New Type of an Adsorption Layer of Organic Molecules with a Cage Structure Condensed at the Electrode/Solution Interface: The Adsorption of Cubane Derivatives on a Mercury Electrode

A synthesis and a study by method of measuring the differential capacitance on a stationary mercury drop of the adsorption of a number of cubane derivatives in a surface-inactive electrolyte are performed. It is established that the compounds studied exhibit a high surface activity. For bromine derivatives of cubane (4-bromomethoxycarbonylcubane, 4-bromohydroxymethylcubane) the formation of two-dimensional adsorption layers is discovered. Values of adsorption parameters for these compounds are evaluated with use made of the Frumkin isotherm.     

Effect of Adsorption of Neutral Molecules on the EDL Capacitance of a Rough Electrode

The perturbation theory is used to design a theoretical model for the Frumkin–Melik-Gaikazyan impedance of a sine electrode with a perturbation parameter equal to the ratio between the amplitude of surface oscillations and its period for a diffusion-controlled adsorption stage. The unequal diffusion access to the interface increases its capacitance. At higher frequencies, the electrode capacitance is defined by its geometric roughness factor. At lower frequencies, the capacitance depends on the adsorption conditions. The adsorption of electroactive substances results in a constant phase angle; the electrode roughness alters it and the frequency range where it remains constant.     

Electrical Double Layer Structure on Electrodes of Platinum Metals: Effect of the Carbon Monoxide Adsorption

Results on the paper's theme are reviewed. Attention is focused mainly on the use of transients of current and open-circuit potential for elucidating changes in the structure of the electrical double layer (EDL) caused by the CO adsorption. It is shown that the high binding energy of CO with surfaces of platinum metals leads to a strong suppression of the total differential capacitance of the electrode, the recharge of the surface, the displacement of strongly adsorbed atoms formed during the adsorption of ions with a total charge transfer, and to other alterations in the EDL plates facing both solution and metal. The importance of allowing for double-layer effects when solving problems of electrocatalysis on platinum metals is emphasized.     

低信膜比条件下金膜电极电位溶出分析法研究

推导并验证了信号与金膜厚度的比值较小（即低信膜比）时金膜电极电位溶出分析法的过渡时间方程式和电位时间方程式。实验确定的理论式的应用条件为τ／ｌ２≤５８×１０１０ｓ／ｃｍ２，并发现当扩散路径约为扩散层厚度的３倍时，便可按半无限扩散条件处理扩散问题。从而解决了利用小信号进行金膜电极电位溶出基本问题，即信号与浓度的定量关系。     

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.     

Spillover on a Platinum Electrode Modified by MWNTs

The spillover phenomenon is observed on the platinum (Pt) disk electrode modified by multi-wall carbon nanotubes (MWNTs). The rate of the spillover of oxygen-containing species produced on Pt surface to and from MWNTs is fast. However for hydrogen-adatoms, the spillover is very weak. The selective spillover on the Pt/MWNTs electrode may provide a novel way to design catalysts.     

Adsorption from a Layer of Finite Thickness on a Planar Electrode

Within the Nernst diffusion model, the effect the convection has on the adsorption at a planar electrode is studied for the case of a diffusion-controlled stage of adsorption and the behavior of the Frumkin–Melik–Gaikazyan finite adsorption impedance is analyzed. Allowing for the convection leads to new functional frequency dependences of constituents of this impedance at low frequencies, where the active constituent depends on the diffusion layer thickness more heavily than the capacitive one. During adsorption of neutral molecules from a layer of finite thickness, an additional relaxation time emerges in an electrochemical system, which results from a finite rate of motion of species in the near-electrode layer. Ignoring the convection may lead to erroneous interpretation of the adsorption mechanism.     

A Simulation of an Anion‐Induced Adsorption of Metal Ions in Pseudopolarography Using a Thin Mercury Film Covered Rotating Disk Electrode

A theory of the influence of anion‐induced adsorption of metal ions in pseudopolarography using the thin mercury film covered rotating disk electrode is developed. The model is developed assuming that the metal ion is forming several labile complexes with the ligand which is present in a great excess, and that only one complex species is adsorbed following a linear isotherm. The results obtained assuming steady‐state conditions are compared with the simulation of transient processes using Galerkin and finite difference methods. It is shown that the adsorption of metal complexes on the disk electrode surface does not prevent the determination of the stability constants.     

Effect of Inorganic Ions on Oleate Adsorption at a Nigerian Hematite–Water Interface

Using “pure” natural hematite selected from a high silica Nigerian hematitic ore, oleate adsorption densities at the hematite–water interface were determined in the presence of various inorganic ions (anions and cations) of different charges and at varying concentrations. Adsorption density was determined using electrical conductivity measurements. The specific surface area of the hematite particles was determined using the method of adsorption of paranitrophenol in aqueous solution. Inorganic ions in solution depressed oleate adsorption at the aqueous hematite surface. The charge of the ion proved to be the dominant factor determining the depression of oleate adsorption. Ionic strength also was an influence, up to a limiting value at which monolayer oleate coverage of the hematite surface occurred. The inorganic ions in solution are considered to function through nonspecific adsorption in the diffuse region of the electric double layer.     

