Ion exchange properties and selectivity of PSS in an electrochemically switchable PPy matrix

A composite of polypyrrole (PPy) and polystyrenesulfonate (PSS) exchanges cations and is a promising material for the technical application of water softening. The ion exchange properties of electrochemically prepared PPy(PSS) are studied by investigating the polymer using a electrochemical quartz crystal microbalance (EQCM) and by analysing the solution surrounding the polymer by atomic adsorption spectroscopy (AAS). The exchange of cations by PPy(PSS) is found to be caused by three driving forces: electrochemical oxidation/reduction of PPy; chemical oxidation of PPy by dissolved oxygen; gradients of cation concentration between polymer and solution. The ion selectivity of PPy(PSS) is investigated and ion exchange isotherms for the binary systems Ca²⁺/Na⁺ and Ca²⁺/Mg²⁺ are determined.     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Multi-ion migration of Ca2+, Mg2+, Na+ and K+ in the CREDI process

In this paper, the migration of Ca²⁺, Mg²⁺, Na⁺ and K⁺ in cation-bed electrodeionisation was studied. The results showed that it was longer for divalent cations to be balanced compared with monovalent cations. At relatively low current densities, the membrane fluxes of monovalent cations were higher than that of divalent cations, whereas the results were reversed at relatively high current densities. In the resin phase, it was observed that the ionic transport was in relation to various hydration ionic radii. The reaction orders for Ca²⁺, Mg²⁺, Na⁺ and K⁺ were 2, 2, 1 and 1.5, respectively.     

Transfer of Monovalent and Divalent Cations in Salt Solutions by Electrodialysis

Abstract

The selectivity mechanism of transport of Na⁺, Ca²⁺ and Mg²⁺ through commercial monovalent‐cation permselective membranes is investigated in batch electrodialysis experiments with synthetic salt solutions containing monovalent and divalent cations. The role of hydration energy, steric effect, kinetic effect as well as effects of permselectivity of cation exchange membrane has been elucidated with electrodialysis of single solutions (NaCl, CaCl₂, MgCl₂). The mechanism of interferences is investigated in (Na⁺/Ca²⁺, Na⁺/Mg²⁺, Ca²⁺/Mg²⁺ and Na⁺/Ca²⁺/Mg²⁺) mixtures.     

Use of the empirical Hill equation for characterization of the effect of added cations on the viscosity of aqueous solutions of partially hydrolyzed polyacrylamide

Summary An empirical method based on the Hill equation has been developed to characterize the effects of added cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) on the viscosities of aqueous solutions of partially hydrolyzed polyacryl-amide.     

Quantum chemical consideration of CO adsorption over cation exchanged faujasite

CNDO/2 calculation for atomic charges, Wiberg bond orders and adsorption energies of CO molecules on the cluster model whose Si/Al ratio varied were carried out. The data for the normal cluster and dealuminated cluster were compared. Decationization energies of the cations increased with the charge densities of cation and number of aluminum involved. Adsorption process of CO on the monovalent cations such as H⁺, Li⁺, Na⁺ and divalent cations, Be²⁺, Ca²⁺, and Mg²⁺ was supposed to be occurring by the donation of non-bonded electrons from CO. The decationization energies of cations obviously decreased by the dealumination process. Adsorption energies of CO on the cations generally decreased as the dealumination look place except the case of H⁺ and Na⁺.     

Cation exchange kinetics on carboxylic acid resins in a multicomponent system H-Me+Me2+

The exchange kinetics in systems where a carboxylic cation exchange resin in the free acid form comes into contact with solutions, containing Na⁺, Mg²⁺, Ca²⁺, HCO^?₃ and SO^2?₄ have been followed by a shallow bed technique.The relations between the sorption rates of univalent and bivalent cations as well as kinetics of competitive exchange in a ternary system $\text{H}\text{-}$Na⁺Mg²⁺ were studied at low solution concentrations. The effect of polymer matrix crosslinking is studied. The behavior of sulfonic acid resin under the same conditions is given for comparison. The results are discussed in terms of different degrees of selectivities and degrees of dissociation of the carboxylic and sulfonic functional groups.     

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.     

