Ion Transport Mechanisms Research Articles

Polymer electrolytes based on interactions between [solvent-Li+] complex and solvent-modified polymer

Poly(vinylidene fluoride) (PVDF) is the most popular electrode binder in the current lithium ion batteries (LIBs). Depending on solvent content, polymer electrolytes are classified into solid polymer electrolyte (SPE; solvent-free) and gel polymer electrolytes (GPE; solvent-rich). PVDF-based electrolytes with high contents of solvent undisputedly belong to GPE. However, the affiliation (SPE or GPE) of the PVDF-based electrolyte with low content of “solvent” is in argument as its “solvent” cannot be eliminated till 80 °C in vacuum and its structure and ion transport mechanism remain unclear. By a series of studies, we demonstrate that this is actually a polymer electrolyte based on the interactions between the [solvent-Li + ] complex and the polymer in structure and in Li-ion transport mechanism. The “residual solvent” (N,N-dimethylformamide, DMF, for example) plays critical roles in constructing the polymer electrolyte and in determining its ion transport and therefore such electrolyte cannot be assigned to any of the known polymer electrolytes. The Li + -associated DMF becomes difficult to be eliminated while the DMF-dehydrofluorinated PVDF has a larger dielectric constant, enhances the dissociation of the lithium salt and interacts with the [DMF-Li + ] complex, the charge carrier of the electrolyte. These [solvent-Li + ] complex-based polymer electrolytes have high ionic conductivity (10 −4 S cm −1 at room temperature), Li-ion transference number (0.44) and Young's modulus (45.87 MPa) and will find important applications in the solid lithium batteries and as an ion-conducting binder for the electrodes. These findings will enrich the gallery and deepen the fundamental understandings of the polymer electrolytes, spurring designing of novel electrolytes.

Study on the chloride ion transport mechanism of recycled mixed aggregate concrete based on evolution characteristics of pore structure

• An interface model of RMA concrete considering pore structure characteristics was established. • The evolution characteristics of the microscopic pore structure for RMA concrete were studied. • The chloride ion transport mechanism of RMA concrete was studied based on microstructure parameters. The difference in pore structure characteristics is the fundamental reason that the chloride ion transport mechanism of recycled mixed aggregate (RMA) concrete is different from that of ordinary concrete. In this paper, the chloride ion penetration tests were performed on eight groups of specimens with different water-binder ratios (w/b) and coarse aggregate types. The specimens’ micromorphology, pore structure, fractal dimension, and microhardness were analyzed in detail. The results show that the pore structure of the specimen has an important influence on the chloride ion transfer process. With the increase in curing age, the porosity of new mortar (NM) and mortar attached to the surface of brick aggregate (BM) decreased, while the total fractal dimension increased, and the porosity of BM decreased more than that of NM. The brick aggregate is wrapped in a dense hydration layer, which prevents chloride ions from penetrating the brick aggregate to a certain extent. The anti-chloride ion transport performance of NM is weaker than that of BM due to the NM contains more capillary and large pores. Different pore size distribution ranges of the specimens have similar fractal characteristics. The fractal dimension first increases and then decreases with the change of the pore size range from small to large. The interface pore model of RMA concrete was established to provide a reasonable basis for further research on the durability of the specimens.

ЦИСТАМИН И ЦИСТИН ПОДАВЛЯЮТ ТРАНСПОРТ Na+ В ЭПИТЕЛИИ КОЖИ ЛЯГУШКИ

Amphibian skin and other isolated epithelial systems are classical model objects for studying the mechanisms of transepithelial ion transport. Na+ transport in osmoregulatory epithelium is a complex, multicomponent system, which involves Na+ transporting proteins and signaling cascades localized in various cell membranes. The protein components of this system may be a target for oxidative stress. At the same time, the effect of oxidizing and reducing agents on Na+ transport in native epithelial systems, such as frog skin epithelium, practically has not been studied. Using voltage-clamp technique the effect of disulfide-containing oxidizing agents cystine and cystamine on Na+ transport in frog skin was investigated. It has been shown for the first time that the treatment of the skin of the Rana temporaria frog with cystamine or cystine at a concentration of 10 μg/ml suppresses the transepithelial Na+ transport. It was also found that the preincubation with dithiothreitol, which reduces disulfide bonds in proteins, prevents the inhibitory effect of cystamine and cystine. The obtained results indicate that Na+ transport in the frog skin is sensitive to oxidative stress and is modulated by disulfide-containing oxidizing agents, such as cystamine or cystine, and also that the effect of cystamine and cystine on Na+ transport in the frog skin epithelium is mediated by their interaction with functionally important cysteine residues of Na+-transporting proteins.

