based Bio-Mimetic Nanopores for Protein Sequencing and Beyond.

Protein sequencing using nanopores represents the next frontier in bio-analytics. However, linearizing unfolded proteins and controlling their translocation speed through solid-state nanopores pose significant challenges in protein sequencing. In order to address these issues, this work proposes a biomimetic graphite-based nanopore construction. These nanopores feature a nanometer-sized pore with a constriction zone, mimicking the structure of the α-hemolysin protein pore. Ourall-atom Molecular Dynamics simulations demonstrate the high practical potential of these nanopores by revealing how their charge state renders them complete ion-selective and generates an electro-osmotic flow. This study shows that this nanopore construction can detect peptides at the single amino acid level by analyzing the ionic current traces generated as peptides traverse the nanopore. The novelty of the proposed nanopore lies in its ability to modulate the hydrodynamic drag induced by electro-osmotic flow, relative to the electro-phoretic force. This investigation reveals that tuning these forces helps to linearize translocating peptides and extend the residence time of individual amino acids at the constriction zone of the pore. This significantly enhances the detection and sequencing efficiency of the pore. Furthermore, the high relevance of the proposed nanopores is underscored for seawater desalination through electrodialysis and extends to ion separation under salinitygradients.

Energy Efficiency Analysis of Hydrate and Ionic Liquid-Based Binary Gas Separation Processes

Energy Efficiency Analysis of Hydrate and Ionic Liquid-Based Binary Gas Separation Processes

Guanidinium‐Based Covalent Organic Framework Membranes for Superior Mono‐ and Divalent Cations Separation

Biological membranes exhibit extraordinary efficiency in processing ion permeability and selectivity. However, creating artificial membranes for an ideal ion separation is still challenging due to the subtle distinctions in valence and size among different ions. In the realm of biological recognition, the ultimate selectivity of ion channels is considered to stem from the specific binding interactions and appropriate charge density. Designing artificial membranes to achieve similar performance not only helps the understanding of complex ion transport in bioprocesses but also facilitates critical industrial separations. Inspiring by the remarkable performance in biological systems, a guanidinium‐based covalent organic framework membrane is designed, which exhibits an excellent capability to recognize mono‐/divalent cations, achieving K+/Mg2+ selectivity up to 202 in a mixed salt solution. Furthermore, the membrane displays rapid ion transport owing to the uniform sub‐2 nm channels. The experimental results and molecular dynamics simulations illustrate that the charge‐assisted hydrogen bonding sites and the Cl− counter ions within 1D channels play critical roles in cations sieving. Specifically, divalent ions passing through the positively charged channels need to overcome higher energy barriers than monovalent ions. These findings offer promising avenues for the development of advanced multifunctional membranes for efficient ion separation and sustainable water‐related separations.

Lysine-regulated turing structure membrane via interfacial polymerization for enhanced Li+/Mg2+ separation

The development of advanced membranes with precise ion selectivity is essential for efficient Li+/Mg2+ separation. In this study, we synthesized a novel Lys-TMC membrane via a nucleophilic addition reaction between Lysine and trimesoyl chloride (TMC), yielding in a negatively charged surface interconnected by amide bonds. We systematically investigated the effects of varying Lys:TMC ratios on the membrane’s chemical structure, surface morphology, and ion separation performance. Our results revealed that the degree of cross-linking increases initially with the Lysine content, reaching an optimum at a Lys:TMC ratio of 10:1, where the membrane exhibited prominent Turing patterns on its surface. These patterns were critical for achieving effective ion separation. In contrast, excessive Lysine led to spontaneous polymerization, resulting in irregular ‘stone-like’ structures and the loss of Turing patterns. The optimally cross-linked Lys-TMC membrane displayed superior Li+/Mg2+ separation performance, highlighting the crucial role of controlled cross-linking and Turing structure formation in enhancing ion selectivity. This work provides a mechanistic understanding of the relationship between Turing structure formation and ion sieving performance, offering a promising strategy for designing advanced separation membranes.

