Function Of Ion Size Research Articles

Ion-Size Dependent Adsorption Crossover on the Surface of a Water Droplet.

The adsorption of ionic and neutral spherical solutes on the surface of a liquid water droplet are investigated using molecular dynamics simulations and theoretical analyses. The results reveal a crossover in the sign of the adsorption free energy as a function of ion size, with ions larger than iodide predicted to be increasingly surface active. Adsorption free energies are decomposed into competing energetic and entropic contributions arising from direct solute-water interaction energy and its fluctuations. The entropically driven surface activity of large ions is predicted to increase with ion size, while small ions are typically driven away from the interface by a more delicate balance of energetic and entropic contributions, with a nonmonotonic ion size dependence linked to the ion's hydration-shell structure and stability. The physical interpretation of the results is illuminated by comparisons with dielectric linear response and cavity formation predictions and implications to interfacial acidity and enhanced chemical reactivity are discussed.

Implementation of Tin Dioxide/Graphene/Graphene Oxide for High Capacity and Long Cycle Life Supercapacitors and As Anode Material for Lithium Ion Batteries

Energy storage and conversion mechanism are different for on lithium ion batteries (LIB) and supercapacitors (Electrical Double Layer Capacitors- EDLCs), materials that can be used for both could lead in the future the energy storage and conversion technologies. We explored a non-conventional process to synthesize SnO2/G/GO composite powder which is conformal structure was characterized under different techniques. Comprehensive analysis of the structural and chemical properties reveals that the material consists of highly dispersed SnO2 nanoparticles in G/GO matrix. The dispersed SnO2/G/GO suspension was coated an aluminum foil for the supercapacitors electrodes. We examine the electrical conductivity of the electrodes by atomic force microscope (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM). We assembled the Al coated SnO2/G/GO composite as a supercapacitor inserting one solid-state electrolyte between two electrodes, assembled into a sandwich structure. The specific capacitance and cycle-life stability of the supercapacitor was investigated by cyclic voltammetry analysis. For LIB applications, the SnO2-G/GO composite exhibited high capacity and excellent electrochemical performance as anode material. For both applications, the quantitative/qualitative results show that G/GO is providing contact areas which results in more energy density at the interface electrode/electrolyte and that the SnO2 provides additional ions to the EDL and the electrochemical process. The Overscreening phenomena observed, which is a function of ionic size, surface charge density of the electrodes, can also be a function of concentration of the electrolyte, porosity of the electrodes (G/GO) and the ions provided to the electrode/electrolyte interface by the electrode.

Synthesis, characterization, biological and electrical conductivity studies of some Schiff base metal complexes

Metal complexes of VO(IV), Zr(IV), Th(IV) and UO2(VI) with Schiff base ligands derived from 4-nitrobenzoylhydrazide with 2-hydroxy-5-methylacetophenone (H2L1) or 2-hydroxy-5-chloroacetophenone (H2L2) have been prepared. All the complexes have been characterized on the basis of elemental analyses, magnetic susceptibility measurement, electronic and IR spectra and thermogravimetric analysis. The IR spectral data suggested that the ligands behave as dibasic tridentate moiety towards the central metal ion coordinating through phenolic oxygen, enolic oxygen and azomethine nitrogen atoms. The elemental analyses show a 1:1 metal:ligand stoichiometry for all the complexes except Th(IV) which has 1:2 stoichiometry. The thermal analysis evidenced that thermal transformations of complexes are processes according to TG curves including dehydration, thermolysis and oxidative degradation of Schiff base. The final product of decomposition is the most stable metallic oxide. The kinetic analysis of the thermogravimetric data was performed by using the Coats-Redfern method. Solid state electrical conductivity of the complexes has been measured in their compressed pellet form over a 310-413 K temperature range. All the complexes show semiconducting behavior as their conductivity increases with increasing temperature and a function of ionic size. All the complexes along with ligands were also screened for their antibacterial and antifungal activities. KEY WORDS: Aroylhydrazones, Metal complexes, Biological activity, TGA, Electrical conductivity Bull. Chem. Soc. Ethiop. 2014, 28(2), 255-264.DOI: http://dx.doi.org/10.4314/bcse.v28i2.9

The Effective Temperature of Ions Stored in a Linear Quadrupole Ion Trap Mass Spectrometer

The extent of internal energy deposition into ions upon storage, radial ejection, and detection using a linear quadrupole ion trap mass spectrometer is investigated as a function of ion size (m/z 59 to 810) using seven ion-molecule thermometer reactions that have well characterized reaction entropies and enthalpies. The average effective temperatures of the reactants and products of the ion-molecule reactions, which were obtained from ion-molecule equilibrium measurements, range from 295 to 350 K and do not depend significantly on the number of trapped ions, m/z value, ion trap q z value, reaction enthalpy/entropy, or the number of vibrational degrees of freedom for the seven reactions investigated. The average of the effective temperature values obtained for all seven thermometer reactions is 318 ± 23 K, which indicates that linear quadrupole ion trap mass spectrometers can be used to study the structure(s) and reactivity of ions at near ambient temperature.

