NaI Solutions Research Articles

Simulation of the flow of aqueous solutions through carbon nanotubes

The flow of aqueous NaCl and NaI solutions through carbon nanotubes is treated by extensive molecular dynamics simulations. The dependence of diverse transport features on the solute specificity, the nanotube geometry, and the various atomic models employed, including polarizability, is addressed in detail. The interpretations are developed in conjunction with the structural details of the solution and the energy barriers the solute components have to overcome.

Generation, propagation, and breaking of an internal wave beam

We report upon an experimental study of internal gravity waves generated by the large-amplitude vertical oscillations of a circular cylinder in uniformly stratified fluid. Quantitative measurements are performed using a modified synthetic schlieren technique for strongly stratified solutions of NaCl or NaI. The oscillatory forcing leads to the development of turbulence in the region bounding the cylinder. This turbulence is found to be the primary source of the observed quasimonochromatic wave beams, whose characteristics at early times differ from theoretical predictions and experimental investigations of waves generated by small-amplitude cylinder oscillations. In particular, their wavelength is set by the Ozmidov scale rather than the size of the cylinder. The wave frequency is set by the buoyancy frequency N if the cylinder frequency is larger or much less than N. Otherwise it is set by the cylinder oscillation frequency. Over long times the finite-amplitude waves that have propagated away from their source are observed to break down and the process is examined quantitatively through conductivity probe measurements and qualitatively through unprocessed synthetic schlieren images. From an analysis of the location of wave breakdown we determine that the likely mechanism for breakdown is through parametric subharmonic instability. This conclusion is supported by fully nonlinear numerical simulations of the evolution of a temporally, although not spatially, monochromatic internal wave beam.

Direct Measurement of Vertical Electron Binding Energies of Solvated Electrons in Methanol and Ethanol

Abstract Time-resolved photoelectron spectroscopy at ultralow kinetic energy was applied to liquid beams of NaI solutions in methanol and ethanol. Solvated electrons were formed from I− ions in these solutions by charge transfer to solvent reactions. The vertical electron binding energies of the solvated electrons were determined for the first time. Both of the binding energies were found to be 3.10 ± 0.1 eV. This is in reasonable agreement with the dielectric continuum model of solvated electrons using the previously measured vertical binding energy of a hydrated electron. This indicates that the cavity radii of solvated electrons in water, methanol, and ethanol are approximately the same (0.33–0.35 nm).

Molecular dynamics simulations of ion transport through carbon nanotubes. I. Influence of geometry, ion specificity, and many-body interactions

Extensive molecular dynamics simulations of the flow of aqueous NaCl and NaI solutions through carbon nanotubes are presented, evidencing the dependence of diverse transport features on the solute specificity, the nanotube geometry, and the various atomic models employed, including polarizability. The simulated properties are in agreement with published results, indicating that ion translocation sets in only for nanotubes with chiralities higher than (7,7), and extend the explanation of the mechanisms governing ion transport to larger chiralities. The interpretation of the various dynamic quantities is developed in close connection with the structural details of the solution and the energy barriers the solute components have to overcome. Also, the role and relevance of water and ion polarizabilities are discussed in detail.

Molecular dynamics simulations of nonpolarizable inorganic salt solution interfaces: NaCl, NaBr, and NaI in transferable intermolecular potential 4-point with charge dependent polarizability (TIP4P-QDP) water.