Structure and function of H+/K+ pump mutants reveal Na+/K+ pump mechanisms

Ion-transport mechanisms evolve by changing ion-selectivity, such as switching from Na+ to H+ selectivity in secondary-active transporters or P-type-ATPases. Here we study primary-active transport via P-type ATPases using functional and structural analyses to demonstrate that four simultaneous residue substitutions transform the non-gastric H+/K+ pump, a strict H+-dependent electroneutral P-type ATPase, into a bona fide Na+-dependent electrogenic Na+/K+ pump. Conversion of a H+-dependent primary-active transporter into a Na+-dependent one provides a prototype for similar studies of ion-transport proteins. Moreover, we solve the structures of the wild-type non-gastric H+/K+ pump, a suitable drug target to treat cystic fibrosis, and of its Na+/K+ pump-mimicking mutant in two major conformations, providing insight on how Na+ binding drives a concerted mechanism leading to Na+/K+ pump phosphorylation.

Tuning cationic transport in Nisalen polymers via pseudo-crown functionality

Polymeric films based on nickel complexes with salen-type ligands have received considerable attention recently owing to electrocatalytic, electrochromic, and charge storing properties. The latter makes them suitable metal-organic materials for electrochemical power sources, i.e., batteries and supercapacitors. Optimization of the properties of electrode materials is closely linked to the understanding of charge storage mechanisms. The introduction of CH3O substituent into the molecule results in peculiar ionic transport mechanism, owing to the possibility of alkaline ions coordination. Here we study the recharging mechanism of poly[Ni(CH3Osalen)] films in various electrolyte solutions. In presence of alkali ions, the electronic effects of methoxy substituent provide mixed anionic and cationic charge compensation mechanism, as cations reversibly coordinate to the present pseudo-crown functionality. By applying the combination of XRD, CV/EQCM and EIS methods to the film in electrolytes containing Li+, Na+, K+, and Et4N+ cations, and BF4−, ClO4− and bistrifluoromethanesulfonimidate (TFSI−) anions, we propose a model that describes the ionic transport in such polymeric films and allows to estimate the anionic and cationic contribution to the total amount of transferred species during charging and discharging.

Study on the Transport Mechanism of Soil Water Ions in Unsaturated Zone

In order to understand the law of solute transport in the unsaturated zone, this paper selects a beach of the Yellow River in jiaozuo area as the study area, and uses Hydrus software to simulate some typical hydrochemical ions in the unsaturated zone. The Hydrus software is a numerical model developed by the National Saline soil Improvement Center in 1991 for simulating water, energy and solute transport in variably saturated porous media. Hydrus-1d is a one-dimensional version of the Hydrus software, which is commonly used to simulate water and solutes. The results show that Hydrus-1D can simulate the study area well with a high degree of fitting. Due to agricultural activities around the simulated area, the actual value of Cl- is higher than the simulated value.

Li+ Transport in Single-Ion Conducting Side-Chain Polymer Electrolytes with Nanoscale Self-Assembly of Ordered Ionic Domains

