Potentiometric Cross-Sensitive Sensors Based on Perfluorinated Membranes Treated at Different Relative Humidity for Codetermination of Cations and Anions in Alkaline Solutions of Amino Acids

The results of studying characteristics of potentiometric DP-sensors (sensors with the Donnan potential as their analytical signal) are presented for alkaline solutions of a sulfur-containing amino acid with perfluorosulfonic cation exchange membranes subjected to thermal treatment and mechanical deformation at different relative humidity. Correlation between the distribution of sensitivity of DP-sensors towards cations and anions and diffusion permeability of membranes was found. A multisensor system including two DP-sensors based on membranes with optimized properties and a glass electrode for codetermination of potassium cations and amino acid anions and zwitterions in solutions at pH >7 are developed.     

Electrodialytic recovery of chromium(VI) from hydrochloric acid solutions with liquid membranes based on tri-n-octylamine

A study of the process of electrodialytic recovery of chromium(VI) from a solution of 0.01 M K₂Cr₂O₇ in 0.1 M HCl with liquid membranes containing tri-n-octylamine with addition of di(2-ethyl hexyl)phosphoric acid in1,2-dichloroetrhane to dilute solutions of various acids determined the optimal process conditions: electrodialysis current density and the composition of the starting and receiving aqueous solutions and liquid membranes. It was found that all the liquid membranes studied provide a complete recovery of chromium(VI) anions from the starting solution.     

Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

Vibrational and 29Si NMR spectroscopies of soluble silicate oligomers

Vibrational spectroscopy has been used to correlate the features of silicate solution spectra with ²⁹Si NMR spectra, as a function of SiO₂:Na₂O ratio and SiO₂ concentration. Assignments of infrared and Raman component bands have been made for different anion types and are consistent with results reported for crystalline silicates and silicate glasses. The extent of depolymerization of larger anions has been found to differ, depending on both the degree of dilution and alkalinity. The relative amounts of polymeric (Q⁴) silica and larger three dimensional (Q³_4R) anions are greater for the more siliceous solutions (3.3 and 2.95 ratio) at high concentrations. These large anions continue to be major contributors to the anion distribution even at 15 to 50 fold dilution. In the case of more alkaline solutions, especially below 2.5 ratio, the relative contribution of the large anions to the distribution drops rapidly, even with 2 or 3 fold dilution. At low concentrations, in very alkaline solutions, the anion distribution is mainly monomer, dimer and cyclic trimer. Vibrational spectroscopies show great promise for observing changes in anion distribution on a much shorter time scale than is possible with ²⁹Si NMR and can be useful for following reactions involving silicate solutions.     

Variations of activity coefficients in concentrated electrolyte solutions at constant lonic strength

Measurements of different types on various (trace) electrolytes in HClO₄–Na(Li)ClO₄ solutions at several (constant) values of the ionic strength have been used to determine the variation of their activity coefficients with changing amount of perchloric acid in the solution. These variations (with respect to the hydrogen ion) differ considerably among different cations and anions. The results for the alkali metal ions and the anions are interpreted in the light of the recent work of Pitzer on short-range ionic interactions. The results for the cations with outerd-electrons and the alkaline earth metal ions are interpreted in terms of ion-solvent interactions. It is concluded that the use of HClO₄–NaClO₄ solutions of high ionic strength (rather than the use of HClO₄–LiClO₄ solutions) is advisable in studies where the variation in activity coefficients must be accounted for. Finally, it is shown that the usual interpretation of the influence of the salt medium in studies of complex equilibria and reaction kinetics is sometimes questionable.     

