Irreversible dissociation of water molecules on the ion-exchange membrane-electrolyte solution interface in electrodialysis

The fluxes of hydrogen ions through the cation-exchange membrane and hydroxyl ions through the anion-exchange membrane in the electrodialysis were measured using the method of selective polarization. The experiments, which were conducted in a wide range of current densities, enabled us to obtain the results of ionic transport different from the literature data and to explain them on the basis of chemical reactions proceeding in the system. It is shown that a decrease in the hydration of ionogenic groups intensifies the ionic fluxes of the medium in the electrodialysis.     

H+-Cu2+ ion exchange on a Cu0-KU-23 sulfocation exchanger nanocomposite in solutions with various pH values

The influence of solution pH on H⁺-Cu²⁺ exchange equilibrium was studied for the disperse copper- KU-23 (15/100 S) macroporous strongly acid sulfocation exchanger nanocomposite. In dilute solutions of copper(II) sulfate in weakly acid media (pH 3–6), ion exchange limitation is related to the consumption of hydrogen counterions and the formation of copper counterions in a side reaction between copper particles and impurity oxygen. The concentration of hydrogen counterions in the nanocomposite is replenished as pH decreases because of their sorption from solution together with copper ions. Original Russian Text ? E.V. Zolotukhina, T.A. Kravchenko, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 5, pp. 934–938.     

Ab Initio Calculation of the Structure and Functions of Sulfo Cation Exchangers

An ab initio calculation has been carried out for hydrated lithium, sodium, potassium, and rubidium toluenesulfonates, modeling the structure of sulfo cation exchangers in the form of alkali metal ions. In the optimized structure, water molecules are incorporated between the fixed ion and the counterions. This leads to dissociation of the ionogen groups, which increases the diffusion mobility of the counterions. Analysis of an elementary ion exchange process has revealed that cleavage of hydrogen bonds between the hydration water molecules of the fixed ion and the counterions plays a critical role in the ion exchange mechanism.     

Detection of interfacial hydroxyl ions (OH− AND OD−) on Ag electrodes by surface enhanced Raman scattering

The stretching mode of hydroxyl ions (OH^? and OD^?), which are located at the Ag electrode-electrolyte interface, has been observed. Two distinct peaks in the surface enhanced Raman spectra of interfacial hydroxyl ions were observed. The assignment of Raman peaks to hydroxyl ions was confirmed by adding KOH or HCl to the electrolyte or by electrochemically generating hydroxyl ions and hydrogen gas at the electrode interface.     

Short communications

The transport of carbonic acid anions through an anion-exchange membrane (AEM) during electrodialysis is studied. At current densities above limiting diffusion values, fluxes of hydrocarbonates and carbonates are lower than those of strong-electrolyte anions. The reason for the decreased fluxes is the recombination of carbonic acid ions with hydrogen ions that form during irreversible dissociation of water molecules at the solution/AEM interface     

Computer modeling of the structure of supramolecular systems: An example of ion exchangers

A method is proposed for the determination of the structure of supramolecular systems based on spectrum-structure correlations and quantum-chemical and molecular dynamic modeling. Application of the developed approach to the analysis of the structures carboxy- and sulfo-cation exchangers as alkali metal salts and an amino acid (glycine) suggests that the ion pairs in the studied systems are dissociated. This allows a conclusion that the retention of ions in the ion exchangers in chromatographic separation is due to not only the electrostatic interaction of the fixed and mobile ions, but also hydrogen bonding between the hydration shells of the counterions.     

Ion exchange and redox reactions in metal-ion exchanger nanocomposites

The reducing sorption of oxygen dissolved in water with the use of metal-containing nanocomposites is considered taking into account the bifunctional nature of sorbents possessing both redox and ion exchange properties. A physicochemical model of the process including metal particle dispersity, their distribution over a grain, and the special features of the chemical oxidation of metals was used. Based on this model, a mathematical formulation of the problem including the stage of the interdiffusion of metal ions (metal oxidation products) and hydrogen ions (matrix counterions) is given.     

