SYNTHETIC INORGANIC ION-EXCHANGE MATERIALS. XLVIII. ION-EXCHANGE REACTION OF ALKALI METAL IONS/H+ ON MONOCLINIC ANTIMONIC ACID

The pH titration curves of monoclinic antimonic acid (M-SbA) showed apparently monobasic acid for the systems of alkali metal ions/H⁺. The uptake order of the metal ions were K⁺ < Rb⁺ < Cs⁺ < Na⁺ < Li⁺ throughout the pH range studied. The low uptakes of K⁺, Rb⁺, Na⁺ and Cs⁺ at high pH might be due to steric or ion sieve effects for large unhydrated cations on M-SbA. Thermodynamic data were derived for Li⁺/H⁺ exchange on M-SbA from pH titration curve.     

Adsorption of metal cations from aqueous solutions onto the pH responsive poly(vinylidene fluoride grafted poly(acrylic acid) (PVDF-PAA) membrane

This study investigated the influence of pH of adsorption medium and co-adsorptive metal cations for the adsorption of potassium (K⁺) and magnesium (Mg²⁺) ions onto poly (vinylidene fluoride) grafted poly(acrylic acid) (PAA-PVDF) membrane. At pH 4.8, the adsorption of potassium and magnesium was minimal, because of nearly non-dissociated carboxylic acid groups of PAA-chains, but adsorption increased with increasing ion concentration. The interaction of the studied cations between PVDF-PAA membranes increased considerably at pH 7.0 the dissociation of carboxylic acid groups of PAA. The addition of ionic substances (calcium (Ca²⁺) and sodium (Na⁺) to the adsorption medium reduced the adsorption of potassium and magnesium onto the membrane, because of co-adsorption. Divalent calcium reduced more effectively than univalent sodium the adsorption of potassium and magnesium onto the membrane. In conclusion, co-adsorbing ions reduced the adsorbed amount of potassium and magnesium ions due to binding competition. The percentual adsorbed values suggest that adsorption affinity of studied ions onto the PVDF-PAA membrane followed the order Na⁺ < K⁺ < Mg²⁺ < Ca²⁺. The effect of metal cations on drug adsorption from biological fluids needs research in the future, because e.g. PVDF-PAA membrane has been used in drug separation processes.     

THERMODYNAMICS OF ALKALI AND ALKALINE EARTH METAL ION - EXCHANGE ON CERIUM(IV) HYDROGEN PHOSPHATE

ABSTRACT

Thermodynamics of alkali and alkaline earth metal ions/hydrogen ions exchange on a fibrous cerium(IV) hydrogen phosphate have been investigated. Selectivities for alkali and alkaline earth metal ions increase in the order; Na⁺<<K⁺<Rb⁺<Cs⁺ and Mg²⁺<Ca²⁺<Sr²⁺<Ba²⁺, respectively. The enthalpy changes for alkali metal and Ba2+ ions/H⁺ exchange are negative, those for the other alkaline earth metal ions/H⁺ exchange are positive, indicating that the enthalpy changes for monovalent ions are more favorable than those for divalent ions. In comparison with ions of the same valency, the enthalpy change decreases with the atomic number of the metal ion corresponding to a decrease in the entropy change of dehydration in response to enthalpy-entropy compensation.     

LITHIUM-ION SIEVE PROPERTY OF λ;-TYPE MANGANESE OXIDE

The adsorptive properties of A-Mn0₂for mono and divalent metal ions were investigated by pH titration and by measurements of the distribution coefficients(Kd's) of the metal ions. The pH titration curve showed an apparently monobasic acid type for a H⁺-Li⁺exchange. Those for H⁺-K⁺and H⁺-Cs⁺exchanges were nearly the same as that for blank titration. The lithium ion uptake increased with increasing solution pH and reached 5 meq/g at pH 11. X-ray diffraction analyses showed that the adsorption of lithium ions caused an increase in the lattice constant of a cubic unit cell. The potassium and cesium ion uptakes were nearly zero over a pH range between 4 and 11. A-Mn0₂showed a remarkably high Kd value for lithium ions, compared to a cation exchange resin. The selectivity sequences were Na⁺< K⁺< Rb⁺< Cs⁺<< Li⁺for alkali metal ions, Mg²⁺< Ca²⁺< Sr²⁺< Ba²⁺for alkaline earth metal ions, and Ni²⁺< Zn²⁺< Co²⁺< Cu²⁺for transition metal ions.     