Li-ion batteries based on organic liquid electrolytes have been commercialized for decades. However, the flammability of the liquid electrolyte and propensity for reaction with metallic lithium anodes warrants the study of alternative electrolyte materials to satisfy modern demands such as higher safety and energy density. Polymer electrolytes are less flammable than organic liquids, more easily processable than inorganic solids, and more inert toward lithium metal and electrochemical side reactions. But the ionic conductivity in common polymer electrolytes, such as poly(ethylene oxide)-based polymer electrolytes, is limited by the segmental relaxation of the polymer matrix that is solvating the lithium cation. Recently, metal ion-containing polymers with regulated, repeating chain architecture have drawn attention as ion conductors due to their ionic domain segregation. In this contribution, we investigate the ion transport mechanism in a series of metal ion-containing polymers with ionic groups located on the side chains to explore their potential as Li+ conductors. Four side-chain polymers having different numbers (n = 6, 10, 12, and 15) of methylene groups as side spacers between the polymer backbone and terminally bound anions, titrated with Li+ counterions, were synthesized and characterized. These polymers were found to have strong nanoscale phase segregation with predominantly 1-D ionic domains. Through dielectric spectroscopy analysis, their conductivity was found to be linearly scaled with the dielectric relaxation rate. Short side chains (n = 6) resulted in a slower dielectric relaxation rate and lower DC conductivity compared to polymers with longer side chains (n ≥ 10). The long-range Li+ transport in these polymers is found to be coupled to the ionic cluster relaxations.

Fast Ion Transport Mechanism and Electrochemical Stability of Trivalent Metal Iodide-based Na Superionic Conductors Na3XI6 (X = Sc, Y, La, and In).

The exploration of solid-state sodium superionic conductors with high sodium-ion conductivity, structural and electrochemical stability, and grand interface compatibility has become the key to the next-generation energy storage applications with high energy density and long cycling life. Among them, halide-based compounds exhibit great potential with the higher electronegativity of halogens than that of the sulfur element. In this work, combined with first-principles calculation and ab initio molecular dynamic simulation, the investigation of trivalent metal iodide-based Na superionic conductors C2/m-Na3XI6 (X = Sc, Y, La, and In) was conducted, including the fast ion transport mechanism, structural stability, and interface electrochemical compatibility with electrode materials. Along with the tetrahedral-center saddle site-predominant three-dimensional octahedral-tetrahedral-octahedral diffusion network, C2/m-Na3XI6 possesses the merits of high Na ionic conductivities of 0.36, 0.35, and 0.20 mS cm-1 for Na3ScI6, Na3YI6, and Na3LaI6, respectively. Benefiting from its structural stabilities, C2/m-Na3XI6 exhibits lower interface reaction energy and better electrochemical compatibility in contact with both Na metal and high-voltage poly-anion (fluoro)phosphate cathode materials than those of sulfide-based ones. Our theoretical work provides rational design principles for screening and guiding iodide-based C2/m-Na3XI6 (X = Sc, Y, La, and In) as promising Na superionic conductor candidates used in all-solid-state energy storage applications.

Investigating calcification-related candidates in a non-symbiotic scleractinian coral, Tubastraea spp.

In hermatypic scleractinian corals, photosynthetic fixation of CO2 and the production of CaCO3 are intimately linked due to their symbiotic relationship with dinoflagellates of the Symbiodiniaceae family. This makes it difficult to study ion transport mechanisms involved in the different pathways. In contrast, most ahermatypic scleractinian corals do not share this symbiotic relationship and thus offer an advantage when studying the ion transport mechanisms involved in the calcification process. Despite this advantage, non-symbiotic scleractinian corals have been systematically neglected in calcification studies, resulting in a lack of data especially at the molecular level. Here, we combined a tissue micro-dissection technique and RNA-sequencing to identify calcification-related ion transporters, and other candidates, in the ahermatypic non-symbiotic scleractinian coral Tubastraea spp. Our results show that Tubastraea spp. possesses several calcification-related candidates previously identified in symbiotic scleractinian corals (such as SLC4-γ, AMT-1like, CARP, etc.). Furthermore, we identify and describe a role in scleractinian calcification for several ion transporter candidates (such as SLC13, -16, -23, etc.) identified for the first time in this study. Taken together, our results provide not only insights about the molecular mechanisms underlying non-symbiotic scleractinian calcification, but also valuable tools for the development of biotechnological solutions to better control the extreme invasiveness of corals belonging to this particular genus.