Studies on the nature of hydrated zinc oxide. Part II

Summary Three samples of hydrated zinc oxide have been precipitated with (1) 10% deficient alkali (2) just equivalent and (3) 10% excess alkali. The adsorption of hydrogen and hydroxyl ions by these three samples have been studied at two different temperatures. It has been found that adsorption of hydroxyl ions is maximum with sample (1) whereas sample (3) adsorbs hydrogen ions preferentiably. Ageing and heating decreases the adsorption of hydrogen and hydroxyl ions. Ageing is more prominent for sample (3). The effect of ageing of the different samples has been explained from the amphoteric behaviour of the hydrated zinc oxide.

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Zusammenfassung Drei Proben von hydratisiertem Zinkoxyd wurden mit 10% Unterschu? (1) mit ?quivalenter Menge (2) und mit 10% überschu? (3) an Alkali ausgef?llt. Die Adsorption von Wasserstoff und Hydroxylionen wurde an diesen Proben bei zwei verschiedenen Temperaturen untersucht. Probe 1 adsorbiert die Hydroxylionen maximal, w?hrend Probe 3 bevorzugt den Wasserstoff adsorbiert. Altern und Erhitzen vermindert die Adsorption, Alterung ist besonders für die Probe 3 ausgepr?gt. Der Effekt der Alterung der verschiedenen Proben wurde wiederum durch den amphoteren Charakter des Zinkoxyds erkl?rt.

     

Plane-wave density functional theoretic study of formation of clay-polymer nanocomposite materials by self-catalyzed in situ intercalative polymerization.

It has recently been shown that the intercalation and subsequent in situ polymerization of organic monomers within the interlayer of clay minerals yields nanocomposites with novel material properties. We present results of plane-wave density functional theory (DFT) based investigations into the initial stages of the polymerization of methanal and ethylenediamine within the interlayer of sodium montmorillonite. Nucleophilic attack of the amine on the aldehyde is only observed when the aldehyde is protonated or coordinated to a metal ion. No evidence is found for the dissociation of water in the hydration sphere of the sodium counterions. The Br?nsted acidity of the hydroxyl groups present in the silicate layers is significantly affected by their proximity to sites of isomorphic substitution. However, the most obvious Br?nsted acid sources are shown to be unlikely to catalyze the reaction. Instead catalysis is shown to occur at the clay mineral lattice-edge where hydroxyl groups and exposed aluminum ions act as strong Br?nsted and Lewis acid sites, respectively.     

A systematic study of the interactions between chemical partners (metal, ligands, counterions, and support) involved in the design of Al2O3-supported nickel catalysts from diamine-Ni(II) chelates

1.5 Ni wt %/Al2O3 catalysts have been prepared by incipient wetness impregnation using [Ni(diamine)x(H2O)(6-2x)]Y2 precursors (diamine = 1,2-ethanediamine (en) and trans-1,2-cyclohexanediamine (tc); x = 0, 1, and 2; Y = NO3- and Cl-), to avoid the formation, during calcination, of difficult-to-reduce nickel aluminate. N2 was chosen for thermal treatment to help reveal and take advantage of the reactions occurring between Ni2+, ligands, counterions, and support. In the case of [Ni(en)2(H2O)2]Y2 salts used as precursors, in situ UV-vis and DRIFT spectroscopies show that after treatment at 230 degrees C Ni(II) ions are grafted to alumina via two OAl bonds and that the diamine ligands still remain coordinated to grafted nickel ions but in a monodentate way, bridging the cation with the alumina surface. With Y = Cl-, the chloride counterions desorb as hydrogen chloride, and hydrogen released upon decomposition of the en ligands is able to reduce a fraction of nickel ions into metal as evidenced by XPS. In contrast, with Y = NO3-, compounds such as CO or NO are formed during thermal treatment, indicating that nitrate ions burn the en ligands. After thermal treatment at 500 degrees C, a surface phase containing Ni(II) ions forms, characterized by XPS and UV-vis spectroscopy. Temperature-programmed reduction shows that these ions can be quantitatively reduced to the metallic state at 500 degrees C, in contrast with the aluminate obtained when the preparation is carried out from [Ni(H2O)6]2+, which is reduced only partly at 950 degrees C. On the other hand, a total self-reduction of nickel complexes leading to 2-5-nm metal particles is obtained upon thermal treatment via the hydrogen released by a hydrogen-rich ligand such as tc, whatever the Y counterion. An appropriate choice of the ligand and the counterion allows then to obtain selectively Ni(II) ions or a dispersed reduced nickel phase after treatment in N2, as a result of the reactions occurring between the chemical partners present on alumina.     

