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1.
Adsorption of iodide ions at the Bi(111) and Cd(0001) electrodes from the aqueous solutions with constant ionic strength 0.1x M KI + 0.1(1−x) M KF and 0.1x M KI + 0.033(1−x) M K2SO4 has been studied by impedance spectroscopy. It was found that, to a first approximation, the classical Frumkin–Melik–Gaikazyan equivalent circuit with the slow diffusion-like and adsorption steps can be applied for fitting the experimental impedance data for iodide ions adsorption on Bi(111) and Cd(0001) from aqueous solutions with constant ionic strength. The modified Grafov–Damaskin circuit can be used in the region of electrode potentials, where parallel faradic processes (electroreduction of protons, oxygen traces) are probable. The more complicated Ershler equivalent circuit, taking into account the slow diffusion-like, adsorption and charge transfer steps, is not applicable for characterization of the adsorption process of I at Bi(111) and Cd(0001) electrodes.  相似文献   

2.
The adsorption parameters for systems Ga/[NMF + 0.1m M KCl + 0.1(1 ? m) M KClO4], Ga/[NMF + 0.1m M KBr + 0.1(1 ? m) M KClO4], and Ga/[NMF + 0.1m M KI + 0.1(1 ? m) M KClO4] are calculated by using the regression analysis of the adsorption potential shift vs. electrode charge dependences for the following molar fractions m of the surface-active anion: 0.05, 0.1, 0.2, 0.5, and 1 within the framework of two models. The models are based on the Frumkin isotherm with the free adsorption energy dependent on the electrode charge, of which one model takes into account the diffuse layer and the other ignores it. It is shown that for electrode charges q ?? 16 ??C/cm2, both models provide equal accuracy; however, for higher q, preference should be given to the model that takes into account the contribution of the double layer diffuse part.  相似文献   

3.
It is shown that the weak specific adsorption of ions not involving the recharging of the electrode surface is characterized by the following unusual features: practical absence of any shift of p.z.c.; a very small discrepancy between the experimental differential capacity curves and similar curves calculated under the assumption that specific adsorption is absent (q1 = 0); insensitivity of the total surface excess of cations to their distribution between the dense and diffuse layers; practical independence of q1 of temperature and the bulk concentration of binary electrolyte; practical coincidence of c.t.p. calculated for different concentrations of surface-active supporting electrolyte assuming q1 = 0. It is also shown on the basis of the experimental data for the system {mc CsCl + (1 ? m)c LiCl} that the main fraction of the effective charge, determined by the mixed electrolyte method of Hurwitz—Parsons, results from the true specific adsorption of Cs+ cations at the Hg/H2O interface and only a small fraction of this charge (?20%) can be associated with different positions of the o.H.p. for Li+ and Cs+ ions.  相似文献   

4.
By the regression analysis of dependences of the adsorption potential shift (E ads) on the electrode charge in systems (Tl-Ga)/[NMF + 0.1m M KI + 0.1(1 ? m) M KClO4], (Tl-Ga)/[NMF + 0.1m M KBr + 0.1(1 ? m) M KClO4], and (Tl-Ga)/[NMF + 0.1m M KCl + 0.1(1 ? m) M KClO4] with the following m fractions of the surface-active anion: 0.05, 0.1, 0.2, 0.5, and 1, the adsorption parameters are calculated in terms of two models based on the Frumkin isotherm both considering the free adsorption energy as a quadratic function of the electrode charge, where one model takes into account the diffuse layer and the other ignores it. It is shown that for the studied electrode charges q ≤ 2 μC/cm2, both models provide equal accuracy in calculating E ads in the systems under study.  相似文献   

5.
The adsorption of iodine and iodide anions on a Pt/Pt electrode (0.5 M H2SO4 as a supporting solution) is compared using potentiodynamic and galvanostatic charging curves, transients of the current and open-circuit potential (OCP), and analytical measurements. Variations in the charge and OCP during the adsorption obey relationships derived for strong adsorption of neutral species and ions on a hydrogen electrode with the formation of irreversibly adsorbed atoms. The main product of the I2 and I chemisorption in acid solutions is adsorbed iodine atoms. However, adsorption of iodine occurs in noticeable amounts and above a monolayer in the form of species that undergo electrodesorption during a cathodic polarization to potentials of the beginning of hydrogen adsorption. In the presence of a monolayer of adsorbed iodine atoms, potential of the zero total charge of a Pt/Pt electrode is in the oxygen adsorption region.  相似文献   

