Composite Polyaniline/MF-4SK Membranes: A Chemical Template Synthesis and the Sorption and Conduction Properties

The sorption and hydrophilic properties of composite membranes PAN/MF-4SK, obtained by a chemical template synthesis, are studied. The synthesis is performed in static and dynamic conditions for perfluorinated sulfo-cationite membranes MF-4SK in 0.01 M aniline solutions in 0.5 M H₂SO₄ and 0.01 M FeCl₃ in 0.5 M H₂SO₄. The aniline sorption and polymerization kinetics is studied by conductimetry, radioisotope, and optical methods. The polymerization rate is found to depend on the oxidant concentration and the sequence of the membrane saturation with aniline. An increase in the intensity of the color of a composite film, which depends on the balance between the quinoimine, amine, and radical-cation fragments in the perfluorinated matrix, does not lead to any substantial changes in the moisture content or the ac electroconductivity. Implanting polyaniline chains into the perfluorinated matrix presumably leads to a molecular reorganization of water at the expense of a change in its association at the point where redox fragments of polyaniline converge with side segments of the template matrix.     

The electric transport of proton-bound water in MF-4SK/PAni nanocomposite membranes

Electrochemical characteristics of MF-4SK/PAni nanocomposite membranes prepared at different times of chemical polymerization of aniline are studied. Electroosmotic permeability and conductivity of membranes in solutions of acids and sodium chloride are determined. It is revealed that the conductivity of nanocomposites in the proton form at 30-day synthesis is approximately 3 times as low as that of the base membrane and composite membrane formed at 5-h synthesis. The transport number of water slightly depends on the structural type of membrane and changes from 3.3 to 2 mol H₂O/mol H⁺ with an increase in the concentration of HCl solution from 0.1 to 3 M. The ratio of transport number to the water content rises about twofold in composites as compared to the initial membrane. It is shown that water is transferred with proton as hydronium structures [H₅O₂]⁺ and [H₉O₄]⁺ by the migration mechanism whose contribution to the total proton transfer in composite membranes increases.     

Peculiarities of electrotransport characteristics of composite membranes PANi/MF-4SK in sulfuric acid solutions

A methodological approach towards assessing the conducting, diffusion, and selective properties of perfluorinated membranes MF-4SK and also their composites with polyaniline (PANi/MF-4SK) is presented. Studying these properties in NaCl and H₂SO₄ solutions makes it possible to elucidate the role played by the nature of counter-ions and co-ions in the charge and mass transfer. It is shown that both individual and composite membranes in their protonic forms are highly selective and, on average, have a conductivity that is higher by a factor of 3.5 as compared with their sodium forms. In contrast, the diffusion permeability is 4-times lower, in line with variation in the charge of the ions that define the mass transfer (co-ions Cl^? or HSO ₄ ^? ). Within the framework of model assumptions on the structure of ion-exchange membranes, the transport and structure parameters of MF-4SK and PANi/MF-4SK are determined in H₂SO₄ solutions for a PANi-saturation of 25%. It is found that aromatic PANi chains localized in aqueous clusters of the template inhibit the diffusion transfer through the PANi/MF-4SK films, whereas the conductivity and transport numbers of PANi/MF-4SK in both NaCl and H₂SO₄ remain virtually unchanged.     

Mechanism of ion transport in hybrid materials based on MF-4SC perfluorinated sulfonation-exchange membranes and acid zirconium phosphate nanoparticles

The relationship between the transport properties of various salt forms (H⁺, Li⁺, Na⁺, Cs⁺) of MF-4SC hybrid membranes containing nanoparticles of crystalline acid zirconium phosphate Zr(HPO₄)₂ at various relative humidities are investigated with the use of impedance studies and NMR spectroscopy. Modification of the membranes leads to a marked increase in ion mobility, and the maximum effect is observed under reduced humidity conditions. The conductivity of a modified membrane at a relative humidity of 10% is 1.6 × 10^?4 Ω^?1 cm^?1, that is, almost 1.5 orders of magnitude greater than the conductivity of an initial membrane under the same conditions.     

