NaI Solutions Research Articles

Synthesis of zinc sulphide nanoparticles by thiourea hydrolysis and their characterization for electrochemical capacitor applications

A simple method is applied to prepare nanocrystalline ZnS using zinc nitrate and thiourea in aqueous solutions. Cubic sphalerite ZnS is obtained in phase pure form when S/Zn mole ratio is 1 and 2. A mixed phase of hexagonal wurtzite and cubic sphalerite ZnS is obtained when S/Zn mole ratio is 4. Transmission electron microscope and X-ray diffraction confirm the formation of ZnS nanoparticles. These nanoparticles are immobilized on the surface of paraffin impregnated graphite electrode (PIGE) and electrochemical characterization in neutral solutions by cyclic voltammetry revealed that the material is ideal to be used as electrode in electrochemical double layer capacitors. The most singularly interesting result is the voltages observed in 0.1 M LiCl, NaCl, NaI and KI solutions. They are 3.0, 2.7, 2.0 and 1.8 V versus Ag/AgCl and significantly higher than the expected value of 1.23 V (pH ∼ 7) in aqueous medium. Such a large voltages are usually obtained for non-aqueous electrolytes and the present study showed a surprising and significant interesting result that can be owed to the over potentials of H 2/O 2/Cl 2 gas evolutions. An attempt to understand these highly significant results in terms of band edge bendings (conduction band and valence band) associated with the positive and negative ion adsorption at the interface of semiconductor ZnS/solution is made.

Is There an Anionic Hofmeister Effect on Water Dynamics? Dielectric Spectroscopy of Aqueous Solutions of NaBr, NaI, NaNO3, NaClO4, and NaSCN

A systematic study of the dielectric relaxation spectra of aqueous solutions of NaBr, NaI, NaNO(3), NaClO(4), and NaSCN has been made over a wide range of frequencies (0.2 < or = nu/GHz < or = 89) and solute concentrations (0.05 < or = c/M < or = 1.5) at 25 degrees C. The spectra could be adequately described by a single Cole-Cole (CC) process, symmetrically broadened relative to that of pure water. However, similar quality fits were also obtained with a three-Debye-process (3D) model consisting of a small ion-pair contribution at lower frequencies and two solvent relaxations at higher frequencies. Assuming the ions to be solvent separated, the 3D model provided estimates of their association constants and their rate constants for formation and dissociation. The bulk water relaxation times obtained from both models showed almost no dependence on the nature of the anion. Nevertheless, there were subtle differences in the concentration dependences of the relaxation times which correlated with some, but not all, of the anion properties that are believed to be relevant for explaining the anionic Hofmeister series.

Evidence for an Enhanced Hydronium Concentration at the Liquid Water Surface

The recent demonstration of enhanced surface anion concentrations for aqueous electrolyte solutions strongly contrasts current textbook descriptions. Small cations are still expected to be repelled from the surface, but recent simulations predict that hydronium (H3O+) cations are instead preferentially adsorbed at the interface. Here we describe a comparative second harmonic generation (SHG) study of aqueous solutions of hydriodic acid (HI) and alkali iodides (NaI and KI), which establish lower limits of 55% and 34% larger surface iodide concentrations for HI solutions relative to NaI and KI solutions, respectively. This result implies that hydronium ions must exist in much higher densities near the liquid surface than do the alkali ions, in support of the theoretical predictions.

Molecular Dynamics Simulation of Aqueous NaF and NaI Solutions near a Hydrophobic Surface

We present results from molecular dynamics simulation of aqueous solutions of alkali halide salts (NaI and NaF) at the interface with hydrophobic objects. The primary objective of this study is to investigate the structural properties of the salt solutions at the hydrophobic surface. An alkane crystal has been taken as the parent model for a hydrophobic surface. A hexagonal hole was created on it, which was half a nm deep and 2.5 nm wide. The density distributions of different species (water, anions, and cations) are studied as a function of distance from the surface. While iodide prefers the interface, the fluoride ions stay inside the bulk water region. The higher concentration of iodide ions at the interface drags sodium counterions to the interface. It also decreases the water density at the interface because of steric effects of the iodide ions. The number of contacts between the surface carbons and water decreases in the case of NaI solutions but is unchanged for NaF solutions. The orientation of the water-ion and the water-water hydrogen bond vector orientations near the interface is discussed in detail.