硼酸根与甲阶酚醛树脂中酚羟基和邻位羟甲基的螯合反应

通过溶液pH值的测定和红外光谱分析，研究硼砂与甲阶酚醛树脂水溶液的反应表明：在水溶液中硼砂能与甲阶酚醛树脂很快地发生反应；硼砂水解产生的B／（OH)4^-，以定量的方式与树脂中酚羟基和邻位羟甲基以共价配键相结合，形成具有四面体结构的螯合物，并放出H^ 离子。     

Mechanism of proton conductivity in polyvinyl alcohol-phenolsulfonic acid membranes from <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR data

With line narrowing during magic angle spinning in solid-state NMR, molecular mobility and hydration in composite membranes based on polyvinyl alcohol (PVA) and phenol-2,4-disulfonic acid (PSA) were studied as functions of the ratio of the acidic and polymeric components, the degree of cross-linking in the polymeric matrix, and the moisture content. It is shown that at high relative humidity proton transport takes place by means of the network of hydrogen bonds, which are formed by the H⁺ counterions, sulfonate groups, and water molecules. At low moisture content, the hydroxyl groups in PVA play an active role in proton transport.     

Interpretation of chromatographic behavior of ions based on the electric double-layer theory

A retention model based on electrostatic theories is applied to the analysis of the ion-exchange chromatographic separation of ions. The adsorption of counterions and the ion-pair formation between ion-exchange sites and counterions are included in the model; these represent separation selectivity. A nonstoichiometric contribution, the accumulation of ions in an electrical double layer, is also involved in the model. The retention of ions is calculated by assuming these ionic properties for both eluent and solute ions. The comparison of calculated retention factors with experimental values gives insight into the ion-exchange nature of ions; e.g. a strongly adsorbed ion should have higher ion-pair formation ability, and vice versa.     

The effect of charge on hydroxyl loss from ortho-substituted nitrobenzene ions

An abundant loss of hydroxyl in decompositions of ortho-substituted nitroarene cations is commonly observed when the substituent contains one or more labile hydrogen atoms. The major loss of hydroxyl also takes place from many but not all of the corresponding molecular anions. Data are reported for the collisionally activated decompositions of the cations and anions of o-nitrotoiuene, o-nitrophenol and o-nitroaniline. Data for some dinitro ions are also reported. The results can be rationalized on the basis of a greater degree of charge developed at the substituent in the transition state of the anions that leads to a rearranged ion. It is from this structure tint hydroxyl is lost via simple bond cleavage. This can be viewed most simply as a proton transfer from the substituent to the nitro group in the anion as opposed to hydrogen transfer in the analogous step for the cation. The degree to which hydroxyl loss occurs is therefore largely determined by the tendency for hydrogen (cations), or proton (anions), transfer from the substituent to the nitro group.     

New Insight on Carbon Dioxide-Mediated Hydrogen Production**

A new approach to hydrogen production from water is described. This simple method is based on carbon dioxide-mediated water decomposition under UV radiation. The water contained dissolved sodium hydroxide, and the solution was saturated with gaseous carbon dioxide. During saturation, the pH decreased from about 11.5 to 7–8. The formed bicarbonate and carbonate ions acted as scavengers for hydroxyl radicals, preventing the recombination of hydroxyl and hydrogen radicals and prioritizing hydrogen gas formation. In the presented method, not yet reported in the literature, hydrogen production is combined with carbon dioxide. For the best system with alkaline water (0.2 m NaOH) saturated with CO₂ under UV-C, the hydrogen production amounted to 0.6 μmol h⁻¹ during 24 h of radiation.     

