Radius Of Hydrated Ion Research Articles

Organic molecular intercalation regulated hydrated vanadate cathodes with improved electrochemical properties and fast kinetics for aqueous zinc-ion batteries

Due to the large hydrated zinc ion radius resulting from the stable solvation structure with six water molecules in electrolyte, the interlayer spacing of most vanadium-based materials fails to meet the requirements for efficient insertion and extraction of Zn2+. Therefore, it is crucial to optimize and reconstruct the VO layer structure in order to achieve rapid and stable zinc storage. In this paper, composites of phenylalanine methyl ester (PM) inserted hydrated V2O5 (PMVO) are prepared using a one-step hydrothermal method. With the increase of PM insertion, the electrochemical properties initially exhibit enhancement followed by subsequent decline. Notably, PMVO-1.6 presents exceptional electrochemical performance, including a high capacity of 464 mAh g−1 at 0.1 A g−1, excellent rate capability with 220 mAh g−1 at 7 A g−1, and superior cycling stability with 97.5 % capacity retention after 1000 cycles at 4 A g−1. The incorporation of PM not only serves as stable structural pillars, but also reduces the solubilization of vanadium, facilitates the diffusion kinetics of hydrated zinc ions, and enhances the surface pseudo-capacitance effect.

Hybrid bilayered vanadium oxide electrodes with large and tunable interlayer distances in lithium-ion batteries

The interlayer distances in layered electrode materials, influenced by the chemical composition of the confined interlayer regions, have a significant impact on their electrochemical performance. Chemical preintercalation of inorganic metal ions affects the interlayer spacing, yet expansion is limited by the hydrated ion radii. Herein, we demonstrate that using varying concentrations of decyltrimethylammonium (DTA+) and cetyltrimethylammonium (CTA+) cations in chemical preintercalation synthesis followed by hydrothermal treatment, the interlayer distance of hybrid bilayered vanadium oxides (BVOs) can be tuned between 11.1 Å and 35.6 Å. Our analyses reveal that these variations in interlayer spacing are due to different amounts of structural water and alkylammonium cations confined within the interlayer regions. Increased concentrations of alkylammonium cations not only expand the interlayer spacing but also induce local bending and disordering of the V-O bilayers. Electrochemical cycling of hybrid BVO electrodes in non-aqueous lithium-ion cells show that specific capacities decrease as interlayer regions expand, suggesting that the densely packed alkylammonium cations obstruct intercalation sites and hinder Li+ ion transport. Furthermore, we found that greater layer separation facilitates the dissolution of active material into the electrolyte, resulting in rapid capacity decay during extended cycling. This study emphasizes that layered electrode materials require both spacious interlayer regions as well as high structural and chemical stabilities, providing guidelines for structural engineering of organic–inorganic hybrids.

Revisit the classical theories of the conductance of unassociated electrolytes. Is there reality in relaxation?

The experimental results of the ionic conductance of the electrolytic solution can be explained without the use of relaxation until almost 2M concentration of the NaCl solution within 97% agreement with two parameters: the hydrated ion radii for cations and anions. No other fitting parameters were introduced, and no ion association was assumed. The theory is based on a newly introduced electrochemical potential that incorporates the interaction between ions and fluctuations in electrolyte concentration in the nanosized region. It was found that the concept of local chemical potential, fluctuation in the nanosized area, and symmetry of the system are closely related to the Boltzmann distribution of ions. Extending the concept of a local chemical potential to the case of an external field, the derived ionic mobility automatically includes the effect of electrophoresis. The so-called electrophoretic retardation was found to be equivalent to the shielding effect of the external field. Relaxation bears a minor effect and may contribute to the ion transport of electrolytic solution at most 3%, if exists.

