A neutron inelastic scattering investigation of the diffusion kinetics of H2O molecules and hydration complexes in concentrated ionic solutions

Intermolecular frequencies of H₂O's and the diffusion kinetics have been investigated by neutron inelastic scattering for concentrated ionic solutions containing small and/or multiply charged cations (e.g., Cr⁺³, Mg⁺², Ca⁺², and Li⁺¹). As higher concentrations are approached such that the majority of H₂O's are in hydration layers, their exchange time can exceed the neutron interaction time. Then the diffusion kinetics depart functionally from activated reorientations of individual H₂O's characteristic of lower concentrations and evolve to continuous diffusion processes of hydration complexes characterized by small self-diffusion coefficients. The general features of the observed evolution in the functionality of the diffusion kinetics are found to be functionally consistent with an approximate model which includes contributions from the delayed diffusional exchange of individual H₂O's as well as the continuous diffusion of hydrated ions. At a given concentration, the temperature interval over which this evolution in functionality occurs increases both with increasing strength of the primary cation-H₂O coordination and with anion basicity. Further, as the temperature decreases, frequencies of defined cation-water hydration complexes gradually sharpen in a continuous manner, showing no abrupt variations at glass transitions. Anions of increasing basicity decrease the self-diffusion coefficients of the ion-water complexes and perturbed frequencies characteristic of cation-water hydration complexes. Such anion effects, at high concentrations, correspond to an increasing degree of time-average indirect or direct ion pairing with increasing anion basicity. This results, in turn, both in a distortion or partial disruption of the cation hydration sheaths and in a degree of coupling and/or bridging between anions and hydrated cations so as to increase the effective masses and friction coefficients associated with their diffusional motions.     

Effects of the composition of acid solutions and the presence of organic acids on oxygen electroreduction to hydrogen peroxide in a carbon black gas-diffusion electrode

This paper reports on the effects of the K₂SO₄, H₂SO₄, NaCl, HCl, and tetrabutylammonium bromide concentrations (0.01–0.0002 M) and the presence of formic, acetic, and butyric acids in the electrolyte on the kinetic characteristics of oxygen reduction to H₂O₂ in a carbon black gas-diffusion electrode (GDE) and on the H₂O₂ accumulation kinetics in electrolyte at current densities of 30–100 mA/cm². The introduction of K₂SO₄ and tetrabutylammonium bromide in the electrolyte led to an increase in the transfer coefficient α and a decrease in the coefficients in the Tafel equation. The concentration and the current efficiency of H₂O₂ decreased with the salt to acid concentration ratio. The organic acids reduced the current efficiency of H₂O₂ and increased the electrode polarization. Peracids with a current efficiency of up to 0.27% and concentration of up to 7.5 mM were obtained. Solutions of H₂O₂ with concentrations of 0.6–3.3 M and current efficiencies of 17–75% were obtained at current densities of 30–100 mA/cm² in electrolytes with salt and inorganic acid concentrations of 0.9–40 g/l and in the presence of organic acids.     

Extraction of sulfuric and hydrochloric acids with macromolecular aliphatic alcohols of varied structure

Extraction of HCl and H₂SO₄ with isomers of monoatomic aliphatic alcohols C₇?C₁₀ was studied. The distribution coefficients of the acids were determined in relation to their concentration in the system, length of the hydrocarbon chain of an aliphatic alcohol, and nature of an acid being extracted. It was found that the alcohol nature affects the rate of phase stratification in aqueous re-extraction of the acids.     