6.
By the regression analysis of dependences of the adsorption potential shift (E ads) on the electrode charge in systems (In-Ga)/[NMF + 0.1m M KCl + 0.1(1 - m) M KClO4, (In-Ga)/[NMF + 0.1m M KBr + 0.1(1 ? m) M KClO4], and (In-Ga)/[NMF + 0.1m M KI + 0.1(1 - m) M KClO4] with the following m fractions of the surface-active anion: 0.05, 0.1, 0.2, 0.5, and 1, the adsorption parameters are calculated in terms of two models both based on the Frumkin isotherm and considering the free adsorption energy as a function of the electrode charge, where one model takes into account the diffuse layer and the other ignores it. It is shown that for the studied electrode charges q ≤ 10 μC/cm2, both models provide equal accuracy in calculating E ads and the differential capacitance (C) in the systems under study. However, for determination of adsorption parameters, the regression analysis of E ads vs. q curves has several advantages over the analogous analysis of C vs. q curves.  相似文献   

7.
Using the method of phase modeling, the pH values of solutions corresponding to the uncharged surface of passive iron and ferric oxide γ-Fe2O3 (pH0) are compared. According to the theory of connected places, the charge of metal oxide surface is determined by the adsorption or desorption of hydrogen ions leading to a change in the potential drop at the oxide/solution interface. Preliminarily passivated iron electrode was washed with twice-distilled water and placed into 0.5 M NaNO3 solution with various pH values; the variation in the potential (ΔE) with time was studied. The pH0 value for passive electrode under the open-circuit conditions was determined by the dependence of ΔE on the pH value (pH0 6.2 ± 0.1). The pH0 value was close to that for γ-Fe2O3 (pH0 6.2), which was determined by the method of potentiometrical titration of oxide suspension in the nitrate solution. The introduction of surface-active ions Ba2+ and Cl? changes the charge of passive iron surface: Ba2+ ions increase the electrode potential, while Cl? ions decrease it. Comparing the pH0 values for passive electrode and metal oxides, one can identify the composition of passive electrode surface.  相似文献   

8.
9.
A “solvionic” model of a multicomponent electrochemical system (mixed electrolyte) is considered. An ion in the solution is considered as a point charge rigidly fixed inside its solvation shell. The corresponding equations for the diffuse layer on an ideally polarizable electrode are derived, and an effective method of their numerical solution is formulated. The calculations are performed in order to follow the changes in the diffuse layer structure with variations in the electrode charge and electrolyte composition. Far from the zerocharge potential of solution, the dependences of distributions of solution components over the diffuse layer on the electrode charge radically differ from those within the classic Gouy-Chapman theory. Analytical equations (asymptotics at large electrode charges) for concentrations of solvated ions in the plane of their maximum approach and for their “surface excesses” (diffuse adsorption) are determined. Results of numerical calculations for a 0.2 M LiCl + 0.05 M BaCl2 solution are plotted.  相似文献   

10.
Adsorption behavior of anions at liquid (Ga-In)-electrode at a temperature of 305 K is studied by electrochemical impedance spectroscopy and cyclic voltammetry. The above-listed methods allowed evaluating the adsorbability of different ions. Equivalent circuit describing the experimental data in the presence and in the absence of ions Br and Cl is a contour comprising a resistance connected in series to a capacitance whose value remains constant over the frequency range from ∼300 Hz to 10 kHz. Analysis of the experimental data obtained by the mixed electrolyte method with excess of surface-inactive ion Cl and constant ionic strength 0.1 M in electrolyte solutions acidified down to pH 3 gave the charge of specifically adsorbed ions Br and Cl1) at the liquid (Ga-In)-electrode surface as 5.24 and 1.67 μC/cm2, respectively, at the adsorbate maximal concentration and zero-charge potential. These values are characteristic of very weak specific adsorption. The σ1 values found for the (Ga-In)-electrode were used in the calculations of different isotherms, aiming at the determination of adsorption parameters. The results of the study were compared with literature data obtained by different researchers for different metals in the presence of specifically adsorbing bromide and chloride ions.  相似文献   

11.
Electrochemical characteristics for the nanoporous carbon|Et4NBF4+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et4NBF4+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material.  相似文献   

