Adsorption of n-pentanol from KPF6 aqueous solution on the (100) and (110) faces of Ag single crystal electrodes

The potential dependence of the adsorption of n-pentanol (NP) on the (100) and (110) faces of Ag single crystal electrodes from aqueous KPF₆ solutions has been studied at 10 mV s⁻¹ potential scan rate by measuring the impedance both at constant frequency (f) and by sweeping f from 11 kHz to 0.1 Hz. The adsorption of NP has been found to be strongly dependent on crystal orientation. The results have been compared with those obtained on Ag(111) with the same kind of single crystal preparation, as well as with Ag(100) electrolytically grown in a Teflon capillary [A. Popov, O. Velev, T. Vitanov, J. Electroanal. Chem. 256 (1988) 405].     

Cyclic voltammetry on Ag(111) and Ag(100) faces in sodium hydroxide solutions

The electrochemical behavior of silver (100) and (111) single crystal surfaces was examined by cyclic voltammetry in aqueous NaOH solution. In the `double layer' region (between −1.2 and 0.1 V (SCE)) adsorption of OH⁻ ions followed by phase transformation into an Ag–OH monolayer was found to take place. The difference in peak potentials recorded in 0.1 and 0.01 mol dm⁻³ NaOH solutions of about 60 mV indicates that one electron is exchanged in the overall electrochemical reaction, implying a complete charge transfer between OH⁻ ions and the silver surface. The adsorption process has been modeled to a Frumkin adsorption isotherm. Further oxidation of silver into Ag₂O takes place at more positive potentials. The formation of bulk Ag₂O results in considerable change to the original single crystal surface. This is likely to be due to roughening of the silver surface as a consequence of the formation and reduction of the oxide.     

Photochemical Preparation of Nanoparticles of Ag in Aqueous-Alcoholic Solutions and on the Surface of Mesoporous Silica

Stable nanoparticle colloids of silver were obtained by irradiation of aqueous-alcoholic solutions of AgNO₃ in the presence of mesoporous SiO₂ powder and films modified with benzophenone (BP/SiO₂). Colloidal solutions of Ludox silica were used to stabilize the photochemically produced nanoparticles of silver in solution. Formation of nanoparticles of Ag on the surface of mesoporous silica occurred on irradiation of SiO₂ modified with silver ions (Ag⁺/SiO₂) in the presence of benzophenone solution.__________Translated from Teoreticheskaya i Eksperimental’naya Khimiya, Vol. 41, No. 2, pp. 100–104, March–April, 2005.     

Acetonitrile as Adsorbate or Solvent to Probe the Crystal Face Specificity of Metal–Water Interaction at Silver Electrode/Solution Interfaces

The crystal face specificity of metal–water interaction at Ag electrode/solution interfaces is investigated by using acetonitrile (ACN) as a probe molecule of the water interfacial structure or as a solvent in which water is a solute. Capacitance and voltammetric curves suggest that ACN is weakly adsorbed from aqueous solution on Ag in the order (111) > (100) > (110). Apparent inconsistencies of adsorption parameters are explained by the occurrence of two ACN adsorption modes: (i) directly on the metal surface and (ii) on the water layer adsorbed on the metal surface. Ag surface oxidation in ACN in the presence of variable amounts of water suggests that water has an inhibiting effect on Ag oxidation, the diminution of the water content in ACN leading to free anodic dissolution of the metal surface.     

Molecular–Continuum Model for the Cyanide Ion Adsorption from Aqueous Solutions on Copper Metals

Quantum-chemical calculations of the cyanide ion adsorption from aqueous solutions on copper metals are performed for the first time in a combined molecular–continuum model of polar solvent. The calculations use the cluster model of the surface and are carried out by the density functional in the B3LYP version. The effect of the adsorption system's polar dielectric environment is considered in a self-consistent reactive field model, namely, the SCIPCM model. The dielectric cavity is built in SCIPCM self-consistently with the particle's electron density distribution in solution. Calculations show that the CN^– adsorption energy decreases in the sequence Au > Cu > Ag. The calculated energy agrees best with the experimental data when the molecular–continuum model is used, rather than the simpler molecular and continuum models.     