The use of the cohen–turnbull model for calculation of the self-diffusion coefficients of liquid dichloroalkanes

The paper presents the self-diffusion coefficients calculated for liquid dichloroalkanes C₆H₁₂Cl₂, C₈H₁₆Cl₂, C₁₀H₂₂Cl₂ and C₁₂H₂₄Cl₂, with the use of the Cohen and Turnbull model. Determination of self-diffusion coefficients permits a separate analysis of intra- and intermolecular motions and provides information on geometrical and dynamical properties of molecules. The self-diffusion coefficients of selected dichloroalkanes have been determined by X-ray diffraction and compared with the corresponding NMR results. The suitability of the Cohen–Turnbull model of the translating motion for prediction of self-diffusion coefficients for molecules whose shape significantly differs from the spherical symmetry is analysed. Angular distributions of X-ray scattered intensity were measured, and differential radial distribution functions of electron density (DRDFs) were calculated. The mean coordination numbers were obtained from the area delimited by the minima of the DRDFs, and their dependence on the length of the methylene chain is also presented subsequently. On the basis of the DRDFs the average free volume of the molecules and total free volume of the liquids were calculated. The activation volume of the diffusion was found to make about 0.6 of the van der Waals volume of the molecule. As expected the diffusion coefficients decrease with increasing molecular weight. The equation relating the self-diffusion coefficient with the volume of the coordination spheres in the liquid has been derived.     

Sims analysis of the distribution of hydrogen absorbed by gold electrodes during the evolution of hydrogen

Gold electrodes were charged with hydrogen by strong cathodic treatment in 0.5 M H₂SO₄. The concentration of hydrogen was then studied by SIMS both along the surface and in depth by etching in the ion beam. With electrodes consisting of a small number of crystals, the absence of abnormal hydrogen concentration at the grain boundaries seems to rule out diffusion along this route. The profiles observed seem to be consistent with a simple model of uniform bulk diffusion.     

Ion conduction mechanisms and thermal properties of hydrated and anhydrous phosphoric acids studied with 1H, 2H, and 31P NMR

To understand the behaviors of phosphoric acids in fuel cells, the ion conduction mechanisms of phosphoric acids in condensed states without free water and in a monomer state with water were studied by measuring the ionic conductivity (sigma) using AC impedance, thermal properties, and self-diffusion coefficients (D) and spin-lattice relaxation times (T1) with multinuclear NMR. The self-diffusion coefficient of the protons (H+ or H3O+), H2O, and H located around the phosphate were always larger than the diffusion coefficients of the phosphates and the disparity increased with increasing phosphate concentration. The diffusion coefficients of the samples containing D2O paralleled those in the protonated samples. Since the 1H NMR T1 values exhibited a minimum with temperature, it was possible to determine the correlation times and they were found to be of nanosecond order for a distance of nanometer order for a flip. The agreement of the ionic conductivities measured directly and those calculated from the diffusion coefficients indicates that the ion conduction obeys the Nernst-Einstein equation in the condensed phosphoric acids. The proton diffusion plays a dominant role in the ion conduction, especially in the condensed phosphoric acids.     

A simple and efficient method of preparing α-bromo carboxylic acids

A new and convenient method for α-bromination of aliphatic carboxylic acids is reported. Heating carboxylic acids for 16 hours at 85 °C in trifluoroacetic acid with 1.5 equivalents of N-bromosuccinimide and a catalytic amount of concentrated H₂SO₄ leads to good yields of the respective α-bromocarboxylic acids.     

Diffusion and Ion Association in Concentrated Solutions of Aqueous Lithium, Sodium, and Potassium Sulfates

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous Li₂SO₄ solutions at concentrations from 0.09 to 2.62 mol-dm^-3 at 25°C. The Li₂SO₄ results and previously reported diffusion coefficients for aqueous Na₂SO₄ and K₂SO₄ are compared with predictions made by treating the limiting electrolyte diffusion coefficients as reference values and applying corrections for nonideal solution behavior, ionic hydration, and viscosity changes as the concentration is raised. Good agreement is obtained if the M⁺ + SO ₄ ^2- ? MSO ₄ ^- (M = Li, Na, K) association equilibria are included in the analysis. Extents of formation of the MSO ₄ ^- ion pairs are evaluated by fitting Pitzer's mixed electrolyte equations for aqueous M⁺–MSO ₄ ^- –SO ₄ ^2- ions to osmotic coefficient data. Diffusion coefficients for hypothetical solutions of the completely dissociated M₂SO₄ electrolytes are calculated to illustrate the effects of ion association on diffusion. Association of the M⁺ and SO ₄ ^2- ions increases the overall mobility and thermodynamic driving forces for their diffusion.     

