Chemisorption Of Ions Research Articles

The effect of sulfide ion chemisorption on the kinetics of gold dissolution in cyanide solutions

The effect of sodium sulfide additions (from 5 × 10−6 to 2 × 10−5 M) on the kinetics of gold dissolution in cyanide solutions of the following composition, M: 0.1 KCN, 0.02 KAu(CN)2, 0.5 K2SO4, pH 10–13 is studied. Hydrosulfide ions are shown to exert a strong catalytic effect on the dissolution kinetics of this metal in a potential range where their adsorption is accompanied by the formation of polysulfides (−0.2 < E < 0.4 V). The reaction acceleration depend on the potential and is 100-fold for E ≃ 0.1 V. The effect becomes more pronounced as the concentration of hydrosulfide ions increases to 10−4 M and is almost pH-independent in the pH range from 10 to 13. An attempt to explain the found relationships is undertaken.

Tailoring silver nanoparticle construction using dendrimer templated silica networks

We have examined the role of the internal environment of dendrimer templated silicanetworks in tailoring the construction of silver nanoparticle assemblies. Silica networksfrom which 3,5-dihydroxybenzyl alcohol based dendrimer templates have been completelyremoved, slowly wet with an aqueous solution of silver acetate. The latter then reacts withinternal silica silanol groups, leading to chemisorption of silver ions, followed by the growthof silver oxide nanoparticles. Silica network constructed using generation 4 dendrimercontains residual dendrimer template, and mixes with aqueous silver acetate solution easily.Upon chemisorption, silver ions get photolytically reduced to silver metal undera stabilizing dendrimer environment, leading to the formation of silver metalnanoparticles.

Kinetics of silver dissolution in sulfide containing thiocarbamide electrolytes

Effective values of reaction order with respect to ligand P, transfer coefficient α, and exchange current i 0 at constant silver surface coverages θ by sulfide ions are measured. The employed solutions contained from 0.4 to 0.05 M thiocarbamide, 0.5 M HClO4, 10−4 M AgNO3, and from 10−5 to 10−4 M Na2S. It is shown that the exchange current grows approximately linearly from 10−5 to 1.5 × 10−4 A/cm2 at θ increase in the range from zero to 0.8, while α and P values grow negligibly in the ranges of 0.4–0.45 and 0.9–1.1, accordingly. The obtained results are compared with the data of similar studies of the gold behavior in acidic thiocarbamide solutions. The possible reasons for the different effects of sulfide ion chemisorption on the anodic dissolution of gold and silver in the studied solutions are discussed.

Electron emission degradation of nano-structured sp2-bonded amorphous carbon films

The initial field electron emission degradation behaviour of original nano-structured sp2-bonded amorphous carbon films has been observed, which can be attributed to the increase of the work function of the film in the field emission process analysed using a Fowler–Nordheim plot. The possible reason for the change of work function is suggested to be the desorption of hydrogen from the original hydrogen termination film surface due to field emission current-induced local heating. For the explanation of the emission degradation behaviour of the nano-structured sp2-bonded amorphous carbon film, a cluster model with a series of graphite (0001) basal surfaces has been presented, and the theoretical calculations have been performed to investigate work functions of graphite (0001) surfaces with different hydrogen atom and ion chemisorption sites by using first principles method based on density functional theory-local density approximation.

Synthesis of novel amino(alkylamino)deoxychitosans and those thiol-derivatives and the chemisorption behaviors of an acid dye and Hg2+ ion onto the resulting polymers