Interactions of Some Hofmeister Cations with Sodium Dodecyl Sulfate in Aqueous Solution

In this work, we have investigated the influence of some alkali metal ions on the Krafft temperature (T_K) and critical micelle concentration (CMC) of a classical ionic surfactant, sodium dodecyl sulfate (SDS), over a wide range of temperature. The alkali metal cations such as Li⁺, Na⁺, Cs⁺, and K⁺ are found to affect the solubility and hence the T_K of the surfactant. It was observed that kosmotropic Li⁺ lowers the T_K of the surfactant. Due to the common ion effect, the solubility of SDS decreases in the presence of Na⁺, resulting in an increase in the T_K. On the other hand, chaotropic K⁺ and Cs⁺, capable of forming contact ion pairs with the chaotropic dodecyl sulfate ion, lower the solubility and hence elevate the T_K. In terms of decreasing the T_K, the ions follow the trend: Li⁺ > Na⁺ > Cs⁺ > K⁺ except for 0.0025 M CsCl. The added cations screen the charge of the micelle surface and facilitate closer packing of the surfactant with a consequent decrease in the CMC. In terms of the effectiveness in lowering the CMC, the ions follow the order: Cs⁺ > K⁺ > Na⁺ > Li⁺. In the presence of added electrolytes, the γ_CMC values are found to be lower than the corresponding values in pure water. The thermodynamic parameters (Gibbs free energy, enthalpy, and entropy changes) of micellization were calculated to gain insights into the mechanism of the process.     

Preparation of unsaturated polyester–styrene beads using gamma irradiation and chemical polymerization routes for use in the recovery of some alkali metal ions

Suspension polymerization of unsaturated polyester–styrene was carried out in different media using different routes of polymerization. The effects of matrix type and concentration hold up, viscosity, irradiation dose, and the agitation speed on the resultant polymer characteristics were examined. The formed beads were physically identified using scanning electron microscopy, hardness, and particle size analysis techniques. They were smooth having typical spherical surfaces; the beads diameters were in the range of about 5–200 μm. The size of the resin beads was found to decrease with increase in the concentration and viscosity of the dispersant and impeller speed. The resultant beads were applied in the recovery of Li⁺, Na⁺, K⁺, and Cs⁺ ions from acidic media. The distribution coefficients of the alkali metal ions were calculated; the order of selectivity was Li⁺ > Na⁺ > K⁺ > Cs⁺ in case of the chemically processed resin beads, while the selectivity lies in the order of Li⁺ < Na⁺ < K⁺ < Cs⁺ in case irradiation processed ones. Finally, the economics of production of the unsaturated polyester–styrene resins using different methodologies was studied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1149–1160, 2007     

Ion-Exchange Properties of lon-Sieve-Type Manganese Oxides Prepared by Using Different Kinds of Introducing Ions