The effect of hydration of ions of inorganic salts on the shape of the Raman stretching band of water

The shape of the Raman stretching band of water molecules in aqueous solutions of electrolytes KBr, KCl, KI, NaCl, and NaI is studied. It is confirmed that the characteristics of the stretching band strongly depend on the concentration and type of salt. The behavior of different parameters of the band is explained in terms of the theory of hydration of salts. © 2005 Pleiades Publishing, Inc.

Apparent molar volumes and adiabatic compressibilities of L-glycine in aqueous solutions of (CH3)4NI, NaBr and NaI at 298.15 K

Apparent molar volumes and adiabatic compressibilities of L-glycine in aqueous solutions of (CH3)4NI, NaBr and NaI at 298.15 K

The effect of electrolyte on the morphology of vesicles composed of the dialkyl polyoxyethylene ether surfactant 2C 18E 12

Small-angle neutron-scattering (SANS) studies were performed on vesicles composed of 1,2-di- O-octadecyl- rac-glyceryl-3-(ω-methoxydodecaethylene glycol), in deuterium oxide (D 2O) solutions with various ionic strengths of LiCl, NaCl and NaI. Gross vesicle morphologies, examined using freeze-fracture electron microscopy, showed that NaCl promoted the formation of multilamellar vesicles. Model fitting of the SANS data showed changes in bilayer parameters such as thickness and repeat spacings, in response to the presence of ions in the bulk solution. 2C 18E 12 vesicles in D 2O are shown to exist as predominantly unilamellar structures with a bilayer thickness of ∼51 Å. Vesicles in increasing concentrations of LiCl and NaCl exhibit decreased layer thickness and increased lamelarity. Little change was observed for vesicles formed in NaI solutions. We suggest that these changes result from intrusion of E 12 headgroups into the alkyl chain region of the vesicle bilayers, in response to the increase in concentration of ions present and their charge density.

Single Ionic Volumes in Acetonitrile–Organic Cosolvent Mixtures at 298.15 K

Abstract Densities of binary nonaqueous mixtures of acetonitrile (AN) with 2-methoxyethanol (ME), N,N-dimethylacetamide (DMA) and propylene carbonate (PC) were determined over the whole composition range at 298.15 K. The excess molar volumes and the partial molar volumes of both components were calculated from these data. Densities of solutions of NaI, NaBPh4 and Ph4PI in solvent mixtures AN + ME and AN + DMA and of NaI solutions in mixtures of AN + PC were measured over the whole composition range of the mixed solvents at an electrolyte concentration equal 0.05 mol dm−3. From these densities, apparent molar volumes of electrolytes and ions were evaluated and analyzed. The relationship between the apparent molar volumes of ions and (κT /ε) parameter was tested and discussed.

Probing the Molecular Structure and Bonding of the Surface of Aqueous Salt Solutions

The surfaces of aqueous solutions of NaF, NaCl, NaBr, and NaI have been examined using vibrational sum-frequency spectroscopy. Spectra of these salts in mixtures of HOD/H2O/D2O have been used to provide insight into how simple salts alter the hydrogen bonding structure of water in the surface region. As the anion is changed, the observed interfacial hydrogen bonding also changes, indicating the presence of anions in the interfacial region. The isotopic dilution experiments performed on each solution enable separation of the contributions arising from interfacial water with differing degrees of hydrogen bonding. Frequency shifts in the peaks attributed to tetrahedrally coordinated water molecules within the interfacial region display the structure-making characteristics of F- and the structure-breaking characteristics of Cl-, Br-, and I-. However, water molecules residing in the topmost surface layer show minimal perturbation by the presence of these anions as probed by the characteristics of the donor OH mode of water molecules that straddle the air/water interface. These results indicate a significantly diminished population of the anions at the uppermost layer of the surface region.

