Reduction of Trivalent Chromium Ions on Stationary Mercury Electrode in Concentrated LiCl Solutions

The effect of supporting-electrolyte (LiCl) concentration on the first stage Cr(III) + e Cr(II) of Cr(III) reduction on a stationary mercury electrode is studied by linear voltammetry. It is found that an increase in the LiCl molar concentration m from 0.4 to 7 weakly affects the position of the cathodic current peak potential E _P1 corresponding to this process. In the mentioned concentration range, [Cr(H₂O)_{6 – n} Cl _n ]^{3 – n} (0 n < 3) ions are preferentially reduced. The further increase in m up to 19.1 results in a substantial positive shift of E _P1, which is associated with the formation (upon passing the complete hydration limit) of the [Cr(H₂O)₃Cl₃] (n = 3) complex, which is followed by its reduction.     

Efficient Adsorption of Chromium Ions from Aqueous Solutions by Plant-Derived Silica

Nowadays, there is great interest in the use of plant waste to obtain materials for environmental protection. In this study, silica powders were prepared with a simple and low-cost procedure from biomass materials such as horsetail and common reed, as well as wheat and rye straws. The starting biomass materials were leached in a boiling HCl solution. After washing and drying, the samples were incinerated at 700 °C for 1 h in air. The organic components of the samples were burned leaving final white powders. These powders were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), scanning electron microscopy (SEM), and low-temperature nitrogen sorption. The amorphous powders (biosilica) contained mainly SiO₂, as indicated by FTIR analysis. Horsetail-derived silica was chosen for testing the removal of dichromate ions from water solutions. This biosilica had a good ability to adsorb Cr(VI) ions, which increased after modification of the powder with the dodecylamine surfactant. It can be concluded that the applied procedure allowed obtaining high purity biosilica from plant waste with good efficiency. The produced biosilica was helpful in removing chromium ions and showed low cytotoxicity to human endothelial cells, suggesting that it can be safely used in environmental remediation.     

On the Intrinsic Volumes of Ions in Aqueous Solutions

Various methods that have been proposed in the literature for the estimation of the intrinsic volumes of electrolytes in aqueous solutions are briefly discussed. Most of these depend on the radii of the constituent ions. A method that is independent of the radii but requires a long extrapolation from the temperatures involved in salt melts is also mentioned. A new method is developed here, independent of ionic radii, which employs the partial molar volumes of salts in their concentrated solutions (and is, therefore, limited to highly soluble salts). These are extrapolated to a virtual concentration at which all the water present is as closely packed as possible, hence no longer capable of being electrostricted. The resulting intrinsic volumes of salts are reasonable when compared to other estimates of these quantities.     

The State of Copper Ions in Aqueous and Aqueous Ammonia Solutions of Copper Acetate

Stabilization of Cu²⁺ ions in aqueous and aqueous ammonia solutions of copper acetate was studied for a wide range of ammonia concentrations. The structure of copper acetate hydrate complexes was shown to markedly change upon dissolution in water. In aqueous solutions, copper is stabilized as strongly bound Cu²⁺ associates (dimers) in a distorted octahedral environment composed of water molecules and acetate groups oxygen atoms in equatorial positions with strong exchange interaction via acetate groups. In solutions of copper acetate in aqueous ammonia, the concentration of ammonia has a crucial effect on the ordering of Cu²⁺ ions in associates. At high ammonia concentration, disordered copper tetra-ammoniate associates with the \({d_{{x^2} - {y^2}}}\) ground state are formed, whereas at low ammonia concentration, bulky Cu²⁺ ion associate structures are generated, with the \({d_{{x^2} - {y^2}}}\) ground state, hydroxyl groups in the equatorial plane, and water molecules in the axial positions.     

水溶液中六价铬在碳纳米管上的吸附

针对用碳纳米管对水溶液中六价铬的吸附净化进行了研究, 考察了溶液浓度、溶液pH值、共存的三价铬离子等因素对吸附行为的影响. 实验结果表明, 碳纳米管在室温下对于六价铬的吸附量随着平衡浓度的增大而升高, 在铬浓度为493.557 mg•L−1时碳纳米管吸附量达到最大值为532.215 mg•g−1; 六价铬的浓度在300~700 mg•L−1的范围内, 碳纳米管对铬的吸附量变化不大；大于700 mg•L−1时, 随着铬的平衡浓度的升高碳纳米管对铬的吸附量降低, 铬浓度为961.074 mg•L−1时, 碳纳米管吸附量降至194.631 mg•g−1. 在pH值为2~7的范围内, 碳纳米管对六价铬的吸附量随着溶液pH值的减小而增大; 而在碱性条件下, pH值对碳纳米管吸附六价铬的影响不大. 溶液中存在三价铬时, 碳纳米管对六价铬的吸附量明显降低, 表明三价铬与六价铬有竞争吸附. 此外, 活性炭的对比吸附实验表明, 在低浓度时, 譬如在六价铬浓度为190 mg•L−1吸附时, 碳纳米管对铬的吸附量约为活性炭的6倍；而在高浓度下, 譬如六价铬浓度为493 mg•L−1时, 碳纳米管对铬的吸附量约为活性炭的2倍.     

