Adsorption Of Halide Ions Research Articles

Calculation of the characteristics of Cl − and Br − ions adsorption on bismuth single-crystal planes from solutions in 2-propanol

The values of the surface excess and the Gibbs energy of adsorption of halide ions on the (111) and (001) Bi single-crystal planes in solutions in 2-propanol have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its charge image in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency does not depend on the electrode charge. In contrast, on the more active Bi(001) plane there is a noticeable dependence of the electrosorption valency on the electrode charge. The dipole value formed by an adsorbed halide ion and its charge image in Bi significantly diminishes when changing from negative to positive electrode charge density and at the higher positive charges the covalent bonding between the Bi(001) surface atoms and Br − anions is probable. The more complicated dependence of the dipole value on electrode charge at the Bi(111) planes was attributed to the change in solvent structure on the electrode surface. It was concluded that the dipole formed is significantly screened by the solvent molecules and the metal electron gas.

Calculation of thermodynamic and inner layer characteristics of halide ions adsorbed on bismuth single crystal planes from solutions in methanol

The values of the surface excess and the Gibbs energy of adsorption of halide ions on the (111), (001) and ( 01 1 ̄ ) Bi single crystal planes in methanolic solutions have been calculated from the previously obtained experimental data using electrode potential as the independent electrical variable. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident. The electrosorption valency and the dipole moment of the dipole formed by an adsorbed halide ion and its image charge in the Bi plane have been calculated. It was found that on the Bi(111) plane, where the chemical bonds are all saturated, the electrosorption valency does not depend on electrode charge and in the measured range of potentials a weak dependence of the dipole value formed by an adsorbed halide ion and its image charge in Bi on the electrode charge was found. In contrast, on the more active Bi planes there is noticeable dependence of both characteristics on electrode charge and at higher positive charges, covalent bonding between Bi( 01 1 ̄ ) surface atoms and I − anions is probable. It was concluded that the dipole formed is screened significantly by the solvent molecules and the metal electron gas.

Adsorption of pyridine on a polycrystalline gold electrode surface studied by infrared reflection absorption spectroscopy

The adsorption behavior of pyridine on a smooth polycrystalline gold electrode surface was investigated over a wide wavenumber region (2000–500 cm−1) by in situ infrared reflection absorption spectroscopy (IRAS). The reversible adsorption/desorption of pyridine was observed upon the change in applied electrode potential, and the adsorption state at positive potentials was found to depend strongly on the kind of halide ion used as a supporting electrolyte. Symmetry analysis of absorption bands observed revealed that pyridine molecules adsorb with the molecular axis (C2 axis) perpendicular to the electrode surface (vertical configuration) at positive potentials in 0.5 M KF, KCl and KBr solutions. A band due to the out-of-plane bending mode of the adsorbed pyridine molecule was observed at potentials more negative than ca. 0 V for 0.5 M KF solution containing 100 mM pyridine. We concluded that even in the 100 mM pyridine solution, adsorbed pyridine forms a monolayer and that the molecules reorient from a flat (parallel) to the vertical configuration as the potential becomes less negative. No bands due to adsorbed pyridine were detected for 0.5 M KI solution. The amount of adsorbed pyridine was found to depend strongly on the strength of specific adsorption of halide ions.

A New Approach to Interfacial Energy. 4. Effects of Adsorption of Halide Ions and Gelatin on Solid−Liquid Interfacial Energies of Silver Halides

Based on the fundamental theory of interfacial energy in parts 1 (J. Colloid Interface Sci. 1996, 181, 259; 1996, 183, 299), 2, and 3, theoretical formulas have been derived for the specific interfacial energy γ of solid−liquid interface changing with adsorption of the constituent anions or cations of the solid and foreign adsorbates to different crystal faces. Adsorption isotherms of silver and halide ions and experimental results for γ obtained from potentiometry of silver ions on the basis of the Gibbs−Thomson effect in AgCl, AgBr, and AgI sol systems under the influence of the adsorption of the constituent halide ions and gelatin were analyzed in light of the theoretical formulas. Finally, the characteristics of the adsorption behavior of these species including the slight deviations from the theory have been discussed.