Adsorption of 2-amino-5-nitropyridine on the (111) and (210) silver faces

The adsorption isotherms of 2-amino-5-nitropyridine (ANP) on the (111) and (210) silver faces from an aqueous solution of 0.09 M KClO₄ + 0.02 M NaOH were determined at −0.4 V vs. the 1 mol⁻¹ calomel electrode using double-potential-step chronocoulometry. The surface concentration Γ_ANP of ANP was obtained by stepping the applied potential from −0.4 V, where ANP is electroinactive, to −1.2 V, where ANP is electroreduced to 2,5-diaminopyridine. The charge involved in this step, once corrected for the diffusive and capacitive contributions, yields 6FΓ_ANP directly. The maximum surface concentration and standard Gibbs energy of adsorption are equal to 3.6 × 10⁻¹⁰ mol cm⁻² and −35 kJ mol⁻¹ on Ag(111) and 5.2 × 10⁻¹⁰ mol cm⁻² and 42 kJ mol⁻¹ on Ag(210), thus demonstrating the strong effect of surface crystallography on the energetics of ANP adsorption.     

Adsorption of bromide at the Ag(100) electrode surface

The adsorption and phase formation of bromide on Ag(100) has been studied by chronocoulometry and surface X-ray scattering (SXS). With increasing electrode potential, bromide undergoes a phase transition from a lattice gas to an ordered c(2×2) structure (θ=0.5). The degree of lateral disorder was estimated by comparing the SXS- and the electrochemical measurements. Based on chronocoulometric experiments, a thermodynamic analysis of charge density data was performed to describe the bromide adsorption at the Ag(100) electrode. The Gibbs surfaces excess, electrosorption valencies, Esin–Markov coefficients, and the Gibbs energy of adsorption, lateral interaction energies as well as surface dipole moments have been estimated. The experimental θ versus E- isotherms are modeled employing (i) a quasi-chemical approximation as well as (ii) the results of a recent Monte Carlo simulation. An attempt is made to discuss the structure data and thermodynamic quantities of bromide adsorption on Ag(100) on the basis of the Grahame–Parsons model of the Helmholtz layer.     

Interaction of Chloride Anion and Chlorine Atom with Indium and Gallium Surfaces: A Quantum-chemical Study

The adsorption of the chloride ion and chlorine atom on clusters simulating the surface of the (111) and (001) faces of the crystal lattice of indium and liquid gallium are calculated using the Hartree–Fock–Roothaan and density functional (B3LYP) quantum-chemical methods. The energy of adsorption of chloride ions from a gas phase at these faces increases in the following series: bridgehollow < on-top positions and equals to 179 kJ mol^–1 for In(111) and 183 kJ mol^–1 for gallium in the on-top position. Both metals exhibit similarity in the formation of bonds between their surface atoms and the adsorbate. The adsorbate charge does not depend on the adsorbed form (chloride ion or chlorine atom) and equals 0.5e. Parameter of a virial adsorption isotherm is estimated with allowance for coulombic interactions near the metal/electrolyte interface.     

Computer Simulation of the Initial Stage of the Nucleation of Water Vapors on the Silver Iodide Crystal Surface: 2. Thermodynamics

The formation work of the condensed phase nucleus from the vapor on the surface of silver iodide at 273 K is calculated by the method of bicanonical statistical ensemble. The energy barrier of the formation of a nucleus of a monolayer on the surface is located in the region of extremely small sizes and its height does not exceed the energy of thermal motion k _B T. Such a barrier cannot markedly decelerate the nucleation. A point crystal defect in the form of an extra ion on the surface qualitatively changes the pattern of the formation work curve: the minimum with a depth of about 100k _B T corresponding to a thermodynamically stable nucleus appears on this curve. As the vapor pressure increases, “spots” of water molecules are formed and grow on the substrate surface around point crystal defects. These spots tend to coalesce and cover the entire surface as a monolayer; however, the high free energy barrier prevents the formation of further layers.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 561–572.Original Russian Text Copyright © 2005 by Shevkunov.     