Multi-metal ions co-regulated vanadium oxide cathode toward long-life aqueous zinc-ion batteries

Interlayer intercalation engineering shows great feasibility to improve the structure stability of the layered oxides. Although high Zn-storage capability has been attained based on the pillar effect of multifarious intercalants, an in-depth understanding the synergistic effect of intercalated multiple metal ions is still in deficiency. Herein, alkali metal ion K+, alkaline earth metal ion Mg2+ and trivalent metal ion Al3+ are introduced into the VO interlayer of V2O5. Due to the different electronegativity and hydrated ion radius of K+, Mg2+ and Al3+, adjusting the relative proportions of these metal ions can achieve an appropriate interlayer spacing, stable layer structure and regular morphology, which facilitates the transport kinetics of Zn2+. Under the synergistic effect of pre-intercalated multi-metal ion, the optimal tri-metal ion intercalated hydrated V2O5 cathode exhibits a high specific capacity of 382.4 mAh g−1 at 0.5 A g−1, and long-term cycling stability with capacity retention of 86 % after 2000 cycles at the high current density of 10 A g−1. Ex-situ and kinetic characterizations reveal the fast charge transfer and reversible Zn2+ intercalation mechanism. The multi-ion engineering strategy provides an effective way to design desirable layered cathode materials for aqueous zinc-ion batteries.

Effects of ultrasounds and microwaves on the morphology and adsorption capacity of calcium alginate

Three non-conventional strategies have been used to prepare calcium alginate (CaAlg) from sodium alginate (NaAlg) by a batch process: ultrasound (US); microwave (MW) and combined US-MW. The calcium alginates obtained were used to remove Pb(II) and Cd(II) from single and binary aqueous solutions. The resulting adsorption capacities were compared to those obtained by conventional synthesis of calcium alginate. Scanning electron microscopy (SEM) revealed that the use of microwave and ultrasound produced CaAlg beads with roughened surfaces and consequently with increased specific surface area. The optimum parameters for the removal of Pb(II) and Cd(II) ions from single and binary solutions were determined in terms of pH, contact time, adsorbent dose and initial heavy metal concentration. A significant increase of the maximum adsorption capacity of Cd(II) and Pb(II) ions determined from Langmuir isotherm model was recorded in the case of CaAlg particles prepared in the combined microwave and ultrasound system. These values are 1.7389 ± 0.0585 mmol/g for Cd(II) and 1.5872 ± 0.0657 mmol/g for Pb(II) compared to 0.9305 ± 0.0926 mmol/g and 0.9735 ± 0.0572 mmol/g, respectively recorded for CaAlg particles prepared and matured using the conventional method. The differences between the values of the adsorption capacity of CaAlg-C-C for Pb(II) compared to Cd(II) ions is due to the Pb(II) ions characteristics (ion radius, hydrated ion radius, electronegativity). Thus, it can be stated that use of a combination of microwave and ultrasound improved the adsorption capacity of CaAlg for the removal of heavy metal ions from polluted effluents.

Aqueous Organic Batteries Using Proton as Charge Carrier.

Benefiting from the merits of low cost, non-flammability and high operational safety, aqueous rechargeable batteries have emerged as promising candidates for large-scale energy storage applications. Among various metal-ion/non-metallic charge carriers, proton (H+ ) as a charge carrier possesses numerous unique properties such as a fast proton diffusion dynamics, a low molar mass and a small hydrated ion radius, which endow aqueous proton batteries (APBs) with a salient rate capability, a long-term life span and an excellent low-temperature electrochemical performance. In addition, redox-active organic molecules, with the advantages of structural diversity, rich proton-storage sites and abundant resources, are considered as attractive electrode materials for APBs. However, as far as application is concerned, the charge storage and transport mechanisms of organic electrodes in APBs is still in infancy. Therefore, finding suitable electrode materials and uncovering the H+ storage mechanisms are significant for the applications of organic materials in APBs. Herein, the latest research progresses on organic materials such as small molecules and polymers for APBs are reviewed. Furthermore, a comprehensive summary and evaluation of APBs employing organic electrodes as anode and/or cathode is provided, especially on their low-temperature and high-power performances, along with systematic discussions for guiding the rational design and the construction of APBs based on organic electrodes. This article is protected by copyright. All rights reserved.

