Proton NMR studies on concentrated aqueous sulfuric acid solutions and Nafion-H

Sulfuric acid containing limited amounts of water, H₂SO_4.nH₂O with 0.23≤n≤4, has been studied by ¹H broad-line NMR at 4 K and MAS NMR at room temperature. The broad-line NMR spectra indicate the formation of H₃O⁺ and HSO₄ ^- ions. H₂SO_4.2H₂O is correctly written as H₃O⁺HSO₄ ^-.H₂O. The results are compared with the Nafion- H/water system. This revised version was published online in July 2006 with corrections to the Cover Date.     

THERMODYNAMICS OF ALKALI AND ALKALINE EARTH METAL ION-EXCHANGE ON ZIRCONIUM SULPHOPHOSPHONATES

The thermodynamics of alkali and alkaline earth metal ion exchange on a layered zirconium sulphophosphonate having the general composition Zr(O₃PC₆H₄SO₃H) _×(HPO₄) _2?× yH₂O have been investigated. Enthalpy and entropy changes accompanying the M²⁺ - H⁺ exchange (M = Na⁺, Cs⁺, Mg²⁺ and Ba²⁺)were determined by the temperature variation method. For the monovalent ions, Na⁺ and Cs⁺, the enthalpy terms favor exchange whereas the entropy terms are unfavorable. In contrast, for the divalent ions, Mg²⁺ and Ba²⁺, the exchange is due to highly favorable entropy terms.     

Hydrogen-ion transport numbers in cation exchange membrane determined by emf method

The electromotive force of the membrane cells /Hg/Hg₂SO₄/H₂SO₄, a′/ lon exchange Nafion membrane /H₂SO₄ a″/Hg₂SO₄/Hg/ with different solution concentrations from 0.01 to 2 mol kg^?1 H₂O were measured. On that basis the apparent transport number of H⁺-ions and its dependence on external electrolyte concentration were determined. The dependence was then used for the calculation of both the transport number of H⁺-ions and the water transference numbers. It was found that the apparent transport number of H⁺-ions decreases with increasing external concentration while the transport number of H⁺-ions and the transference number of water remain constant up to concentrations of 1.2 moles kg^?1 h₂O.     

The effect of different lithium salts on conductivity of comb-like polymer electrolyte with chelating functional group

The behaviors of lithium ions in a comb-like polymer electrolyte with chelating functional group complexed with LiCF₃SO₃, LiBr and LiClO₄ were characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, AC impedance, and ¹³C solid-state NMR measurement. The comb-like copolymer was synthesized from poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). FT-IR spectra reveal the interactions of Li⁺ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. FT-IR spectra also indicate an increasing anion-cation association consistent with increasing LiCF₃SO₃ concentrations. Moreover, the ¹³C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. T_g and T_d of copolymers doped with salts clearly increase, as shown by DSC and TGA measurements. These results indicate the interactions of Li⁺ with both PEGMEM and GMA-IDA segments form transient cross-links inside the copolymers. The Vogel-Tamman-Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chain in this study. The maximum conductivity of copolymers relates to the composition of the copolymers and the concentration of doping lithium ions. In summary, the GMA-IDA unit in the copolymer promotes the dissociation of the lithium salt, the mechanical strength and the conductivity of the polyelectrolyte.     

Intermolecular Interactions Between Methanol/Water Molecules and Nafion™ Membrane: An Infrared Spectroscopy Study

The intermolecular interactions between methanol/water and Nafion™ membranes have been investigated using IR spectroscopy. The evolution of IR spectra of the Nafion™ membranes, immersed in various concentrations of methanol solution depends strongly on the methanol concentration. The O–H bending vibration modes at 1,636, 1,660 and 1,672 cm^–1 associated with the hydrogen bonding of (H₃O⁺…SO₃^–) as well as (CH₃OH₂⁺…SO₃^–), and at 1,702, 1,717 and 1,711–1,736 cm^–1 associated with the hydrogen bonding of (CF₂…H–O–CH₃), (CF₂…H–OH), (CF₂…⁺H₃O) and (CF₂…H–OSO₂^–) were observed. The vibration mode of (CF₂…H–O) was found to be appearing obviously at 3,821–3,900 cm^–1 when the Nafion™ membrane was immersed in the methanol solution with concentration higher than 6 M. On the other hand, the wavenumber of the O–H stretching peak increases with an increase in the methanol concentration. Results of IR spectra revealed that the methanol molecules show better capability to penetrate into the hydrophobic domain of the Nafion™ membrane than water. The intermolecular interaction between the hydrophobic domains of Nafion™ and methanol molecules becomes more observable at a higher methanol concentration.     