葡萄糖水溶液氢键结构和动力分析

利用分子动力学模拟方法研究了不同浓度下葡萄糖水溶液的氢键结构和氢键生存周期. 分析了参与i个氢键(分子内、分子间、所有类型)的葡萄糖分子和水分子的百分比分布. 研究发现存在一个特征数N, 参与N个氢键的分子的比例最高, 当iN时, 参与i个氢键的分子的比例随着浓度的增加而减小. 还分析了不同类型氢键(葡萄糖分子内、葡萄糖分子间、水分子间、葡萄糖分子与水分子间、所有类型)的连续和截断自相关函数, 并计算了对应的氢键生存周期.     

Reduction of Triple-Charged Chromium Ions on Indium Cathode in Alkaline Sulfate Solutions

The problem of how the surface coverage of an indium electrode with chromium adatoms formed during the discharge of Cr(III) ions affects electrolytic evolution of hydrogen in alkaline solutions is studied using linear and cyclic voltametry. The method used permits stating that, in alkalinized media, the chromium deposition abruptly decelerates due to the formation of a hydroxide film on the electrode surface. Based on the results obtained, it is assumed that this film consists of mixed Cr(III)- and Cr(II)-containing hydroxo compounds (of the chromite type) and coadsorbed Cr_n clusters formed in the course of electrolysis.     

Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various ¹H NMR techniques (¹H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be non-aggregated in the range 0–10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY ¹H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.     

The Physical Properties of Aqueous Solutions of the Ionic Liquid [BMIM][BF4]

We report here the systematic study of the effect of concentration on the physical properties of aqueous solutions of the room-temperature ionic liquid [BMIM][BF₄]. The measurements of density, ρ, refractive index △n, viscosity η, specific conductivity κ and surface tension, γ, were made over the whole concentration range. The equivalent conductance Λ _m was calculated. The observed linear variations of density and refractive index with the molar concentration are established as those of an ideal solution. The surface tension varied most rapidly in the dilute region whereas the viscosity changed much more rapidly in the concentrated region. Two regions with different composition dependences were found after the analyses of the relationship between the conductivity and the concentration of [BMIM][BF₄]. A proposed model for a structural change in the mixtures was described. The physical origin of the observed concentration dependence of these properties is discussed. The physical properties of the solutions vary with changes of association between anions and cations and the interaction between [BMIM][BF₄] and water.     

The Photolysis of Polyvinylpyrrolidone in Aqueous Solutions in the Presence of Oxygen and Cupric Ions

Abstract

The oxidative photolysis of polyvinylpyrrolidone with light of λ = 2537 Å has been studied over a range of oxygen pressures and polymer concentrations. The results show that chain scission and cross linking take place simultaneously. In the range where cross linking is a negligible component, a mechanism based on chain scission due to components which lead to chain scission without intervention of oxygen, and a component which leads to chain scission via hydroperoxide side groups, has been proposed. This mechanism accounts satisfactorily for all observed features of the reaction. The degree of degradation at any one time decreases with oxygen pressure. Cupric ions, with or without oxygen present, have very little influence on the degradation process. However, the UV spectra of PVP in the presence of cupric ions are different from those without them.     

Complexation of Calcium Ions with Dicarboxylic Acids in Aqueous Solutions

Complexation of calcium ion with malonic, succinic, glutaric, adipic acids at 25°C, ionic strength I = 0.3 (KCl) was studied by pH-potentiometric titration.     

Chitosan-Based Materials for the Removal of Nickel Ions from Aqueous Solutions

Russian Journal of Physical Chemistry A - Sorption of Ni(II) ions from liquid effluents utilizing chemically modified chitosan; (vanillin, polymer I) and (ortho-vanillin, polymer II) is studied...     

The Effect of Temperature on the Rate of Alkaline Hydrolysis of Esters in Concentrated Aqueous Solutions of Et4NCl

The rate of alkaline hydrolysis of 4-nitrophenyl toluenesulfonate, 4-nitrophenyl diethyl phosphate, and 4-nitrophenyl dimethylcarbamate (with Et₄NOH as reagent) in concentrated aqueous solutions of Et₄NCl (0-4.5 M) at 15, 25, 40, and 60 °C was studied. The nature of the effect of Et₄NCl on the reaction rate was explained by the action of the electrolyte on the structure of the water. It was shown that the increase in the rate results from change in the solvation component of the free energy of activation.     