The study of the filling behaviour of carbon nanotubes using the radioactive-tracetechnique

The washing and elution behaviour of carbon nanotubes (CNTs), following soaking in radioactive(125I)NaI and(110mAg)AgNO3 solutions, was investigated using the radioactive-trace technique. High-resolution electronmicroscopy and x-ray energy dispersive spectroscopy observations showed the validity of fillingCNTs with soluble inorganic salts using this simple method. A great difference in the release of(125I)NaI and(110mAg)AgNO3 from CNTs was found and discussed in terms of the chemical transformation occurring inCNT cavities. The amount of the filled materials was also estimated using theradioactive-trace technique.

Aggregation of ions in methanol–water solutions of sodium halides

Molecular-dynamics simulations have been performed for NaCl and NaI solutions in methanol–water mixtures to investigate an association of ions. Molecules of water and methanol have been represented by flexible models. Iodide ion was considered as charged Lennard-Jones sphere, whereas interactions of sodium and chloride ions were described by either the sum of Coulomb and Lennard-Jones potential or the potentials derived from ab initio calculations. Analysis of aggregation has been based on radial distribution functions, association constants, geometry and lifetime of the ion clusters. Computed association constants are in good agreement with experimental data. Clustering of either unlike or like ions occurs in all simulated systems and the ratio of free ions to aggregated ions is independent of the solvent composition.

Vibrational relaxation of liquid water in ionic solvation shells

Femtosecond two-color pump–probe spectroscopy is used to measure the vibrational lifetime of the O–H stretch vibration in solutions of KF, NaCl, NaBr, and NaI in HDO:D 2O. We observe a slow component (roughly 2–4 times slower than in HDO:D 2O) in the decay of the absorption change, which is due to O–H groups that are hydrogen bonded to the dissolved anions. The time constant of this slow component depends on the nature of the anions and is observed to decrease with temperature, in contrast with the temperature dependence of the relaxation of the OH stretch vibration in pure HDO:D 2O.

RETENTION OF IONS IN A MAGNETIC CHROMATOGRAPH USING HIGH-INTENSITY AND HIGH-GRADIENT MAGNETIC FIELDS

The control of the retention and separability of samples to be analyzed with high performance liquid chromatography systems is difficult, and usually requires exchanging of the mobile phase and/or the column. We developed a magnetic chromatography (MC) system, which does not require regular exchanging of the mobile phase and/or the column, and uses a continuous-flow system to separate multiple ionic species with different magnetic properties. To demonstrate experimentally the feasibility of such an MC system, we measured the retention of ions in the MC system for aqueous solutions of either pure NaI, CuSO4, NiCl2, CrCl3, or CoCl2. We applied magnetic fields varying from 0 to 3 T to the aqueous solution of transition element cations and anions flowing in an MC system, and demonstrated that the retention time was delayed by about 20 min, and that for Co(II) the chromatogram broadened with increase in the applied magnetic field intensity (H). Furthermore, our results suggest that for ionized transition elements with a larger Bohr magneton number, the retention time in MC systems becomes longer. We derived experimentally a retention factor, k, that can be simply expressed in terms of an MC parameter, p MCH , which is the product of the Bohr magneton number, the concentration of the cations, and H. The MC parameter can be used to correlate all experimental data in terms of k, as k= 0.0014p MCH 1.47. Hence, k is proportional to about 3/2 power of the MC parameter. We therefore confirmed that there is a significant effect of high-intensity, high-gradient magnetic fields on the behavior of paramagnetic cations in water.