Preparation and characterization of cellulose nitrate-acetate mixed ester fibers

Cellulose nitrate-acetate mixed esters (CNA) were synthesized by nitration of cellulose diacetate, using HNO₃/H₂SO₄ as nitration agent. The CNA structures were confirmed and analyzed by IR and ¹H NMR. A decrease in molecular weight and an increase in nitrate group content were observed with increasing H₂SO₄ ratio and reaction time. The highest degree of nitrate substitution, 9.2%, for CNA was achieved with the reaction time of 6h in concentrated HNO₃. Increasing HNO₃ ratio in nitration media resulted in more thermally stable CNA. CNA fibers were prepared by altering the polymer concentration from 15 to 30% in an 85:15 (w/w) acetone:water solvent. The electrospun CNA fibers were characterized by SEM to investigate the influence of different NO₂% on fiber formation, diameters and architectures.     

Effect of Sodium in Ferrierite on Selective Catalytic Reduction of NO by Acetylene

Influence of sodium in ferrierite (HFER) zeolite on selective catalytic reduction of NO by acetylene (C₂H₂-SCR) was investigated. NO _x -TPD and FT-IR indicated that small amount of sodium exchanged into the proton-form zeolite with an exchange level of about 11.8% is beneficial for the title reaction by accelerating active nitrate species formation on catalyst surface from NO₂ and by suppressing the reductant combustion. Nevertheless, no further improved catalytic performance in C₂H₂-SCR could be observed by a larger amount of sodium exchanged into HFER due to some inactive nitrate species formed on the zeolite. Instead, activity of the zeolite for C₂H₂-SCR was drastically reduced, since the capacity of the zeolite for catalyzing NO oxidation and accelerating active NO⁺ species formation was remarkably depressed.     

Study and Characterisation of Activated Carbon Treated with H2SO4 Solutions

Several samples of activated carbon (AC), previously outgassed and treated with H₂SO₄ solutions of varying concentration, were prepared. The contact between the phases and the outgassing of AC were carried out under controlled conditions. The chemical composition and the thermal behaviour as well as the texture of the samples were studied. Techniques used were chemical analysis, FT-IR spectroscopy, thermogravimetric analysis, gas adsorption, mercury porosimetry and density measurements. After the contact of H₂SO₄ solutions with AC, the mass of samples increased greatly. It was associated with the uptake by AC of components of the solution, especially H₂SO₄. The presence in the samples of HSO₄⁻ and SO₄²⁻ ions was shown by the FT-IR spectra. The mass increase was strongly dependent on the method of preparation of the samples. In the heat treatment of the samples between 30 and 800°C a great mass loss occurred below 400°C. However, it was small at higher temperatures and when the samples were outgassed at 120°C for 12 h, at 133×10⁻³ Pa. The introduction of H₂SO₄ solution in AC pores produced a drastic reduction in the surface area and in the microporosity of the material. It also affected the pore-size distribution in the mesopore and macropore ranges. © 1997 SCI.     

