The influence of H2SO4 electrolyte concentration on proton transfer resistance of membrane/solution interface

The proton transfer resistance of membrane/solution interface is investigated in this paper by employing H₂SO₄ aqueous solution with different concentration. Two commercial cation exchange membranes, Nafion1135 and PE01 membranes with different ion exchange capacity were selected as test membranes; Proton transfer resistance measurements were made by A.C impedance techniques. The proton transfer resistance of membrane/solution interface increases quickly from 0.059 to 2.22 Ω with the decrease of H₂SO₄ concentration from 2.0 to 0.05 mol/L. The ion exchange capacity of the membrane, or more exactly, the surface charge of the membrane has obviously effect on the membrane/solution resistance due to the formation of electrical double layer (EDL). The effect of electrolyte concentration on membrane/solution interface resistance can be explained by the electrical interactions between ions and charged groups of the membrane: high concentration of ions in the medium can compress the EDL and reduce the electrical interactions between ions and charged groups of the membrane.     

Analysis of diffuse-layer effects on time-dependent interfacial kinetics

We investigate the subtle effects of the diffuse charged layer on interfacial kinetics by solving the governing equations for ion transport (Nernst–Planck) with realistic boundary conditions representing reaction kinetics (Butler–Volmer) and compact-layer capacitance (Stern) in the asymptotic limit =λ_D/L→0, where λ_D is the Debye screening length and L is the distance between the working and counter electrodes. Using the methods of singular perturbation theory, we derive the leading-order steady-state response to a nonzero applied current in the case of the oxidation of a neutral species into cations, without any supporting electrolyte. In certain parameter regimes, the theory predicts a reaction-limited current smaller than the classical diffusion-limited current; this over potential effect is not due to ohmic drop effects in the bulk of the cell but rather to antagonist processes involved in the surface charge transfer and diffuse layer charging respectively. We demonstrate that the charging of diffuse charge, since it is intimately coupled to the surface reaction and cannot be considered independently, plays a fundamental role in nonequilibrium surface reactions when the transport of one of the reacting species is coupled to the total interfacial response of the compact and diffuse layers.     

Diffusion Impedance in Natural Convection Conditions

An expression for the diffusion impedance in conditions of natural convection, when the diffusion layer thickness depends on the redox pair concentration, is obtained. The theory predicts a decrease in the steady-state diffusion resistance R _dby 1.25 times and a change in the coordinates of the extremum in an impedance spectrum and in the dimensionless R _dfrequency at this point (3.2 instead of 2.5) as compared to the classical theory, which is confirmed by experimental data for a reversible [Fe(CN)₆]^3–/4–system. The theoretical results are employed for correct determination of the concentration coefficient of the solution density.     

Accurate analytic potential energy function and spectroscopic study for CH(XΠ) radical using coupled-cluster theory in combination with the correlation-consistent quintuple basis set

The coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory in combination with the correlation-consistent quintuple basis set (aug-cc-pV5Z) is used to investigate the spectroscopic properties of the CH(X²Π) radical. The accurate adiabatic potential energy curve is calculated over the internuclear separation ranging from 0.07 to 2.45 nm and is fitted to the analytic Murrell–Sorbie function, which is employed to determine the spectroscopic parameters, ω_eχ_e, α_e and B_e. The present D_e, R_e, ω_e, ω_eχ_e, α_e and B_e values are of 3.6261 eV, 0.11199 nm, 2856.312 cm⁻¹, 64.9321 cm⁻¹, 0.5452 cm⁻¹ and 14.457 cm⁻¹, respectively. Excellent agreement is obtained when they are compared with the available measurements. With the potential obtained at the CCSD(T)/aug-cc-pV5Z level of theory, a total of 18 vibrational states is predicted when J = 0 by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced for the CH(X²Π) radical when J = 0 for the first time, which are in good agreement with the available RKR data.     

Spectroscopic investigations on AsH(XΣ) radical using CCSD(T) theory in combination with correlation-consistent quintuple basis set

The equilibrium internuclear separations, harmonic frequencies and potential energy curves of the AsH(X³Σ⁻) radical have been calculated using the coupled-cluster singles–doubles–approximate-triples [CCSD(T)] theory in combination with the series of correlation-consistent basis sets in the valence range. The potential energy curves are all fitted to the Murrell–Sorbie function, which are used to reproduce the spectroscopic parameters such as D_e, ω_eχ_e, α_e, B_e and D₀. The present D₀, D_e, R_e, ω_e, ω_eχ_e, α_e and B_e obtained at the cc-pV5Z basis set are of 2.8004 eV, 2.9351 eV, 0.15137 nm, 2194.341 cm⁻¹, 43.1235 cm⁻¹, 0.2031 cm⁻¹ and 7.3980 cm⁻¹, respectively, which almost perfectly conform to the measurements. With the potential obtained at the UCCSD(T)/cc-pV5Z level of theory, a total of 18 vibrational states is predicted when the rotational quantum number J is set to equal zero (J = 0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J = 0 for the first time, which are in excellent agreement with the experiments.     