离子排斥色谱法测定黄酒中的13种有机酸

建立了离子排斥色谱法（ion-exclusion chromatography,IEC）测定黄酒中有机酸含量的分析方法。使用Waters离子排斥色谱柱（300 mm×7.8 mm,7 μm）,流动相为H₂SO₄溶液（A）与乙腈（B）的混合溶液（体积比为98：2）,线性梯度程序：0~40 min,流动相A的浓度由0.01 mol/L 上升到0.02 mol/L;40~50 min,流动相A的浓度为0.01 mol/L ;流速为0.5 mL/min,柱温50 ℃,进样量10 μL,检测波长210 nm。结果表明,该方法可在30 min内实现草酸、马来酸、柠檬酸、酒石酸、苹果酸、抗坏血酸、琥珀酸、乳酸、富马酸、乙酸、丙酸、异丁酸和丁酸的完全分离与定量,13种有机酸在0.001~1.000 g/L范围内线性关系良好,回归方程的线性相关系数在0.9997以上。黄酒中13种有机酸的加标回收率为93.4%~103.8%,相对标准偏差为0.1%~1.5%（n=5）。该方法简单快捷、准确、重复性好,可用于黄酒中有机酸的测定。     

The formation of aryloxenium ion in the reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with strong acids

The reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine (1) with conc. H₂SO₄ affords 4-nitropyrocatechol and that with conc. sulfonic acids (RSO₃H where R = Me, CF₃) affords 2-hydroxy-5-nitrophenyl-R-sulfonates in yields of 80?C85%. These reactions are assumed to proceed through an intermediate (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺, which eliminates the N₂O molecule to form the aryloxenium ion [NO₂C₆H₄O]⁺. The latter reacts with acid anions at the ortho-carbon atom of the phenyl ring. The thermodynamical parameters of the elementary reactions resulting in the formation of the (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺ and aryloxenium ion [NO₂C₆H₄O]⁺ were calculated in the B3LYP/6?311+G(d) study of the combined molecular system (nitrohydroxylamine 1 + [H₃SO₄]⁺). The reaction of nitrohydroxylamine 1 with aqueous solutions of strong acids (??70% H₂SO₄, CF₃SO₃H) affords mainly 4-nitrophenol. It appears that the mechanism of this reaction does not involve the formation of the aryloxenium ion.     

Diffusion with hydrolysis and ion association in aqueous solutions of beryllium sulfate

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous solutions of beryllium sulfate at concentrations from 0.005 to 1 mol-L^–1 at 25°C. Least-squares analysis of the dispersion profiles shows that diffusion of the partially hydrolyzed salt produces a small additional flow of sulfuric acid, about 0.04 mol sulfuric acid per mole of total beryllium sulfate. Ternary diffusion coefficients measured for the aqueous BeSO₄–H₂SO₄ system are qualitatively consistent with Nernst-Planck predictions based on the formation of beryllium sulfate ion pairs, bisulfate ions, and the hydrolysis equilibria 2Be²⁺+H₂O= Be₂OH³⁺+H⁺, 3Be²⁺+2H₂O=Be₃(OH) ₂ ⁴⁺ +2H⁺. Except for very dilute solutions, the predicted flow of sulfuric acid is small compared to the flow of beryllium sulfate because most of the beryllium ions are protected from hydrolysis by the formation of BeSO₄ ion pairs, and most of the hydrogen ions produced by hydrolysis are converted to less-mobile bisulfate ions.     

Investigation on Concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） Redox Reaction by Rotating Disc Voltammetry

The kinetic characteristics of the concentrated Ⅴ（Ⅳ）/Ⅴ（Ⅴ） couple have been studied at a glassy carbon electrode in sulfuric acid using rotating-disc electrode and cyclic voltammetry. The kinetics of the Ⅴ（Ⅳ）/Ⅴ（Ⅴ） redox couple reaction was found to be electrochemically quasi-reversible with the slower kinetics for the Ⅴ（Ⅴ） reduction than that for the Ⅴ（Ⅳ） oxidation. And, dependence of diffusion coefficients and kinetic parameters of Ⅴ（Ⅳ） species on the Ⅴ（Ⅳ） and H2SO4 concentration was investigated. It is shown that the concentration of active species Ⅴ（Ⅳ） should be over 1 mol·L^-1 for the redox flow battery application. Further, with increasing the Ⅴ（Ⅳ） and H2SO4 concentration, the diffusion coefficients of Ⅴ（Ⅳ） were gradually reduced whereas its kinetics was improved considerably, especially in the case of Ⅴ（Ⅳ） and H2SO4 up to 2 and 4 mol·L^-1.     