Abstract

Three ion-sieve-type manganese oxides, HMnO(Li), HMnO(Na), and HMnO(K), were prepared by acid treatments of Li⁺-, Na⁺-, and K⁺-introduced manganese oxides, respectively. Three oxides were obtained from γ-MnO² and the corresponding alkali metal hydroxides by heating at 600°C. The ion-exchange properties of the adsorbents were investigated by pH titration, K_d measurements, and the adsorption of metal ions from seawater. The selectivity sequences of alkali metal ions were Na⁺ < Cs⁺ < Rb⁺ < K⁺ < Li⁺ for HMnO(Li) and Li⁺ Na⁺ < Cs⁺ < K⁺ < Rb⁺ for HMnO(Na) and HMnO(K). The high selectivity of Li⁺ on HMnO(Li) can be ascribed to an ion-sieve effect of spinel-type manganese oxide which was produced from LiMn₂O₄ Since HMnO(Na) and HMnO(K) had [2 × 2] tunnels of edge-shared [MnO₆] octahedra, the high selectivities of K⁺ and Rb⁺ on these samples were used to explain that the sizes of the [2 × 2] tunnels were suitable for filling ions of about 1.4 Å in radius in a stable configuration. The order of metal-ion uptake from seawater was Sr²⁺ < K⁺ < Mg²⁺ < Ca²⁺ < Na⁺ < Li⁺ for HMnO(Li), Li⁺ < Sr²⁺ < Mg²⁺ < Ca²⁺ < Na⁺ < K⁺ for HMnO(Na), and Li⁺ < Sr²⁺ < Ca²⁺ < Mg²⁺ < K⁺ < Na⁺ for HMnO(K).     

Counter‐ion‐specific helix formation of poly(γ‐methyl L‐glutamate) derivatives containing sulfonate group in aqueous alcohols

Charged polypeptides containing sulfonate groups were prepared by transesterification of poly(γ‐methyl L ‐glutamate) with isethionic acid. The coil–helix transition of the sulfonated polypeptides was investigated in aqueous alcohols. Marked counter‐ion specificity was observed for helix formation: Li⁺ < Na⁺ < Cs⁺ ≦ Rb⁺ ≦ K⁺; this was different to that for poly(L ‐glutamate) (PLG): Cs⁺ ? K⁺ < Li⁺ < Na⁺. Specific helix stabilization by counter‐ion mixing, which has been found for the PLG system, was not observed for the sulfonated polypeptides. The counter‐ion‐ and solvent‐specific helix formation is discussed and compared with that in PLG. © 2001 Society of Chemical Industry     

SYNTHETIC INORGANIC ION-EXCHANGE MATERIALS. XXXXI. ION EXCHANGE EQUILIBRIA OF ALKALI METAL IONS/HYDROGEN IONS ON TIN(IV) ANTIMONATE

Ion exchange equilibria of alkali metal ions (Li⁺, Na⁺, K⁺,, Rb⁺, and Cs⁺)H⁺, systems have been studied in MNO-j-HNOj media with ionic strength of 0.1 at 30, 45 and 60 °C on tin(IV) antimonate as a cation exchanger. The ion exchange isotherms have been measured for both forward and backward reactions by the batch technique. The isotherms showed S-shaped curves for all exchange systems studied. The selectivity coefficients (logarithmic scale) vary with the equivalent fraction X_M of alkali metal ions in the exchanger and give two linear functions of X_M with a break point (X_M= 0.14, except 0.04 for Li⁺, /H⁺) indicating two different exchanging sites. The selectivity sequence, Na⁺, ? K⁺, ? Rb⁺, ? Cs⁺, ? ? Li, holds in the range of Xu= (0 - 0.04) and the sequence, Cs < Rb ⁺, ? K ⁺, ? Na ⁺, < Li ⁺, applies when X_M is higher than 0.14.

Hypothetical thermodynamic data on “zero loading” of the ion exchange reaction was evaluated.     

Selective Transport of Alkali and Alkaline Earth Metallic Ions through a Supported Liquid Membrane Containing Tripentyl Phosphate as a Carrier

Abstract

A selective transport system for alkali and alkaline earth metallic ions with a perchlorate ion as a pairing ion species through a supported liquid membrane (SLM) containing tripentyl phosphate (TPP) as a carrier is described. The SLM used is a porous polypropylene membrane impregnated with TPP solution in o-nitrophenyloctylether. The effects of the pairing ion species, the initial perchlorate concentration, and the TPP concentration on metallic ion transportability are examined under various experimental conditions. The permeation velocities of the metallic ions in the transport system followed the sequence Li⁺?Na⁺>K⁺>Mg²⁺; that is, a highly selective transport for Li⁺ ion was observed. Compared with the transport rates of alkali metallic ions, those of transition metallic ions such as Cu²⁺ and Fe³⁺ ions are very low. The permeation velocities of alkali and alkaline earth metallic ions through an SLM are dependent on the concentrations of perchlorate and TPP. Equations for the permeation velocities of Li⁺, Na⁺, K⁺, and Mg²⁺ ions through an SLM, based on two concentrations of perchlorate and TPP, are proposed.     