Evaluation of test procedures for durability and permeability assessment of concretes containing calcined clay

The durability and permeability of concrete could be investigated by different test methods that evaluate various transport mechanisms of water and ions in cement-based materials. This research has investigated the suitability of conventional permeability and durability assessment test methods for evaluating the properties of concrete mixtures containing calcined clays and limestone calcined clay cements (LC3). The water absorption, capillary water sorptivity, water penetration, surface electrical resistivity, rapid chloride ions migration coefficient, chloride ions’ penetration profile, and diffusion coefficient were examined in concrete mixtures. A rapid approximation method has also been proposed to estimate the kaolinite content of clays based on the chemical composition data. According to the results, water absorption test based on BS 1881-122 could not accurately specify the permeability properties of binary and LC3 blends. Further, the initial rate of capillary water absorption had an appropriate correlation with the results of water penetration and electrical resistivity test methods.

Governing mechanism of ion transport in lithium-iron-phosphate glasses

We show a fundamental relationship between network structural attributes and ionic transport of lithium iron phosphate glasses xLi2O–2Fe2O3–3 P2O5 (xLFPO; x = 0.375, 0.75, 1.5, 3.0) used for a cathode in lithium-ion batteries. The glass samples have been synthesized using a solid-state reaction method. We have investigated the electrical characteristics of the glass by combinational measurements of electrical impedance in the frequency 100 Hz – 30 MHz and temperature from ambient to 240 °C, differential thermal analysis, X-ray diffraction pattern, and Raman spectroscopy. The ionic hopping and relaxation processes in xLFPO glasses are analyzed by using Cole-Cole, power law, and modulus representations. We reveal that the exponential increase in dc conductivity with increasing Li2O in xLFPO glasses is caused by the combination of an increase in non-bridging oxygen sites and a change in the bonding forces of iron valence surrounding the iron phosphate clusters inside the network. The power law conductivity, which is driven by the fractional Rayleigh equation, exhibits that the rate of increase in dc ionic conductivity is the same as the rate of increasing numbers of the ionic charge carriers. Raman spectra show that the increase of depolymerization of the iron phosphate network with the addition of Li2O content is due to the conversion of Q2 to Q1 and Q0 species.

Use of sodium-glucose cotransporter-2 inhibitors and the risk for sudden cardiac arrest and for all-cause death in patients with type 2 diabetes mellitus.

Sodium-glucose cotransporter-2 inhibitors (SGLT-2is) are antidiabetic agents that can have direct cardiac effects by impacting on cardiac ion transport mechanisms that control cardiac electrophysiology. We studied the association between SGLT-2i use and all-cause mortality and the risk of sudden cardiac arrest (SCA) in patients with type 2 diabetes. Using data from the UK Clinical Practice Research Datalink, a cohort study among patients initiating a new antidiabetic drug class on or after January 2013 through September 2020 was conducted. A Cox regression with time-dependent covariates was performed to estimate the hazard ratios (HRs) of SCA and all-cause mortality comparing SGLT-2is with other second- to third-line antidiabetic drugs. Stratified analyses were performed according to sex, diabetes duration (<5 or ≥5 years), and the presence of cardiovascular disease. A total of 152 591 patients were included. Use of SGLT-2i was associated with a reduced HR of SCA when compared with other second- to third-line antidiabetic drugs after adjustment for common SCA risk factors, although this association marginally failed to reach statistical significance [HR: 0.62, 95% confidence interval (95% CI): 0.38-1.01]. The HR of all-cause mortality associated with SGLT-2i use when compared with other second- to third-line antidiabetics was 0.43 (95% CI: 0.39-0.48) and did not vary by sex, diabetes duration, or the presence of cardiovascular disease. SGLT-2i use remained associated with lower all-cause mortality in patients without concomitant insulin use (HR: 0.56, 95% CI: 0.50-0.63). SGLT-2i use was associated with reduced all-cause mortality in patients with type 2 diabetes. The association between use of SGLT-2i and reduced risk of SCA was not statistically significant.