Enhanced Elastic Migration of Magnesium Cations in alpha‐Manganese Dioxide Tunnels Locally Tuned by Aluminium Substitution

AbstractThe harsh conditions of large hydrated ion radius of Mg2+ cations and the strong electrostatic interaction with the host material put forward higher requirements for high‐performance aqueous magnesium ion (Mg2+) energy storage devices. Herein, substituted aluminium ions (Al3+) doped α‐MnO2 materials are prepared. The introduction of Al3+ cations adjust the local chemical environment inside the tunnel structure of α‐MnO2 and precisely regulates the diffusion behavior of inserted Mg2+ cations. The shortened oxygens’ distance and abundant oxygen defects result in a substantially enhanced elastic migration pattern of Mg2+ cations driven by strengthened electrostatic attraction, which brings the lower diffusion energy barrier, improved reaction kinetics, and adaptive volume expansion as evidenced by Climbing Image‐Nudged Elastic Band density function theory calculations coupled with experimental confirmation in X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and galvanostatic intermittent titration technique. As a result, this rationally designed cathode exhibits a high reversible capacity of 197.02 mAh g‐1 at 0.1 A g‐1 and stable cycle performance of 2500 cycles with 82% retention. These parameters are among the best of Mg‐ion capacitors reported to date. This study offers a detailed insight into the local tunnel structure tunning effect and opens up a new path of modification for tunnel‐type structural materials.

Intensification of a continuous adsorption system by applying an external magnetic field for the removal of heavy metals in the ionic state

Were carried out adsorption studies in a continuous system subjected to external magnetic fields of three different intensities; non intensity (NI), low intensity (LI) and high intensity (HI), generated from permanent magnets, in order to evaluate the removal of three different heavy metals in ionic state (Cd2+, Pb2+ and Zn2+). The design of magnetic field application systems is supported by finite element computational simulations. The results show that the application of an external magnetic field improves the adsorbate retention proportionally to the intensity of the applied magnetic field, intensifying said process compared to a system without the application of a magnetic field, increasing the maximum adsorption capacity. The results show an increase in adsorption capacity of 16.02% for the removal of Cd2+ and 6.81% for Zn2+; however, the removal of Pb2+ had a small difference of 2.41%, which is attributed to the subtle differences in the physicochemical and magnetic characteristics of this adsorbate and the others such as hydrated ion radius and magnetic susceptibility. Additionally, a proposal of the mathematical model that could describe the phenomenon based on the variables shown here is made.

Molecular dynamics simulation of the adsorption properties of graphene oxide/graphene composite for alkali metal ions

As one of the effective methods to remove heavy metals, graphene (G) composite adsorption technology is irreplaceable in water pollution control and water purification, but its adsorption mechanism is not clear. Materials Studio (MS) software was used to simulate the molecular dynamics of the interaction between graphene oxide/graphene (GO/G) composite and alkali metal ion (M+). Based on the calculation of the interaction energy, diffusion coefficient and radial distribution function (RDF), The adsorption law of GO/G on M+ was investigated and its mechanism was revealed. It provides a theoretical basis for the research and development of the adsorption performance of G composite electrode. The calculated results show that the interaction energy between different M+ and GO/G is negative, indicating that the interaction between them is mutual attraction. The energy of GO/G composites and the total energy of M+-GO/G increase with the increase of M+ radius. The larger the hydrated ion radius of M+ is, the larger the diffusion coefficient is. Cs+ diffusion coefficient is slightly lower than rubidium. According to RDF analysis, M+-GO and M+ − O (GO) both have bonding within 3.5 Å and non-bonding after 3.5 Å, and the non-bonding interaction of M+-GO is greater. However, the bonding interaction between M+-O(GO) is larger than the non-bonding interaction, indicating that there are bonding and non-bonding interactions in the system when GO/G composite adsorb M+. The interaction between M+ and GO surface is mainly provided by non-bonding interaction, while the interaction between M+ and O atoms of GO surface is mainly provided by bonding interaction.