Theoretical insights into PF6 and its alkali metal ion pairs: geometries and vibrational frequencies

The structures, vibrational frequencies, infrared and Raman intensities of hexafluorophosphate anion (PF₆⁻) and M⁺PF₆⁻ (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺) ion pairs have been studied by ab initio calculations. It is shown that the tridentate coordination of cation by PF₆⁻ is the most stable structure in gas phase. The vibrational spectroscopies of the most stable geometries were calculated and the changes in band position were used to probe the ion associations.     

Complexation Equilibrium Constants of Poly(vinyl alcohol)-Borax Dilute Aqueous Solutions – Consideration of Electrostatic Charge Repulsion and Free Ions Charge Shielding Effect

Equilibrium dialysis experiments of dilute poly(vinyl alcohol) (PVA) in borax aqueous solution (PVA concentration was 2 g/L and borax concentration ranged from 0.0 M to 0.05 M) were carried out to determine the concentration of free borate ions in equilibrium with the PVA-borate complex at 25°C, and hence the amount of borate bound to PVA. The binding isotherm of borate ion on PVA molecules was investigated. The concentration of borate ion bound on PVA was found to increase with increasing borax concentration and reached an asymptote at high borax concentrations. The complexation equilibrium constant between borate and PVA diol was found to decrease initially then increases and finally decreases with increasing borax concentration while PVA concentration was fixed in a constant value. The equlibrium constant of free borate ion with borate-PVA diol complex was a balance result of excluded volume of PVA molecular chains, electrostatic charge repulsion between free borate ions and borate-PVA diol complexes, and electro-shielding of free Na⁺ ions on negatively charged PVA-borate complexes. In this study, the electrostatic charge repulsion between free borate ions and borate-PVA diol complex ions and free Na⁺ ions shielding effect are considered in the estimation of equilibrium constants of PVA diol-borate complexation. A fixed value of equilibrium constant is obtained with increasing borax concentration while borax concentraion is below a critical concentration [borax]_crt. As borax cocentration is higher than [borax]_crt, a lots of PVA diols form complexes with borate ions and a high shielding of free Na⁺ ions on negatively charged borate-PVA diol complexes causes the PVA-borate complexes to behave like neutral polymers. Few free PVA diol binding sites are available for reaction with free borate ions while borax concentration is higher than [borax]_crt resulting in a decrease in equilibrium constant with increasing borax concentration.     

The Translocation of Na+ Ion Inside Human Thrombin Accounts for the Activation of the Enzyme

Thrombin is a member of the chymotrypsin family that splits the peptide bond next to arginine. The catalytic activity of thrombin is accelerated by Na⁺. Inspection of the crystal structure reveals an ion binding site 17 Å from the active-site, leading to ambiguous definition of its mode of rate-enhancement. During unbiased Molecular Dynamics simulations in the presence of Na⁺ ions, the Na⁺ ion was noticed to alternate between two locations: the crystal-structure site (adjacent to R221a and K224) and another site next to D189, very close to the binding and the active sites. There is a free passage between the two locations, and both sites can exchange ions with the bulk. When the ion is close to D189 it can assume position between the guanidino moiety of the product and the carboxylate of D189, thus weakening the protein-product interaction. This transient structure either ejects the Na⁺ ion out of the protein or releases the product from the enzyme. We propose that the enhancement of the catalysis by the ion is a reflection of its ability to destabilize the product-enzyme complex.     

