Studies of a Mixed Adsorption Layer of Butan-1-ol and o-Toluidine on Mercury Electrode

2002 ◽  
Vol 67 (11) ◽  
pp. 1579-1588 ◽  
Author(s):  
Dorota Sieńko ◽  
Dorota Gugała ◽  
Jolanta Nieszporek ◽  
Joanna Jankowska ◽  
Jadwiga Saba
Keyword(s):  
Thermodynamic Analysis ◽  
Adsorption Layer ◽  
Supporting Electrolyte ◽  
Mercury Electrode ◽  
Interaction Constant ◽  
Repulsive Interaction ◽  
Surface Excess ◽  
Adsorption Parameters ◽  
Frumkin Isotherm ◽  
Adsorption Layers

The results of thermodynamic analysis of o-toluidine adsorption on a mercury electrode in the presence of various butan-1-ol amounts complete our previous studies on properties of mixed adsorption layers of toluidine isomers-butan-1-ol. The values of the relative surface excess Γ'°T obtained for o-toluidine show that adsorption of this compound decreases with increasing of butan-1-ol concentration. Analysis of adsorption parameters derived from the Frumkin isotherm indicates that in the presence of 0.33 M BuOH in 1 M NaClO4 with adjusted pH 3 as supporting electrolyte, ∆G0 values for o-toluidine are the highest and, at the same time, the strongest repulsive interaction occurs. In the presence of 0.11 M butan-1-ol, smaller values of ∆G0 for o-toluidine correspond to weaker repulsive interaction. Therefore the change of the Γ'°T value for o-toluidine as a function of butan-1-ol concentration is the result of mutual changes of ∆G0 and interaction constant A between adsorbate molecules.

Adsorption of Cytosine on a Mercury Electrode

2006 ◽  
Vol 71 (10) ◽  
pp. 1393-1406 ◽  
Author(s):  
Dorota Sieńko ◽  
Jolanta Nieszporek ◽  
Krzysztof Nieszporek ◽  
Dorota Gugała ◽  
Jadwiga Saba
Keyword(s):  
Charge Density ◽  
Standard Gibbs Energy ◽  
Mercury Electrode ◽  
Repulsive Interaction ◽  
Surface Excess ◽  
Adsorption Parameters ◽  
Frumkin Isotherm ◽  
Constant Charge Density ◽  
Constant Charge ◽  
Zero Frequency

The electrosorption behavior of cytosine at the mercury electrode/acetic buffer of pH 4 and 5 interfaces was determined from the double-layer differential capacity measurements extrapolated to zero frequency. Solutions of cytosine were prepared to cover the range from 1 × 10-4 to 6 × 10-3 mol dm-3. Adsorption of cytosine was described by the adsorption isotherms constants derived from the surface pressure data as a function of electrode charge density and bulk concentration. The obtained values of the relative surface excesses Γ′ were higher in the acetic buffer of pH 4 than of pH 5. Maximum of cytosine adsorption in the mentioned buffers was at -581 and -551 mV, respectively. The values of the standard Gibbs energy ∆G° obtained from the Frumkin isotherm were higher in the buffer of pH 4 than of pH 5. The values of the interaction parameter A indicated weaker repulsive interaction between adsorbed molecules of cytosine in the former buffer. The adsorption parameters obtained from the virial isotherm confirmed corresponding parameters obtained from the Frumkin isotherm. The dependences of ΦM-2 on the relative surface excess at a constant charge density were analyzed in order to calculate the electrostatic parameters of the inner layer.

Studies of a Mixed Adsorption Layer of n-Butanol and m- and p-Toluidine on Mercury Electrode

1995 ◽  
Vol 60 (9) ◽  
pp. 1457-1468 ◽  
Author(s):  
Jadwiga Saba
Keyword(s):  
Rate Constants ◽  
Concentration Ratio ◽  
Adsorption Layer ◽  
Mercury Electrode ◽  
Wide Concentration Range ◽  
Surface Excess ◽  
Adsorption Layers

The mixed adsorption layers of n-butanol-m-toluidine and n-butanol-p-toluidine were studied and the surface excess of pure components and their mixtures was determined. The occurrence of synergetic coadsorption was observed. The rate constants of Zn(II) ion reduction were determined in 1 mol l-1 NaClO4 in presence of n-butanol as an inhibitor, m- and p-toluidine as accelerating substances and in their mixtures. It was found that the inhibiting or accelerating effect depends on the concentration of n-butanol and m- or p-toluidine. Compensation of these effects achieved at the concentration ratio of CBU : CpT ~ 35 and CBU : CmT ~ 85 in a wide concentration range is an evidence of toluidine predominance in the formation of a mixed adsorption layer.