Multifunctional poly(methacrylate ester)s-based terpolymer cryogels with basic amino groups: Correlation of elasticity and structural properties with composition

Dual-responsive cryogel-structured materials open up a whole new field of bio-applications. Either dimethylaminoethyl methacrylate (DMAEMA) as a carrier of basic amino groups or glycidyl methacrylate (GMA) as a carrier of epoxy rings was introduced into hydroxypropyl methacrylate (HPMA) skeleton. pH/thermo-responsive cationic terpolymer cryogels were successfully prepared by varying the feeding DMAEMA/GMA mol percent ratio from 80/0 to 0/80. The presence of GMA imparts hydrophobic character that reduces swelling and provides additional crosslinks leading to a significant increase in the flexibility. Reducing the polymerization temperature below the freezing point of the solvent resulted in harder and non-brittle cryogels. Up to 48% reduction in hydration was observed for terpolymer cryogels containing 70 mol% DMAEMA upon increasing pH of bathing medium from 2.1 to 8.0. This trend confirmed pH-modulated swelling of amine-containing terpolymer gels, and pH-dependent transition point was found to be 7.7. Oscillating swelling/deswelling in response to pH cycles was studied. The water transport was strongly affected by incorporation of hydrophobic component GMA and protonation of amine functional groups. The swelling mechanism was shifted from anomalous to diffusion controlled with increasing GMA and overall swelling processes followed Schott second order dynamic equation. Lower equilibrium volume swelling at constant temperature was achieved by increasing GMA content of the terpolymers. In low temperature range, while DMAEMA-rich terpolymer gels were swollen, swelling decreased significantly when the gels were enriched in GMA and the temperature was raised above 55 °C. Regardless of salt type and Na+ or K+ hydrated ion radii, a significant difference was observed in salt-sensitive swelling in dilute salt solution (below about 10−3 M), which is controlled by the amount of DMAEMA in terpolymer structure. This study would provide novel ideas for the design of (meth)acrylate ester-based cationic terpolymer cryogels and elucidate the relationship between the gel matrix and their special swelling behavior.

Purification of Wet-Process Phosphoric Acid via Donnan Dialysis with a Perfluorinated Sulfonic Acid Cation-Exchange Membrane.

This work reports the application of an electromembrane process, Donnan dialysis (DD), for the purification of so-called wet-process phosphoric acid (WPA). Nitric acid is used as the stripping solution to remove metallic cations (mostly Fe3+, Al3+, and Mg2+) that are harmful to the further processing of WPA. The paper first presents a set of experimental data on the measurements of the metallic cation fluxes through a perfluorinated sulfonic acid cation-exchange membrane. Not only WPA, but also synthetic phosphoric acid solutions with mixed metallic cations (MPA) and with a single metallic cation (SPA) were studied. This confrontation confirms (1) that the order of metallic cations fluxes is Mg2+ > Al3+ > Fe3+; (2) that, compared with MPA, the purification effect of WPA causes only negligible change; (3) that, by comparing the DD processes with SPA and MPA solutions, the reason for the low transmembrane fluxes of Fe3+ and Al3+ could be explained by the large ionic charge and large hydrated ion radius. Furthermore, by analyzing the ion composition of membranes equilibrated in SPA solutions, we conclude that the forms of cations in the membrane are most likely Fe3+, Al3+, and Mg2+.

Charge Storage in Graphene Oxide: Impact of the Cation on Ion Permeability and Interfacial Capacitance.

The charge storage and membrane applications of graphene oxide (GO) materials are dictated by its intrinsic material properties. Structure-function relationships correlating periodic parameters, such as the hydrated ion radius and ion-GO interactions, are currently lacking yet are needed to provide insight on the charge storage and ion transport mechanism. We report the use of scanning ion conductance microscopy to measure the ion permeability of GO films and evaluate its relationship with the measured capacitance. We demonstrate that species (namely K+) with strong electrostatic interactions with the oxygen functionalities of GO provide the benefit of higher capacitance but suffer from inhibited ion mobility due to constriction of the GO interlayer spacing.