Controlled-potential electrosynthesis of glucosaminic acid from glucosamine at a gold electrode

The electrocatalytic oxidation of d-glucosamine (2-amino-2-deoxy-d-glucose) in alkaline and neutral solutions was examined using a carbon felt electrode modified with 2 nm core sized gold nanoparticles (Au_2 nm nanoparticles) and a gold plate electrode. The electrocatalytic voltammetric oxidation curves of d-glucosamine were obtained in both solutions. The voltammetric responses for the electrocatalytic oxidation at a Au_2 nm nanoparticle-modified electrode in both alkaline and neutral solutions were almost the same to those at a gold plate electrode. The oxidized product was identified to be d-glucosaminic acid (2-amino-2-deoxy- d-gluconic acid) generated by the 2-electron oxidation product of d-glucosamine by electrospray ionization time-of-flight mass spectra (ESI TOF-MS). The HPLC results also indicated that the oxidation product was d-glucosaminic acid.The controlled-potential electrolysis of d-glucosamine was performed at the Au_2 nm nanoparticle-modified carbon felt electrodes in both alkaline and neutral solutions. In the alkaline solution, at a potential of −0.2 V, d-glucosaminic acid was formed with a current efficiency of 100%. In the neutral solution, electrolysis at 0.4 V on d-glucosaminic acid was obtained with current efficiencies of 70%.     

碱处理PVDF膜对制备高电导率质子交换膜的作用

燃料电池是一种高能量密度、低污染的新型能源. 质子交换膜是燃料电池的核心组件之一. 在对聚偏氟乙烯(PVDF)膜进行了碱处理改性的基础上制备了高电导率的聚偏氟乙烯接枝聚苯乙烯磺酸(PVDF-g-PSSA)质子交换膜, 对碱处理后的PVDF膜进行了傅立叶变换红外光谱(FTIR)、傅立叶变换拉曼光谱(FT-Raman)及电子自旋共振(ESR)分析. 振动光谱显示在处理后的膜中存在共轭碳碳双键. 首次用ESR检测到碱处理后的PVDF膜中形成了自由基, 其浓度在10¹⁶ spin/g. 研究表明碱处理引起的膜结构变化有利于接枝反应的进行, 对提高所合成的质子交换膜的电导率有重要作用, 电导率提高一个数量级, 至6.40×10^－2 S/cm.     

Interaction of pyridine‐ and 4‐hydroxypyridine‐2,6‐dicarboxylic acids with heavy metal ions in aqueous solutions

Interactions between pyridine‐2,6‐dicarboxylic acid and 4‐hydroxypyridine‐2,6‐dicarboxylic acid with Cu(II), Pb(II), and Cd(II) ions were characterized in aqueous solutions (20°C; I = 0.4 (KNO₃)) by means of dc‐polarography. In solutions with excess of ligand, Cu(II), Pb(II), and Cd(II) form 1:2 complexes with the tridentate dianion of pyridine‐2,6‐dicarboxylic acid (dipic²⁻) from weak acid to alkaline solutions. The values of log β₂ for Cu(II), Pb(II), and Cd(II) are 16.1, 11.8, and 11.0, respectively. The complexing ability of pyridine‐2,6‐dicarboxylic acid is higher in acid solutions and lower in alkaline solutions than that of 4‐hydroxypyridine‐2,6‐dicarboxylic acid. This difference is attributed to the OH‐group, which can deprotonate in basic pH. In acid solutions the OH‐group acts as an electron acceptor and reduces the electron donation available to the nitrogen atom in 4‐hydroxypyridine‐2,6‐dicarboxylic acid, whereas in alkaline solutions the OH‐group is deprotonated, and the deprotonated O₋ group acts as an electron donor and increases the coordination ability of the ligand. The triple‐deprotonated anion of 4‐hydroxypyridine‐2,6‐dicarboxylic acid (chel^3‐) forms a stable diligand complex with Cu(II), the stability constant logarithm being 21.5 ± 0.2.© 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:625–632, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10203     

Low-voltage thin-layer electrophoresis of inorganic anions on silica gel-G and titanium (IV) tungstate layers: separation of coexisting F−, Cl−, Br− and I−, I−, IO3− and IO4−, Fe(CN)64− and Fe(CN)63−