Hydration of the H<Superscript>+</Superscript>, Li<Superscript>+</Superscript>, Na<Superscript>+</Superscript>, and Cs<Superscript>+</Superscript> ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes modified with inorganic dopants

The hydration, state, and mobility of protons and Li⁺, Na⁺, and Cs⁺ ions in MF-4SK perfluorinated sulfonic acid cation-exchange membranes doped with silicon dioxide and phosphotungstic acid have been investigated by NMR and impedance spectroscopy. The dopants increase the moisture content of the membrane and change the system of pores and channels in which ion transport takes place. At low humidities, the dopant particles are involved in ion transport. The greatest effect is observed for the membranes doped with both SiO₂ and phosphotungstic acid. The water molecules sorbed by dopant particles as a material participate in the hydration of alkali metal cations in the membrane.     

Thermodynamic representation of the NaCl + Na2SO4 + H2O system with electrolyte NRTL model

A comprehensive thermodynamic model based on the electrolyte NRTL (eNRTL) activity coefficient equation is developed for the NaCl + H₂O binary, the Na₂SO₄ + H₂O binary and the NaCl + Na₂SO₄ + H₂O ternary. The NRTL binary parameters for pairs H₂O-(Na⁺, Cl⁻) and H₂O-(Na⁺, SO₄²⁻), and the aqueous phase infinite dilution heat capacity parameters for ions Cl⁻ and SO₄²⁻ are regressed from fitting experimental data on mean ionic activity coefficient, heat capacity, liquid enthalpy and dissolution enthalpy for the NaCl + H₂O binary and the Na₂SO₄ + H₂O binary with electrolyte concentrations up to saturation and temperature up to 473.15 K. The Gibbs energy of formation, enthalpy of formation and heat capacity parameters for solids NaCl_(s), NaCl·2H₂O_(s), Na₂SO_4(s) and Na₂SO₄·10H₂O_(s) are obtained by fitting experimental data on solubilities of NaCl and Na₂SO₄ in water. The NRTL binary parameters for the (Na⁺, Cl⁻)-(Na⁺, SO₄²⁻) pair are regressed from fitting experimental data on dissolution enthalpies and solubilities for the NaCl + Na₂SO₄ + H₂O ternary.     

Synthesis of hydrochloric acid solution for total mercury determination in natural waters

Total mercury (Hg_T) determination requires the addition of concentrated hydrochloric acid solution (≥10 mol L⁻¹ HCl) in relatively high amounts to preserve the samples and to prepare reagent solutions. A method for the preparation of concentrated HCl with Hg_T concentration of lower than 5 ng L⁻¹ is described in this article. It is based on the well-known chemical reaction: 2 NH₄Cl + H₂SO₄ → (NH₄)₂SO₄ + 2 HCl. This method is validated thanks to the US Environmental Protection Agency method 1631 and standard reference materials BCR-579 (mercury in coastal seawater).     

Template synthesis and electrotransport behavior of polymer composites based on perfluorinated membranes incorporating polyaniline

A method of chemical template synthesis is described for producing composites based on a perfluorinated matrix with polyaniline chains implanted. It has been shown that the choice of experimental and conditioning techniques is relevant for the composites’ investigation. The conductivity, diffusion permeability, selectivity, and electroosmotic permeability of the composites have been investigated in comparison with the same properties of the initial MF-4SC membrane. A model describing the transport behavior of the composites in the doped state as a fibrous-cluster system is proposed. A set of transport and structural parameters of the composites in a H₂SO₄ solution has been calculated and an analysis of the results observed has been carried out. The set of electrotransport properties is explained by the morphological features of the composites, taking into account the redox heterogeneity of polyaniline. The contribution of electron conductivity to the mixed conductivity of composites with a certain saturation degree by polyaniline has been estimated.     

Ion-Selective Electrodes Prepared with Polyaniline Membranes

Polyaniline is a conductive polymer that has electrochemical activity. For this reason, it has many different uses in electrochemical area. In this study, polyaniline was prepared by electrochemical oxidation of aniline in concentrated H₂SO₄ and HCl solutions. Then, membranes were obtained from a mixture of these polymers and paraffin at a weight ratio of 50%. Ion-selective electrodes were prepared with these membranes and AgCl/Ag electrodes. Properties of prepared membranes were investigated with potentiometric measurements made in HCl, KCl, H₂SO₄, and HClO₄ solutions of different concentrations. The E–logc plots obtained with these ion-selective electrodes were found to be linear in a distinct concentration range. Their slopes depend on the membrane type and the doping ion in the test solution. The difference between these membranes was explained according to the morphological structures of polyaniline membranes.     