Solid Li- and Na-Ion Electrolytes for Next Generation Rechargeable Batteries

We dedicate this paper to Prof. John B. Goodenough’s 100th birthday, who has made several seminal contributions to the modern electrochemical energy storage and conversion technologies that made significant social and economic impacts on humankind. This review paper reports two battery systems that he contributed in the early stage of solid-state ionics (SSIs). The development of advanced Li and or Na batteries based on solid-state (ceramic) electrolytes (SSEs) is being focused on because of their safety, high energy density, and design flexibility for high power and energy density applications. Several SSEs exhibit a higher electrochemical stability window, enabling various high voltage cathodes to improve the power density compared to organic liquid electrolytes-based batteries (except for sulfide-based electrolytes). However, most SSEs have lower (at least an order of magnitude) ionic conductivity and poor interface compatibility compared to liquid electrolytes. Attempts have been made to improve the ionic conductivity and interface of SSEs and electrodes and develop hybrid solid electrolytes with improved ionic conductivity and stability with an elemental anode and high voltage cathodes. Here, we discuss the materials aspects of SSEs and hybrid SSEs for next-generation Li and Na batteries. Various solid-state electrolytes, including hydride-type, silicates, LISICONs, NASICON-type oxides, glassy-type oxides, covalent organic frameworks, perovskite-type oxides, antiperovskites, Li-stuffed garnet-related structure oxides, and metal halides have been developed. The chemical composition–structure–ionic conductivity relationship of several key SSEs and the ion transport mechanism have been discussed in this study. Moreover, interfacial engineering methods for some typical SSEs and battery applications have also been discussed.

Oxygen-Deficient (Ln,Sr)2NiO4- δ Nickelates for Oxygen Electrodes of Solid Oxide Fuel and Electrolysis Cells: Anisotropic Thermochemical Expansion and Thermomechanical Constraints

Perovskite-like and perovskite-related oxides based on variable-valence transition metals may exhibit substantial changes in oxygen content in the course of temperature cycling or under variation of oxygen chemical potential at elevated temperatures. This gives rise to a chemical contribution to the thermal expansion (chemical expansion/contraction or chemical strain) originating mainly from the accompanying changes in the average oxidation state of transition metal cations and, consequently, their ionic radii. Excessive dimensional changes caused by the chemical expansion impose constraints on the applicability of functional oxides at elevated temperatures and under variable redox conditions (due to thermomechanical instability or incompatibility with other materials) and complicate the processing of oxide ceramics at high temperatures. Another unfavorable phenomenon is microcracking caused by a strongly anisotropic expansion of crystal lattice, with effects on the microstructural and mechanical integrity and electrical and electrochemical properties. The present work is a representative study case that focuses on layered Ln2NiO4-based ceramic materials for oxygen electrodes of solid oxide fuel/electrolysis cells (SOFC/SOEC).Ln2NiO4+δ–based oxides (Ln = La, Pr, Nd) with perovskite-related K2NiF4-type structure demonstrate high oxygen diffusivity and surface exchange kinetics in combination with comparatively high electronic conductivity and are considered, therefore, as attractive mixed ionic-electronic conductors for oxygen electrodes of high-temperature SOFC/SOEC [1]. Acceptor-type substitution of Ln3+ by Sr2+ in Ln2NiO4+ δ is compensated by comparatively high oxygen deficiency in Sr-rich Ln2-xSrxNiO4-δ phases at elevated temperatures [2,3]. The transition from oxygen excess to oxygen deficiency is expected to be accompanied by a change in the ionic transport mechanism from prevailing interstitial oxygen diffusion in rock-salt layers to oxygen vacancy diffusion in perovskite-type layers.Ceramic powders of Ln2-xSrxNiO4-δ (Ln = La, Nd, Pr, x = 1.0-1.6) were prepared by the Pechini method with final calcination steps at 1150-1200°C in oxygen. Thermogravimetric studies confirmed that acceptor-type substitution by strontium is compensated by the formation of oxygen vacancies and electron-holes and progressively increases high-temperature oxygen nonstoichiometry (Fig.1A), which reaches as high as δ = 0.36-0.40 for x = 1.6 at 900°C in air. High-temperature XRD studies demonstrated that Ln2-xSrxNiO4-δ nickelates exhibit strongly anisotropic lattice expansion interrelated with oxygen deficiency changes on heating (Fig.1B). Highly anisotropic expansion induces microcracking phenomenon, which, in turn, results in a strong hysteresis in dimensional changes (Fig.1C) and also in variations of electrical conductivity (Fig.1D) on cycling in air for the ceramic samples sintered at 1200-1300°C.An appropriate approach to minimize or neglect the undesirable effects of anisotropic expansion and microcracking is to preserve the grain size in Ln2-xSrxNiO4-δ ceramics or porous electrodes at ~1 micron or submicron level. In particular, spark plasma sintering with subsequent careful oxidation treatment was adopted to avoid grain growth and to produce mechanically stable ceramics with smooth reversible thermochemical expansion and enhanced electrical properties. Acknowledgments: This work was supported by the FCT/MCTES/FEDER (projects CARBOSTEAM (POCI-01-0145-FEDER-032295) and CICECO-Aveiro Institute of Materials (UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020), and PhD grant SFRH/BD/138773/2018).