The electrophoretic behavior of twenty anions has been studied on silica gel-G, titanium (IV) tungstate and silica gel-G- titanium (IV) tungstate admixture layers using 0.1 M solutions of oxalic acid, citric acid, tartaric acid, succinic acid and acetic acid as background electrolyte. The mechanism of migration is explained in terms of adsorption and the solubility of various sodium or potassium salts of the anions in water. Titanium (IV) tungstate behaves only as an adsorbent and not as an ion exchanger. Being a cation exchanger, there is no exchange phenomenon occurring with anions. The migration of halides increase linearly with an increase in the bare ion radii of these ions. Differential migration of the anions on silica gel-G layers led to binary, ternary and quaternary separations of similar anions such as F⁻ – Cl⁻ – Br⁻ – I⁻, I⁻ – IO₃⁻ – IO₄⁻, BrO₃⁻ – IO₃⁻ and Fe(CN)₆³⁻ – Fe(CN)₆⁴⁻. The two cyanoferrate ions are separated from industrial waste water and from fixer and bleach solutions. The migration of anions has also been found to be in accordance with their lyotropic numbers.

     

Modification and characterization of semi-crystalline poly(vinyl alcohol) with interpenetrating poly(acrylic acid) by UV radiation method for alkaline solid polymer electrolytes membrane

Semi-crystalline poly(vinyl alcohol) was modified by UV radiation with acrylic acid monomer to get interpenetrating poly(acrylic acid) modified poly(vinyl alcohol), PVAAA, membrane. The stability of various PVAAA membranes in water, 2 M CH₃OH, 2 M H₂SO₄, and 40 wt% KOH aqueous media were evaluated. It was found that the stability of PVAAA membrane is stable in 40 wt% KOH solution. The PVAAA membranes were characterized by differential scanning calorimetry, X-ray diffraction, and thermogravimetry analysis. These results show that (1) the crystallinity in PVAAA decreased with increasing the content of poly(acrylic acid) in the PVAAA membranes. (2) The melting point of the PVAAA membrane is reduced with increasing the content of poly(acrylic acid) in the membrane. (3) Three stages of thermal degradation were found for pure PVA. Compared to pure PVA, the temperature of thermal degradation increased for the PVAAA membrane. The various PVAAA membranes were immersed in KOH solution to form polymer electrolyte membranes, PVAAA-KOH, and their performances for alkaline solid polymer electrolyte were conducted. At room temperature, the ionic conductivity increased from 0.044 to 0.312 S/cm. The result was due to the formation of interpenetrating polymer chain of poly(acrylic acid) in the PVAAA membrane and resulting in the increase of charge carriers in the PVA polymer matrix. Compared to the data reported for different membranes by other studies, our PVAAA membrane are highly ionic conducting alkaline solid polymer electrolytes membranes.     

Composition and stability of complexes of maleic and succinic acids with Cu2+ ions in water-ethanol solutions at 298 K

The composition and stability of coordination compounds of the anions of maleic (H₂L) and succinic (H₂Y) acids with copper(II) ions in water-ethanol solutions is studied by means of potentiometric titration at a sodium perchlorate ionic strength of 0.1 and a temperature of 298.15 K. The composition of the water-ethanol solvent was varied from 0 to 0.7 molar parts of ethanol for maleic acid and from 0 to 0.4 molar parts for succinic acid. The stability of monoligand complexes of copper ions with the anions of maleic and succinic acids grows with increase of ethanol concentration from 3.86 to 6.62 for logβ_CuL and from 2.98 to 6.01 for logβ_CuY. It is shown that a monotonic rise in stability upon an increase in the content of ethanol in solution is observed, while the values of logβ_CuL change more sharply. The succinic acid anion forms a stronger complex with copper ions than maleic acid anions do at an ethanol content of 0.4 molar parts. The possibility of the formation of a protonated CuHY⁺ particle is established.     