Enhanced removal of fluoride ions using lanthanum-doped coconut shell biochar in PVDF ultrafiltration membranes

Fluoride contamination in surface and ground water poses significant health risks, necessitating a low-energy, cost-effective removal method. Herein, an ultrafiltration (UF) adsorptive membrane doped with lanthanum (La)-based coconut shell biochar was synthesized to effectively remove fluoride ions. Based on the results of adsorption and membrane separation performance, it was found that La-based biochar showed a significantly higher adsorption capacity (126.7 mg F/g) compared to bare biochar (27.41 mg F/g), due to the oxygen-containing functional groups from La2O2CO3 that enhance binding sites and electrostatic attraction for fluoride ions. Furthermore, the addition of La-modified adsorbent to the polyvinylidene fluoride (PVDF) UF membrane markedly altered its structure and surface properties, changing the pore structure to porous, narrowing pore size, increasing active adsorption sites, and improving hydrophilicity. These changes boosted fluoride ion rejection from 9.53 % to 62.07 % with tiny effect on membrane permeability. More important, this UF adsorptive membrane exhibited excellent antifouling ability with the lowest flux decline (J/J0 =0.450) compared to pristine PVDF membrane (J/J0 =0.142), which was owing to the better improved surface properties. In all, this study provides a novel strategy for efficient, economic and selective separation of fluoride ions and further extends the application of UF to the field of ion removal.

Gel Composite Membrane with Tannic Acid/Ferric Ion Separation Layer for Organic Solvent Nanofiltration

Gel Composite Membrane with Tannic Acid/Ferric Ion Separation Layer for Organic Solvent Nanofiltration

Mass Spectrometry Imaging with Trapped Ion Mobility Spectrometry Enables Spatially Resolved Chondroitin, Dermatan, and Hyaluronan Glycosaminoglycan Oligosaccharide Analysis In Situ.

Previously, spatially resolved analysis of glycosaminoglycans (GAGs), by type and sulfation state, was unobtainable. Here, we describe a mass spectrometry imaging (MSI) approach which enables the detection, identification, localization, and profiling of GAG oligosaccharides directly from retinal tissue. Through in situ treatment of tissues with relevant chondroitinase enzymes, we liberate and spatially resolve chondroitin, dermatan, and hyaluronan from disaccharides through to hexasaccharides, directly from tissue sections. We demonstrate the separation of isomeric GAG oligosaccharide ions at different histologically relevant regions using trapped ion mobility spectrometry (TIMS). This paper describes the first spatially resolved analysis of multiple GAGs and their oligosaccharide sulfation state(s) directly from tissues.

Enhancing uranium ion adsorption in wastewater: The role of PEI-PVA/CS xerogel

In the process of recovering uranium resources from uranium-containing wastewater (UCW) via adsorption methods, it is imperative to address challenges related to the stability and selectivity of adsorbents in the separation of uranium ions. Xerogel porous adsorbents have garnered significant research interest for their potential application in uranium ion adsorption, owing to their high porosity, robust plasticity, and abundant functional groups. Based on the efficient separation of uranium by acid-resistant polyvinyl alcohol/chitosan (PVA/CS) xerogel, polyethyleneimine (PEI) was selected to adjust its pores. By examining the characteristics of the modified xerogel both prior to and following U(VI) adsorption, optimizing the conditions for its U(VI) adsorption, and analyzing the separation mechanism of U(VI), the results demonstrate that PEI can effectively modify the pore environment of PVA/CS xerogel. Furthermore, PEI-PVA/CS xerogel maintains consistent U(VI) separation efficacy in UCW across a pH range of 2–7. After five cycles of uranium desorption and adsorption, the adsorption recovery capacity exceeds 97.7 %, with minimal interference from cations. The synergistic effect of -NH2 and -OH functional groups is responsible for the efficient separation of U(VI) by PEI-PVA/CS xerogel. This xerogel demonstrates the stability and selectivity required for U(VI) adsorbents, indicating its potential for engineering applications in UCW treatment.

Heterogeneous Covalent Organic Framework Membranes Mediated by Polycations for Efficient Ions Separation.