Improvement of Electrochemical Stability of Layered Oxide Electrodes in Na-Ion Batteries Via Control of Chemical Composition in the Interlayer Region

Layered transition metal compounds with expanded interlayer region, stabilized by structural water, often show high initial capacities but suffer from rapid capacity decay and poor rate capability in Na-ion batteries. High-temperature annealing, accompanied by phase transformation with the formation of more dense atomic structures, has been shown to improve electrochemical stability. However, the capacity of annealed materials decreases compared to their original forms. Here, we for the first time demonstrate that low-temperature annealing (260oC under vacuum) can be used to achieve enhanced electrochemical stability of high capacity Na-preintercalated bilayered vanadium oxide (δ-NaxV2O5·nH2O) nanobelts, while preserving its open layered structure with expanded interlayer region available for insertion and diffusion of a large number of electrochemically cycled Na+ ions. The mechanism of the thermally induced interlayer water loss is discussed. The improved capacity retention exhibited by low-temperature vacuum annealed δ-NaxV2O5·nH2O nanobelts is attributed to the partial removal of the structural water from the interlayer region, formation of additional bonds within the V-O bilayers, and increased stacking order of V-O bilayers. Additionally, we will show the effect of the chemical pre-intercalation of alkali (Li+, Na+, K+) and alkali-earth (Mg2+ and Ca2+) ions in the interlayer region of the bilayered vanadium oxide on electrochemical stability in Na-ion batteries. By altering the nature of the chemically preintercalated ion, interlayer spacing of the synthesized δ-MxV2O5 (M = Li, Na, K, Mg, Ca) materials was varied between 9.62 and 13.40 Å. We show that the interlayer spacing increases with the increase of the hydrated ion radius. The ion (Li+, K+, Mg2+, Ca2+) stabilization effect was investigated in Na-ion cells, with Na-preintercalated phase, δ-NaxV2O5, serving as a reference material. Our analyses indicate that cyclability and rate performance of the δ-MxV2O5 improves with increasing interlayer spacing and decreasing the ionic radius of chemically preintercalated ion. The highest initial capacity, greatest capacity retention, and highest capacity retention at higher current rates were exhibited by Mg- and Li-stabilized δ-V2O5. Low-temperature vacuum annealing ion stabilization achieved via chemical pre-intercalation synthesis approach are proposed as efficient strategies to advance electrochemical stability of the growing family of hydrated transition metal compounds used as electrodes in beyond lithium-ion batteries.

Fabrication of mesoporous nanocomposite of graphene oxide with magnesium ferrite for efficient sequestration of Ni (II) and Pb (II) ions: Adsorption, thermodynamic and kinetic studies

Mesoporous nanocomposite of MgFe2O4 nanoparticles (NPs) and graphene oxide (GO) was synthesized using facile sonication method. Its potential was tested for the removal of Ni (II) and Pb (II) ions from water. The 2:1 w/w ratio of MgFe2O4:GO was optimum for the maximum removal of metal ions. Nanocomposite was characterized employing XRD, FT-IR, VSM, SEM-EDX, XPS, TEM and BET analyses. It possessed higher surface area (63.0 m2 g−1) than pristine NPs. Batch experiments were performed to study the effect of process parameters viz. pH, dose, contact time, initial metal ion concentration, co-existing ions and temperature. Statistical parameters were also determined. Langmuir, Temkin and Freundlich models were followed in perfect way. Langmuir model showed the monolayer adsorption of metal ions onto the homogeneous surface of nanocomposite with maximum adsorption capacity of 100.0 mg g−1 and 143.0 mg g−1 for Ni (II) and Pb (II) ions respectively, which was higher than the same for MgFe2O4 NPs and GO. Kinetic studies demonstrated that the pseudo-second order model well described the adsorption process. The ΔS° and ΔG° values revealed spontaneous nature of adsorption process. Positive ΔH° values using MgFe2O4 NPs and nanocomposite indicated endothermic removal; whereas using GO the removal was exothermic. The observed trend for coexisting ions correlated with hydrated ion radii. Efficiency of the adsorbents was also tested for realistic nickel electroplating industrial effluent. Apart from the higher adsorption potential of nanofabricated composite, its magnetic properties are advantageous in utilizing metal loaded nanocomposite for adsorption-desorption cycles for reuse.