A Local Entropic Signature of Specific Ion Hydration

Monovalent ion hydration entropies are analyzed via energetic partitioning of the potential distribution theorem free energy. Extensive molecular dynamics simulations and free energy calculations are performed over a range of temperatures to determine the electrostatic and van der Waals components of the entropy. The far-field electrostatic contribution is negative and small in magnitude, and it does not vary significantly as a function of ion size, consistent with dielectric models. The local electrostatic contribution, however, varies widely as a function of ion size; the sign yields a direct indication of the kosmotropic (strongly hydrated) or chaotropic (weakly hydrated) nature of the ion hydration. The results provide a thermodynamic signature for specific ion effects in hydration and are consistent with experiments that suggest minimal perturbations of water structure outside the first hydration shell. The hydration entropies are also examined in relation to the corresponding entropies for the isoelectronic rare gas pairs; an inverse correlation is observed, as expected from thermodynamic hydration data.

Analysis of the diffuse layer potential drop in the limit of small fields on the basis of a generalized mean spherical approximation

Analytical expressions have been derived for the functions Ξ o and H o which arise in the description of the diffuse double layer using a generalized mean spherical approximation (GMSA). The analytical expressions are shown to provide a very good alternate method to estimate Ξ o and H o which were calculated on the basis of numerical evaluation of integrals in previous work. They are valid in the limit of small electrical fields, a region in which the GMSA itself is valid. The GMSA results are compared to data obtained in Monte Carlo simulations carried out at the primitive level as a function of ion size and concentration for a 1–1 electrolyte.

Friction Coefficients of Ions in Aqueous Solution at 25 °C

The diffusion coefficients of ions and of uncharged solutes in aqueous solution at 25 °C and at infinite dilution are studied by computer simulation using the SPC/E model for water and solute−water potentials employed in previous work (Koneshan, S.; et al. J. Phys. Chem. 1998, 102, 4193−4204). The mobilities of the ions calculated from the diffusion coefficients pass through a maximum as a function of ion size, with distinct curves and maximums for positive and negative ions in qualitative agreement with experiment. We aim to understand this at a microscopic level in terms of theoretical studies of the friction coefficient ζ, which is related to diffusion coefficient by the Stokes−Einstein relation. This provides one method of calculating ζ, but it can also be obtained in principle from the random force autocorrelation function which is the starting point of molecular theories of the friction. Molecular and continuum theories divide the friction into hydrodynamic and dielectric components calculated in different ways on the basis of certain approximations that are tested in this paper. The two methods of determining ζ give consistent results in simulations of large ions or uncharged solutes but differ by a factor of nearly 1.5 for smaller ions. This is attributed to the assumption, in our simulations and in some molecular theories, that the random force autocorrelation function of a moving ion can be approximated by the total force autocorrelation function of a fixed ion but the observed trends in ζ with ion size are unchanged. Three different separations of the force autocorrelation function are studied; namely, partitioning this into (a) electrostatic and Lennard-Jones forces (b) hard and soft forces, and (c) forces arising from the first shell and more distant forces. The cross-terms are found to be significant in all cases, and the contributions of the sum of the soft term and the cross-terms, which are of opposite sign, to the total friction in the hard−soft separation, is small for all the ions (large and small). This suggests that dielectric friction calculated using this separation, with the neglect of cross-terms, is less accurate than previously supposed and the success of these theories is due to a cancellation of errors in the approximations. This is supported by recent a theoretical study of Chong and Hirata (Chong, C.; Hirata, F. J. Chem. Phys. 1998, 108, 739) which evaluates the cross-terms. A phenomenological theory due to Chen and Adelman (Chen, J. H.; Adelman, S. A. J. Chem. Phys. 1980, 72, 2819) calculates the friction in terms of effective hydrodynamic and dielectric radii for the ions (cf. solventberg picture) and predicts low dielectric friction for large ions and small strongly solvated ions. This also agrees qualitatively with our simulations but a complete molecular theory, applicable to positive and negative ions in hydrogen-bonded solvents such as water, has yet to be developed.