A theoretical approach to the adsorption of ions on metal surfaces

This paper gives a short review of the current status of quantum and simulation studies of the specific adsorption phenomenon. In the light of results of some recent investigations on the adsorption of halide ions on noble metals, the difficult problem of the interfacial interactions is discussed. Several difficulties associated with the modeling of the adsorption process in the simulations are pointed out. Some of them are shown to be related to the cluster model calculations commonly used in the fitting of the analytical potentials for the ion–metal interaction. The adequacy of the additive analytical form of this potential which is usually applied, is also discussed. The problem of the description of the interaction of the ion with the electrode in the intermediate region, when the ion is still surrounded by water molecules, is also addressed.

The potential of mean force on halide ions near the Cu(100) surface

Abstract This paper reports an investigation of the phenomenon of specific adsorption of halide ions on a Cu(100) surface using Monte Carlo simulations. The system was modeled by considering each ion in a water lamina placed between two copper walls. The potentials used in simulations were constructed by fitting to results of quantum calculations. The solvent contribution to the potential of mean force (pmf) was calculated for each of the four halide ions using the free energy perturbation method. Given the difficulty of finding a reliable ion–metal potential, several alternatives, representing extremal models, were tested in combination with the solvent mean force on the ions, F − , Cl − , Br − or I − . The results for the pmf on an ion near the metal surface are discussed in the light of the experimental data available. The sensitivity of the results to the type of ion–metal potential used in the simulations is stressed.

Effect of Halide Ion Adsorption upon Plasmon-Mediated Photoelectron Emission at the Silver/Solution Interface

The effect of the roughening of the silver surface upon photoemission observed in the presence of two different scavengers dissolved in an aqueous solution, CO2 and NO3- ions, was re-examined. The quantum yield of the photocurrent exhibits a sharp maximum at 370−380 nm in the frequency range of surface plasmons on silver. These photoyields were strongly affected by the extent of the roughening of the Ag surface and reached an unusually large value of 0.05 electron per incident photon. Electrochemical oxidation/reduction roughening performed in the presence of Cl-, Br-, and ClO4- ions, similar to that employed in enhanced Raman scattering (SERS) experiments, affected the maximum of the photocurrent and in some cases also its onset potential. Photocurrents arising at potentials more negative than the potential of zero charge (pzc) of silver were principally influenced by changing morphology of the surface resulting from more or less deep roughening performed in different solutions. On the other hand, the photoelectrochemical behavior of silver at potentials positive with respect to the pzc was clearly affected by the specific adsorption of anions of the supporting electrolyte. It was, in particular, the Br- anion that caused in this potential region the strongest enhancement of the photocurrent, associated with the reduction of scavengers and led to an apparent positive shift of the onset potential. The role played by the specifically adsorbed anions is interpreted in terms of slowing down the reverse reactions of solvated electrons and of reaction intermediates (such as, for example, the NO32- anion) returning to the electrode.

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 M 12—X − (M = Cu, Ag, Au; X = F, Cl, Br, I) systems are presented. At the (100) surface, modeled in the present work by the M 12 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 M 12—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.

Effects of adsorbed halide ions on the cyclic-voltammetry current-potential profiles for Pb underpotential deposition at Au

Effects of adsorbed halide ions on the cyclic-voltammetry current-potential profiles for Pb underpotential deposition at Au

Interaction of halide ions with copper: the DFT approach

The applicability of density functional theory to the adsorbate-adsorbent interaction has been tested with the final goal of defining an appropriate combination of the DFT method with basis sets for metal cluster-halide ions studies. The Cu-X − (X = F, Cl, Br, I) systems have been taken as tests cases to probe the different DFT methods (SVWN, BP86 and B3LYP) together with different combinations of basis sets for systems of this type. For comparison, the standard HF and its MP2 and MP4 corrections have also been calculated. Additionally, the results of a test for the Cu 5I − cluster are presented. The good quality of the DFT methods is recorded as they give results comparable to the MP2 and, for some cases, even to the MP4 level of standard calculations. The B3LYP method combined with a fairly inexpensive description of the metal atoms is proposed as an appropriate option for studies of the adsorption of halide ions at noble metal surfaces.