A comparative study of hydroxide adsorption on the (111), (110), and (100) faces of silver with cyclic voltammetry, ex situ electron diffraction, and in situ second harmonic generation

Hydroxide adsorption on the (111), (110), and (100) faces of silver electrodes from mixed NaOH/NaF solution is studied using cyclic voltammetry and in situ second harmonic generation (SHG). Cyclic voltammograms for the three low index silver planes in alkaline electrolytes are for the first time compared. They show two pairs of anodic and cathodic peaks in the potential interval below the equilibrium Ag/Ag(2)O potential. These are attributed to the specific adsorption of hydroxide ions followed by submonolayer oxide formation. The differences in the cyclic voltammograms for the (111), (110), and (100) planes are attributed to different (i) work functions, (ii) surface atomic densities, and (iii) corrugation potentials for these surfaces. Ex situ low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED) show that disordered adlayers are formed on Ag(111) and Ag(100), in contrast to Ag(110), where ordered structures are produced in the region of the first pair of current peaks. In the region of the second pair of peaks, LEED indicates disordered oxide phases on each crystal plane and RHEED shows the presence of small islands of c(2 x 2) structure at some potentials on (110) and (100). SHG measurements were performed (i) in the potential scan mode at constant rotational angle and (ii) at constant potential as a function of the rotational angle. The isotropic (for the (111), (110), and (100) planes) and anisotropic (for the (110) and (111) planes) contributions to the SHG intensity were calculated by fitting the experimental data and are discussed in terms of their dependence on the charge density at the interface, on hydroxide adsorption, and on submonolayer oxide formation.     

Specific Features of the Initial Stages of Oxidation of a Silver Electrode in Weakly Acidified Solutions of Sodium Fluoride

The behavior of a silver electrode, which is renewed in situ by mechanical cutting, in weakly acidified sodium fluoride solutions is studied with the aid of an impedance method and a method of cyclic voltammetry. The application of said procedures makes it possible to record time effects, which reflect the processes of electrochemical adsorption of oxygen at the interface between the silver electrode and the solution, in the potential region extending from −0.7 to 0.2 V (SCE). Approximate calculations of the effect of potential and the time of the electrode’s exposure (after its renewal) in contact with the electrolyte at given values of potential on the amount of adsorbed oxygen are performed on the basis of an analysis of the obtained experimental data. A comparison of the obtained results with the literature data makes it possible to put forth a substantiated opinion as to the reasons for the substantial difference in the intervals of potentials of ideal polarizability of the silver electrode/solution of a surface-inactive electrolyte system, which are presented in works of various authors.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 857–865.Original Russian Text Copyright © 2005 by Safonov, Choba, Oshkin.     

Analysis of the differential capacity at the silver / lithium perchlorate aqueous solution interface

Analysis of the differential capacity of ideally polarized Ag electrodes without specific adsorption is presented. The capacity was measured for three crystal faces of Ag [(111), (100) and (110)] and for polycrystalline Ag in aqueous solutions at different concentrations of LiClO₄. The inner layer contribution C _i was analysed for all the systems studied according to Grahame's concept. Moreover, using the procedure proposed by Amokrane and Badiali, several contributions to C _i, i.e. the metal (C _m), the solvent (C _s) and dipole orientation (C _dip), were calculated. The influence of the kind of crystal face of the Ag electrode on the values of these contributions is discussed. Received: 21 May 1999 / Accepted: 19 November 1999     

Potentiometric determination of the activity of fluoride ion in aqueous solutions at high pressure and high temperature

Summary A fluoride membrane electrode is described for the determination of the activity of fluoride ion in aqueous solutions at high pressure and elevated temperature. An Ag/AgCl electrode is used as a reference. The cell described has a linear potential at temperatures up to 200 °C and pressures up to 1 kbar. The interference of OH^– is only noticeable at fluoride concentration c_f– 10^–5 m in the temperature region between 175 °C and 200 °C.

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Potentiometrische Bestimmung der Aktivität des Fluorid-Ions in wäßrigen Lösungen bei hohem Druck und hoher Temperatur

     

Reversed-phase liquid chromatography and argentation chromatography of the minor capsaicinoids

An investigation of the liquid chromatography of the minor capsaicinoids in a commercial capsaicinoid mixture is reported. Twelve stationary phases including C₈, C₁₈, C₃₀, phenyl, and cation-exchange chemistries were examined in combination with isocratic aqueous methanol and aqueous acetonitrile mobile phases. A phenyl stationary phase and aqueous acetonitrile mobile phase baseline-resolved 7 of 11 capsaicinoids, and selected ion chromatograms (LC–ESI-MS) demonstrated this was the most effective reversed-phase separation. Argentation chromatography with an alkyl or phenyl column and aqueous silver nitrate–methanol mobile phase revealed the presence of the 6-ene-8-methyl and 6-ene-9-methyl homocapsaicin isomers and the absence of 7-ene-9-methyl homocapsaicin. A mixed phenyl–cation-exchange stationary phase (charged with silver ion) enabled unique and useful separations of the capsaicinoids.     