Electrochemical Studies of the Benzoate Adsorption on Au (111) Electrode

Cyclic voltammetry (CV), differential capacity (DC), and charge densitymeasurements have been employed to study the benzoate (BZ) adsorption at the Au(111)electrode surface. Thermodynamic analysis of charge density (_M) data has beenperformed to describe the properties of the adsorbed benzoate ion. The Gibbsexcess , Gibbs energy of adsorption G, and the number of electrons flowingto the interface per adsorbed benzoate ion at a constant potential (electrosorptionvalency) and at a constant bulk concentration of the benzoate (reciprocal of theEsin—Markov coefficient) have been determined. The results demonstrate thatalthough benzoate adsorption starts at negative charge densities, it takes placepredominantly at a positively charged surface. At the most positive potentials,the surface concentration of benzoate attains a limiting value of about 7.3×10^–10mol-cm^–2, which is independent of the bulk benzoate concentration. This valueis consistent with packing density corresponding to a closed-packed monolayerof vertically adsorbed benzoate molecules. At negative charge densities, benzoateassumes a flat (-bonded) surface coordination. The surface coordination ofbenzoate changes, by moving from a negatively to positively charged surface.At the negatively charged surface, the electrosorption bond is quite polar. Thepolarity of the chemisorption bond is significantly reduced due either to a chargetransfer or a screening of the charge on the anion by the charge on the metal.     

Accounting for the Adsorption of Anions When Interpreting the Mechanism of Electrodeposition of Metals from Complex Electrolytes: The Reaction Order by the Electrochemically Active Ion

The relationship between the current and the bulk concentration of complex ions during concurrent specific adsorption of an electrochemically active complex ion and a complexing ligand is considered. The effect of parameters that characterize adsorption of such ions and the structure of the electrical double layer on this relationship is analyzed.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 817–822.Original Russian Text Copyright © 2005 by Rogozhnikov.     

Adsorption of sodium octylbenzene-sulfonate at the liquid/air interface

The surface tensions of aqueous solutions containing sodium octylbenzenesulfonate were measured by means of a processor tensiometer at 20°, 25°, 30° and 35°C. A test for the layer model and thickness of the adsorbed phase is proposed. By means of a linear regression the surfactant area at liquid/air interface was calculated. Finally, the molar-and surface-related thermodynamic functions were discussed.     

Method for Thermodynamic Description of an Elastically Deformed Electrode, Based on Relating Its Extensive Surface Characteristics to a Strainless Electrode

A theoretical approach to thermodynamic describing elastically deformed electrodes made of isotropic materials is suggested. The approach is based on considering the surface of a strainless electrode as a reference one. A surface analog of the Lame elastic constants is introduced. Dependences of the Shuttleworth equation and the Gibbs adsorption equation on the Lame elastic constants characterizing the surface are found in an explicit form.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 993–996.Original Russian Text Copyright © 2005 by Grafov, Paasch.     

ZrC-桑色素络合物在碳糊电极上的二次导数吸附伏安法测定Zr的研究

研究了Zr 桑色素络合物在碳糊电极正电位区的吸附伏安行为 ,并利用其在 0 .74V处的二次导数吸附氧化峰电流与Zr(Ⅳ )浓度为 6 .0× 10 -9～ 2 .0× 10 -6mol/L呈线性而测定Zr;检出限为 3.0× 10 -9mol/L(S/N =3)。最佳测定条件为 :2 .0mol/LHCl、1.0× 10 -5mol/L桑色素 ;富集电位为 0V(vs .SCE) ;扫描速度为2 5 0mV/s。该法不需萃取分离 ,可直接用于岩石样品中Zr的测定 ,结果满意     

尿嘧啶在银电极表面吸附状态的研究

综合分析了尿嘧啶在银电极表面不同条件的表面增强激光Ｒａｍａｎ光谱（ＳＥＲＳ）,利用扩展的Ｈüｃｋｅｌ分子轨道法（ＥＨＭＯ）对尿嘧啶分子在银电极表面的吸附状态进行了计算．结果表明：最稳定的吸附构型能较成功地阐明尿嘧啶吸附在银表面的ＳＥＲＳ谱;尿嘧啶在银表面主要是以Ｎ（３）去质子化的形式吸附;尿嘧啶在银表面的吸附取向是由其浓度和银表面电位共同决定;在较低浓度和较高电位时,Ｎ（３）去质子化的尿嘧啶离子在银表面主要是通过Ｃ（２）及整个嘧啶环上的π电子体系与银表面的相互作用平躺地吸附;在较高浓度和较低电位时,吸附取向发生改变,即主要是通过Ｎ（３）与Ｏ（１０）以及Ｎ（３）与Ｏ（８）垂直地共同吸附在银表面上     