Halide catalysis of the electrochemical oxidation of gold in acetonitrile

The anodic oxidation of metallic gold in acetonitrile, which is normally inhibited by traces of water causing passivation, can be promoted by halide catalysis. The deblocking mechanism is based on displacement of water by concurrent adsorption of halide ions. Only small quantities of halide, enough to cover the anode surface with a monoionic layer, are required for the process. The catalytic effect increases in the order Cl− < Br− ⪡ I−. The effect can be used for the easy preparation of Au+ solutions.

Oscillatory dynamics of the electrochemical oxidation of H 2 in the presence of Cu 2+: Structure sensitivity and the role of anions

We studied the oscillatory galvanostatic H 2-oxidation on the three low-index Pt surfaces in the presence of Cu 2+ and different electrolytes: H 2 SO 4, H 2 SO 4 + Cl − and H 2 SO 4 + Br −. It was found that both surface orientation of the Pt-electrode as well as the nature of the anions strongly influence the dynamics. Halide ion adsorption plays an essential role for the occurrence of oscillations; their binding strengths on the different single-crystal electrodes correlate with the dynamic behaviour of the respective system. The reaction was further investigated using ring-disk electrodes ( Pt Pt and Pt Au ). This allowed the quantitative determination of the change of the copper coverage and the H 2-current during oscillations as well as their phases relative to the electrode potential. From these studies a simple threevariable model (taking into account the coverages of copper and anions as well as the potential) was deduced, based on competitive adsorption of halides and Cu. The model explains the occurrence of oscillations and predicts the correct phase relationships of the oscillating variables.

The kinetics of inhibitor adsorption on iron

The kinetics of adsorption of Cl − and Br − ions and 2-naphthol-3,6-disulphonic acid (NDSA) on Armco iron electrodes cathodically polarized in 0.5 M H 2SO 4 was carefully analyzed. Contrary to the initial expectation that the adsorption of these species should be faster on such cathodically protected surfaces as compared to the rates of adsorption during anodic polarization when the metal surface changes permanently, the obtained adsorption rate constants were about 10 −2 mol −1 dm 3 s −1 both for halogen ions and NDSA with a small dependence on electrode potential for halogen ions. The kinetics were analyzed by using a computerized curve fitting procedure based on a Frumkin-type isotherm for the quasi-equilibrium state and Roginskii—Zeldovich-type equations for the adsorption and desorption processes. A computer analysis of the experimental θ vs. time data provided good estimations of k a and a, while the estimation of k d was less reliable, depending on the precision of the experimental data. For halide ion adsorption it was found that n = 1 and a < 0 (repulsive forces), while for NDSA n = 3 and a > 0 (attractive forces). The slow adsorption rates during cathodic polarizations are explained by the “anomalous” dissolution of iron during cathodic polarization by a mechanism similar to that for the anodic polarizations.

Adsorption of halide ions Cl −, Br − and I − on the basal face of a cadmium single crystal

A qualitative and quantitative study of the adsorption of halide ions on the electrolytically grown (0001) face of a cadmium single crystal is described. It is found that adsorption increases in the order Cl − < Br − < I −. Comparison with the results for other electrodes shows an increase in the adsorption in the sequence Cd(0001) < Cd poly < Ag(100) < Ai(111). An attempt is made to explain this sequence in terms of the hydrophilicity of the electrode investigated.

Effects of surface charge on the second harmonic generation from a Cu electrode

The charge density of a polycrystalline Cu surface is electrochemically varied in the absence and in the presence of adsorbed halide ions. The surface is optically probed with second harmonic generation at a fundamental wavelength of 1064 nm. The second harmonic intensity shows a deviation from the charge dependence expected from the free electron polarization of the surface. Furthermore, the adsorption of halide ions shows no significant effects in the optical data. These results for Cu are different from previous findings of similar experiments on Ag and Pt. The observed second harmonic response of the Cu electrode fits appropriately with a mechanism involving the bound electrons of the metal surface. This mechanism is described in terms of a charge induced Stark effect on an interband (d-p) transition in Cu.