ToF-SIMS investigation with 18O isotopic tracer of the ion transport mechanisms in surface oxides on nickel-chromium and nickel-chromium-molybdenum alloys

Ion transport mechanisms in growing oxide films on Ni-20Cr and Ni-20Cr-10Mo alloys have been investigated by ToF-SIMS with in situ re-oxidation using 18O isotopic tracer. Whereas the growth is controlled by pure anionic diffusion on Ni-20Cr alloy, the behavior is drastically modified by Mo addition. A mixed cationic and anionic growth mechanism and a reduced diffusion rate of moving species are observed on the alloy containing molybdenum.The passivation in sulfuric acid, which increases the inner Cr oxide barrier layer thickness, also reduces the diffusion rate of the moving species for both Ni-20Cr and Ni-20Cr-10Mo alloys. Significantly higher re-oxidation temperatures are needed to observe the ion transport mechanisms in passive oxides formed on Ni-20Cr and Ni-20Cr-10Mo alloys, as compared to native oxides.Mo addition and electrochemical passivation have synergistic effects that reduce the diffusion rate of moving species through the surface oxide films and thus reinforce the corrosion resistance of the oxide films formed on Ni alloys.

Thio‐/LISICON and LGPS‐Type Solid Electrolytes for All‐Solid‐State Lithium‐Ion Batteries

AbstractAs an integral part of all‐solid‐state lithium (Li) batteries (ASSLBs), solid‐state electrolytes (SSEs) must meet requirements in high ionic conductivity, electrochemical/chemical stability toward the electrode. The ionic conductivity of the Li super ionic conductor (LISICON) is limited, and the thio‐LISICON is improved by replacing O2− in the LISICON with S2−. Currently, the ionic conductivity of Li10GeP2S12 (LGPS) has exceeded 10 mS cm−1, which meets the demands of commercial ASSLBs. However, poor stability of SSEs, baneful interfacial reactions, Li dendrite growth, and other factors have impeded the development of ASSLBs. Hence, this review first traces the development progress of thio‐/LISICON and LGPS‐type SSEs, analyzes the complicated ion transport mechanism, and summarizes the effective strategies for improving ionic conductivity. Moreover, exciting methods focusing on electrode interface engineering are outlined separately. As to SSE/anode interface, poor chemical or electrochemical compatibility, poor interfacial contact, and the mechanisms of dendrite formation are discussed. For the SSE/cathode interface, poor interfacial stability and non‐intimate solid–solid contact are daunting challenges. Then, effective methods to improve interface stability and electrochemical performance of ASSLBs with LGPS‐type SSEs are introduced. Finally, combined with the present chances and challenges, the possible future developing directions of LGPS‐based ASSLBs and the perspectives are proposed.

Mechanisms of ionic liquids on the enhancement of interfacial transport of lithium ions in crown ether system

Lithium and lithium isotopes are important for clean energy development. By introducing ionic liquid, the extraction performance of crown ethers for lithium ions can be significantly improved. However, the enhancement mechanism of ionic liquids in the system is not clear, which directly limits the selection of suitable ionic liquids for various applications. In this work, the synergy mechanisms of different ionic liquids with crown ether during the extraction process were investigated by molecular dynamics simulations and verified by experimental results. There were two molecular mechanisms to capture lithium ions for ionic liquids in the crown ether system: co-extraction and assisted extraction. It was generally considered that the cation exchange mechanism was responsible for the extraction of lithium ions in the crown ether-ionic liquids system. Here, a novel perspective was revealed that one [Li·H2O]+ complexed with crown ether and then the chelate cation coordinated with the anion of the ionic liquid to form a neutral molecule based on the simulation of the whole extraction process with molecular dynamics that favored the transport of Li+ from aqueous solution to organic solution. In the system without ionic liquids, Li+-crown ether chelates were distributed only at the interface and did not enter the organic phase which is supported by very low extraction efficiency. It was attributed that charge equilibrium cannot be achieved when Li+-crown ether chelates enter into organic solution in the absence of ionic liquids. Overall, a new insight into the interfacial transport mechanisms of lithium ions was proposed, in which the anion of ionic liquids played a key role in capturing lithium ions at the interface of aqueous solution and organic solution.