Effect of Electrolyte Concentration on the Stern Layer Thickness at a Charged Interface

The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO₂) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles’ surface potential by X‐ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased.     

Electrochemical Properties of Electrode Materials of the Composition (Yb,Y)0.5Ca0.5MnO3

Electrochemical characteristics, such as the parameter of resistance (/d) of an intermediate layer at the electrode material/electrolyte interface and the polarization resistance (R ) of the three-phase boundary gas/solid-electrolyte/electrode under study, are studied as a function of the electrode layer thickness, temperature, and oxygen content in the gas phase for electrode materials of the composition (Yb, Y)_0.5Ca_0.5MnO₃. Established is the similarity in the behavior of /d and R from the above parameters. The determined effect on these characteristics is exerted by the composition of the electrode material. In the temperature range 300–1100 K, at = 10²–10⁵ Pa, the least values of the parameter of resistance and polarization resistance are intrinsic to samples with the thickness of the electrode layer 100 mg cm^–2 of the composition Y_0.5Ca_0.5MnO₃. For systems studied, the least temperature of establishment of electrochemical equilibrium at the three-phase boundary is 875 (±5) 5 K.     

Über Reaktionen von Arylbiguaniden mit Benzoin beimpH der Biguanidbasen

Summary Arylbiguanides2 a–e react with benzoin (1) at thepH of the base to two different products.1 undergoes in presence of the base2 a–e oxidation to benzil and benzoic acid, which reacts fast with the arylbiguanides2 a–e to yield N-[4-(arylamino)-6-phenyl-1,3,5-triazine-2-yl]benzamides3 a–d. After lowering thepH of the reaction mixture, the bases2 b–e react with benzil to yield 2-[1-aryl-5-oxo-4,4-diphenyl-2-imidazoline-2-yl]guanidine4 b–e. The mechanism of the formation is discussed. The structure of4b was established from a single crystal x-ray structure analysis. The analysis was carried out at 100K: C₂₃H₂₁N₅O,M _r=383.5, monoclinic, C 2/c,a=15.842(6),b=8.419(3),c=30.223(10) Å, =98.44(3)°,V=3 987.3(9) ų,Z=8,d _x=1.277 g/cm³, =0.81 cm^–1,R=5.89%R _w=4.97% (1 537 observations, 233 parameters).

     

Chemical bond breaking/forming as a Franck–Condon electronic process

We describe chemical bond changes as Franck–Condon electronic processes within a new theoretical ansatz that we call ‘rigged’ Born–Oppenheimer (R-BO) approach. The notion of the separability of nuclear and electron states implied in the standard Born–Oppenheimer (BO) scheme is retained. However, in the present scheme the electronic wave functions do not depend upon the nuclear coordinate (R-space). The new functions are obtained from an auxiliary Hamiltonian corresponding to the electronic system (r-coordinates) submitted to a Coulomb potential generated by external sources of charges in real space (α-coordinates) instead of massive nuclear objects. A stationary arrangement characterized by the coordinates α_0A, is determined by a particular electronic wave function, ψ(r;α_0A); it is only at this stationary point, where an electronic Schrödinger equation: H_e(r,α_0A)|Ψ(r;α_0A)=E(α_0A)|Ψ(r;α_0A) must hold. This equation permits us to use modern electronic methods based upon analytic first and second derivatives to construct model electronic wave functions and stationary geometry for external sources. If the set of wave functions {Ψ(r;α_0A)} is made orthogonal, the energy functional in α-space, E(α;α_0A)=Ψ(r;α_0A)|H_e(r,α_0A)|Ψ(r;α_0A) is isomorphic to a potential energy function in R-space: E(R;α_0A)=Ψ(r;α_0A)|H_e(r,R)|Ψ(r;α_0A). This functional defines, by hypothesis, a trapping convex potential in R-space and the nuclear quantum states are determined by a particular Schrödinger equation. The total wave function for the chemical species A reads as a product of our electronic wave function with the nuclear wave function (Ξ_ik(R;α_0A)): Φ_ik(r,R)=Ψ_i(r,α_0A)Ξ_ik(R;α_0A). This approach facilitates the introduction of molecular frame without restrictions in the R-space. Two molecules (characterized with different electronic spectra) that are decomposable into the same number of particles (isomers) have the same Coulomb Hamiltonian and they are then characterized by different electronic wave functions for which no R-coordinate ‘deformation’ can possibly change its electronic structure. A bond breaking/forming process must be formally described as a spectroscopic-like electronic process. The theory provides an alternative to the adiabatic as well as the diabatic scheme for understanding molecular processes. As an illustration of the present ideas, the reaction of H₂+CO leading to formaldehyde is examined in some detail.     