Potentiometric measurements and impedance characteristics of Li0.30La0.57TiO3 membrane in lithium anhydrous solutions

The potentiometric response of the Li⁺ ion-selective electrode based on the fast ion conductor Li_3xLa_2/3−xTiO₃ (x = 0.10) membrane (named LLTO) as well as the impedance of the LLTO membrane/Li⁺ solution in either anhydrous or hydrated PC solvent have been carried out. A four-electrode configuration has been used for the investigation of the interfacial phenomenon. It has been shown that the LLTO membrane can be used to detect the Li⁺ activity in anhydrous solutions through a Li⁺ ion exchange mechanism. The potentiometric response shows a Nernstian behavior with a Li⁺ sensitivity of −72 mV/decade at 25 °C. This high sensitivity can be correlated to a localised hydroxylation of the oxide surface with the residual water present in the solution in combination to the Li⁺ exchange reaction. An apparent standard current density of 12 μA/cm² and a charge-transfer coefficient of 0.29 have been determined. However, as water content in the electrolyte increases, the activity domain of the detection decreases to lead to the disappearance of the Li⁺ ion exchange mechanism in Li⁺ aqueous solution. This annihilation of the exchange process may be due to the predominant catalytic reaction of [Ti-O]⁻ with H₂O and/or to the formation of a water layer on the oxide surface.     

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.     

Synthesis, Crystal Structure, Spectroscopic and Thermal Investigations of a Novel 2D Sodium(I) Coordination Polymer Based on 2-Aminoterephthalic Ligand

The reaction of sodium hydroxide with 2-aminoterephthalic acid leads to the formation of a complex of the general formula: [Na₂(atpt)(H₂O)₅]·H₂O, where atpt?=?[NH₂C₆H₃(COO)₂]^2?. Sodium 2-aminoterephthalate was synthesized and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, thermal analysis and coupled TG–FT-IR technique. Crystallographic study of the sodium complex reveals that the compound crystallizes in the triclinic system, the space group P-1 with a?=?7.983(3) ?, b?=?8.405(3) ?, c?=?11.311(5) ?, α?=?70.74(3)°, β?=?76.57(3)°, γ?=?83.12(3)° and V?=?696.1(5) ?³. On heating in air atmosphere the compound in question loses all water molecules in two steps in the temperature range 30–205?°C. The anhydrous form of the complex is stable up to 370?°C and then decomposes to sodium carbonate.     

Bio‐electrochemical denitrification by a novel proton‐exchange membrane electrodialysis system—a batch mode study

BACKGROUND: Contamination of nitrate in ground and surface water has become an ever‐increasing and serious environmental problem. Biological methods hold the promise of converting nitrate into harmless nitrogen. A novel denitrification system which combines proton‐exchange membrane electrodialysis with simultaneous bio‐electrochemical autotrophic denitrification has been developed. The proton‐exchange membrane was used to transfer current and to exclude oxygen or other oxidative chemicals generated in the anode reaction. The H₂ generated by the cathode was utilized by autotrophic denitrifying microorganisms in the cathode cell to reduce nitrate. In this study, the transport of H⁺, a denitrification kinetics model and factors influencing the denitrification rate were explored in batch mode. RESULTS: The addition of 0.03 mol L^?1 H₂SO₄ into the anode cell enhanced proton transport and maintained the pH of the cathode cell in an appropriate range for biological denitrification. The denitrification rate was affected by applied current and biomass. Under adequate current conditions, the kinetics of the denitrification process followed a zero‐order kinetics model; the average denitrification rate for unit biomass was calculated to be 9.36 mg NO₃^?‐N VSS g^?1 h^?1. CONCLUSIONS: Results indicate that the system is suitable for denitrification. Owing to its simple structure and operation, it has the potential for use as a system to reduce nitrate in water. Copyright © 2010 Society of Chemical Industry     

Studies on the mechanism of the hydrogen electrode reaction by means of deuterium tracer—II. The reaction mechanism

The exchange reaction between deuterium gas and light water was conducted with Ni, Rh, and Pt catalyst. Through analysis of isotopic composition of the gaseous hydrogen during the exchange reaction, the exchange rates of the individual steps, H₂ ? 2H(a) and H(a) + B ? H⁺B + e, of the hydrogen electrode reaction were determined at various hydrogen pressures and solution pH's, where H(a) is a hydrogen adatom and B = H₂O or OH^?. The rates of the steps were widely different among the metals studied but, throughout these metals, the hydrogen pressure dependence of the rate of the first step was with the power of 1·0–0·9, and that of the second step, 0·2–0·5. Both the rates were independent of solution pH. Generally, the former step is virtually rate-determining under low hydrogen pressures, whereas the latter takes over the role with increasing hydrogen pressure. Under ordinary pressures, the first step is virtually rate-determining on Pt but neither step is singly rate-determining on Rh and Ni.     