Supramolecular Mechanosensitive Potassium Channel Formed by Fluorinated Amphiphilic Cyclophane.

Inspired by mechanosensitive potassium channels found in nature, we developed a fluorinated amphiphilic cyclophane composed of fluorinated rigid aromatic units connected via flexible hydrophilic octa(ethylene glycol) chains. Microscopic and emission spectroscopic studies revealed that the cyclophane could be incorporated into the hydrophobic layer of the lipid bilayer membranes and self-assembled to form a supramolecular transmembrane ion channel. Current recording measurements using cyclophane-containing planer lipid bilayer membranes successfully demonstrated an efficient transmembrane ion transport. We also demonstrated that the ion transport property was sensitive to the mechanical forces applied to the membranes. In addition, ion transport assays using pH-sensitive fluorescence dye revealed that the supramolecular channel possesses potassium ion selectivity. We also performed all-atom hybrid quantum-mechanical/molecular mechanical simulations to assess the channel structures at atomic resolution and the mechanism of selective potassium ion transport. This research demonstrated the first example of a synthetic mechanosensitive potassium channel, which would open a new door to sensing and manipulating biologically important processes and purification of key materials in industries.

Elucidating ion transport mechanism in polyelectrolyte-complex membranes

Polyelectrolyte-complex (PEC) nanofiltration (NF) membranes attract much attention, however, the mechanisms governing ion separation in PEC films is not well understood. Here, we elucidate the ion transport in PECs using a recently reported Nafion-polyvinylamine (PVAm) membrane prepared via double-coating approach tuned to “rejection neutrality”, i.e., similar rejection of MgCl2 and Na2SO4 as single salts. New insights are gained by examining ion rejection for single- and mixed-salt solutions of NaCl, MgCl2 and Na2SO4 of varying concentrations and pH. The single salt permeability was found to vary with concentration, obeying a power law with an exponent around 0.4, matching neither the Donnan-dielectric nor a proposed PEC dissociation model. This is explained by progressive dissociation of the complex, which raises membrane swelling and dissociation constants, and weakenis dielectric exclusion, when salt concentration increases. Nevertheless, the membrane remains highly stable in all conditions, which is ascribed to the insolubility of Nafion in water. The results also indicate that “rejection-neutral” PEC still possesses a net negative charge, affecting ion selectivity at low salinities. The insights and physical picture proposed here may help understand and tune separation performance of PEC NF membranes and facilitate their implementation in applications such as purification and reuse of contaminated waters, resource recovery, and ion separations.

Heterogeneous asymmetric passable cavities within graphene oxide nanochannels for highly efficient lithium sieving

Lithium is a critical energy element that plays a pivotal role in transitions to sustainable energy. Numerous two-dimensional (2D) membranes have been developed to extract Li+ from different resources. However, their Li+ extraction efficacy is not high enough to meet industrial requirements. Here, we introduce an approach that boosts Li+ selectivity of 2D membranes by inducing asymmetricity in the morphology and chemistry of their nanochannels. Our approach provides an opportunity to manipulate cation hydration shells via a sudden change in the nanochannel size. Then, the addition of nucleophilic traps in the nanochannel intersections results in high Li+ selectivity. Our design leads to a new ion transport mechanism named “Energy Surge Baffle” (ESB) that substantially enriches Li+ in the feed by increasing the monovalent/lithium-ion selectivity up to six times that of other graphene oxide-based membranes. Our approach can be extended to other 2D materials, creating a platform for designing advanced membranes.