Effect of charge transfer on bandshape analysis for low‐wavenumber Raman spectra of alkali metal halide aqueous solutions

AbstractLow‐wavenumber Raman scattering spectra of aqueous NaI solutions were measured with 488.0 and 514.5 nm excitation. The enhancement of the spectral intensity caused by I− ion does not depend on the excitation wavelength. We can apply the phenomenological analysis to the low‐wavenumber Raman spectra of alkali metal halide aqueous solutions even when the ‘pre‐resonance effect’ of proton transfer changes the mode intensity. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Effect of sodium halides on the structure of methanol-water mixture — MD simulation studies

Molecular dynamics (MD) simulations have been performed for methanol-water solutions of NaCl and NaI to examine a possible effect of ions on the structure of the bulk solvent. Radial distribution functions (RDF), running integration numbers and residence times in the co-ordination shells of solvent molecules in the bulk of the electrolyte solutions have been compared with those obtained for the corresponding binary solvents. In the analysis a distinction was made between like- and unlike-neighbours of solvent molecules. No effect from the presence of ions on the position of the first peak of the RDFs has been found but their heights depend on either the methanol content or the salt addition. A linear dependence of the co-ordination numbers of solvent molecules on x M has been found. An effect of sodium halides on the bulk solvent is only observed at a methanol mole fraction x M = 0.1.

MD Simulation Studies of Selective Solvation in Methanol−Water Mixtures: An Effect of the Charge Density of a Solute

MD simulations have been performed for NaCl, NaI, and fictitious solutions of discharged counterparts of Na+ and Cl- ions to investigate an effect of the charge density of a solute on its solvation in methanol−water mixtures. Solvent−solvent interactions have been described in terms of flexible models, whereas solutes have been considered as charged or uncharged Lennard-Jones spheres. An analysis of solvation shells has been based on radial distribution functions, angular distributions, coordination numbers, and residence times of solvent molecules. Preferential solvation of anions by methanol molecules becomes less pronounced with decreasing charge density of a solute and vanishes for the discharged chloride ion. In contrast to preferential hydration of Na+ in water deficit solvents, its uncharged counterpart Na0 is preferentially solvated by methanol molecules over the whole range of solvent composition. Results for NaCl solution have been compared with those obtained with ab initio ion−solvent potentials and the same model of solvent molecules. The type of ion−solvent potential has small effect on the structure and composition of ionic shells, but its influence on the persistence of the coordination shells is more noticeable.

Determination of phase transfer parameters for the uptake of HNO3, N2O5 and O3 on single aqueous drops

A new method for the investigation of phase transfer on gas–liquid interfaces is introduced. It allows the in situ analysis of single drops that are produced inside a flow tube gas phase reactor. Using this technique, the uptakes of HNO3 and N2O5 on pure water as well as the uptake of O3 on NaI solutions were examined. For HNO3, uptake coefficients γ in the range from 3.1 × 10−3 to 11.8 × 10−3 were measured dependent on the total pressure at 298 K. For N2O5, γ = 3.7–9.1 × 10−3 at 293 K was obtained. For iodide concentrations ranging from 2 × 10−2 M to 4 M, the uptake coefficient of O3 was in the range of 2.0 × 10−4 to 1.5 × 10−2. After correction for the effect of the gas phase diffusion by means of a computer model, the mass accommodation coefficients α were derived from these γ-values, resulting in αHNO3 > 3 × 10−2, αN2O5 = (1.1−0.6 + 1.2) × 10−2, and αO3 > 2 × 10−2. Additionally, the ratio of the rate constants for the reactions of NO2+ with iodide and water, respectively, was determined to be 40 ± 12.

A unified ion chromatographic system for the determination of acidity and alkalinity.