Lichen Substances Affect Metal Adsorption in <Emphasis Type="Italic">Hypogymnia physodes</Emphasis>

Lichen substances are known to function as chelators of cations. We tested the hypothesis that lichen substances can control the uptake of toxic metals by adsorbing metal ions at cation exchange sites on cell walls. If true, this hypothesis would help to provide a mechanistic explanation for results of a recent study showing increased production of physodalic acid by thalli of the lichen Hypogymnia physodes transplanted to sites with heavy metal pollution. We treated cellulose filters known to mimic the cation exchange abilities of lichen thalli with four lichen substances produced by H. physodes (physodic acid, physodalic acid, protocetraric acid, and atranorin). Treated filters were exposed to solutions containing seven cations (Ca²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Mg²⁺, Mn²⁺, and Na⁺), and changes to the solution concentrations were measured. Physodalic acid was most effective at influencing metal adsorption, as it increased the adsorption of Fe³⁺, but reduced the adsorption of Cu²⁺, Mn²⁺, and Na⁺, and to a lesser extent, that of Ca²⁺ and Mg²⁺. Reduced Na⁺ adsorption matches with the known tolerance of this species to NaCl. The results may indicate a possible general role of lichen substances in metal homeostasis and pollution tolerance.     

Complexation of poly(methyl methacrylate-g-propylene oxide) and alkali-metal ions

Summary Copolymers of poly(methyl methacrylate-g-propylene oxide) with grafted branches having different molecular weights were complexed with K⁺, Na⁺ and Ca²⁺. The efficiency of the graft copolymers in binding cations was evaluated from salt distribution equilibria in water-methylene chloride. Among the used cations, K⁺ was more easily complexed than Na⁺ and Ca²⁺.     

Ion-selective detection of non-intercalating Na using competitive inhibition of K intercalation in Prussian blue nanotubes sensor

A nanotubes sensor for Na⁺ is fabricated using electrodeposition of iron hexacyanoferrate polymer within the nanochannels of a nanoporous metal-coated membrane. The sensing signal is derived from the influence of Na⁺ on the cathodic peak potential of the voltammetric response of the Prussian blue (PB) nanotubes immersed in a background solution containing K⁺, giving a 2K⁺:1e⁻ Nernstian response, instead of the usual 1K⁺:1e⁻ process in the absence of Na⁺. A competitive-inhibition reaction scheme is proposed which gives excellent agreement of theoretical values derived from equilibrium consideration, with experimental data obtained under reversible, slow scan rate conditions. A wide linear range over three orders of magnitude for Na sensing can be achieved by simple adjustment of background K⁺ levels. Specific and accurate detection of Na⁺ using the PB nanotubes sensor is demonstrated in a solution containing potential interfering ions: K⁺, Mg²⁺, Ca²⁺.     

31P NMR of tissue phospholipids: Competition for Mg2+, Ca2+, Na+ and K+ cations

Phosphatidylcholine (PC), phosphatidylethanolamine (PE), ethanolamine plasmalogen (EPLAS), sphingomyelin (SPH), phosphatidylinositol (PI), phosphatidylserine (PS), cardiolipin (CL), phosphatidylglycerol (PG) and phosphatidic acid (PA) were dispersed together in Cs(ethylenedinitrilo)tetraacetic acid-scrubbed chloroform/methanol solution, and high resolution³¹P nuclear magnetic resonance spectra were recorded. In separate titration experiments, Mg²⁺ and Ca²⁺ were added to the dispersed phospholipid mixture to determine the relative interaction potentials of each of the phospholipids for each of the added cations. The association of cations with individual phospholipids was indicated by³¹P chemical-shift changes, signal broadening, signal quenching or a combination of these. The titrations revealed that CL had the highest, and PA the next highest, interaction potential for Mg²⁺ cations. In contrast, PS and PA had the highest, and CL the next highest, interaction potential for Ca²⁺. Considering only interactions with Ca²⁺ ions, the phospholipids can be divided into three distinct groups: PS and PA (high interaction potential); CL, PI and PG (intermediate interaction potential); and EPLAS, PE, SPH and PC (essentially no interaction potential). The two phospholipids with the least interaction potential for either of the alkaline-earth cations were PC and SPH. Na⁺ and K⁺ ion interactions with PA, CL, PI and PG were unique and resulted in positive chemical-shift changes relative to the chemical shifts in the presence of Cs⁺ ions. Relative to both Cs⁺ and K⁺ ions, chemical shifts in the presence of Na⁺ ions were deshielded δ>0.1 ppm in the order PA>CL>PI>PG.     