In situ encapsulation of tin oxide and cobalt oxide composite in porous carbon for high-performance energy storage applications

Herein, we report the preparation of porous carbon from palm kernel shell and loading of tin oxide‑cobalt oxide in its pores using a facile in-situ encapsulation synthesis strategy. The as-synthesized SnO2/Co3O4@C composite was characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy techniques. This composite was used as an electrode for supercapacitors. Electrochemical charge storage capabilities of the composite were measured using cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectroscopy in aqueous 6 M KOH and 1 M Na2SO4 electrolytes. The SnO2/Co3O4@C composite showed over 70% higher specific capacitance (177 F g−1) than the pure porous carbon (106 F g−1) in 6 M KOH. Among these electrolytes, the composite exhibited an enhanced electrochemical performance in KOH electrolyte due to its smaller hydrated ion radius, high ionic mobility and lower equivalent series resistance than Na2SO4.

Structure and size of ions electrochemically doped in conducting polymer

Among electroactive polymers (EAPs) for softactuators, conducting polymers have been intensively studied because of the large strain and stress caused by a low voltage operation. A larger deformation is desirable to extend their cycle life by reducing the operation voltage, and this is advantageous for their potential use in wider applications. The deformation is generated by the insertion of ions by electrochemical oxidation; hence, the magnitude of the strain depends on the bulkiness of the ions in the electrolytes. It is important, therefore, to clarify the structure and size of the ions during the electrochemical cycle, in order to achieve better performance of actuation.Anion and cation sizes (radii) in polypyrrole (PPy) film have been estimated using the precise measurement of strain against the amount of charge injected during the electrochemical cycles, assuming isotropic deformation of the film. The anion size was estimated using an anion-drive film, which was electrodeposited in TBABF4/methyl benzoate. The film was electrochemically cycled in sodium electrolytes, and the strain was measured simultaneously using a laser displacement meter. The cation size was obtained using a cation-drive film, being electropolymerized in aqueous dodecylbenzene sulfonic (DBS) acid. The cation-drive film was cycled in chloride electrolytes and measured the strain. The Cl−, Br−, , , and radii were found to be approximately 235, 245, 250, 270 and 290 pm, respectively. The radii of K+, Na+ and Li+ were approximately 230, 237 and 274 pm, respectively. The results were discussed and took the crystalline ion radius and hydrated ion radius (Stokes radius) into consideration. It was found that the structure and size of the anions were slightly larger than the crystalline ion radius. Contrary to the anions, the cation radii were close to the hydrated ion radius, being larger than the crystalline ion radius.

Estimation of ion dimension doped in conducting polymers electrochemically

ABSTRACTElectroactive conducting polymers are suitable for soft actuators (artificial muscles). The actuation is induced by electrochemical oxidation of conducting polymer (film) in an electrolyte solution, due to insertion of bulky counter ions (dopant ions). The magnitude of deformation (strain) depends on the size of dopant ions and the degree of oxidation. It is worthwhile to know the relationship between the magnitudes of deformation and ion size. An electrodeposited Polypyrrole film was electrochemically cycled in aqueous electrolytes of NaCl, NaBr, NaNO3, NaBF4 and NaClO4. The strain of film during electrochemical oxidation and reduction was precisely measured using a laser displacement meter and a handmade apparatus. From the strain and electrical charges inserted in the film during oxidation, the volumes and radii of dopant ions were estimated, assuming the isotropic expansion of the film. The estimated anion radii of Cl-, Br-, NO3-, BF4- and ClO4- were 235, 246, 250, 270 and 290, respectively. The results were discussed taking the crystallographic and hydrated ion radii in literatures into consideration.