Scavenging Ratios in an Urban Area in the Spanish Basque Country

For a period of six years (1995–2000) the scavenging ratio, which is the ratio of a pollutant's concentration in water to its concentration in air, collected at an urban site in the Spanish Basque Country was studied. The aerosol is characterized by SO₄ ^2? and NO₃? with 1.79 and 1.61 μg m^?3, respectively. Greater fractions of SO₄ ^2?, NO₃?, and NH₄+ ions were present in the fine particle range, while greater fractions of other ions appeared in the coarse range. The most important species found in the precipitation is SO₄ ^2? with 3.0 mg l^?1. NO₃?, Ca²⁺, and Cl^? are the second most important ions. The volume-weighted mean concentration of H⁺ is 4.6 μg l^?1 (pH = 5.3). The concentration of all analyzed ions (except H⁺) decreases throughout the rain event, showing the washout phenomenon of the rainwater. The scavenging ratio for the anthropogenic ions NO₃?, SO₄ ^2?, NH₄+, and K⁺ is lower than the scavenging ratio for the marine-terrigenous ions, Cl^?, Na⁺, and Ca²⁺.     

Surface chemical modification of polypropylene fiber waste by H2SO4: Mechanistic investigation and application as cation‐exchange adsorbent

In this work, polypropylene (PP) fiber waste was modified by the reaction with concentrated H₂SO₄. IR, TG, Raman, CHN, acid titration, SEM, and XRD suggested that sulfuric acid at about 105°C reacts with PP to produce mainly surface sulfonic groups. The kinetic experiments showed that these SO₃H groups decompose to form SO₂ gas leading to an aromatization of the polymer to form amorphous and graphitic carbon. Adsorption isotherms of the cationic model molecule methylene blue showed that the modified PP fibers have a great potential as ion‐exchange adsorbent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solvent extraction of zirconium(IV) from acidic chloride solutions using the thiosubstituted organophosphorus acids Cyanex 301 and 302

Solvent extraction of zirconium(IV) from acidic chloride solutions has been carried out with the thiosubstituted organophosphorus acids Cyanex 301 and Cyanex 302. The extraction follows an ion exchange mechanism: MO²⁺_(aq) + 2 HA_(org) ? MOA_2(org) + 2 H⁺_(aq), where, M = Zr(IV); HA = Cyanex 301 or Cyanex 302. The plots of log D (distribution ratio) vs log [HA], are linear with slopes of 2, indicating the association of two moles of extractant with the extracted metal species. The plots of log D vs log [H⁺] gave straight lines with a negative slope of 1.7 for Cyanex 301 and 1.8 for Cyanex 302, indicating the exchange of two moles of hydrogen ions for every mole of Zr(IV). Addition of sodium salts enhanced the extraction of metal. The stripping behavior of metal from the loaded organic (LO) with HCl and H₂SO₄ was studied. Increase of temperature during the extraction and the stripping stage increases the metal transfer, showing the process is exothermic. Mixed extractants, the extraction behavior of associated elements such as Hf(IV), Ti(IV), Al(III), Fe(III) and the IR spectra of the metal complexes were studied. Copyright © 2004 Society of Chemical Industry     