电极/溶液界面单分子吸附层的统计力学处理 IV. 水溶液中银单晶电极的内层微分电容

根据本文系列I~[6]提出的电极/溶液界面溶剂化层偶极取向分布模型, 拟合计算Ag(111)、Ag(100)及Ag(110)/水溶液界面的内层微分电容(C_1)～表面电荷密度(σ)变化关系。表明在银电极上, 吸附水分子似分别稳定在金属原子点阵的顶位(111)或穴位(100)及(110)。讨论了溶剂化层的结构与性质对C_1～σ曲线可能产生的影响。     

Synthetic Semiconductor Diamond Electrodes: Electrochemical Characteristics of Individual Faces of High-Temperature-High-Pressure Single Crystals

Effects of crystal structure on the electrochemistry of boron-doped high-temperature-high-pressure diamond single crystals grown from an Ni–Fe–C–B melt are studied. On the {111}, {100}, and {311} faces, the linear and nonlinear electrochemical impedance spectra and the electrochemical kinetics in the Fe(CN)₆ ^3_/4_ redox system are measured. The acceptor concentration in the diamond interior adjacent to these faces was determined from the Mott–Schottky plots and the amplitude-demodulation measurements. It varies in the 10¹⁸ to 10²¹ cm^–3 range. The difference in the electrochemical behavior of individual crystal faces is primarily attributed to different boron acceptor concentrations in the growth sectors associated with the faces.     

Quantum calculations on the adsorption of halide ions on the noble metals

The interaction of halide ions with the three noble metals has been investigated using the B3LYP density functional method and the cluster model approximation. The results of calculations for the M—X⁻ and M₁₂—X⁻ (M = Cu, Ag, Au; X = F, Cl, Br, I) systems are presented. At the (100) surface, modeled in the present work by the M₁₂ cluster, all halide ions have been found to adsorb preferentially at the hollow site, followed by the bridge and by the top positions. The adsorption energy has been found to decrease when going from fluoride to iodide in both atom—ion and cluster—ion cases. The opposite trend is observed for the estimates of the charge transfer from the ions to the surface. When different metals are compared, the M₁₂—X⁻ interaction energies decrease in the order Au > Ag > Cu, but for the smaller ions some deviations from this line do appear. The relative values of the calculated harmonic vibrational frequencies do agree with those found experimentally, but their magnitude is much smaller as a result of the effect of the lower surface coverage.     

{[Ag(ATO)~2]ClO~4}~n的制备和分子结构

通过4-氨基-1,2,4-三唑-5-酮(ATO)水溶液与高氯酸银溶液反应,制备了聚高氯酸二(4-氨基-1,2,4-三唑-5-酮)合银(I)。并用X射线衍射、红外光谱和TG-DTG对其进行了结构表征。晶体属三斜晶系,空间群为P1,a=0.7534(1)nm,b=0.8505(1)nm,c=1.0257(1)nm;α=69.47(1)ⅲ,β=72.69(1)ⅲ,γ=86.00(1)ⅲ;V=0.5872(1)nm^3,Z=2,D~c=2.305g/cm^3,F(000)=400;偏离因子R为0.0358。中心银离子表现为较为特殊的三配位。     

Electrochemical Behavior of the LaF3:Eu2+/Me Interface (Me = Sm,Ce, Gd,V, Ag)

The electrochemical behavior of the LaF₃ : Eu²⁺| interface (Me = Sm, Ce, Gd, V, Ag) is studied using stripping voltammetry. Current–voltage curves for cells Ag, AgCl|KCl and KF|LaF₃ : Eu²⁺|Sm (or Ce) may be viewed as background curves for analyzing solid-phase reactions with other metallic electrodes. The substrate material is found to affect properties of interfaces LaF₃ : Eu²⁺/Gd (or V), which are characterized either by solid-phase reactions involving the fluoride ion of a solid electrolyte or by reactions involving oxygen. Regularities, obtained for silver in contact with LaF₃ : Eu²⁺, link electrochemical signals of the reaction of the silver fluoride formation with the contact area.