A unified ion chromatographic (IC) system was developed for the determination of acidity or alkalinity. Separation column used was a reversed-phase ODS packed column, which had been modified by saturating it with lithium dodecylsulfate. A slightly acidified LiCl (50 mM LiCl and 0.05 mM H2SO4) aqueous solution was used as the eluent. By conditioning the separation column in this way, both H+ and Li+ ions became bound to the stationary phase. Dodecylsulfate groups with Li+ counterions acted as cation-exchange sites for the separation of hydrogen ions (free acidity determination). The remaining dodecylsulfate groups, with H+ counterions acted as a titrant, which reacted with basic species (total alkalinity determination). The acidity or alkalinity of each sample was measured according to the change in conductance from the eluent baseline level. A positive peak was observed from those samples with a free acidity greater than their total alkalinity, due to the separation/elution of free H+ ions. A negative peak was observed from those samples with a free acidity less than their total alkalinity. This was due to an equivalent amount of eluent H+ ions being re-supplied to the stationary phase while the "solid titrant" consumed by the acid-base reaction was regenerated. The retention time for the peak corresponding to the acidity or alkalinity was governed by the retention time for H+ ions in this IC system. Samples with a free acidity greater than 2.25 microM (tested by determination of H+ ions in pure water in equilibrium with atmospheric CO2) could be analyzed by this method. A very similar detection level was obtained for alkalinity (tested by analyzing standard aqueous NaHCO3 solutions). Aqueous solutions of some strong-acid/strong-base inorganic salts were found to be slightly alkaline. This was measured as a percentage, relative to an NaHCO3 solution at the same concentration. Solutions of NaClO4, Na2SO4, NaI, NaNO3, and NaCl, gave comparative alkalinity values of 8.75%, 1.83%, 0.42%, 0.35%, and 0.33%, respectively.

Enthalpic interactions of glycine in aqueous sodium halide solutions

Dilution enthalpies of glycine in aqueous NaF and NaI solutions of various molalities at 298.15 K have been determined, respectively, by mixing flow microcalorimetry. The results have been analyzed according to the modified McMillan–Mayer model to obtain homogeneous enthalpic interaction coefficients. The effect of the anions on enthalpic pair-wise interaction coefficients has been discussed from the point of view of electrostatic interaction and structural interaction.

Direct measurement of ion evaporation kinetics from electrified liquid surfaces

When concentrated solutions of NaI in formamide with electrical conductivities K larger than 1.1 S/m are electrosprayed from a Taylor cone-jet in a vacuum, ions are evaporated at substantial rates from the surface of the meniscus and the drops. This constitutes a new source of ions and nanoparticles, where the relative importance of these two contributions is adjustable. The currents of ions are measured independently from those associated with drops by a combination of stopping voltage analysis and preferential scattering in a gas background. The magnitude E of the electric field at the surface of the drops and at the apex of the cone-jet is controlled through the electrical conductivity K of the liquid and its flow rate Q through the jet. E is related through available scaling laws for Taylor cone-jets to the ratios K/Q or I/Q, where I is the current of drops emitted by the jet. Ion currents are very small or null at typical K/Q values used in the past. A relatively small initial ion current is attributed to a few particularly sharp features present, perhaps associated with small satellite drops. At still higher K/Q this first ionization source saturates, and ion evaporation from the main drops begins to dominate (E∼1 V/nm). E can then be determined with little ambiguity, and the associated ion current is also measured over a broad enough range of electric fields to determine the ionization kinetics. At still higher K/Q the ion current from the drops approaches saturation, and ion evaporation directly from the meniscus becomes dominant. The total spray current then presents the anomaly of increasing rapidly at decreasing liquid flow rate. The ion current from the meniscus can also be measured in this regime over a broad range of K/Q, with qualitative agreement with the ionization measurements from the drops. But the relation established between K/Q and E becomes suspect because ion and drop currents are now comparable. A third approach to infer the ionization rate is based on the related disappearance of Coulomb explosions of the drops above a critical K/Q. These results are congruent with the model of Iribarne and Thomson, with an activation barrier for ion evaporation equal to 1.7 eV−(e3E/4πε0)1/2.