The effect of some soluble inorganic admixtures on the early hydration of portland cement

The effects of the soluble chlorides, bromides, nitrates, sulphates and acetates of Ca²⁺, Mg²⁺, Li⁺, Na⁺ and Zn²⁺ as well as the corresponding mineral acids on the early hydration of neat Portland cement pastes have been studied. Both the cations and anions are ranked according to their general effectiveness as accelerators of the hydration of the Ca₃SiO₅ phase: Ca²⁺>Mg²⁺>Li⁺>Na⁺>H₂O>Zn²⁺ and OH^? >Cl^?>Br^? >NO₃^?SO₄²～H₂O > CH₃CO₂^?.     

Composite cation exchangers

Sulfonated phenol formaldehyde resins containing different amounts of sulfonated sawdust were prepared. The thermal and chemical stabilities, scientific weight capacity, and apparent capacities for the exchange of Na⁺, Ca²⁺, and Mg²⁺ at different concentrations were detemined for both H⁺ and Na⁺ forms of resins. Composites containing up to 30%–50% of sawdust, while being very much cheaper, are comparable in their properties to the pure polymeric resin. Thus, cheaper exchangers can be prepared by substituting part of the polymer by sawdust.     

Adsorption of β-carotene: II. On cation exchanged bleaching clays

X-ray diffraction patterns of a number of commercial bleaching earths indicate that they consist mainly of montmorillonite mixed with smaller amount of kaolinites as well as mica, quartz and cristobalite. The active sites in these earths for the adsorption of β-carotene are identified through ion exchange and found to be the protonic sites and some metallic ions. The efficiencies of the various cations in imparting activities to the earths are found to be in the order Mg²⁺ > Fe³⁺ > H⁺ > Ca²⁺ > Na⁺. For Fe³⁺ and H⁺ exchanged clays, the activity was found to be linear function of the concentration of these ions. The high activities of Mg²⁺ and Ca²⁺ exchanged clays are discussed. Presented in part as paper T12 in the International Conference on Palm Oil Product Technologies in the Eighties, Kuala Lumpur, May 1981.     

Synergistic interaction of konjac glucomannan and gellan gum investigated by rheology and texture analysis

The rheological kinetics of konjac glucomannan and gellan gum mixed sols were studied using rotational concentric cylinder viscometer. The effects of polymers weight ratio, shear rate, and temperature were systematically investigated. The curves showed a Newtonian plateau followed by strong shear thinning that can be described by a power law dependence on the shear rate. The dynamic viscoelastic character was evaluated by measurements of small-deformation oscillatory. After adding some cations, the mixed sols turned into mixed gels. The contribution of Na⁺, K⁺, Ca²⁺, and Zn²⁺ at different concentration was also evaluated by texture analysis. The results reveal a strong dependence of the structural properties of different samples on their preparation conditions. A fine turning of the properties of the mixed sols is possible through the change of the temperature preparation and/or the polymer weight ratio. The texture properties of the mixed gels were also possibly influenced significantly by the cations. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Inward Migration of Glass‐Modifier Cations During Heat Treatment Under an N2 Atmosphere

An Na⁺/Ca²⁺‐deficient layer is observed to form on the glass surface region up to a depth of hundreds of nanometers when a soda‐lime‐silicate glass is heat treated under an N₂ atmosphere near its glass‐transition temperature. The measurements were performed using X‐ray photoelectron spectroscopy with C₆₀‐ion sputtering (C₆₀‐XPS) and dynamic secondary‐ion mass spectrometry (D‐SIMS) with consideration of the mass and charge balances. The increase in the amount of hydrogen is substantially less than the decrease in the total charge due to the loss of modifier cations in the Na⁺/Ca²⁺‐deficient layer; furthermore, the oxygen concentration in this layer is lower than the bulk value, suggesting that the silanol groups in the surface layer of the glass are dehydrated. A high‐concentration layer of Ca²⁺ is also confirmed in the dehydration layer of the glass heat treated under an N₂ atmosphere, suggesting that Na⁺ and Ca²⁺ ions migrate inward into the glass via an ion‐exchange reaction with protons, which migrate toward the surface from the bulk. We also confirmed that a thicker Na⁺/Ca²⁺‐deficient layer is formed on glass surfaces with higher water content. Our results suggest that the dehydration of the silanol groups is the driving force of the inward migration of Na⁺ and Ca²⁺ ions.     