Introducing an additional functionality to chitosan, novel chitosan-based materials were synthesized. The reactions of tosylchitosan with ammonia, ethylenediamine, and hexamethylenediamine have been studied, and the chemisorption behavior of a typical acid dye (CI Acid Orange 7) onto the resulting polymers has been evaluated. Thiol groups were introduced to the above chitosan derivatives having additional amino group at the C6 position, and the chemisorption behavior of Hg2+ ion onto the resulting polymers was measured and compared with that of N-thioacetylchitosan. The successful synthetic reaction was demonstrated by the infrared spectroscopic measurements. It has been confirmed that the abilities of the chitosan derivatives with additional amino groups to the chemisorption of an acid dye were significantly high, and that the saturation value of the chemisorption amount of CI Acid Orange 7 toward one of 2′-aminoethylaminodeoxychitosans was significantly high as 6.16 mol/kg. The results also showed that the saturation amounts of Hg2+ ion chemisorption were larger with the increase in the thiol group content of the chitosan derivatives with the thiol groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Preparation and characterization of polyoxometalate-modified carbon nanosheets

We report an original approach for the preparation of quasi two-dimensional graphite sheets by exfoliation of highly oriented pyrolytic graphite. Pieces of HOPG were sonicated for variable time in aqueous solutions of phosphomolybdic acid. This leads to a gradual cleavage of the HOPG along the basal plane. The driving force of the process is the free energy resulting from the well-known strong chemisorption of phosphomolybdate ions on carbon. The resulting carbon nanostructures exhibit certain properties of the adsorbed polyoxometalate-anions. They form colloidal suspensions due to the negative surface charge and can be immobilized on surfaces containing cationic groups.

Electrochemical study of silver thiosulphate reduction in the absence and presence of ultrasound

The electrochemical reduction of silver thiosulphate was studied potentiostatically on platinum electrodes in the absence and presence of ultrasound (20 kHz). This system is irreversible and the reaction is both diffusion and kinetically controlled. The slowest step is the kinetic reaction especially the chemisorption of ions at the electrode surface. Ultrasound greatly improves the mass transport, which can be explained by changing from diffusion to mainly convection. This paper reports the effect of ultrasound upon electrode kinetic and mass-transport parameters at various RDE rotation speeds and ultrasonic intensities. It was found that the heterogeneous rate constant ( k f) is improved in the presence of ultrasound due to the increase in the formal or standard heterogeneous rate constant ( k 0) (approximately by 10-fold under sonication).

Chemisorption of Hydrogen Ions on Aminosilica Surfaces at Different Temperatures

The chemisorption of hydrogen ions by silicas chemically modified with aliphatic amines was discussed. The sorption kinetics followed the model of sorption from a semi-infinite solution, with sorption being of a two-stage nature. The first stage, involving the overwhelming majority of sorption centres, was very fast. In contrast, the second stage was rather slow and diffusion-controlled. A proper description of the protolytic equilibria on the aminosilica surface required account to be taken not only of the protonization of the grafted amino groups but also of their homoconjugation. The latter reaction resulted from interactions between neighbouring groups and led to the non-random (islandlike) coverage of the surface by amino groups. Both the nature of the background electrolyte in the solution and its concentration had no effect on the model structure. The thermodynamic equilibrium constants for the heterogeneous protonization reaction were determined from the dependencies of the mixed equilibrium constants on the concentration of the background electrolyte in solution. Chemisorption of H+ ions, accompanied by penetration of the counterions into the subsurface layer, was of an endothermic nature and associated with increasing entropy.

The ion adsorption effect on selectivity of liquid state, O, O′-didecylodithiophosphate chelate based ion-selective electrodes

Ion-selective electrodes with liquid membranes including O, O′-didecylo-dithiophosphate complexes of Tl(I), Pb(II), Cd(II) and Ni(II) are characterised and results of the study on their selectivity are reported. A short review of problems related to determination and interpretation of selectivity coefficients of ion-selective electrodes is presented with particular emphasis on the drawbacks of the hitherto used methods. A new method is proposed, which in the experimental part is close to that of mixed solutions recommended by IUPAC but can be applied also when the latter is of no use. The method proposed for determination of selectivity coefficients simultaneously allows concluding about the mechanism of potential generation. A few examples of relations between selectivity coefficients of the electrodes and concentrations of disturbing ions in solutions, are given. An interpretation of the above relations as results of the processes of ion adsorption at the interface of the electrode membrane and water solution is proposed. The results obtained have confirmed the hypothesis given by Pungor, according to which the main role in the mechanism of generation of ion-selective electrodes potential is played by the processes of ion chemisorption at the interface of the membrane and water solution.