Effect of Mg2+ Ions on the Stability of PolyA/2PolyU Three-Stranded Helices in Aqueous Solutions

The influence of Mg²⁺, Na⁺ and temperature on the conformational state of three-stranded helical polyA/2polyU (A2U) has been studied by the thermal denaturation method. At Na⁺ concentrations of 0.01–0.1 M , on heating the transition A2U→AU+U (the 3→2 transition) and then AU→A+U transition (the 2→1 transition) are observed. (AU is double helix polyA/polyU; A and U are single-stranded polyA and polyU, respectively.) With 0.01 M and 0.03 M Na⁺ these transitions occur at Mg²⁺ concentrations within (0 ÷ 0.003) M . At these ionic concentrations, there is a narrow temperature region (3 ÷ 5°C) at which double-helical AU formed by the 3→2 transition is resistant to heating. In 0.1 M Na⁺, a rise in the Mg²⁺ concentration leads to a continuous decrease in the temperature range of this region, and above a critical concentration of Mg²⁺ (ca. 3.6×10^–5 M )_cr there is only one transition (the 3→1 transition) instead of the successive transitions 3→2→1. The constants of Mg²⁺ ion association with polyU, polyA and A2U were calculated using equilibrium binding theory. The data obtained helped explain the reasons for the different phase diagrams for A2U + Mg²⁺ complexes in solution at high and low Na⁺ concentrations.     

Electron Transport Properties of Ions in Aqueous Solutions of Sodium Selenite

Ion diffusion kinetics has been studied using the data of conductivity measurements for aqueous solutions of sodium selenite with different concentrations and at different temperatures. Molecular and ionic self-diffusion coefficients have been determined for infinitely dilute solutions in the temperature range 288 K-313 K. The limiting values of ion mobility and changes in the energies of translation of water molecules from ions’ hydration shell have been found. At elevated temperatures, ΔE _tr ⁰ increases for both ions in direct proportion to the crystallographic radius of the latter. Ion hydration numbers at 298 K have been calculated. The results of this study are interpreted in the light of Samoilov’s theory on positive and negative hydration of ions.Original Russian Text Copyright © 2004 by L. T. Vlaev and S. D. Genieva__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 870–876, September–October, 2004.     

Chromium Electrodeposition Kinetics in Solutions of Cr(III) Complex Ions

An equation of polarization curve for electroreduction of Cr(II) ions as intermediates in electrolysis of aqueous solutions of Cr(III) complex ions is deduced and analyzed. Kinetic parameters for the discharge of Cr(II) ions are determined. The theoretical results are compared with experimental data obtained from chromium deposition on a rotating disk electrode from Cr(III) solutions containing formate and oxalate.     

Low-Temperature Catalytic Oxidation of Sulfide Ions in Aqueous Solutions on a Ni-Oxide System

Catalytic oxidation of sulfide ions in aqueous solutions by air oxygen has been investigated using a Ni-oxide system as a catalyst. The kinetics and the selectivity of the oxidation process were studied by varying the pH, catalyst amount and reaction temperature. A reduction/oxidation mechanism of the reaction has been supposed comprising interaction between the surface active oxygen of the catalyst and HS^– and reoxidizing of the reduced catalyst by the dissolved oxygen. The results obtained show that the Ni-oxide system is a promising catalyst for practical application.     

Models for the Immediate Environment of Ions in Aqueous Solutions of Neodymium Chloride

Radial distribution functions of neodymium chloride aqueous solutions in a wide range of concentrations under ambient conditions are calculated from experimental data obtained earlier via X-ray diffraction analysis. Different models of the structural organization of the system are developed. The optimum versions are determined by calculating theoretical functions for each model and comparing their fit to the experimental functions. Such quantitative characteristics of the immediate environment of Nd³⁺ and Cl^? ions as coordination numbers, interparticle distances, and varieties of ion pairs are determined. It is shown that the average number of water molecules in the first coordination sphere of the cation falls from 9 to 6.2 as the concentration rises. The structure of the systems over the whole range of concentrations is determined by ion associates of the noncontact type.     

Ligand Exchange Reactions for the Fluorescent Detection of Nanogram Amounts of Metal Ions on TLC Plates

Abstract

A number of metal ions have been separated as their diethyldithiocarbamate chelates by thin-layer chromatography and detected by means of a ligand exchange reaction between a metal/calcein complex and the diethyldithiocarbamate chelate. Visual detection limits, after development, are 0.1 to 2 ng per spot for the metal ions studied. The potential of this new method for the fluorescent analysis of metal ions is discussed. It is particularly promising as a simple field method. Spiked natural water samples are analyzed to demonstrate its usefulness.