Precise ions sieving at angstrom-scale is gaining tremendous attention thanks to its significant impact at the water-energy nexus. Herein, a novel polycation-modulated interfacial polymerization (IP) strategy is developed to prepare a heterogeneously charged covalent organic frameworks (COFs) membrane. Cationic poly(diallyldimethylammonium chloride) (PDDA) regulates the growth and assembly of anionic COFs nanosheets, which thus provides a negative, smooth top surface and positive, rough bottom surface, indicating the presence of heterogeneously charged angstrom-scale channels through the membrane. Experiments and simulations are conducted to understand the facilitated ions transport behavior relative to specific interactions raised by heterogeneously charged channels and angstrom-scale steric hinderance as well, rendering the membrane with robust mono-/divalent cations sieving capabilities. The selectivity (61.6) of Li+ to Mg2+ in mixed saline under the continuous cross-flow filtration mode is superior to most of the reported nanofiltration membranes. This polycation-mediated interfacial polymerization strategy offers a compelling opportunity to develop versatile heterogeneously charged COF membranes for exquisite ion sieving.

Atomistic insights into the K+/Na+ separation across amino modified graphene nanopore: The assisting role of Cl−

K+/Na+ separation has always been considered the most challenging. We adopted molecular dynamics to compare graphene nanopores modified with positively charged amino groups and their pristine counterparts to unravel the mechanism underlying the effect of positively charged amino groups on K+/Na+ separation and evaluate the assisting effect of Cl−. Two pore diameters of approximately 1 nm were selected. Results demonstrated that nanopore modification can effectively improve the K+/Na+ selectivity, and the spatial distribution and residence time of Cl− near the nanopores indicated that modification with positively charged amino groups can induce the dynamical adsorption of Cl− around the nanopores. In the studied nanopores, the prolongation of the residence time of Cl− at the pore mouths can increase the difference between K+ and Na+ dehydration and thus can increase their transport resistance difference. The latter effect is conducive to improving the selectivity for K+. Our findings can provide useful insight for the further design of K+ separating two-dimensional materials as sensors and ion separators.

Toward circular greenhouse wastewater reuse: advancements in cation exchange membranes for selective Na+/K+ separation using electrodialysis systems

ABSTRACT Driven by the growing need for alternative water sources and forthcoming stringent nutrient discharge regulations, there is growing interest in developing selective membrane solutions to facilitate circular greenhouse wastewater reuse (as emphasized in the European Union's Horizon 2020 ULTIMATE project). For electrodialysis systems, sodium (Na+) over potassium (K+) selective membranes are essential to achieve minimal liquid discharge. This study addresses the challenge of developing selective, efficient, and scalable Na+/K+ cation exchange membranes. State-of-the-art cation exchange membrane developments were reviewed and the functionalization of commercial membranes with crown ethers was identified as a promising approach. Two crown ether–modified membranes (15-crown-5 (15C5) and 18-crown-6 (18C6)) were developed, characterized, and tested in equimolar and greenhouse wastewater binary feed ratios. While the results demonstrated low overall selectivity, the 15C5-modified membrane showed a marginal enhancement in K+ selectivity, suggesting the need for further optimization. The study concludes with recommendations for the future development of Na+/K+ selective membranes, highlighting the potential of machine learning approaches to expedite progress. This research provides a foundational step toward practical and scalable Na+/K+ ion separation solutions, for achieving minimal liquid discharge in greenhouse horticulture.

2D Membranes Interlayered with Bimetallic Metal-Organic Frameworks for Lithium Separation from Brines.

Efficient lithium extraction from salt lakes is essential for a sustainable resource supply. This study tackles the challenge of separating Li+ from Mg2+ in complex brines by innovatively integrating two-dimensional (2D) graphene oxide (GO) with bimetallic metal-organic frameworks (MOFs). Zn2+ and Co2+ ions are confined within GO interlayers through an in situ synthesis, forming a 2D Zn-Co MOFs/GO membrane (Zn-Co-GOM). This design exploits the unique advantages of bimetallic MOFs, including enhanced structural stability and superior ion separation capabilities due to the synergistic effects of Zn and Co. The Zn-Co-GOM demonstrates an impressive separation factor of 191 for Li+ over Mg2+, significantly surpassing traditional membranes. This exceptional selectivity is achieved through a combination of size exclusion effects and ion transport energy barriers. Our approach not only enhances the practical application of membrane technology for lithium extraction from salt lakes but also provides valuable insights into the underlying separation mechanisms.