Calibrated Contamination Spiking Method for Silicon Wafers in the 1010 – 1012 Atom / cm2 Range

Applying diluted iron, nickel, and copper solutions to front and back side spin‐on, respectively, and to immersion spiking, we investigated the contamination mechanism of silicon wafers. The immersion procedure was found to be advantageous as a batch process,with the drawback that it can only be applied at lower concentration levels than the spin‐on technique and, therefore, it was much more tedious to control. The immersion technique led to a chemisorption of metal ions on the native oxide. In comparison to iron and nickel, copper was less readily adsorbed on the wafer surface by immersion. A thermodynamic model interprets the conspicuous results of copper contamination. Spin‐on spiking led to a dried film of the contamination solution on the wafer. Chemisorption processes could not be confirmed under the given spin‐on conditions. Thus, the contamination level on the wafer was the same for nickel, iron, and copper when spiking solutions of the same concentration were used. After the metal drive‐in step for nickel and copper at 800°C and for iron at 1000°C, a recovery rate of 50–100% was found by chemical analysis. In order to avoid cross contamination, different concentration levels or different spiking elements should not be treated in the same thermal drive‐in batch process. Charge‐to‐breakdown measurements of capacitors were used to evaluate the influence of surface metal contamination and, after drive‐in, for gettering studies. © 1999 The Electrochemical Society. All rights reserved.

Silica chemically modified with N-benzoyl- N-phenylhydroxylamine in chemisorption of hydrogen and metal ions

New chemically modified silicas – macroporous and pyrogenic – with covalently bonded chelating groups of N-benzoyl- N-phenylhydroxylamine (SiO 2–BPHA) were obtained in three-step surface reaction. From elemental analysis, metal chemisorption and pH titration the concentration of bonded groups was determined as 0.076 and 0.21 mmol g −1 for Silochrome and Aerosil, correspondingly. In both cases about 50% transformation of initial aminopropyl groups to BPHA was achieved. A chemisorption of hydrogen and some metal ions (Fe(III), V(V), Nb(V), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II)) from aqueous and acetonitrile media was investigated. The adequate approximation of interfacial equilibria was only possible if strong lateral interactions between bonded ligands were presumed. From the results of a quantitative physicochemical analysis it was found that dissociation constant of bonded BPHA considerably rose in comparison with the dissociation constants of analogs in solution. Bonded complexes with all studied metals were less stable. Linear correlation between stability of complexes in dioxane–water solution and on the silica surface was found as log β(surf.)=log β(sol.)−2.9. Strong fixation of counter-ions near the surface was concluded from experiments. In aqueous media SiO 2–BPHA demonstrates high selectivity towards Fe(III) and V(V). Linear correlation that was found between concentration of sorbed Fe 3+ and the Kubelka–Munk function for SiO 2–BPHA can be used for ion optical sensoring. Vanadium(V) forms several bonded complexes with different composition instead.

Ab initio Studies of Electronic Charge Density Injection in Water and Hydroxyl Ion Chemisorption Processes on GaAs

<i>Ab initio</i> Studies of Electronic Charge Density Injection in Water and Hydroxyl Ion Chemisorption Processes on GaAs

Metabolic inhibition by transition metal ions in a slow-growing, toluene-enriched microbial population