Conformation,Coordination and Ion Selectivity of the Ionophore X206

The conformation and the cation coordination of the ionophore X206, which selectively transports potassium over sodium, are evaluated in an effort to correlate the structural features of the ionophore with its ion selectivity. For this purpose, the crystal structure of the Na⁺-complex of X206 has been determined by X-ray diffraction and is compared with those of the free acid form of X206, its Ag⁺-complex and the K⁺-complex of the closely related ionophore alborixin. The ionophore conformation is very similar in all four structures. The carboxylic acid end is essentially invariant, but small changes in torsion angles of up to 26° at the other end of the molecule, combined with differences in the positions of the cations, result in very different coordination geometries for the cations. The conformations of the Ag⁺- and K⁺-complexes resemble the free acid conformation more closely than does that of the Na⁺-complex. The K⁺ ion is 8 coordinate while the Ag⁺ and Na⁺ ions are 6 and 5 coordinate, respectively. Empirical calculations of the bond strength on the basis of the coordination bond lengths show a stronger binding of K⁺ than of Na⁺ which is consistent with the greater selectivity for binding of the former.     

Pervaporation separation of water–ethanol mixtures using metal‐ion‐exchanged poly(vinyl alcohol) (PVA)/sulfosuccinic acid (SSA) membranes

Poly(vinyl alcohol)/sulfosuccinic acid (PVA/SSA) membranes in the hydrogen form were converted to monovalent metal ion forms Li⁺, Na⁺, and K⁺. The effect of exchange with metal ions was investigated by measuring the swelling of water–ethanol (10/90) mixtures at 30 °C and by the pervaporative dehydration performance test for aqueous ethanol solutions with various ethanol concentrations at 30, 40, and 50 °C. In addition, electron spectroscopy for chemical analysis (ESCA) analysis was carried out to study the quantity of metal ions in membranes. From the ESCA analysis, the lithium ion quantity in the resulting membranes is greater than that of any other metal ions in question because of the easy diffusion of a smaller metal ion into the membrane matrix. The swelling ratio was in the following order: PVA/SSA‐Li⁺ > PVA/SSA‐Na⁺ > PVA/SSA‐K⁺ membranes. For pervaporation, the PVA/SSA‐Na⁺ membrane showed the lowest flux and highest separation factor for all aqueous ethanol solutions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1867–1873, 2002     

Synthetic ionophores for the separation of Li, Na, K, Ca, Mg metal ions using liquid membrane technology

Carrier-assisted transport through liquid membranes is one of the important applications of supramolecular chemistry. This work investigates the use of synthetic carrier (ionophore) for the separation of metal ions. We have tested the effect of structure of ionophore on the separation of metal ions. For this purpose, we have used a new series of non-cyclic ionophores having different end groups and chain length (R₁–R₅). 1,5 bis (2-naphthyloxy)-3-oxapentane (R₁), 1,8 bis (2-naphthyloxy)-3,6-di-oxaoctane (R₂), 1,11 bis (2-naphthyloxy)-3,6,9-tri-oxaundecane (R₃) 1,11-(dianthraquinonyloxy) 3,6,9-trioxaundecane (R₄), 1,8 (dianthraquinonyloxy) 3, 6-dioxaoctane (R₅) have been used in extraction, bulk liquid membrane (BLM) and supported liquid membrane (SLM) transport of alkali (Li⁺, Na⁺, K⁺) and alkaline earth metal cations (Ca²⁺, Mg²⁺). The supported liquid membrane consisted of a porous cellulose nitrate and and an onion membrane support impregnated with ionophore using chloroform as a solvent. The results reveal that ionophores R₁, R₂ and R₃ are better extractants for K⁺ while R₄ and R₅ are better extractants for Ca²⁺. Among these ionophores R₃ and R₄ are best extractants for K⁺ and Ca²⁺ ions. The results of BLM reveal that ionophores R₁, R₂ and R₃ transport Na⁺ at a greater extent, while R₄ and R₅ transport Ca²⁺ and K⁺ at a greater extent. In SLM experiments using a cellulose nitrate membrane support, it was observed that naphthyl end group bearing ionophores (R₁–R₃) transports Na⁺ > K⁺, and anthraquinone bearing ionophores (R₄ and R₅) transport K⁺ > Na⁺ > Ca²⁺ respectively. In the onion membrane support R₄ transports Ca²⁺ and Na⁺ equally and R₅ transports K⁺ selectively. On comparing the membrane support, the cellulose nitrate membrane is found better support for the transport of metal ions. The results suggest that due to the presence of different end groups and chain lengths the selectivity of non-cyclic ionophores towards metal ions is enhanced. Thus selectivity of ionophores may have fruitful application in ion selective electrodes and separation of metal ions.     