We present molecular dynamics simulations of the liquid-vapor interface of 1M salt solutions of nonpolarizable NaCl, NaBr, and NaI in polarizable transferable intermolecular potential 4-point with charge dependent polarizability water [B. A. Bauer et al., J. Chem. Theory Comput. 5, 359 (2009)]; this water model accommodates increased solvent polarizability (relative to the condensed phase) in the interfacial and vapor regions. We employ fixed-charge ion models developed in conjunction with the TIP4P-QDP water model to reproduce ab initio ion-water binding energies and ion-water distances for isolated ion-water pairs. The transferability of these ion models to the condensed phase was validated with hydration free energies computed using thermodynamic integration (TI) and appropriate energy corrections. Density profiles of Cl(-), Br(-), and I(-) exhibit charge layering in the interfacial region; anions and cation interfacial probabilities show marked localization, with the anions penetrating further toward the vapor than the cations. Importantly, in none of the cases studied do anions favor the outermost regions of the interface; there is always an aqueous region between the anions and vapor phase. Observed interfacial charge layering is independent of the strength of anion-cation interactions as manifest in anion-cation contact ion pair peaks and solvent separated ion pair peaks; by artificially modulating the strength of anion-cation interactions (independent of their interactions with solvent), we find little dependence on charge layering particularly for the larger iodide anion. The present results reiterate the widely held view of the importance of solvent and ion polarizability in mediating specific anion surface segregation effects. Moreover, due to the higher parametrized polarizability of the TIP4P-QDP condensed phase {1.31 A(3) for TIP4P-QDP versus 1.1 A(3) (TIP4P-FQ) and 0.87 A(3) (POL3) [Ponder and Case, Adv. Protein Chem. 66, 27 (2003)]} based on ab initio calculations of the condensed-phase polarizability reduction in liquid water, the present simulations highlight the role of water polarizability in inducing water molecular dipole moments parallel to the interface normal (and within the interfacial region) so as to favorably oppose the macrodipole generated by the separation of anion and cation charge. Since the TIP4P-QDP water polarizability approaches that of the experimental vapor phase value for water, the present results suggest a fundamental role of solvent polarizability in accommodating the large spatial dipole generated by the separation of ion charges. The present results draw further attention to the question of what exact value of condensed phase water polarizability to incorporate in classical polarizable water force fields.

Photooxidation of Halides by Chlorophyll at the Air−Salt Water Interface

Glancing angle laser-induced fluorescence was used to follow the kinetics of chlorophyll loss at the air-salt water interface under the influence of visible radiation. Aqueous solutions of NaCl, NaBr, NaI, KNO(3), and NaNO(2) in a range of concentrations up to approximately 1 M were used as substrates. The first-order reaction rate depends linearly on salt concentration for the halide salts but does not vary with concentration for nitrate or nitrite salts. At the same salt concentration, the chlorophyll loss rate is greatest for the bromide-containing solutions, followed by those containing chloride and then iodide. The results are consistent with a mechanism in which photoproduced chlorophyll cations are reduced by halide anions and subsequently react with the halogen atoms thus produced. This mechanism gives a novel route for gas-phase halogenated species, and possibly nitrogen oxides, to be released to the marine boundary layer.

Structure-thermodynamics relation of electrolyte solutions

The structure of aqueous LiCl, NaCl, KCl, CsCl, KF, and NaI solutions is calculated by molecular dynamics (MD) simulations of the frequently employed Dang force-field in SPC/E water. By using liquid state theory, we integrate the structure to obtain the electrolytes' osmotic coefficient phi and systematically investigate force-field quality and structural consequences to ion-specific bulk thermodynamics. The osmotic coefficients phi(chi) calculated from the exact compressibility route for the cation-Cl(-) force-fields match experiments for concentrations rho approximately < 2M, while NaI and KF parameters fail. Comparison of phi(chi) with phi(v) from the virial route, which relies on the pair potential approximation, shows that many-body effects become important for all salts above rho approximately 0.5M. They can be efficiently corrected, however, by employing a salt-type and rho-dependent dielectric constant epsilon(rho), generalizing previous observations on NaCl only. For physiological concentrations, rho approximately < 0.5M, the specific osmotic behavior is found to be determined by the short-ranged cation-anion pair potential only and is strongly related to the second virial coefficient of the latter. Presented methods and findings, based on simple integrations over the electrolyte structure, enable efficient MD force-field refinement by direct benchmarking to the sensitive electrolyte thermodynamics, instead to noncollective, single ion properties.