Modifications on Bulk Crystallization of Glasses Belonging to M2O-CaO-SiO2-ZrO2 System in A 2.45 GHz Microwave Field

AbstractThe potential for microwave processing of a single phase material is often limited due to the dependence of dielectric losses upon the chemical bonding and temperature of the material. We will present results showing the effect of microwave absorption on bulk crystallization of glasses belonging to M2O-CaO-SiO2-ZrO2 system (where M+ Li, Na, K). The glass samples were devitrified using both microwave and conventional heating. The effect of Li+, Na+, K+ on crystallization is quite remarkable and is a function of ion size. This is true especially in the microwave heating where the important dielectric losses observed in silicate glasses are related to the motion of alkali cations throughout the glass matrix. X-ray diffraction analysis was performed on the powdered samples to determine crystalline phases. Results of microstructure and microanalysis on these glass-ceramic samples will also be presented.

Multiply charged ions in ionspray tandem mass spectrometry

AbstractMultiply charged anions of some 30 species containing multiple carboxylic, sulphonic and/or phosphoric groups generated by ionspray were studied by using tandem mass spectrometry (MS/MS). Two trends emerged: (1) lower‐charged ions are preferentially evaporated, and (2) for more highly charged ions, evaporability is a function of ion size. Triply and quadruply charged ions were observed for azo dyes with molecular masses in the 700‐900 Dalton range. Daughter‐ion mass spectra of selected multiply charged ions are presented.

Generation of hydrophobic zeolite X by exchange with octadecylammonium ion

It is well known that zeolites are a hydrophylic class of materials. It has been proposed that this hydrophylic nature is not due to the Si-O Si linkage, but rather to Si OH or cationic sites associated with tetrahedrally bound aluminium [1, 2]. This theory is supported by the decrease in water sorption capacity that is observed as aluminium sites are extracted from mordenite [1]. Zeolites can, therefore, be made hydrophobic by de-aluminization, but with a concomitant loss of sorption capacity for popular species. Hydrophobic zeolites prepared without de-aluminization could be useful in several applications, including the production of novel gas chromatographic columns and the prevention of particle aggregation in the aqueous slurries. The latter application was proposed for zeolites made hydrophobic by reaction of free OH sites with organosilanes [3, 4]. In addition, the modification of surface properties might make these zeolites useful as lightweight fillers with improved compactibility with hydrophobic polymeric materials. We have investigated the possibility of making the surface of zeolites 13X hydrophobic cationic exchange of long-chain alkylammonium ions (specifically n-octadecylammonium ion) for sodium ion. The alkyl end of the ion would then impart a degree of hydrophobicity to the zeolite surface. Although short chain (i.e. 1 to 6 carbon) alkylammonium ions have been exchanged into zeolites to study exchange rates and distributions as a function of ion size [5, 6], we believe this is the first use of such an exchange with long alkyl chains for the purpose of imparting surface hydrophobicity. A relative measure of hydrophobicity both with and without exchange of different alkylammonium salts was provided by the water contact angle. The effect of exchange with n-hexyl and noctadecylammonium ions could then be compared. Zeolite 13X was obtained from Union Carbide Corporation, Linde Division, as a powder without additives or binders. In order to provide a flat surface for contact angle measurements, 0.38 g powder was taken directly from its container and placed in a Perkin-Elmer KBr die (Model 186-0025) and pressed at 10 000 lb (45 000 N) for 15 sec. This corresponds to 49000psi (3.4 × 108Nm 2) across the die face. The resulting pellets were right cylinders with a 13 mm diameter and 2.5 mm thickness. Exchange was done in a 70 mm × 50 mm crystallizing dish. A solution of the appropiate salt in 100ml ethanol (AAPER Alcohol and Chemical Co, Shelbyville, Kentucky, used as-received) was added to the dish and three pellets were placed in the solution on a wire-mesh platinum basket suspended from the sides of the dish by platinum wires. The solution was stirred with a magnetic stir bar and a watch glass was placed over the dish to retard solvent evaporation. Pellets were exchanged in this way for ~ 40 h. Ethanol was used because of the good solubility of the amines and salts used. Each set of three pellets exchanged together was first weighed to ensure that each exchange solution contained the same concentration of ammonium salt per gram zeolite. The two salts used for exchange were prepared as the chlorides by acidification of the respective amines. For the octadecyl salt, 1.75 g n-octadecylamine (from K and K Laboratories, Plainview, New York, used as-received) was dissolved in 200 ml ethanol and acidified with 1 ml concentrated HC1 (Fisher, reagent grade, used as-received). This represents a 1.8:1 molar excess of HC1. The solvent was stripped off and the residue was verified as the salt by melting point. This procedure was modified slightly for the hexylamine, as addition of the water in the acid led to formation of waters of hydration with unknown stoichiometry. Anhydrous HCI was bubbled through an ethanolic solution of hexylamine (Eastman Organic Chemicals, used as-received) and the solvent stripped off. The resulting salt was stored in a desiccator to prevent the uptake of water. Contact angle measurements were made with a Ram6-Hart goniometer. A measure of the hydrophobicity of a surface can be obtained from the angle a drop of water makes with the flat surface. Unfortunately, the angle measured is dependent on several experimental variables, principally the roughness of the surface [7]. The relationship between the true contact angle, 0, and the measured angle, 0', is given by:

Theoretical results for dielectric and structural properties of aqueous electrolytes. The influence of ion size and charge

The present paper describes a theoretical investigation of aqueous electrolytes in the infinite dilution limit. The linearized hypernetted chain theory is applied to solutions of hard spherical ions in a waterlike solvent at 25 °C and the properties of solution are studied as a function of ion size and charge. We examine both dynamical and equilibrium contributions to the apparent ‘‘dielectric constant’’ of solution and compare with previous theoretical calculations as well as with experimental measurements. Ion–solvent correlation functions and ion–ion potentials of mean force for several common electrolytes are also presented and discussed.

Dielectric friction and dielectric dispersion in electrolyte solutions with spin

A self-consistent continuum model of dielectric friction on a moving ion is developed in which the only adjustable parameters are the hydrodynamic boundary conditions and a ’’rotational viscosity’’ hR. Ion mobility and the solution dielectric properties are calculated as a function of ion size, ion charge, low and high frequency dielectric constants of the solvent, dielectric relaxation time of the solvent, rotational viscosity, and solvent shear viscosity. The consequences of varying hR are investigated: For hR→∞ the continuum theory analyzed by Hubbard and Onsager (HO) is recovered; for small hR, however, the polarization and ’’spin’’ fields in the solvent near the ion differ significantly from the HO model. While this has remarkably little effect on calculated ionic mobilities, the solution dielectric properties are noticeably altered. In particular, the kinetic dielectric decrement diverges as ln hR as hR vanishes.

Neutron-Scattering Investigation of the Dynamics of H2O Molecules in Ionic Solutions

Intermolecular frequencies (below 900 cm−1) and diffusive motions of H2O molecules in ionic solutions relative to water were investigated by slow neutron scattering as function of ionic size, charge, and concentrations and of the temperature. For solutions containing small or highly charged ions (e.g., LaCl3, MgCl2, LiCl, and KF), vibrations, which intensify with increasing concentration, appear at similar frequencies to the ion-water librational and stretching frequencies of the corresponding solid hydrates. In contrast, solutions containing large, singly charged ions (e.g., CsCl, KCl) show new frequencies, but these are comparatively broader and weaker. At 1° and 25°C, the diffusive kinetics generally follow a delayed diffusion mechanism. Small or highly charged ions decrease the self-diffusion coefficient and increase the residence time relative to water. The low charge-to-radius ions have the inverse effect. At higher temperatures, the diffusion kinetics depart from the delayed diffusion behavior. [Work supported by the Office of Saline Water, Department of the Interior.]

Rare-Earth Polymorphism and Phase Equilibria in Rare-Earth Oxide-Water Systems

A high-water-pressure high-temperature study was conducted of the systems Y/sub 2/O/sub 3/-H/sub 2/O, Sm/sub 2/O/sub 3/-H/sub 2/O, N d/sub 2/O/sub 3/-H/sub 2/O, and La/sub 2/O/sub 3/-- H/sub 2/O. The trihydroxides La(OH)/sub 3/ , Nd(OH)a, an d this group. On the other hand, the oxyhydroxides YOOH, SmOOH, and NdOOH are isomorphous; LaOOH, if it exists, cannot be stable in the presence of water at room temperature. Pressure-temperature curves for the equilibrium between the trinydroxide, oxyhydroxide, and a new hydroxy compoud were determined for each of the three smaller ions. The reversibility of the transition between the A-, B-, and C-type rare earths was established, and new x-ray data on the B structure are listed. Ths relations between the polymorphs as a function of ionic size are changed from those given by Goldschmidt. The very marked difference in stability in air between the A- and C-type structures suggests the obvious desirability of converting rareearth oxide cermnics into the C structure with proper compositional variation and thermal treatment. (auth)