Extraction of molybdenum(VI) by 4-(5-nonyl)pyridine in benzene from aqueous mineral acid solutions containing thiocyanate ions

Extraction of Mo(VI) by 4-(5-nonyl)pyridine (NPy) in benzene from mineral acid solutions containing thiocyanate ions has been investigated at room temperature (23±2°C). From mineral acid (HCl, HNO₃, and H₂SO₄) solutions alone Mo(VI) is not extracted quantitatively while the presence of small amounts of KSCN in the system augments the extraction by a large factor. Stoichiometric studies indicate that ion-pair type complexes (NPyH)₂·[MoO₂(SCN)₄] are responsible for the extraction. Separation factors determined at fixed extraction conditions (0.1M Npy/C₆H₆–0.1M acid +0.2M KSCN) reveal that Ag(I), Cu(II), Co(II), Zn(II), Hg(II) and U(VI) are co-extracted while a clean separation from alkali metals, alkaline earths and some transition metals like Ln(III), Zr(IV), Hf(IV), Cr(III), Cr(VI) and Ir(III) is possible. Some of the complexing anions like oxalate, citrate, acetate, thiosulfate or ascorbate do not affect the degree of extraction of Mo(VI) allowing it to be recovered from diverse matrices.     

<Superscript>29</Superscript>Si NMR Spectroscopy Investigation of Alcoholic Phenyltrimethyl Ammonium Silicate Solutions

²⁹Si NMR spectroscopy is a powerful tool for studies of the silicate species existing in both aqueous and non-aqueous solutions. In this report ²⁹Si NMR spectroscopy was used to characterize species present in alkaline alcoholic silicate solutions. Phenyltrimethylammonium (PTMA) hydroxide was used as a base. The effects of polymerization/depolymerization of silicate anions in alcoholic alkaline solutions were investigated with different alcohols by ²⁹Si NMR spectroscopy. The esterification of monomeric silicate, Si(OH)₄, in the presence of different alcohols was also studied. Esterification depends on the alkyl chain as well as number of hydroxyl groups in the alcohol.     

Determination of glycine,alanine, and leucine at different solution ph with the aid of donnan potential sensors based on hybrid membranes

The cross sensitive sensors whose analytical signal is the Donnan potential (PD-sensors) were developed for the determination of the amino acids glycine, alanine, and leucine in acidic and alkaline solutions. Hybrid materials based on perfluorinated sulfo cation-exchange membranes Nafion and MF-4SC with incorporated zirconium dioxide and silicon dioxide nanoparticles, including those with modified surfaces containing proton-acceptor groups, were used in the PD-sensors. The sensitivity of the PD-sensors to hydronium ions, which interfere with the determination of amino acids at pH < 7, was considerably decreased due to the use of the membranes obtained by an in situ method that contained silicon dioxide nanoparticles with amine-containing groups. The greatest sensitivity of the PD-sensors to the anions of amino acids at pH > 7 and the smallest sensitivity to the cations K⁺ were observed in hybrid membranes, which combined an increased rate of anion transfer and a low moisture capacity. The use of the PD-sensors based on hybrid membranes makes it possible to determine the cations, anions, and zwitterions of amino acids over a wide range of pH with a sufficiently high accuracy.     

Novel pore shape and self-organization effects in n-GaP(111)

n-type GaP(111) has been porosified in HCl, H₂SO₄, HBr, NaBr, and alkaline NaBr in the dark. The pore morphology strongly depends on the electrochemical conditions and on the chemical nature of anions in the electrolyte. Independent of the pH-value of bromide-containing solutions, layers of triangular pores with a defined cross-section were growing under an irregular pore nucleation layer. Optimized conditions led to a regular structure of equally sized triangular pores with a side length of (98 ± 5) nm. The pore walls are determined by (110)-crystal planes of GaP. In other electrolytes such as HCl or H₂SO₄ it was not possible to form triangular pores during the electrochemical etching process.     

Arsenic sorption and redox transformation on iron‐impregnated ordered mesoporous carbon

Ordered mesoporous carbon has been actively investigated for its potential applications as catalyst supports, electrochemical materials and gas separation media. In this study, we tested an iron‐modified ordered mesoporous carbon (FeOMC) for its ability to adsorb arsenic from the aqueous phase. The FeOMC synthesis involved the preparation of an ordered silica template SBA‐15, in situ polymerization of acrylic acid in the template, carbonization and template removal to obtain the ordered mesoporous carbon, and iron impregnation. Batch experiments showed that the pH level of the solution had a major impact on arsenic sorption. Further, we found that the presence of anions (i.e. PO₄^3? and SiO₃^2?) could significantly decrease the sorption of both arsenate and arsenite. Arsenite oxidation to arsenate was observed in alkaline solutions, with or without anions being present. The oxidation of arsenite was attributed to both direct and catalytic reactions with the surface functional groups on the ordered mesoporous carbon. Adsorption of arsenic on FeOMC could be well explained by the surface complexation model. Copyright © 2007 John Wiley & Sons, Ltd.     