Ion specific effects on phase transitions in protein solutions

A recent Monte Carlo simulation determined the potential of mean force between two lysozyme molecules in various aqueous solutions [M. Lund, Phys. Rev. Lett. 100, 258105 (2008)]. The study involved a combination of explicit solvent and continuum model simulations and showed that there are significant ion-specific protein-protein interactions due to hydrophobic patches on the protein surfaces. In this paper we use the results of their study to determine the phase diagram for lysozyme for aqueous solutions of NaCl and NaI. Two of the three phase diagrams have a stable fluid-fluid critical point, while the third has a slightly metastable critical point. This results from a secondary extremum in the potential associated with a repulsive interaction. This repulsive interaction reduces the effective range of the attractive interaction and produces a metastable critical point. We compare the results of one of these phase diagrams with that for a model that includes ion-dispersion forces, but does not contain solvent structural effects.

Control growth of uniform platinum nanotubes and their catalytic properties for methanol electrooxidation

Uniform platinum nanotubes have been synthesized by directly mixing Ag nanowires and H 2PtCl 6 in saturated NaI solutions at room temperature. The crystal structure of the obtained Pt nanotube has been investigated in detail by field-emission scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Furthermore, their electrocatalytic behaviors for methanol oxidation in alkaline media have also been studied. Compared with conventional Pt/C catalysts, these hollow nanostructures possess high electrochemical active areas and demonstrate higher current densities.

Ion Specific Protein Assembly and Hydrophobic Surface Forces

Large anions are attracted to hydrophobic surfaces while smaller, well solvated ions are repelled. Using a combination of explicit solvent and continuum model simulations we show that this leads to significant ion-specific protein-protein interactions due to hydrophobic patches on the protein surfaces. In solutions of NaI and NaCl we calculate the potentials of mean force and find that the resulting second virial coefficients for lysozyme correspond well with experiment. We argue that ionic interactions with nonpolar surface groups may play an important role for biomolecular assembly and Hofmeister-type effects.

Photoionization of Sodium Salt Solutions in a Liquid Jet

A liquid microjet was employed to examine the gas/liquid interface of aqueous sodium halide (Na+X−, X = Cl, Br, I) salt solutions. Laser excitation at 193 nm produced and removed cations of the form H+(H2O)n and Na+(H2O)m from liquid jet surfaces containing either NaCl, NaBr or NaI. The protonated water cluster yield varied inversely with increasing salt concentration, while the solvated sodium ion cluster yield varied by anion type. The distribution of H+(H2O)n at low salt concentration is identical to that observed from low-energy electron irradiated amorphous ice, and the production of these clusters can be accounted for using a localized ionization/Coulomb expulsion model. Production of Na+(H2O)m is not quantitatively accounted for by this model but requires ionization of solvation shell waters and a contact ion/Coulomb expulsion mechanism. The reduced yields of Na+(H2O)m from high concentration (10−2 and 10−1 M) NaBr and NaI solutions indicate a propensity for Br− and I− at the solution surfaces and interfaces. This is supported by the observation of multiphoton induced production and desorption of Br+ and I+ from the 10−2 and 10−1 M solution surfaces.

Comparison of the Solvation Structure of Polarizable and Nonpolarizable Ions in Bulk Water and Near the Aqueous Liquid−Vapor Interface

All-atom molecular dynamics simulations are performed on bulk and aqueous liquid−vapor interfacial systems for neat water and 1 M solutions of NaCl, CsCl, and NaI to more quantitatively characterize ion solvation in these environments and to more fully elucidate trends accompanying the introduction of ion polarizability in the context of a polarizable water potential. In the bulk systems, computed densities, hydration free energies, compressibilities, coordination numbers, and a variety of two- and three-atom distribution functions show that the polarizable ions exhibit smaller effective radii, a slightly increased propensity for bulk hydration (particularly for the anions), and no biased preference for contact ion or solvent-separated ion pairing relative to the corresponding nonpolarizable cases. For the interfacial systems employing long (>40 ns) sampling times, we obtain good convergence for a variety of interfacial characteristics such as slab thicknesses and interfacial widths, depth-dependent water and ion density profiles, surface excesses, and depth-dependent transverse distribution functions. We compare interface characteristics derived from fits to both a hyperbolic tangent and error function form and find negligible differences in the resulting parameters. For all three salt solutions, we observe that ion polarizability leads to a slight contraction of the liquid slab and simultaneous expansion of the interfacial thickness arising from the strong surface enhancement of polarizable anions. Computed values of the surface excess show that for the present Drude ion models and polarizable fluctuating charge water model the introduction of ion polarizability consistently leads to a slightly less-negative surface excess, implying a significant but incomplete cancellation of the surface enhancement by the corresponding subsurface anion depletion. Depth-dependent, transverse correlation functions for the oxygen−oxygen separation indicate slight water relaxation at the interface of both neat TIP4P-FQ water and the corresponding salt solutions.