Aggregation and Adsorption Properties of Tetramethylsulfonatoresorcinarenes and their Associates with Nonionogenic Guest Molecules in Aqueous Solutions

Present paper reports on tensiometric studies of tetramethylsulfonatoresorcinarenes 1 and 2 with nonionogenic guests 3 and 4, pyrimidin derivative and O,O-dymethyl-1,1-dimethyl-3-oxobutylphosphonate, respectively. Association of resorcinarenes with these guests leads to dramatic change of adsorption characteristics of their solutions. CCMs₁ of associates (1&3, 1&4, 2&3, and 2&4) are lower and the estimated surface activity, as well as the height of adsorption layers are higher than for individual substances. Aggregation of compounds 1–4 and association of 1 with 3 and 4 in solution were confirmed by ¹H NMR spectra and studied by diffusion NMR with impulse magnetic field gradient.     

锆-茜素红络合物在多壁碳纳米管修饰碳糊电极上的阳极吸附伏安法研究

制备了多壁碳纳米管修饰碳糊电极并研究了锆-茜素红络合物在该电极上的阳极吸附伏安行为,采用二阶导数线性扫描伏安法进行分析,实验结果表明,在0.128 mol/L氨基乙酸-0.048 mol/L邻苯二甲酸氢钾缓冲液(pH 4.0)中,在200 mV富集60 s,在200~1200 mV范围内以200 mV/s的速率线性扫描,络合物吸附在该修饰电极表面,于832 mV(vs.SCE)处产生一个灵敏的氧化峰,为络合物中配体茜素红的氧化所产生。络合物的峰电流与锆的浓度在1.0×10-11~2.0×10-7mol/L范围内呈良好的线性关系;检出限(S/N=3)为6.0×10-12mol/L(富集时间180 s)。方法用于岩矿样品中痕量锆的测定,结果满意。     

Theoretical Study on Adsorption and Diffusion of N Atoms on Cu Low-index Surface

The adsorption and diffusion of N atoms on the three low-index Cu planes were studied using 5-parameter Morse potential (5-MP) method, and the best theory-experiment agreement was obtained. N atoms of Cu(100) surface sit on the fourfold hollow site with the vertical height of 0.018 nm closely coplanar with the topmost copper layer, and the four Cu-N bond lengths are 0.182 nm and the fifth Cu-N distance is 0.199 nm. For Cu(111) system, the existence of aberrant Cu(100) reconstructed structure is approved at higher coverage, and at low coverage the structure is almost an ideal Cu(111) surface structure. With respect to Cu(110) system, the N atoms are adsorbed at LB and H3 sites, not at SB site. The diffusion passage and diffusion barrier of adsorbed N atoms were also studied.     

Specific features of the behavior of an electrochemical system in the case of the Hopf instability for a spherical electrode

Model approximations are developed that allow establishing a quantitative relationship between the geometrical parameters of a spherical electrode, the faradaic impedance, and instabilities of the electrochemical system for an electrode reaction under potentiostatic conditions for the adsorption of species preceding their discharge. It is shown that the control parameter ω_H in the Hopf bifurcation point depends on the electrode size. The effect of the Nernst diffusion layer is observed at low frequencies in the range of negative faradaic impedance values.     

Sensitive Adsorption Stripping Voltammetric Determination of Reserpine by a Glassy Carbon Electrode Modified with Multi-Wall Carbon Nanotubes

Adsorption stripping voltammetry, a very sensitive electroanalytical method, was employed to determine reserpine, a kind of anti-hypertensive drug. In 0.1M phosphate buffer with a pH of 6.0, reserpine was accumulated at a multi-wall carbon nanotubes (MWNT)-modified glassy carbon electrode (GCE) surface under the condition of open-circuit. In the following anodic sweep from 0.20 to 1.00V, reserpine, adsorbed at the MWNT-modified GCE surface, was oxidized and yielded a sensitive oxidation peak at 0.64V. Due to its unique structure and extraordinary properties, MWNT shows a ten times higher accumulation efficiency toward reserpine, compared with a bare GCE. Hence, the amount of reserpine at the MWNT-modified GCE surface increases significantly, and finally the oxidation peak current improves greatly. The experimental conditions, such as supporting electrolyte, pH value, the amount of MWNT-DHP suspension, accumulation time and scan rate, were optimized for the measurement of reserpine, and a sensitive electroanalytical method was proposed for reserpine determination. The oxidation peak current varies linearly with the concentration of reserpine over the range of 2×10^–8 to 1×10^–5M, and the detection limit is 7.5×10^–9M after 4min open-circuit accumulation. The relative standard deviation at 1×10^–6M reserpine was about 4.7% (n=7), indicating excellent reproducibility. This new method was successfully demonstrated with reserpine injections and tablets.