Adsorption of diprotonated cryptand [2.2.2.] on the mercury electrode

The adsorption behavior of diprotonated cryptand [2.2.2.] (DPCR), which represents a two-charged complex with one proton localized inside the ligand intramolecular cavity and the other proton localized on the external surface of the ligand molecule at the nitrogen atom, is studied at the Hg electrode/aqueous solution interface by the impedance method. The obtained data indicate the presence of tem-poral processes of the reconstruction of the DPCR adsorption layer, which depend on the potential of the onset of adsorption and on the cryptand [2.2.2.] concentration.     

Cationic mobility in Li3?2xNbxFe2?x(PO4)3 complex phosphates

Synthesis and ionic conductivity of Li_3−2x Nb _x Fe_2−x (PO₄)₃ complex phosphates were studied by X-ray powder diffraction and impedance spectroscopy. These phosphates are formed only at 900–1000°C. Variations in their thermal expansivity and unit cell parameters induced by aliovalent doping were characterized. The conductivity of these materials increases monotonically in the series Li_0.5Nb_1.25Fe_0.75(PO₄)₃-LiNbFe(PO₄)₃ and Li_1.2Nb_0.9Fe_1.1(PO₄)₃-Li₃Fe₂(PO₄)₃, which is explained by consecutive occupation of the Li(1) and Li(2) positions in their structures. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, A.B. Yaroslavtsev, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 12, pp. 1957–1962.     

Kinetics of H<Superscript>+</Superscript>/Na<Superscript>+</Superscript> solid-phase ion exchange on iron(III) hydrogen sulfate

The kinetics of solid-phase reaction between iron(III) hydrogen sulfate and sodium chloride was studied by thermal analysis followed by analysis of leaving gases. The exchange kinetics are described by the soft cylinder model. The hydrogen and sodium ion interdiffusion coefficients were determined for various temperatures, as well as the activation energy of interdiffusion. Sodium ion diffusion through the product layer is the rate-controlling stage of the reaction.     

Transport properties of hydrous-silica-modified MF-4SK membranes

Composites are manufactured on the basis of MF-4SK perfluorinated cation-exchange membranes modified with hydrous silica nanoparticles 2–5 nm in size. Modification improves the ionic conductivity and diffusion permeability of the membrane. The modification efficiency increases with decreasing modifier particle size. The enhancement of transport processes is maximal when hydrous silica nanoparticles are synthesized directly in the membrane matrix.     

Lead bipyridyl hexacyanoferrate complex

A low-solubility complex [PbBipy₂]₆[Fe(CN)₆]₄ · Bipy · 14H₂O was prepared and characterized by physicochemical methods. Although containing [PbBipy₂]₂[Fe(CN)₆] discrete species and a {[PbBipy₂][Fe(CN)₆]} _n infinite chain in the crystal structure, the complex has weak antiferromagnetic properties over a wide temperature range. The irreversible thermal destruction of the complex, which starts at 192°C, is preceded by complete dehydration.     

Water self-diffusion and ionic conductivity in perfluorinated sulfocationic membranes MF-4SK

Water self-diffusion and ion mobilities in various ionic forms (H⁺, Li⁺, Na⁺, Rb⁺, Cs⁺, and Ba²⁺) of perfluorinated sulfocationic membranes MF-4SK were studied by NMR and impedance spectroscopy. When degrees of hydration are low, the self-diffusion coefficients of water and ionic conductivities are considerably affected by the water content of the membrane. The self-diffusion coefficients decrease in the order H⁺ > Ba²⁺ > Cs⁺ > Rb⁺ > Na⁺ > Li⁺, whereas the ion mobility decreases in the order H⁺ > Li⁺ > Na⁺ > Cs⁺ > Ba²⁺.     

Adsorption of surface-active compounds with the skeleton molecular structure from dimethylsulfoxide solutions on carbon nanotubes

The adsorption of adamantane, adamantanol, thiocamphor, and sodium cryptate on electrodes of single-walled carbon nanotubes (SWNT) from dimethylsulfoxide (DMSO) solutions is studied by measuring the differential capacitance (C) vs. potential (E) dependences and cyclic voltammograms. In the tested systems, the high surface activity of these surfactants is observed to result in a noticeable increase in the C of such electrodes in the range of 0.2 ≤ E ≤ −(0.9−1.1) V (SCE). As in the case of aqueous solutions, this experimental fact is explained by the appearance of the so-called Rehbinder effect (the adsorption-induced decrease in the strength), which, in this particular case, consists in a decrease in the surface energy of a solid with the formation of adsorption layers on the side surfaces of SWNTs combined into bundles to afford the partial splitting of these bundles and, as a consequence, the increase in the nanotube surface accessible to the electrolyte. At the same time, the obtained results suggest that for the adsorption of surfactants from nonaqueous solvents (in contrast to aqueous), the interaction between solvent and adsorbate molecules may become important.     

Electrochemical behavior of electrodes containing nanostructured carbon of various morphology in the cathodic region of potentials

Voltammograms for electrodes containing nanostructured carbon of various morphology (single-walled carbon nanotubes, filament, columnar structures) are obtained in neutral aqueous electrolytic solutions. Experimental proofs for the existence of injection of solvated electrons into electrolytic solutions at moderate cathodic potentials are presented for all the electrodes. It is established that this effect is connected with the presence of atomically sharp areas on the electrode surfaces. It is assumed that the reason for the appearance of solvated electrons is the autoelectron emission at the interface between the conducting surface of the carbon material and the electrolytic solution. By studying the nitrate anion reduction it is shown that the reduction over-voltage of stable compounds may be lowered by substituting a fast homogeneous reaction of solvated electrons with the initial substance for the hindered heterogeneous stage of the first electron transfer.     

Electroreduction of Anions and Silver Kryptate on a Mercury Electrode in Conditions of Adsorption of Kryptate Complexes

Electroreduction of persulfate, hexacyanoferrate, and perbromate anions on a mercury electrode is studied in conditions of individual adsorption of kryptate complexes of cations and in the case of their co-adsorption with surface-active substances that form two-dimensional condensed layers on the electrode/solution interface. The electroreduction dramatically accelerates during both individual adsorption of kryptate complexes and their co-adsorption with 1-adamantanol, due to an electrostatic effect. The behavior of electrochemically active kryptate complexes is investigated by studying the Ag⁺ kryptate. In the system studied the [Ag⁺ 222] complex undergoes diffusion-controlled reduction.