Nonisothermal membrane phenomena across perfluorosulfonic acid-type membranes,Flemion S: part I. Thermoosmosis and transported entropy of water

Solvent transports across the perfluorosulfonic acid-type membrane Flemion S were measured for aqueous electrolyte solutions under a temperature difference and under an osmotic pressure difference. H⁺, Li⁺, Na⁺, K⁺, NH ₄ ⁺ , CH₃NH ₃ ⁺ , (CH₃)₂NH ₂ ⁺ , (CH₃)₃NH⁺, (CH₃)₄N⁺, (C₂H₅)₄N⁺, (n-C₃H₇)₄N⁺ and (n-C₄H₉)₄N⁺ were used as counterions. Water flux across the membrane in HCl solution is higher than that in the other electrolyte solutions because hydrogen ions can exchange with the hydrogen of the neighbor water molecules and contribute to the water transport across the membrane as a proton jump in conductivity. The direction of thermoosmosis across the membrane in HCl, NaCl, (CH₃)₄NCl and (C₂H₅)₄NCl solutions was from the cold side to the hot side and that in LiCl, KCl, NH₄Cl, CH₃NH₃Cl, (CH₃)₂NH₂Cl and (n-C₄H₉)₄NBr solutions was from the hot side to the cold side, although thermoosmosis across anion-exchange membranes always occurs toward the hot side.     

Komplexone XL. Die Protonierungskonstanten einiger Komplexone in verschiedenen wässerigen Salzmedien (NaClO4, (CH3)4NCl,KNO3)

The protonation constants of the anions of thirteen polyaminocarboxylic acids have been determined in solutions containing different inert salts: KNO₃, NaClO₄ and N(CH₃)₄Cl. The formation constants of the following species: H₅EDTA+, H₆EDTA²⁺, H₅CDTA⁺ and H₄NTA⁺ have been obtained from solubility measurements with ethylenediamine tetraacetic acid (H₄EDTA), 1,2-diaminocyclohexane tetraacetic acid (H₄CDTA) and nitrilotriacetic acid (H₃NTA) in acid solutions between pH = 3 and 0 at ionic strength 1M (NaClO₄ + HClO₄).     

Formation of extractable species from metal sulfate and amine chlorides

The extraction of Fe, Zn and In by La₂HCl from H₂SO₄ solutions has been studied. The formation of the aqueous complexes H₂Fe(SO₄)₂HSO₄, HZn(SO₄)HSO₄ and HInSO₄(HSO₄)₂ is discussed. The formation of mixed ligand species H₂Fe(SO₄)₂Cl, HZnSO₄Cl and HInSO₄Cl₂ from the interaction of Cl⁺ in aqueous solution or in LA₂HCl before extraction is explained. The reactions in the system to produce the extractable species are discussed. The possible separations are given.     

Interaction parameters and (solid + liquid) equilibria calculation for KCl–H2O–HCl–C2H5OH,K2SO4–H2O–H2SO4 and K2SO4–H2O–C2H5OH mixed solvent-electrolyte systems

This work deals with the prediction and experimental measurements of the (solid + liquid) equilibrium (SLE) in acid medium for industrial purposes. Specific systems including KCl–ethanol–water–HCl and K₂SO₄–water–H₂SO₄ were analyzed. At first, a critical discussion of SLE calculations was given, based on the well-known UNIQUAC extended and LIQUAC models. Two new proposals were derived, considering the explicit necessity of a new reference state for SLE calculations for the studied (solvents + acid) mixtures. The solubility of KCl in water–ethanol–HCl mixed solvents was measured in the temperature range of 300.15 to 315.15 K using an analytical gravimetric method. These results combined with some other experimental data reported in the open literature let us to propose a set of parameters for the new models. They included the interaction parameters between ethanol and the H⁺ ion. The prediction capability of the new models, for calculations in acid medium, was illustrated. Experimentally, it was observed that the (K₂SO₄ + water + H₂SO₄) system presented the unusual behavior of increasing K₂SO₄ solubility with an increase in the sulfuric acid concentration. This was accurately predicted by the newly proposed models.     