The adsorption of methyl red at the dropping mercury electrode

1970 ◽  
Vol 23 (1) ◽  
pp. 43 ◽  
Author(s):  
KG Boto ◽  
FG Thomas
Keyword(s):  
Sodium Nitrate ◽  
Supporting Electrolyte ◽  
Mercury Electrode ◽  
Methyl Red ◽  
Surface Excess ◽  
Solution Interface ◽  
Dropping Mercury Electrode

Surface excess concentrations of methyl red at the mercury-solution interface have been determined at pH 7.00, 9.80, and 12.30 from electrocapillary measurements using 0.lM sodium nitrate as supporting electrolyte. The results are interpreted in terms of a reorientation of the methyl red anion between -0.4 V and -0.6 V (v. S.C.E.)

Polarography of nickel in concentrated chloride media

1966 ◽  
Vol 19 (8) ◽  
pp. 1343 ◽  
Author(s):  
TM Florence
Keyword(s):  
Ionic Strength ◽  
Graphite Electrode ◽  
Supporting Electrolyte ◽  
Anhydrous Methanol ◽  
Pyrolytic Graphite ◽  
Hydration Number ◽  
Mercury Electrode ◽  
Specific Adsorption ◽  
Dropping Mercury Electrode ◽  
Pyrolytic Graphite Electrode

In concentrated chloride media, nickel is reduced at far more positive potentials than in dilute solutions. The positive shift in half-wave potential increases as the ionic strength is raised, and is also greater when the cation of the supporting electrolyte has a high hydration number. Evidence is presented to show that the reduction in overpotential is due to the formation of a nickel chloride complex, [Ni(H2O)5Cl]+, which has a stoicheiometric stability constant of 0.094 � 0.009 at an ionic strength of 10.0. Spectrophotometric results show that this nickel species is not formed in low ionic strength solutions. In anhydrous methanol saturated with lithium chloride, nickel is present as the tetrachloro complex, [NiCl,]2-, which has similar polarographic behaviour to the monochloro complex. Current-potential curves recorded at a rotated pyrolytic graphite electrode enabled the behaviour of nickel to be studied in the absence of specific adsorption of the chloride ion. Nickel is reduced at more positive potentials at a dropping mercury electrode than at the pyrolytic graphite electrode, and the results indicate that this difference is due to specific adsorption of chloride on the mercury electrode.

Hydroxyproline adsorption on a mercury electrode in neutral solution

1991 ◽  
Vol 69 (10) ◽  
pp. 1528-1534 ◽  
Author(s):  
M. M. Gómez
Keyword(s):  
Dipole Moment ◽  
Adsorption Process ◽  
Normal Component ◽  
Mercury Electrode ◽  
Hydroxyl Group ◽  
Neutral Solution ◽  
Pyrrolidine Ring ◽  
Adsorption Parameters ◽  
Gibbs Energies ◽  
Comparison Of The Results

The adsorption of hydroxyproline (HPRO) on mercury in aqueous solutions of 10−2 M KClO4 has been determined from electrocapillary and capacity measurements. Comparison of the results obtained for HPRO with those reported for proline (PRO) shows that the presence of a hydroxyl group in the molecule has a small effect on the adsorption process. The respective values for adsorption parameters are −7 and −5 μC cm−2 for the charges of maximum adsorption, −13.0 and −10.4 kj mol−1 for the standard Gibbs energies of adsorption at zero charge, and −1.28 and +0.6 for the α parameter in the Frumkin isotherms. According to the analysis carried out for the normal component of the dipole moment of HPRO, −0.8 D, the more probable orientation of this aminoacid adsorbed on mercury is with the pyrrolidine ring parallel to the electrode surface resting the OH group away from the surface. Key words: adsorption, double layer, aminoacids, hydroxyproline.

Analysis of the Electrode Kinetics of Ni(II) Reduction in Thiocyanate Media on the Dropping Mercury Electrode

2000 ◽  
Vol 65 (3) ◽  
pp. 326-342
Author(s):  
María S. Crespo-Pinilla ◽  
Fernando Mata-Pérez ◽  
Rosa M. Villamañán
Keyword(s):  
Ionic Strength ◽  
Compensation Effect ◽  
Supporting Electrolyte ◽  
Mercury Electrode ◽  
Electrode Kinetics ◽  
Surface Process ◽  
Experimental Conditions ◽  
Dropping Mercury Electrode ◽  
Kinetics Of

A study of two prewaves of the Ni(II)-SCN- system was carried out under the experimental conditions when the influence of electroreduction of SCN- is negligible. Kinetics of Ni(II) reduction in thiocyanate media on the dropping mercury electrode was studied by DC Tast Polarography (DCTP) via determination of Koutecký's parameter χ; the influence of different variables was analyzed. The study of prewaves was performed using various polarographic techniques. Values of χ depend on the SCN- concentration, pH, ionic strength (Ψ-effect) and on the nature of the supporting electrolyte. The number of electrons n, the transfer coefficient α, the stoichiometric number ν, ∆H≠, and ∆S≠ were determined (compensation effect). The first prewave has character of a reaction in the solution, the second prewave is a surface process. Main features of both mechanisms are common: catalytic nature, one-electron step discharge and the rate-determining process between species of opposite charges.

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