Deposition behaviors and patterning of TiO2 thin films on different SAMs surfaces from titanium sulfate aqueous solution

Patterning of TiO₂ thin films was successfully obtained on different self-assembled monolayers (SAMs) in aqueous solution by micro-contact printing (μCP) method. The substrates were immersed in an aqueous solution containing titanium sulfate (Ti(SO₄)₂) and hydrogen peroxide for deposition at 80 °C. The growth rates on various surfaces were as follows: sulfonic (–SO₃H) > amino (–NH₂) > methyl (–CH₃) > hydroxyl (–OH). According to the XPS results, SAMs with the terminal groups of –SO₃H and –NH₂ were favorable for the deposition. The TiO₂ film deposited on the SAM with the terminal group of –CH₃ could be easily peeled off. Clearly, TiO₂ patterns were obtained on the prepatterned surfaces of –SO₃H/–CH₃ and –NH₂/–CH₃ SAMs. The deposition mechanism might be relevant to electrostatic interaction, Stern layer, lone pair electrons and Van der Vaals forces. The TiO₂ film was anatase after annealing at 500 °C and comprised particles with an average diameter of ca. 10 nm.     

Scalar and quadrupolar intensity contributions in two-photon hyperfine structure transitions in europium

Two-photon transitions from the Eu I ground state 4f ⁷ 6s ² a ⁸ S _7/2 to odd levels with alsoJ=7/2 in the energy range of 34,000 – 36,700 cm^–1 were analysed due to their scalar and quadrupolar contributions. Their ratioR (g, e) were determined experimentally. In most cases the quadrupole contributions are dominant, i.e. 0R (g, e) _exp <>^–3. In the two-photon transition to the level 4f ⁷ 5d ^{2 8} F _7/2 the ratio is remarkably strong:R (g, e) _exp =134 (4)·10^–3. A theoretical estimation ofR (g, e) is not yet satisfying, due to strong configuration mixing in Eu.     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.     

Solubilization of Homologous ω-Phenylalkanols into Gel and Liquid-Crystalline Liposome Membranes of Dipalmitoylphosphatidylcholine

The gel-to-liquid-crystalline phase transition temperature T _m of dipalmitoylphosphatidylcholine (DPPC) liposome membrane was measured in the presence of homologous -phenylalkanols (phenol to 8-phenyl-1-octanol). The decrease in T _m induced by the alkanols allowed us, by applying the van't Hoff equation for freezing-point depression, to estimate two partition coefficients of each alkanol: gel membrane/bulk water K _x ^g and liquid-crystalline membrane/bulk water K _x ¹ . Shorter alkyl chain alkanols were solubilized only in the liquid-crystalline membrane, i.e., K _x ^g =0, whereas longer-chain alkanols were solubilized not only in the liquid-crystalline membrane but also in the gel membrane. The former result suggests that the fraction of liquid-crystalline phase in the liposome membrane is 0.83 at T _m. From the latter result, the values of the free energy changes of transfer of the alkanol molecules from bulk water to liposome membrane were estimated to be – 3.46 kJ-mol^–1 (liquid-crystalline membrane) and – 3.85 kJ-mol^–1 (gel membrane) per CH₂ group in the alkanol molecules.     

Linear relationships in α,β-unsaturated carbonyl compounds between the half-wave reduction potentials, the frontier orbital energies and the Hammett σp values

A linear relationship between the half-wave reduction potentials of α,β-unsaturated carbonyl compounds R–CHCH–COX and the Hammett σ_p values of R and X is proposed: E_1/2=−1.341σ_p(X)σ_p(R)+1.123σ_p(X)+1.746σ_p(R)−1.694. A linear relationship is also observed for the LUMO's energy values, the absolute chemical hardness η, the chemical potential μ, the electrophilicity power ω, or the polarisation of the ethylenic double bond with the Hammett σ_p values of R and X.     