The Interaction Between Thiolic Antifoggants and Silver Subcolloid on the Interface

AbstractThe visible spectral absorption at 390 nm of a dear tight-yellow silver subcolloid partly shifted to 510-550 nm due to the adsorption of phenylmercaptotetrazole (PMT) or mercaptobenzo- thiazole (MBT), which produced an enhanced surface Raman scattering effect.The normal Raman spectra (NRS) of solid PMT and MBT and their surface enhanced Raman spectra (SERS) on the surface of the silver subcolloidal particles are reported and compared. The adsorption of halide ions competes with that of PMT and MBT. However, halide ions have a completely different influence from PMT and MBT on the spectral absorption of the silver sol.

The specific adsorption of halides on mercury in non-aqueous acetonitrile

The adsorption behaviour of various tetraalkylammonium halides R 4NX (R = Et, Bu; X = I −, Br −) and sodium iodide at the mercury/acetonitrile interphase has been investigated employing capacity measurements and measurements of the potential of zero charge at variable ionic strength. The results indicate strong specific adsorption of halide ions in the range between negative and positive electrode charges. For NaI, a more detailed study of the adsorption process based on the virial isotherm was performed including the evaluation of the standard Gibbs energy of adsorption and the interaction parameter. Moreover, the distance ratio ( x 2 − x 1/ x 2 and the Esin-Markov coefficients could be estimated. From differences between the Esin-Markov coefficients determined for all salts under investigation, a counter-ion effect with respect to the halide adsorption could be deduced. The specific adsorption of halide ions in acetonitrile will be discussed, particularly with regard to the influence of solvent and ion association.

A theoretical analysis of the electrochemical noise during the induction period of pitting corrosion in passive metals: Part 1. The current noise associated with the adsorption/desorption processes of halide ions on the passive film surface

It has been demonstrated theoretically that the adsorption/desorption process of halide ions on the surface of a passive metal can cause electrochemical noise during the induction period of pitting corrosion on passive metals. The process was considered by using a model in which the lattice cation of a passive film makes a transitional complex with the halide ions in the solution, followed by local dissolution into the solution. A stochastic analysis was applied to the system, and the distribution function was obtained for the coordination number around the surface cation of the lattice of the passive film. The noise level was determined as the uncertainty of the distribution function for the coordination number. The noise level was rather low when the probability for the formation of the transitional halide complex was high. The noise level increased as the coordination number of halide ions necessary for the formation of the transitional complex increased, or as the activity of the halide ions in the solution decreased. When the van der Waals condition was established concerning the adsorption of halide ions on the passive film, the noise level reached the maximum value.

Superficial structure of gold and silver faces and adsorption from liquid phase

Are the structures of gold and silver single-crystal faces when in contact with aqueous solutions the ones described by ideal models and/or those observed in UHV ? Comparison of some results obtained by traditional electrochemical methods : with models and with results obtained by in-situ physical methods is discussed, first for the potential of zero charge in the case of no or slight specific adsorption, then for adsorption of halide ions and finally for underpotential deposition of metal ions on a substrate of a foreign metal.

The slow adsorption of halide ions and some organics and their influence on corrosion rate determination from low polarization data

It is shown that halide ions and some organic inhibitors (quinoline) adsorb slowly on the anodically dissolving Armco iron in 0.5 M H 2SO 4 solution, and that they desorb with an increase in the anodic current. This leads to a change in the coverage with the inhibiting species with a change in the anodic current, and also to the appearance of a hysteresis effect when the direction of the polarization in reversed. The apparent anodic Tafel slopes, b a, are shown to depend on the type and concentration of the inhibiting species, the contact time of iron with the solution and the anodic pre-polarization. The consequences of these factors on the shape of cathodic polarization curves in the low polarization region, and the applicability and limitations of electrochemical corrosion rate determining methods are discussed.