Determination of glycuronic acids by high-performance anion chromatography with pulsed amperometric detection

Summary Acid hydrolysis (0.25M H₂SO₄) coupled with enzyme catalysis (pectolyase and β-D-glucuronidase) were employed to extract galacturonic and glucuronic acids from microbial polysaccharides, plant residues, animal wastes, sewage sludge and soil. The glycuronic acids were separated by high-performance anion chromatography (HPAC) on a strong anion-exchange column using 0.1M sodium hydroxide with 0.25M sodium acetate as the mobile phase and determined by pulsed amperometric detection (PAD). HPAC-PAD was found to be superior to high-performance liquid chromatography with ultra-violet (UV) detection in terms of resolution and sensitivity of glycuronic acids. HPAC-PAD was not subject to interferences present with low UV detection (210 nm) and was highly selective for glycuronic acids. Enzymatic hydrolysis after treatment with mild acid (0.25M H₂SO₄) released galacturonic acids from orange peel and pectin, while glucuronic acid was released from Acacia powder. Large amounts of glycuronic acids were also extracted from plant materials. Low levels of uronic acids were detected in poultry manure, sewage sludge and organic-amended soils.     

Determination of inorganic acids by ion chromatography with n-tetradecylphosphocholine (zwitterionic surfactant) as the stationary phase and pure water as the mobile phase

A new ion chromatographic (IC) system, in which n-tetradecylphosphocholine (TDPC, a phosphobetaine type of zwitterionic surfactant) was used as the stationary phase, pure water as the mobile phase, and conductivity as the method of detection, has been developed for the determination of inorganic acids. Five model acids, HCl, HNO₃, HClO₄, H₂SO₄, and H₃PO₄, were separated to baseline and eluted in the order H₃PO₄ > HCl > HNO₃ > H₂SO₄ > HClO₄. When peak areas were plotted against the concentrations of the acids in samples, linear calibration curves were obtained. Ultimate determination limits were approximately 1 mmol L^–1, but the discrimination of the method between solutions of different concentration was better than 10 μmol L^–1 for those model analytes. Salts of divalent cations could also be separated, but they were eluted faster than the acids. No separation was observed for the salts of monovalent cations. This newly proposed approach is applicable to the simultaneous determination of the inorganic acids (produced by reactions of NO_x, SO_x, and HCl with water) in aerosols.     

The solubility of ozone in aqueous solutions of sulfuric, phosphoric, and perchloric acids

The solubility of ozone in pure water and aqueous solutions of sulfuric, phosphoric, and perchloric acids was determined at 20°C. An increase in the concentration of H₃PO₄ and HClO₄ (to 14.8 and 9.5 M, respectively) caused a monotonic decrease in the solubility of ozone. The solubility of ozone in sulfuric acid was minimum at a 12 M concentration; the solubility then increased and, in 17.9 M H₂SO₄, reached almost the same value as in pure water. The ratio between the concentrations of O₃ in solution and the gas phase was 0.276 in pure water, 0.122 in 12 M H₂SO₄, and 0.265 in 17.9 M H₂SO₄. The results obtained are compared with the available literature data.     