Unique Solubility of Switchable Alkyl-Amine Surfactants in Water

Because many amine surfactants are soluble in both water and CO₂ phases, they attract interest with regard to stabilizing CO₂-in-water dispersion systems. In our recent research, we find that the solubility of alkyl-amine surfactant in water can be significantly enhanced by salts, even though the salts are usually “salting-out” to other surfactants. The influence of various anions (NO₃⁻, Br⁻, Cl⁻, and SO₄²⁻) and cations (Na⁺, Ca²⁺, and Mg²⁺) on the alkyl-amine surfactants is investigated. The results are contrary to Hofmeister series and show that all the anions can enhance the solubility (salting-in) in the order of: NO₃⁻ > Br⁻ > Cl⁻ > SO₄²⁻, while the impact of the cations is insignificant. A physical–chemistry model based on the switchable property of the surfactant is proposed and well explains the experimental results. Therefore, the switchable alkyl-amine surfactants have potential to be applied under high-salinity and high-temperature conditions, for example, in enhanced oil recovery processes for a hot and salty carbonate reservoir.     

Chemical durability of borosilicate pharmaceutical glasses: Mixed alkaline earth effect with varying [MgO]/[CaO] ratio

Glass for pharmaceutical packaging requires high chemical durability for the safe storage and distribution of newly developed medicines. In borosilicate pharmaceutical glasses which typically contain a mixture of different modifier ions (alkali or alkaline earth), the dependence of the chemical durability on alkaline earth oxide concentrations is not well understood. Here, we have designed a series of borosilicate glasses with systematic substitutions of CaO with MgO while keeping their total concentrations at 13 mol% and a fixed Na₂O concentration of 12.7 mol%. We used these glasses to investigate the influence of R = [MgO]/([MgO] + [CaO]) on the resistance to aqueous corrosion at 80°C for 40 days. It was found that this type of borosilicate glass undergoes both leaching of modifier ions through an ion exchange process and etching of the glass network, leading to dissolution of the glass surface. Based on the concentration analysis of the Si and B species dissolved into the solution phase, the dissolved layer thickness was found to increase from ~100 to ~170 nm as R increases from 0 to 1. The depth profiling analysis of the glasses retrieved from the solution showed that the concentration of modifier ions (Na⁺, Ca²⁺, and Mg²⁺) at the interface between the solution and the corroded glass surface decreased to around 40%–60% of the corresponding bulk concentrations, regardless of R and the leaching of modifier cations resulted in a silica-rich layer in the surface. The leaching of Ca²⁺ and Mg²⁺ ions occurred within ~50 and <25 nm, respectively, from the glass surface and this thickness was not a strong function of R. The leaching of Na⁺ ions varied monotonically; the thickness of the Na⁺ depletion layer increased from ~100 nm at R = 0 to ~200 nm at R = 1. Vibrational spectroscopy analysis suggested that the partial depletion of the ions may have caused some degree of the network re-arrangement or re-polymerization in the corroded layer. Overall, these results suggested that for the borosilicate glass, replacing [CaO] with [MgO] deteriorates the chemical durability in aqueous solution.     

The design of cyclic fixed-bed ion-exchange operations—III. Softening solutions containing Na+, Mg2+, Ca2+

The method presented in parts 1 and 2 for the design of simple cyclic ion-exchange processes in foxed beds is extended to the case where Na⁺, Mg²⁺ and Ca²⁺ are all present in the saturation solution. Two properties are established: firstly that the breakthrough curves corresponding to Ca²⁺ and Na⁺ mixtures in different proportions can be reduced to a single curve by using generalised coordinates, and secondly that Ca²⁺ and Mg²⁺ can be considered as a single ion of “hardness”. This means that the ternary mixture can be treated as a binary possessing the first property. These effects are incorporated into the cyclic material balances allowing the treatment given in parts 1 and 2 to be used.