We studied the effects of common first-row transition metal ions, Mn(II), Fe(III), Co(II), Cu(II), Zn(II), on the respiration of a mixed microbial population enriched for toluene degradation. Dissolved oxygen consumption, i.e., respiration rate, was used to measure metabolic activity of a slow-growing consortium of toluene-enriched microorganisms. Respiration rates decreased within 30 s of exposure to the metal ions and did not measurably recover during observation times (<80 min.). Metal ion toxicity increased with metal-phosphate binding affinities, consistent with cell damage by conformational changes in the phospholipid bilayer membrane to accommodate geometry requirements of complexes with transition metal ions. Changes in normalized metabolic activity (AN) with aqueous composition were compared with an equilibrium free-ion toxicity mechanism relating the fraction of membrane phosphatic ligands affected by metal ion chemisorption to diminished metabolic activity. AN measurements agreed with model predictions that the toxicity function (AN−1−1) is proportional to the free metal ion concentration when hydrogen ions do not compete with metal ions for the phosphatic membrane sites and proportional to the square root of the free metal ion concentration if hydrogen ions effectively compete with metal ions for membrane phosphate ligands. Transition metal ion uptake and toxicity were diminished by concentrations of competing Ca(II) and Mg(II) metal ion concentrations an order of magnitude larger than concentrations of transition metal ion. The Cu(II)-EDTA complex was nontoxic compared to Cu(II) ions. Metabolic inhibition produced by Cu(II) ions was not significantly reversed by sequestering Cu(II) ions using EDTA, suggesting that membrane damage is irreversible. Published 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 249–261, 1998

Thermodynamic and ab initio calculations of properties of chemisorbed ions and application to adsorbed sulfur oxide anions

We discuss thermodynamic conditions for the chemisorption of ions and show that, in the low coverage limit, chemisorbed cationic and anionic specie having the same stoichiometric formulas produce surface adsorbates that are virtually indistinguishable from each other and from the chemisorbed neutral species. This is also observed from high quality ab initio (RECP HF + correlation) calculations of small ions chemisorbed on silver surfaces including H +, H −, OH +, OH −, SO 2− 3 and SO 2− 4. The additional demand on the cluster model of the surface in ab initio calculations due to the charge of the ion is investigated. For ionic adsorbates bigger clusters are required than in the case of neutral adsorbates. The structure of adsorbed sulfate was optimized at the Hartree-Fock level and the geometry changes upon chemisorption were found to be consistent with the principle of bond order conservation. The nature of the chemisorbed ions is discussed together with the implications that this has in the modeling of surface reactions and, in particular, in the chemistry of sulfur oxides on metal surfaces.

ESR Study of Cu Centers Supported on Al-, Ti-, and Zr-Pillared Montmorillonite Clays

Cu-doped Al-, Ti-, and Zr-pillared montmorillonites obtained by various procedures have been investigated with the aid of electron spin resonance (ESR). The major species present in pillared montmorillonites exchanged with copper at low pH are physisorbed square planar tetraaquo-complexes [Cu(H2O)4]2+. Only at the surface of uncalcined Al pillars does a chemisorption of copper ions occur, giving an inner-sphere square planar complex [Cu(AlO) n (H2O)4- n] x. Calcination of the samples at 673 K brings about a significant change of the Cu2+ ion environment reflected in the change of ESR parameters. The most characteristic feature is the increased covalency of the Cu–O in-plane σ bonding due to the attachment of copper to lattice oxygens. The spectra show that cupric ions form links with the pillars rather than with the silicate sheet. In the case of Al- and Ti-pillared samples, copper species of different degrees of σ in-plane covalency are obtained depending on the preparative procedure. Catalytic tests with hydroxylation of phenol demonstrate that copper centers of higher covalency show superior catalytic performance. This effect is interpreted in terms of the higher in-plane σ covalency facilitating electron transfer between the donor and the acceptor sites at the catalyst surface. The ESR spectra of almost all copper-exchanged samples show, besides the isolated Cu2+ ions, a component due to the exchange-coupled clustered cupric ions.

Adsorption of iodine ions on a quasi-perfect Cd(0001) electrode

The temperature dependence of the double-layer capacity of a quasi-perfect Cd(0001) electrode in iodine-containing solutions was investigated. The data were used to evaluate several adsorption parameters as well as the entropy of double-layer formation. It was assumed chemisorption of iodine ions occurs at positive electrode charges.