Probing C-H...X hydrogen bonds in amide-functionalized imidazolium salts under high pressure

We have probed under high pressure the C-H hydrogen bonds formed by N,N(')-disubstituted imidazolium ions having PF(6) (-) and Br(-) counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N-H...F unit) in the infrared spectrum of the PF(6) (-) salt indicates that conventional N-H...O and N-H...N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C(2)-H...F interactions, combined with other weak hydrogen bonds, disturb the formation of N-H hydrogen bonds in the PF(6) (-) salt. This finding is consistent with the pressure-dependent results, which reveal that the C(2)-H...F interaction is enhanced upon increasing the pressure. In contrast to the PF(6) (-) salt, the imidazolium C-H bonds of the Br(-) salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br(-) and PF(6) (-) ions.     

Mass spectrometry of pyridine compounds—II: Hydrogen exchange in the molecular ions of isonicotinic—and nicotinic acid as a function of internal energy

From the mass spectra of site-specifically deuterated analogues of isonicotinic acid it appears that the molecular ion eliminates hydroxyl and water after an exchange between the hydroxylic and β-hydrogens. The percentage of exchange in these reactions depends on the internal energy of the molecular ion and is shown to be 53 to 57% in the ion source, 92 to 97% in the first and ∽ 100% in the second field free regions. Furthermore, the isotope effect i, operative in the loss of water, increases with decreasing internal energy of the molecular ion, being 1.6, 2.0 and 2.3 in the ion source, first- and second field free regions, respectively. In the molecular ions, losing successively hydroxyl and carbon monoxide as deduced from diffuse peaks in the first-and second field free regions, a substantially lower percentage of exchange (ca. 20%) is found, which is due to the higher internal energy of these molecular ions. In the molecular ion of nicotinic acid only one of the ortho hydrogens (α) is involved in the exchange of hydrogen. The percentage of exchange for loss of hydroxyl in the ion source is 66%. Molecular ions, which successively eliminate hydroxyl and carbon monoxide, show a 45% exchange of hydrogen as calculated from diffuse peaks in the first- and second field free regions.     

Moving reaction boundary and isoelectric focusing: IV. Systemic study on Hjertén's pH gradient mobilization

In this paper, Hjertén's mobilization of pH gradient in IEF was systemically and quantitatively analyzed with the R_r value of judgment expression comparing the fluxes of hydrogen and hydroxyl ions. The theoretical results show that (i) there is R_r = 0, viz., quasi‐equal fluxes of proton and hydroxyl ion, in a classic IEF with sulfuric acid and sodium hydroxide used as the anolyte and catholyte, respectively, this is the main reason why pH gradient is quite stable in IEF; (ii) but if the salt of sodium sulfate is added into the sodium hydroxide, there is R_r > 0, viz., the flux of proton being higher than that of hydroxyl ion, the R_r value implies a cathodic mobilization of pH gradient, and the higher the R_r value is the faster the cathodic mobilization becomes; (iii) if the salt is added into the sulfuric acid, there is R_r < 0, the R_r value indicates an anodic mobilization, and the smaller the R_r value is the faster the anodic mobilization turns. To test these theoretical results above, a novel procedure was developed for the run of classic IEF followed by Hjertén's mobilization of pH gradient. The strict experiments were in well coincidence with the theoretical results. The results have obvious significances for the mechanism and development of Hjertén's mobilization.     

Formation of Salt Bonds in Polyampholyte Chains

In this paper we study the influence of the formation of intrachain ion pairs (salt bonds) and the distribution of counterions on the behavior of single polyampholyte chains in a dilute solution. It has been shown that neutral polyampholyte chains can undergo jump‐like collapse transition from the swollen state to the globular state with the formation of ion pairs between oppositely charged ions of the chain. A polyampholyte chain with an excess charge shows the behavior of a conventional polyelectrolyte chain and counterions play an important role in the chain behavior. We distinguish three possible states of counterions: free counterions inside and outside the macromolecule, and a bound state of counterions forming ion pairs with the corresponding ions of the polymer chain. We found a non‐monotonous behavior of the chain upon increasing the excess charge on the chain: the chain swells from a compact state to elongated conformation and shrinks again to the compact state when the excess charge of the chain is increased.