Ionizing properties of complexes with strong symmetrical hydrogen bonds in acid solutions in aprotic solvents

The acidity functions H₀ of solutions of trifluoroacetic acid (TFA) in DMF and methanesulfonic acid (MSA) in 2-pyrrolidone over an acid (HA) concentration range of 0–100% and of H₂SO₄ solutions in 2-pyrrolidone (66.7–100 mol % HA) at 25°C were determined using the indicator method. Data were obtained on the relative ionizing powers of the quasi-ion pairs S· · · H· · ·A (S is a solvent molecule) formed by DMF with acids (HCl, MSA, and TFA) and by MSA with DMF and 2-pyrrolidone. The effects of the acid anion (with MSA and H₂SO₄ solutions in 2-pyrrolidone acting as examples) and the counterion SH⁺ (with MSA solutions in DMF and 2-pyrrolidone acting as examples) on the ionizing power of (Ä · · ·H· · ·A)^– ions with strong symmetrical H-bonds were studied. It was found that, under comparable conditions, the replacement of a 2-pyrrolidone molecule by a DMF molecule in the SH⁺ cation insignificantly decreased the acidity of solution, whereas the (Ä· · ·H· · ·A)^– ions in H₂SO₄ solutions exhibited a much higher ionizing power than that of structurally similar anions in MSA solutions.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 44–49.Original Russian Text Copyright © 2005 by Kislina, Sysoeva, Librovich.     

Diffusion mobility of alkali metals in perfluorinated sulfocationic and carboxylic membranes as probed by <Superscript>1</Superscript>H, <Superscript>7</Superscript>Li, <Superscript>23</Superscript>Na,and <Superscript>133</Superscript>Cs NMR spectroscopy

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.     

二（2-乙基己基）二硫代磷酸溶剂萃取铊的热动力学

在Tl₂SO₄＋Na₂SO₄＋二（2-乙基己基）二硫代磷酸＋n-C₈H₁₈＋水体系中， 测定了0.1－2.0 mol•kg^－1离子强度范围内Tl^＋ 的平衡摩尔浓度。水相中电解质Na₂SO₄ 控制溶液离子强度， 有机相中萃取剂取278.15 K至303.15 K范围内的恒定摩尔浓度。通过外推法和多项式近似得到了不同温度下的标准萃取常数K⁰，计算了萃取过程的热动力学量。     

Quadrivalent uranium as a reducing agent in potentiometric titrations: Estimation of ferric and ceric salts

Quadrivalent uranium is found to be a suitable reducing agent in potentiometric titrations, for the estimation of ferric and ceric salts. The stability of the reagent increases by raising the acidity and becomes considerable in the presence of HCl. The stability is not seriously affected by H₃PO₄ although Zn⁺² and Co⁺² ions enhance its oxidation. Light affects the stability of the reagent only in the presence of air.The redox potential varies with l'acidity, being 0.3 volt at 0.1N HCl or H₂SO₄ rising to 0.53 or 0.61 in 1-7 N HCl or 1–9.N H₂SO₄ and increasing thereafter to ~ 1 volt.     

Studies on the extraction behaviour of zirconium from mixed aqueous media with TBP

A systematic study is presented on the extraction of Zr(IV) by tri-n-butylphosphate from H₂SO₄, HNO₃, HCl and HBr solutions as well from binary mixtures of H₂SO₄ and halogen acids. It has been found that Zr(IV) extraction is appreciably increased by addition of halogen acid to sulphuric acid solutions. On the other hand, the presence of water-miscible alcohols and acetone was found to enhance Zr(IV) extraction from HCl and HNO₃ solutions. An investigation of extracted Zr complexes from pure acids and mixed aqueous media enabled an explanation of the observed enhancements. In the light of the obtained results, an extraction mechanism is suggested.     

Water self-diffusion and ionic conductivity in perfluorinated sulfocationic membranes MF-4SK

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.