Ab initio quantum-chemical studies of halogen atoms and halogenide ions chemisorbed on a Cu(111) surface

Chemisorption of halogen atoms and halogenide ions on model Cu 7 clusters has been investigated at the ab initio Hartree-Fock level using an all electron basis set for copper and electron core potentials (ECP) for halogen atoms. Equilibrium distances, binding energies, harmonic vibrational frequencies and local charges have been calculated. All atomic and ionic species on Cu(111) (except F and F −) are preferentially adsorbed in on-top position. Local negative charges on halogen atoms are in agreement with their electronegativity order.

Adsorption of short-chain tetraalkylammonium bromide on silica

The adsorption of tetraalkylammonium (TAA) ions on silica shifts the isoelec. point to higher pH values. The IEP shift increases with increasing alkyl chain length. Also, tetraethylammonium (TEA) and tetrapropylammonium (TPA) ions can be adsorbed in larger amts. than tetramethylammonium (TMA) ions. The chemisorption of TAA ions can be explained by assuming an attraction between hydrophobically hydrated regions around surface siloxane bridges and around the TAA ions. The adsorption data of TMA ions are compatible with the stimulated adsorption model. [on SciFinder (R)]

Effects of metal ion chemisorption on gallium arsenide surface recombination: picosecond luminescence decay measurements

n-GaAs/KOHSe^(-/2-)(aq) contacts have been studied using real time photoluminescence decay techniques. This system is of interest because metal ion chemisorption improves the steady-state current-voltage properties of GaAs/KOH-Se^(-/2-)(aq)/Pt cells, yielding 16% efficiency under simulated 1-sun illumination conditions. In this work, the luminescence decay dynamics of thin epilayer GaAs samples under high level injection conditions were monitored in contact with KOHSe^(-/2-)(aq) solutions. The photoluminescence signals decayed more rapidly after metal ion chemisorption than after a fresh etch, indicating that the metal ion treatment induced a more active recombination and/or charge-transfer process than the etch. A finite-difference simulation was used to model the decays and to extract a minority carrier surface recombination velocity, S_(min), for these systems. For etched GaAs surfaces, S_(min) = 5 X 10^3 cm s^(-1), while GaAs surfaces that had been etched and then exposed to 0.010 M Co(NH_3)_6^(3+) (pH = 11) solutions displayed S_(min) = 2 X 10^5 cm s^(-1). Qualitatively similar behavior was observed for Rh-, Ru-, and Os-treated GaAs surfaces as well. These data are fully consistent with prior suggestions that the primary effect of metal ion chemisorption is to increase the rate of hole transfer to the Se^(-/2-)(aq) electrolyte, as opposed to decreasing surface recombination processes at the GaAs/liquid contact.

Distinguishing between buried semiconductor/metal contacts and hybrid semiconductor/metal/liquid contacts at n-gallium arsenide/potassium hydroxide-selenium (Se-/2-)(aq) junctions

The current-voltage properties of n-GaAs photoanodes have been evaluated in KOH-Se[sup [minus]]/2[minus]/(aq), CH[sub 3]CN-Fe[sup +]/0, and CH[sub 3]CN-MV[sup 2+]/+ solutions. Chemisorption of transition-metal ions (Rh[sup III], Co[sup III], Ru[sup III], Os[sup III]) onto n-GaAs has been shown previously to effect improved photoanode behavior for n-GaAs/KOH-Se[sup [minus]]/2[minus](aq) contacts, but it is not clear whether the chemisorbed metal forms a buried semiconductor/metal junction or results in a hybrid semiconductor/metal/liquid contact. After chemisorption of transition-metal ions, n-GaAs photoanodes displayed different open circuit voltages in contact with each electrolyte solution investigated. The role of the chemisorbed metal in the n-GaAs/M/KOH-Se[sup [minus]]/2[minus](aq) system is, therefore, best described as catalyzing interfacial charge transfer at the semiconductor/liquid interface, as opposed to establishing a semiconductor/metal or semiconductor/insulator/metal contact that is exposed to, but not influenced by, the electrolyte solution. 65 refs., 6 figs., 2 tabs.