Transport Studies of Monovalent Ions through Nafion-117 Ion Exchange Membrane in Presence of Polyacrylate

The results of equilibrium distribution and transport kinetics of monovalent (Li⁺, Na⁺, and Cs⁺) ions through Nafion-117 ion exchange membrane in presence of polyacrylate anion have been presented. For Na⁺-Li⁺ system, equilibrium distributions in the presence and absence of polyacrylate have been found to be the same indicating that the Donnan membrane equilibrium is not affected by the presence of polyacrylate. For the Na⁺-Cs⁺ system, a favored transport of Cs⁺ ion to the polyacrylate compartment has been observed, indicating the binding of Cs⁺ ion with polyacrylate is stronger than other monovalent ions. This is due to the lower hydration radius of Cs⁺ ions. The deviation from Donnan membrane equilibrium condition has been used to obtain information about the fraction of counter-ions bound to the polyacrylate. The transport profile in the presence of polyacrylate has also been calculated based on the modified Nernst Planck (NP) approach, taking into account the fraction of counter-ions bound to the polyacrylate ion. The Donnan relation has been used to obtain the concentration of ions at the solution/membrane interface. The self-diffusion coefficients of ions and membrane ion exchange capacity have been given as input parameters in the calculations. The calculated time profile has been found to agree well with the experimental time profile.     

Glass electrode response to lithium ion activity. Effects of sodium,potassium, ammonium,tetramethyl-, tetraethyl-, and tetra-n-butyl ammonium ions in water and 50% water-ethanol mixture

Competing effects of Na⁺, K⁺, NH⁺₄ and three quaternary ammonium ions, Me₄N⁺, Et₄N⁺, and n-Bu₄N⁺, on the response of a lithium ion-selective glass electrode have been investigated in water and 50% water-ethanol mixture. The results have been analysed according to an ion-exchange model developed earlier for solutions in propylene carbonate. It appears that the effects of the two groups of cations can be rationalized in terms of the relative ease (or difficulty) or desolvation experienced by a lithium ion, in their presence, prior to its incorporation into the glass phase.     

Chloroform as solvent for the complex formation of alkaline salts with crown ethers and cryptands

The complex formation between different crown ethers and the cryptand (2 2 2) with the ammonium and alkali ions was studied in chloroform as solvent using calorimetric titrations. From the reaction enthalpies for the complex formation with 18-crown-6 and the cryptand (2 2 2) as well as from competitive reactions between both ligands no influence of ion pairs can be detected within the experimental error. Stability constants of the complexes formed could only be obtained in case of the complex formation of Na⁺ with benzo-18-crown-6 and of Cs⁺ with most of the ligands.     

ION EXCHANGE SELECTIVITY OF A RESORCINOL-FQRMALDEHYDE POLYCONDENSATE RESIN FOR CESIUM IN RELATION TO OTHER ALKALI METAL IONS

ABSTRACT

Ion exchange isotherms for the ion-pairs Li⁺ -Cs⁺, Na⁺ -Cs⁺ and K⁺ -Cs⁺ have been measured for a cesium selective resorcinol—formaldehyde polycondensate resin synthesized in the laboratory- The equilibrium data have been used to calculate the thermodynami c equilibrium constants as well as standard free energies of ion ex change and thus arrive at a selectivity series for the above ions- The high selectivity towards cesium as compared to other alkali metal ions has been discussed in the 1ight of existing theories and models of ion ex change phenomena.