Mechanisms of oxidation of K4Fe(CN)6 by hypochlorous acid and catalytic activation by azide, bromide, and iodide

Summary HOCl reacts with Fe(CN) ₆ ^4– to generate an intermediate, presumably FeCl(CN) ₆ ^3– , which exhibits a weak absorption around 282 nm and decays simultaneously with the formation of Fe(CN) ₆ ^3– . When decreasing the HOCl/Fe(CN) ₆ ^4– concentration ratio fromR>1 toR<1, a drastic change in the kinetics of the oxidation is observed. Depending onR, the intermediate obviously oxidizes either Fe(CN) ₆ ^4– or HOCl. AtR1, a further intermediate appears which also precedes the oxidation and absorbs strongly around 360 nm. The intermediates detected may represent reactive high oxidation states of iron (Fe(IV) and Fe(VI)). HOCl induced oxidation of Fe(CN) ₆ ^4– is activated catalytically by Br^–, I^–, and N ₃ ^– , obviously due to generation of stronger oxidants (HOBr, HOI, and ClN₃), but oxidation is efficiently inhibited by CN^– and NCS^–.

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Mechanismen der Oxidation von K₄Fe(CN)₆ durch Hypochlorsäure und katalytische Aktivierung durch Azid, Bromid und Iodid

Zusammenfassung HOCl reagiert mit Fe(CN) ₆ ^4– unter Bildung eines Intermediats, vermutlich FeCl(CN) ₆ ^3– , das bei 282 nm eine schwache Absorption aufweist und parallel zum Erscheinen von Fe(CN) ₆ ^3– verschwindet. Man beobachtet eine drastische Änderung in der Oxidationskinetik, wenn das HOCl/Fe(CN) ₆ ^4– Konzentrationsverhältnis vonR>1 zuR<1 verändert wird. In Abhängigkeit vonR wird offenbar entweder Fe(CN) ₆ ^4– oder HOCl durch das Intermediat oxidiert. FürR1 erscheint ein weiteres Intermediat mit einer starken Absorptionsbande bei 360 nm, das ebenfalls der Oxidation vorangeht. Bei den beobachteten Intermediaten handelt es sich vermutlich um reaktive höhere Oxidationsstufen des Eisens (Fe(IV) und Fe(VI)). Die HOCl-induzierte Oxidation von Fe(CN) ₆ ^4– wird einerseits durch Br^–, I^– und N ₃ ^– katalytish aktiviert (offenbar infolge der Bildung stärkerer Oxidantien wie HOBr, HOI und ClN₃), andererseits durch CN^– und NCS^– effektiv inhibiert.

     

Fabrication and characterization of γ-Al2O3–clay composite ultrafiltration membrane for the separation of electrolytes from its aqueous solution

In this paper, we have reported the preparation of low cost γ-Al₂O₃ membrane on a macroporous clay support by dip-coating method. For the synthesis of γ-Al₂O₃ top layer on the support, a stable boehmite sol is prepared using aluminium chloride salt as a starting material by sol–gel route. The structural properties of the composite membrane as well as γ-Al₂O₃ powder is carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm data, Fourier transform infrared analysis (FTIR) and dynamic light scattering (DLS) analysis. The mean particle size of the boehmite sol used for coating is found to be 30.9 nm. The pore size distribution of the γ-Al₂O₃–clay composite membrane is found to be in the range of 5.4–13.6 nm. Separation performance of the membrane in terms of flux and rejection of single salts solution such as MgCl₂ and AlCl₃ as a function of pH, salt concentration and applied pressure is also studied. The rejection and flux behavior are found to be strongly dependent on electrostatic interaction between the charged molecules and γ-Al₂O₃–clay composite membrane. The intrinsic rejection has been determined by calculating the concentration at membrane surface (C_m) using Speigler–Kedem model. It is found that the observed rejection shows anomalous trend with increase in applied pressure and the intrinsic rejection increases with increase in applied pressure, a trend typical of the separation of electrolyte through charged membranes. At acidic pH, both the salt solution shows higher rejection. With increase in the salt concentration, observed rejection of salt decreases due to the enhanced concentration polarization. The maximum rejection of MgCl₂ and AlCl₃ is found to be 72% and 88%, respectively for salt concentration of 3000 ppm.     