Thermodynamics of Nafion™-vapor interactions. I. Water vapor

Interaction between water vapor and Nafion™ perfluorosulfonate ionomer has been investigated via combined flow microcalorimetry and isothermal sorption over a wide range of water relative pressure. The molar enthalpy of sorption was determined for the untreated polymer, the residual polymer after extraction by aqueous propanol, and the extracted fraction. The extract appears to be low molecular weight Nafion™ but with an equivalent weight more than double that of the unextracted polymer. The equivalent weight of the residual polymer is slightly lower than that of the original Nafion™, apparently due to partial alkylation. Molar enthalpy for formation of the sulfonic acid monohydrate is about the same for the residual and unextracted polymers, but much greater for the extracted fraction. For untreated Nafion™, the magnitude and concentration dependence of the molar enthalpy indicates that sorption of water exhibits a clear progression from hydronium ion formation (≤1 H₂O/SO₃H) through growth of isolated hydrated clusters (≤6 H₂O/SO₃H) to a continuous internal water phase. A more complicated process occurs for the extract and residual polymer fractions in that an endotherm associated with elastic compression of the polymer matrix surrounding isolated water clusters is superimposed on the hydration exotherm over the concentration range of cluster growth. There is only a minor indication of this endotherm for unextracted Nafion™ because of more facile relaxation of the polymer structure due to plasticization by the low molecular weight fraction.     

Studies on the Separation of Cadmium from Solutions by Foam Separation. I. Foam Separation of Cadmium Cations

Abstract

The efficiency of Cd²⁺ foam separation with sodium lauryl sulfate and sodium laurate from sodium sulfate and sodium nitrate solution was tested. Foam fractionation of Cd²⁺ with lauryl sulfate in the form of a hydrated ion pair 2C₁₂H₂₅SO₄, Cd²⁺ is ineffective because of a low recovery and high hydration of the foam. But ion flotation of Cd²⁺ as a low-solubility salt (C₁₂H₂₅COO)₂Cd is highly effective. The presence of electrolyte in the solution has a negative influence on Cd²⁺ foam fractionation with lauryl sulfate because of an increase of inert salt concentration which causes competition for the collector between colligend Cd²⁺ and the added Na⁺ ions, and because of simultaneous increase in the thickness of water sheaths around the gas bubbles. In the case of ion flotation with sodium laurate, the presence of electrolyte improves Cd²⁺ recovery and decreases the thickness of the water sheaths around the gas bubbles. The interpretation of the results is based on the exchange of the collector counterions as well as on the properties of the reaction products.     

Adsorption of CO2+ by stylene‐g‐polyethylene membrane bearing sulfonic acid groups modified by radiation‐induced graft copolymerization

Cation‐exchange hollow fiber membrane was prepared by radiation‐induced grafting polymerization of styrene onto polyethylene hollow fiber membrane and its sulfonation. Adsorption characteristics for the cation‐exchange membranes are examined when the solution of Co²⁺ permeates across the cation‐exchange fiber membrane. The maximum grafting peak was obtained from 70% styrene concentration at 50°C. The degree of grafting (%) was enhanced with additives such as H₂SO₄ and divinylbenzene. The content of  SO₃H groups ranged from 2 to 5 mmol g⁻¹ with chlorosulfonic acid (ClSO₃H) in dichloroethane, from 0.5 to 6 mmol g⁻¹ with ClSO₃H in H₂SO₄, respectively. The adsorption of Co²⁺ by the cation‐exchange membranes increased with increasing  SO₃H content. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2227–2235, 1999     

Dilute solution properties of cationic poly(dimethyl sulfate quaternized dimethylaminoethyl methacrylate)

The dilute solution properties of a cationic polyelectrolyte, poly(dimethyl sulfate quaternized dimethylaminoethyl methacrylate) [poly(DMAEM · C₂H₆SO₄)], are studied by measurements of intrinsic viscosity, degree of binding, and flocculation application. The intrinsic viscosity of this polyelectrolyte is related to the type and concentration of added salt. The intrinsic viscosity behavior for cationic polyelectrolyte resulting from the electrostatic repulsive force of the polymer chain is contrasted with polyampholyte. The polyelectrolyte in the presence of KCl has a lower degree of binding, indicating that the proton ion (H⁺) is relatively difficult to bind to the CH₃SO₄^? at the polymer end. The polymerization of DMAEM · C₂H₆SO₄ in 0.5M KCl aqueous solution proceeded more easily than that of DMAEM · C₂H₆SO₄ in pure water. The polymerization rate of DMAEM · C₂H₆SO₄ is found to pass through an extreme value as a function of pH. Optimum flocculation, corresponding to the complete removal of turbidity in the supernatant, is achieved. Beyond the optimum flocculation, high polymer dosages redisperse the bentonite suspensions.