12.
Electroreduction of Eu(ClO4)3 and Eu2(SO4)3 has been studied at electrochemically polished \textBi( 01[`1] ) {\text{Bi}}\left( {01\bar{1}} \right) single-crystal electrode in an acidic HClO4 or H2SO4 (pH ~3) aqueous solution with LiClO4 or Na2SO4 additions as a surface inactive electrolyte. The Eu3+ cations electroreduction rate depends on the electrode potential applied and the concentration of the supporting electrolyte as well as the concentration of the Eu3+ ions. At the more negative electrode potentials than the zero charge potential (zcp), the diffusion current plateaus were observed. The values of the rate constant for the heterogeneous reaction calculated at zcp are independent of the base electrolyte concentration studied. Analysis of the kinetic data corrected for the electrical double-layer effect shows that the coincidence of the corrected Tafel plots can be achieved, assuming that the effective charge of a reactant (+1.6) is significantly lower than it would be expected (z A = +3).  相似文献   

13.
Experimental solubilities of amorphous silica in several aqueous electrolyte solutions and in aqueous solutions of organic compounds, and theoretical considerations concerning cavity formation, electrostriction collapse, ion solvation, and long- and short-range interaction of the solvated ions with one another(1) permit the calculation of the partial excess free energies and the activity coefficients of aqueous silica. It is shown that, in the case of non-dissociated aqueous organic solutions, the variation of log m (SiO2) with the reciprocal of the dielectric constant of the solution is described by a single linear equation independent of the nature of the organic compound. For aqueous electrolyte solutions, a specific linear relationship between log m (SiO2) and the reciprocal of the dielectric constant occurs for each electrolyte. The success of the equation in reproducing the experimental solubilities of amorphous silica in aqueous solutions of electrolytes and organic compounds supports previous evidence indicating a polar charge distribution in the solvated SiO2 molecule. Our data permit the calculation of the effective local charge of dissolved SiO2 molecules and of the short-range interaction parameters between SiO2 and various ions. The proposed equation of state can be used to calculate the affinity of reactions among SiO2 minerals and complex aqueous solutions.  相似文献   

14.
The adsorption of acetone on a mercury electrode from (CH3)2CO+H2O+HCl solutions has been studied using a thermodynamically rigorous procedure. The chemical potential of the supporting electrolyte has been kept constant by using the concentrations corresponding to the constant e.m.f. of the cell with electrodes reversible to each of the ions in the solutions. It is suggested that the molecule is to some extent oriented with the hydrocarbon part towards mercury. The composition of the surface layer has been calculated.  相似文献   

15.
Electrical double layer and electrochemical characteristics at the nanoporous carbon|acetonitrile interface with additions of Et4NBF4, Et3MeNBF4, EtMe3NBF4, LiClO4, and LiBF4 have been studied by cyclic voltammetry and impedance spectroscopy methods. A value of zero charge potential, dependent on the structure of the cations as well as on the composition of the anions, the region of ideal polarizability, and other characteristics has been established. Analysis of the complex plane plots shows that the nanoporous carbon|acetonitrile+0.1 M electrolyte (Et4NBF4, Et3MeNBF4, or EtMe3NBF4) interface can be simulated by the equivalent circuit, in which the two parallel conduction parts in the solid and liquid phases are interconnected by the double layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer process or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte composition and on the electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. In the region of moderate a.c. frequencies, the modified Randles-like equivalent circuit has been used for simulation of the complex plane plots. In the region of negative surface charge densities, the intercalation process of Li+ ions from LiClO4 and LiBF4 solutions into the surface film is possible and these data can be simulated using the modified Ho et al. model or Meyer et al. model. Electronic Publication  相似文献   

16.
The specific adsorption of chloride ions on the renewable liquid (Cd–Ga) electrode from mixed [0.1m М LiCl + 0.1(1–m) М LiBF4] solutions in dimethyl formamide (DMF) is studied with an ac bridge at the following fractions of surface-active anion m: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5 and 1. It is found that the data on the specific adsorption of Cl anion in the system can be quantitatively described by Frumkin’s isotherm. The free adsorption energy of ClG ads) is a quadratic function of electrode charge. The results are compared with the corresponding data for the Ga/DMF and (In–Ga)/DMF interfaces. It is shown that the adsorption energy of Cl–anions at the metal/DMF interface depends on the metal nature and increases in the series (In–Ga) ≈ (Cd–Ga) < Ga. The energy of metal–DMF chemisorption interaction, which hampers ion adsorption, increases in the same series. The analysis of the data uniquely indicates that the free energy of metal–Cl interaction (ΔG M-CL-) increases in the series (In–Ga) ≈ (Cd–Ga) < Ga. Thus, in the series of electrodes studied, the variations in the energies of metal–Cl and metal–DMF specific interaction are correlated: the higher the energy of metal–DMF chemisorption interaction, the higher the energy of metal interaction with Cl.  相似文献   