Electrosurface and Ion-Selective Properties of Track-Etched Nanofilters: The Effect of Polyvalent Metal Adsorption

The effect of polyvalent metal adsorption on the performance and ion selectivity of poly(ethylene terephthalate) track-etched membranes with pores of 10 nm in diameter was studied. Membrane samples were prepared from the track-etched membranes with pores of 20 nm in diameter by thermal shrinkage. It was shown that an effective pore diameter decreases and selectivity of track-etched membranes increases upon filtration of Al(NO₃)₃ and Cr(NO₃)₃ solutions. The results obtained are explained by ion adsorption leading to the formation of complexes between polyvalent metals and carboxyl groups on the pore surface that is confirmed by IR spectroscopy data. The study of electrosurface properties of modified membranes and the dependence of ion selectivity of track-etched membranes on the concentration of Al³⁺ ions in 10^–2 M KCl solution indicates the decrease of membrane negative surface charge resulted from Al³⁺ adsorption and membrane charge reversal at Al³⁺ concentration in a solution higher than 10^–6 M. The dependences of the ion selectivity on pH and Al³⁺ concentration C _Al in a solution are similar. At pH < 3 and C _Al > 10^–6 M, the _1–2 > _1–1 > _2–1 ion selectivity series characteristic of the initial negatively charged membranes for the 1–1, 1–2, and 2–1 electrolyte solutions is reversed into the _2–1 > _1–1 > _1–2 series characteristic of positively charged membranes.     

Temperature Dependence of Transport Properties and Ion–Molecular Forms of LiAsF6 in γ-Butyrolactone

The solvation and association electrolyte interactions are analyzed in the concentration range of 0–2 m at temperatures of 253.15–313.15 K using measurements of the conductivity and viscosity of LiAsF₆ solutions in -butyrolactone (-BL). Concentrated LiAsF₆ solutions in -BL are considered as molten electrolytic solvates, whose transport processes are considerably influenced by a cooperative restructuring of the system. The concentration dependence of the molar conductivity is linear in the vs. c^1/3 coordinates, which agrees with a theory of quasi-crystalline electrolyte lattice in solution. The Lee–Wheaton model is used to determine the limiting molar conductivities, distance parameters, and association constants and their temperature dependences. The size of solvate spheres increases with decreasing temperature and their overlapping occurs at lower concentrations.     

The phase diagram and supercooling conditions for the Ca(NO3)2−CaCl2−H2O system

The liquidus temperature and induction periods were measured for crystallization in a system of calcium nitrate, calcium chloride, and water over a concentration range of 5–20 mole% Ca(II), i.e., R=4–18 [R=moles H₂O/moles Ca(II)] and y_cl=0–1 [y_cl=moles Cl^–/moles (NO ₃ ^– +Cl^–)]. A ternary phase diagram was constructed, and qualitative dependences of the supercooling at which the solution began to crystallize on the system composition were found. A wide range of stability toward crystallization was found for solutions withR=4–10 and y_cl=0–0.7 The relationships between the system stability toward crystallization and the viscosity, glass-transition temperature, and the liquidus temperature are discussed.     

New Layered Materials in the K–In–Ge–As System: K8In8Ge5As17and K5In5Ge5As14

Exploratory synthesis in the K–In–Ge–As system has yielded the unusual layered compounds K₈In₈Ge₅As₁₇(1) and K₅In₅Ge₅As₁₄(2), both of which contain In–Ge–As layers with interleaved potassium ions, Ge–Ge bonds, InAs₄tetrahedra, As–As bonds, and rows of Ge₂As₆dimers. Compound 1 has As₃groups, while compound 2 has infinite As ribbons on both faces of each layer. Unlike compound 1, compound 2 has substitutional defects where indium partially occupies each of the three independent germanium sites in the ratio of 1:5 for In:Ge. This partial occupancy makes 2 an electron-precise compound. The Ge(In)–Ge(In) bond of 2 is longer than the Ge–Ge bond of 1, and this bond lengthening effect was confirmed by performing DFT-MO calculations on the model compounds H₃Ge–GeH₃and H₃Ge–InH⁻₃. Possible implications of electron imprecise formulas determined by X-ray crystal structure determinations are discussed. Compound 1: space groupP2₁/cwitha=18.394 (8) Å,b=19.087 (7) Å,c=25.360 (3) Å,β=105.71 (2)°,V=8571 (4) ų, andD_calcd=4.45g/cm³forZ=4. Refinement on 4455 reflections yieldedR(R_w)=6.8%(7.8%). Compound 2: space groupC2/mwitha=40.00 (1) Å,b=3.925 (2) Å,c=10.299 (3),β=99.97 (2)°,V=1592 (1) ų, andD_calcd= 4.55g/cm³forZ=8. Refinement on 1206 reflections yieldedR(R_w)=5.6% (5.7%).