Bilayered vanadium oxides by chemical pre-intercalation of alkali and alkali-earth ions as battery electrodes

We report the use of the chemical pre-intercalation synthesis technique to insert alkali (Li+, Na+, K+) and, for the first time, alkali-earth (Mg2+ and Ca2+) ions into the structure of vanadium oxide leading to the formation of the bilayered δ-MxV2O5 (M = Li, Na, K, Mg, Ca) phase with expanded interlayer spacing, enabling a large number of insertion sites for and faster diffusion of charge-carrying ions. By altering the nature of the chemically preintercalated ion, interlayer spacing of the synthesized δ-MxV2O5 materials was varied between 9.62 and 13.40Å. We for the first time show that the interlayer spacing increases with the increase of the hydrated ion radius. The ion (Na+, K+, Mg2+, Ca2+) stabilization effect was investigated in Li-ion cells, with Li-preintercalated phase, δ-LixV2O5, serving as a reference material. Our analyses indicate that cyclability and rate performance of the δ-MxV2O5 improves with increasing interlayer spacing. The highest initial capacity (198 mAh g−1), greatest capacity retention (81.8% after 50 cycles at 20mAg−1), and highest capacity retention at higher current rates (74.5% when current rate was changed from C/15 to 1C) were exhibited by Mg-stabilized δ-V2O5 with the largest interlayer spacing (13.40Å). This research demonstrates the efficacy of a facile chemical pre-intercalation strategy to synthesize ion-stabilized layered electrode materials with improved electrochemical stability. Ion-stabilized layered materials with large interlayer spacing are attractive for applications that involve electrochemically driven movement of ions through two-dimensional diffusion channels, ranging from beyond Li-ion energy storage and electrochromics to actuation and water treatment.

Potential application of graphene oxide membranes for removal of Cs(I) and Sr(II) from high level-liquid waste

Abstract As a new carbon-based membrane material used for ionic and molecular sieving, the graphene oxide (GO) membrane also has potential application in radiochemical separation. In this work, the permeation performances of some typical metallic elements in high level-liquid waste (HLLW) through the ionic sieving 5-μm-thick GO membranes were investigated. It was found that the permeation rates of ions through GO membranes markedly decreased with the increase of hydrated ionic radii. Cs(I) and Sr(II) permeated through GO membranes quickly, whereas lanthanide ions and actinide ions infiltrated much more slowly, thus providing the feasibility of separation according to the difference of hydrated ionic radii. Moreover, the concentrations of initial metal ions and acidity in feed solutions also had influences on the permeation of ions through GO membranes, and higher initial metal ions and feed solution acidity were favorable to the removal of Cs(I) and Sr(II). The barrier separation test indicated that GO membranes had promising ability for the separation of Cs(I) and Sr(II) from lanthanide and actinide ions due to the difference of hydrated ion radius, and the separation factor of Cs(I)/U(VI) and Sr(II)/U(VI) would reach about 10 and 3 in single penetration. The presented results demonstrated that the membrane separation based on GO membrane would be a promising candidate for the removal of Cs(I) and Sr(II) from HLLW.

Finding better draw solutes for osmotic heat engines: Understanding transport of ions during pressure retarded osmosis

The osmotic heat engine (OHE) is a process by which engineered salinity gradients can be utilized as source of energy generation and storage. The OHE collects low grade thermal energy to concentrate a salt solution and then releases that chemical potential energy via pressure retarded osmosis (PRO). The closed loop feature of the OHE allows the user to select any number of solutes for the draw solution so long as they can be thermally regenerated. The potential to generate energy from a particular solute is dependent on the concentration and chemistry of the solute since both diffusivity of the solute and selectivity of the membrane for that solute determine transport. In this work we evaluated three inorganic draw solutes (sodium chloride (NaCl), magnesium chloride (MgCl2) and magnesium sulfate (MgSO4)) on their potentials to be used in OHE. Power densities over 13W/m2 and 14W/m2 were achieved with MgCl2 and NaCl respectively. However, NaCl generated much larger salt flux than MgCl2. Substantially lower power densities were achieved by MgSO4. Differences in power density could be partly attributed to differences in hydrated ion radius which had substantial impacts on reverse solute flux and the subsequent development of internal concentration polarization.