17.
The behaviour of haemoglobin (Hb) at the interface between two immiscible electrolyte solutions (ITIES) has been examined for analytical purposes. When Hb is fully protonated under acidic conditions (pH <pI) in the aqueous phase, it undergoes a potential-dependent adsorption and complexation, at the interface, with the anions of the organic phase electrolyte. When utilised as a simple and fast preconcentration step, consisting of adsorbing the protein at the interface, in conjunction with voltammetric desorption, this opens up the ITIES to the adsorptive stripping voltammetry approach. Utilising a 60 s adsorption step and linear sweep voltammetry, a linear response to Hb concentration in aqueous solution over the range 0.01–0.5 μM was achieved. The equation of the best-fit straight line was I p ? =?7.46 C???0.109, R?=?0.996, where I p is the peak current (in nanoampere) and C is haemoglobin concentration (in micromolar). The calculated detection limit (3σ) was 48 nM for a 60 s preconcentration period, while the relative standard deviation was 13.3 % for six successive measurements at 0.1 μM Hb. These results illustrate the prospects for simple, portable and rapid label-free detection of biomacromolecules offered by electrochemistry at arrays of liquid–liquid microinterfaces.  相似文献   

18.
A new surface based on poly(vinylferrocenium) (PVF+)-modified platinum electrode was developed for determination of Hg2+ ions in aqueous solutions. The polymer was electrodeposited on platinum electrode by constant potential electrolysis as PVF+ClO4. Cl ions were then attached to the polymer matrix by anion exchange and the modified electrode was dipped into Hg2+ solution. Hg2+ was preconcentrated at the polymer matrix by adsorption and also complexation reaction with Cl. Detection of Hg2+ was carried out by differential pulse anodic stripping voltammetry (DPASV) after reduction of Hg2+. Mercury ions as low as 5 × 10−10 M could be detected with the prepared electrode and the relative standard deviation was calculated as 6.35% at 1 × 10−6 M concentration (n = 6). Interferences of Ag+, Pb2+ and Fe3+ ions were also studied at two different concentration ratios with respect to Hg2+. The developed electrode was applied to the determination of Hg2+ in water samples.  相似文献   

19.
A nanocomposite consisting of multiwalled carbon nanotubes wrapped with hydroxyapatite (HA/MWCNTs) was used in the construction of a new composite paste electrode using an ionic liquid as the binder. The stable surface in aqueous solutions as well as the high sorptive behaviors towards heavy metal ions and the favorable charge transfer make the electrode highly efficient especially for stripping or adsorptive analysis. The analysis of Pb2+ as a model of heavy metal ions has been performed. Good sensitivity, detection limit, selectivity and reproducibility were obtained for the suggested sensor. The linear range of the electrode response covered four orders of magnitude (1 nM–10 µM), in two linear ranges. The obtained detection limit for Pb2+ was 2×10?11 M.  相似文献   

20.
Osmotic coefficient data have been obtained for the binary aqueous solutions of alkaline-earth chlorides (MgCl2, CaCl2 and BaCl2) at 298.15 K using a vapor pressure osmometer. The measurements are extended to aqueous ternary solutions (containing a fixed concentration of 0.1 mol⋅kg−1 18-Crown-6 (18C6) having various electrolyte concentrations (0.01–0.2 mol⋅kg−1). The mean activity coefficients of the ions and of 18C6 in binary and ternary solutions were obtained through calculations of activity and osmotic coefficient data. The lowering of activity coefficients of the ions and of 18C6 in ternary solutions is attributed to the presence of host-guest type equilibria due to complexation between them in the case of solutions containing Ca2+ and Ba2+ ions. The data are further subjected to scrutiny by applying the methodology developed by Patil and Dagade based on the McMillan-Mayer theory of solutions to obtain thermodynamic equilibrium constant values through transfer Gibbs energies. It is noted that the size of the crown cavity (diameter 0.266–0.32 nm), charge density of ions (i.e., coulombic interactions) as well as hydrophobic interaction play a major role in governing the occurrence and stability of the complexed species. The results are compared with those reported earlier for alkali-halides and 18C6 complexes and discussed further from the point of view of the importance of ion-pair formation equilibria in aqueous solutions.  相似文献   

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