Iodide ions control galvanic replacement growth of uniform rhodium nanotubes at room temperature

Hollow rhodium nanotubes with uniform and perfect structures have been successfully synthesized through the replacement reaction between Ag nanowires and RhCl3 in saturated NaI solutions at room temperature, and the main effect of iodide ions is found to reduce the redox potential of Ag species and resolve the formed AgI precipitation.

Characterization of α-carrageenan solution behavior by field-flow fractionation and multiangle light scattering

The salt mediated molecular conformation change of alpha ( α)-carrageenan was studied in 0.1 M solutions of NaCl, NaI, and KCl. Asymmetric Field-Flow Fractionation with multiangle laser light scattering (AFFF/MALLS) detection was used to determine the average molecular weight, radius of gyration, and hydrodynamic radius which were in turn used to calculate the molecular density. In the presence of 0.1 M NaCl, an inert salt that does not promote gelation, α-carrageenan has a denser structure compared to κ-carrageenan of a similar molecular weight. A distinct and dramatic increase in the molecular weight (factor of 2) was observed for α-carrageenan in 0.1 M NaI compared to 0.1 M NaCl. This combined with only a slight change in the radius of gyration, suggests intermolecular interaction to a more compact structure (e.g., coaxial helices). A similar increase in molecular weight is observed in 0.1 M KCl, accompanied with an approximate 50% increase in the radius of gyration as well as an increase in polydispersity. This may also be attributed to intermolecular interaction with helix formation (coaxial or lateral) or may be due to K + cations interacting with naturally occurring residual ι-carrageenan in the sample. As previously reported for other carrageenans the random coil to helix transition of α-carrageenan appears to be stabilized by K + cation or I − anion in an aqueous environment.

Interfacial Interactions of DCl with Salty Glycerol Solutions of KI, NaI, LiI, and NaBr

Gas−liquid scattering experiments are used to explore the role of interfacial ions in controlling collisions and reactions of DCl molecules with ∼2.5 M KI, NaI, LiI, and NaBr glycerol solutions. DCl molecules that thermalize upon collision with the surface of each solution follow one of three pathways: they may desorb immediately as DCl, undergo D → H exchange in the near-interfacial region and desorb as HCl, or dissolve and dissociate in the bulk. We find that each salt amplifies the differences among the channels: the fraction of DCl molecules that desorb intact increases from 9% for pure glycerol to 18% on average for the salt solutions, interfacial DCl → HCl exchange increases from 3 to 7%, and bulk dissolution drops from 87 to 75%. Dissolved ions may enhance nonreactive DCl desorption and interfacial D → H exchange by tying up glycerol OH groups, which will impede both DCl−OH bonding and migration of D+ and H+ away from Cl- after DCl ionization. Despite differences in the sizes of the ions and thei...