Sub-nanoporous polyimide membrane with selective and fast K+ transport

Biological ion channels have excellent monovalent ion separation performance, and it is of great significance to develop artificial membrane materials with monovalent ion selectivity based on their mechanism. The latent-track method is a new technology to prepare sub-nanometer channels on polymer membranes by swift heavy ion irradiation. This method has been widely applied in the study of mono/divalent ion separation membranes, but its application in monovalent ion separation membranes still needs to be explored. In this work, polyimide (PI) film was irradiated by swift heavy ion, then water rinsed, and the sub-nanoporous PI membrane with effective channel size in the range of 0.30 and 0.66 nm was fabricated, then its electrical and transport properties were studied. Due to the smaller hydrated diameter and lower hydration energy of K+, the membrane exhibited good selectivity for K+. The selectivity ratio of K+/Li+ is 3.4–3.9, and the maximum K+ flux can reach 0.44 mol m−2 h−1 at 55℃. The sub-nanoporous PI membranes are expected to be applied in salt lake lithium extraction, fine processing of potassium and lithium, and other relevant scenarios.

Modulating metal-centered dimerization of a lanthanide chaperone protein for separation of light lanthanides

Elucidating details of biology's selective uptake and trafficking of rare earth elements, particularly the lanthanides, has the potential to inspire sustainable biomolecular separations of these essential metals for myriad modern technologies. Here, we biochemically and structurally characterize Methylobacterium (Methylorubrum) extorquens LanD, a periplasmic protein from a bacterial gene cluster for lanthanide uptake. This protein provides only four ligands at its surface-exposed lanthanide-binding site, allowing for metal-centered protein dimerization that favors the largest lanthanide, LaIII. However, the monomer prefers NdIII and SmIII, which are disfavored lanthanides for cellular utilization. Structure-guided mutagenesis of a metal-ligand and an outer-sphere residue weakens metal binding to the LanD monomer and enhances dimerization for PrIII and NdIII by 100-fold. Selective dimerization enriches high-value PrIII and NdIII relative to low-value LaIII and CeIII in an all-aqueous process, achieving higher separation factors than lanmodulins and comparable or better separation factors than common industrial extractants. Finally, we show that LanD interacts with lanmodulin (LanM), a previously characterized periplasmic protein that shares LanD's preference for NdIII and SmIII. Our results suggest that LanD's unusual metal-binding site transfers less-desirable lanthanides to LanM to siphon them away from the pathway for cytosolic import. The properties of LanD show how relatively weak chelators can achieve high selectivity, and they form the basis for the design of protein dimers for separation of adjacent lanthanide pairs and other metal ions.

Covalent organic framework membranes with vertically aligned nanorods for efficient separation of rare metal ions

Covalent organic frameworks (COFs) have emerged as promising platforms for membrane separations, while remaining challenging for separating ions in a fast and selective way. Here, we propose a concept of COF membranes with vertically aligned nanorods for efficient separation of rare metal ions. A quaternary ammonium-functionalized monomer is rationally designed to synthesize COF layers on porous substrates via interfacial synthesis. The COF layers possess an asymmetric structure, in which the upper part displays vertically aligned nanorods, while the lower part exhibits an ultrathin dense layer. The vertically aligned nanorods enlarge contact areas to harvest water and monovalent ions, and the ultrathin dense layer enables both high permeability and selectivity. The resulting membranes exhibit exceptional separation performances, for instance, a Cs+ permeation rate of 0.33 mol m−2 h−1, close to the value in porous substrates, and selectivities with Cs+/La3+ up to 75.9 and 69.8 in single and binary systems, highlighting the great potentials in the separation of rare metal ions.