Potentiometric cross-sensitive PD sensors for the simultaneous determination of nicotinic acid and pyridoxine hydrochloride in aqueous solutions

A potentiometric multisensory system is developed for the rapid simultaneous determination of pyridoxine hydrochloride and nicotinic acid in aqueous solutions. Sensors for which analytical signal is constructed by the Donnan potential are used within a multisensory system as cross-sensitive elements. In solutions containing both components in concentrations from 1.0 × 10^?4 to 1.0 × 10^?2 M, the relative error of analysis did not exceed 10%. Standard titrimetry and spectrophotometry methods were used for the reference analysis of the target vitamins in multicomponent solutions.     

Preparation and characterization of polybenzimidazole membranes prepared by gelation in phosphoric acid

Phosphoric acid doped poly (2, 2′‐(m‐phenylene)‐5, 5′‐bibenzimidazole) (PBI) membranes were prepared by dissolving PBI powders in 85% phosphoric acid at 190–200°C and then promoting gelation of the PBI by cooling the solutions to ?18°C. The extent of acid doping of the PBI membranes was controlled by immersing the membrane in aqueous phosphoric acid solutions of different concentrations (acid de‐doping). The process of the acid de‐doping was faster than acid doping of membrane cast from N,N‐dimethylacetamide (DMAc). The de‐doping process caused shrinkage of the PBI membrane and thus an increase in the membrane strength due to the packing of PBI chains according to the X‐ray diffraction analysis. The tensile stress and proton conductivity of the obtained PBI membranes with different acid doping levels were measured. For a PBI (η_IV: 0.58 dL · g^?1) membrane with an acid doping level of 7.0 (molar number of doped acid per mole repeat unit of PBI), the stress at break and proton conductivity at 120°C without humidification were 2.6 MPa and 5.1 × 10^?2 S · cm^?1, respectively. These results were comparable to those of the membranes cast from PBI solutions in DMAc. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvation Accounts for the Counterintuitive Nucleophilicity Ordering of Peroxide Anions

The nucleophilic reactivities (N , s _N) of peroxide anions (generated from aromatic and aliphatic peroxy acids or alkyl hydroperoxides) were investigated by following the kinetics of their reactions with a series of benzhydrylium ions (Ar₂CH⁺) in alkaline aqueous solutions at 20 °C. The second‐order rate constants revealed that deprotonated peroxy acids (RCO₃⁻), although they are the considerably weaker Brønsted bases, react much faster than anions of aliphatic hydroperoxides (ROO⁻). Substitution of the rate constants of their reactions with benzhydrylium ions into the linear free energy relationship lg k =s _N(N +E ) furnished nucleophilicity parameters (N , s _N) of peroxide anions, which were successfully applied to predict the rates of Weitz–Scheffer epoxidations. DFT calculations with inclusion of solvent effects by means of the Integral Equation Formalism version of the Polarizable Continuum Model were performed to rationalize the observed reactivities.     

Complex formation in nickel(II)-glycine-β-lactam antibiotic systems

Complex formation in solutions containing Ni²⁺ cations, glycine anions (Gly^?), and β-lactam antibiotics, namely, ampicillin (Amp), amoxicillin (Axn), and cephalexin (Cpx), is studied by pH-metric titration at 20°C and an ionic strength of 0.1 (KNO₃). Mixed-ligand complexes [NiGlyAmp], [NiGlyAxn], and [NiGlyCpx], which are in equilibrium with the [NiGly]⁺ complexes, are formed in the systems studied in a weakly alkaline medium. The formation constants of the complexes are determined. The distribution diagrams of the complex Ni(II) forms at different pH values of the solutions are constructed.