Infrared spectroscopy of aqueous ionic salt solutions at low concentrations

The analysis by infrared spectroscopy of aqueous solutions of the binary inorganic salts NaI and NaCl and the ternary salts CaCl2 and BaCl2 at concentrations from 1000 to 2 mM was carried out to complement a previous study done at higher concentrations on nine binary salts (alkali halides) and one ternary salt (MgCl2) [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001)]. These salts are completely ionized in aqueous solutions, forming monoatomic species that do not absorb IR but that perturb the surrounding water, modifying its spectrum. The factor analysis of the spectra revealed that all these salt solutions were composed of two water types: pure water and salt solvated water. The authors obtained pure salt solvated water spectra for all the salts using an extrapolation technique. The water types obtained are constant for the binary and ternary salts down to 2 mM. For the binary salts, we determine that 5.0 and 4.0 water molecules are solvated to the Na+-Cl- and Na+-I- ion pairs, respectively. These numbers are the same as that obtained at higher concentrations. For the new ternary salts, we find that 6.0 and 8.0 water molecules are solvated to Ca++-(Cl-)2 and Ba++-(Cl-)2 ion pairs, respectively. These numbers are higher than the four water molecules solvated to Mg++-(Cl-)2 ion pairs determined previously, but show a progression that follows their atomic numbers. These results constitute new experimental results on "simple" systems whose molecular organization is still a matter of debate. The IR method that probes the system at the molecular level is a method different than the macroscopic ones that give the activity coefficients. The IR gives direct observation at the molecular level of the strong ion-water interactions that are often neglected and its water structure not considered in macroscopic methods. The present results and their analysis together with those obtained by other methods will facilitate the determination of the organization of these aqueous systems.

Molecular Dynamics Study of Gas−Liquid Aqueous Sodium Halide Interfaces. II. Analysis of Vibrational Sum Frequency Generation Spectra

The vibrational sum frequency generation (SFG) spectra of gas−liquid interfaces of NaCl and NaI aqueous solutions are computed and analyzed by molecular dynamics (MD) simulations using a flexible and polarizable molecular model. The MD calculations have reproduced the experimental features of SFG spectra, including observed perturbation on the NaI spectra in contrast to little perturbation on NaCl. Analysis of the nonlinear susceptibility revealed that the intermolecular correlation has a significant contribution to the vibrationally resonant amplitude, which largely distorts the generally accepted relationship between the SFG intensity and orientation of individual molecules. In NaI solutions, modest enhancement of ssp intensity in the 3400 cm-1 region is thereby elucidated by this mechanism. Regarding the sps spectra, three spectral components are assigned and elucidated. Calculated remarkable enhancement in the 3400−3800 cm-1 region for NaI solutions is found to be sensitive to the electric double laye...

Viscosity of Aqueous Electrolyte Solutions at High Temperatures and High Pressures. Viscosity B-coefficient. Sodium Iodide

The viscosity of seven (0.062, 0.166, 0.456, 0.552, 1.754, 3.062, and 4.700) mol·kg-1 binary aqueous NaI solutions has been measured with a capillary-flow technique. Measurements were performed at pressures up to 30 MPa. The range of temperature was from (298 to 575) K. The total uncertainty of viscosity, pressure, temperature, and composition measurements was estimated to be less than 1.6 %, 0.05 %, 15 mK, and 0.015 %, respectively. The effect of temperature, pressure, and concentration on viscosity of binary aqueous NaI solutions was studied. The measured values of the viscosity of NaI(aq) were compared with data, predictions, and correlations reported in the literature. The viscosity data have been analyzed and interpreted in terms of the extended Jones−Dole equation for the relative viscosity (η/η0) of strong electrolyte solutions to accurately calculate the values of the viscosity A- and B-coefficients as a function of temperature. The derived values of the viscosity A- and B-coefficients were compar...

Conductivity and association of NaCl, NaBr, NaI, NaNO 3, NaClO 4 and NaSCN in ethanol at 213.15–333.15 K

Based on Krumgalz conductivity data of dilute (1×10−6–5×10−2 mol kg−1) electrolyte solutions of NaCl, NaBr, NaI, NaNO3, NaClO4 and NaSCN in ethanol in the temperature range 213.15–333.15 K (at 10 K intervals), the standard Gibbs energy, enthalpy and entropy of ion-pair formation, as well as contributions of the electrostatic and the non-electrostatic interactions to these functions, have been calculated.

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.