Formation of peracids from corresponding organic acids under oxygen electroreduction in gas-diffusion electrode

The effect of conditions of electrolysis in aqueous solutions of (K₂SO₄ + H₂SO₄) electrolytes was studied in the presence of formic, acetic, and butyric acids on the formation of the corresponding peracids under oxygen electroreduction in carbon black gas-diffusion electrodes. In the presence of organic acids with the concentration of 1.5–4.7 M, as dependent in the electrolysis conditions, the current efficiency of H₂O₂ formation decreases from 70 to 13 % and its concentration drops from 2.3 to 0.4 M. Electrolysis under constant current (50–100 mA/cm²) results in formation of peracids with the concentration of up to 7.5 mM. No direct dependence of the concentration of peracids on the concentration of the obtained H₂O₂ is observed. The presence of tetrabutylammonium bromide in the solution inhibits significantly peracid formation. It is assumed that synthesis of peracids occurs partly on the surface of carbon black through activation of the adsorbed acid by a hydrogen cation and further interaction with the active form of oxygen obtained under oxygen reduction or decomposition of H₂O₂.     

Single ion activities in aqueous sulfuric acid solutions: A new extra-thermodynamic assumption

Single ion activities in aqueous H₂SO₄ have been calculated from the mean ionic activity coefficients of H₂SO₄, the solubilities of PbSO₄ and the degrees of the second dissociation of H₂SO₄ in these solutions by employing a new extra-thermodynamic assumption. The hydrogen ion activities thus obtained are compared with the corresponding acidity function values based on different classes of acid-base indicators.     

The mutual diffusion coefficients of Na2SO4−H2O and MgSO4−H2O at 25°C from Rayleigh interferometry

The volume-fixed mutual diffusion coefficients of Na₂SO₄–H₂O and MgSO₄–H₂O have been measured, from dilute solutions to near saturation, to an accuracy of 0.1–0.2% by free-diffusion Rayleigh interferometry. These results are compared to other available diffusion data for these salts. The diffusion coefficients of Na₂SO₄–H₂O and MgSO₄–H₂O decrease regularly with increasing concentration, while those of many other salts exhibit both a maximum and a minimum as a function of concentration. A few diffusion coefficients have also been measured for KCl–H₂O.Reference to a company or product names does not imply approval or recommendation of the product by the University of California or the U.S. Department of Energy to the exclusion of others that may be suitable.This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.University of Illinois at Urbana-Champaign; tenure served as a participating guest at Lawrence Livermore Laboratory.     

Study of mechanism retention of nonvolatile alkylphosphonic acids on unmodified selected polymer-based ion exchanger columns

The retention of alkylphosphonic acids (MPA, EPA, PPA, and BPA) and inorganic anions (Cl⁻, NO₃⁻, and SO₄²⁻) were studied on two anion exchangers, e.g., Dionex IonPac AS4A-SC (250 ± 4 mm I.D.) and Satisfaction P 4000-SAX (50 ± 4.6 mm I.D.) under isocratic elution conditions with evaporative light scattering detector. The plots of retention factors, k, of organic anions vs. the reciprocal of eluent ion concentration show good linearity. The major retention mechanisms are interpreted as ion exchange and some others interactions. The C effect of organic modifier added to the aqueous buffered mobile phase is also investigated.     

Transport of U(VI) from sulphuric acid medium across supported liquid membrane (SLM) containing di-(2-ethylhexyl) phosphoric acid (D2EHPA)/n-dodecane as a carrier

This paper reports on the supported liquid membrane (SLM) based transport studies of U(VI) from sulphate medium using di-(2-ethylhexyl) phosphoric acid/n-dodecane as carrier. Polytetrafluoroethylene membrane was used as solid support and H₂SO₄ as receiver phase. The effects of various parameters such as receiver phase concentration, feed acidity, carrier concentration, U(VI) concentration, membrane thickness and membrane pore size on U(VI) transport had been investigated. With increase in H₂SO₄ concentrations and pH of feed solution there is an increase in U(VI) transport across the SLM. Similarly with increase in membrane thickness the U(VI) transport decrease whereas in case of pore size variation reverse results are obtained. The membrane thickness variation results showed that the U(VI) transport across the SLM is entirely diffusion controlled and the diffusion coefficient the D _(o) was calculated as 1.36 × 10^?7 cm² s^?1. Based on optimized condition, a scheme had been tested for selective recovery of U(VI) from ore leach solution containing a large number of other metal ions.