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302 results on '"Salvarezza, Roberto"'

53. Influence of capping on the atomistic arrangement in palladium nanoparticles at room temperature

Author

Corthey, Gastón, Olmos Asar, Jimena A., Casillas, Gilberto, Mariscal, Marcelo M., Mejía Rosales, Sergio, Azcárate, Julio César, Larios, Eduardo, Yacamán, Miguel José, Salvarezza, Roberto, Fonticelli, Mariano H., Corthey, Gastón, Olmos Asar, Jimena A., Casillas, Gilberto, Mariscal, Marcelo M., Mejía Rosales, Sergio, Azcárate, Julio César, Larios, Eduardo, Yacamán, Miguel José, Salvarezza, Roberto, and Fonticelli, Mariano H.

Abstract

The role that protecting molecules have on the way that palladium atoms arrange themselves in nanoparticles prepared at room temperature was studied by the analysis of aberration-corrected scanning transmission electron microscopy images and atomistic Langevin dynamics simulations. It was found that the arrangement of Pd atoms is less ordered in thiolate-protected nanoparticles than in amine-protected ones. The experimental and theoretical data showed that the disorder in ∼3 nm thiolate-protected particles is promoted by the strong S−Pd bond in the sulfide layer that surrounds the nanoparticles.

Published
2014

58. Electrochemical study of thiourea and substituted thiourea adsorbates on polycrystalline platinum electrodes in aqueous sulfuric acid

Author

Bolzán, Agustín Eduardo, Piatti, Roberto C. V., Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
Adsorption kinetics, Adsorption isotherms, Methyl thiourea, Tetramethyl thiourea, Thiourea, Química, Adsorbates, Dimethyl thiourea, Platinum
Abstract

The electrochemical response of adsorbates produced on polycrystalline Pt from thiourea, methyl thiourea, 1,3 dimethyl thiourea and tetramethyl thiourea dissolved in aqueous 0.5 M sulfuric acid are comparatively studied using electrochemical routines. The adsorption kinetics of thioureas on Pt follows an Elovich-type equation. Their saturation coverage, measured from the decrease in the H-atom electrosorption charge after correction for molecular size for steric effects, decreases as the size of the molecule producing adsorbates increases. Adsorption data fulfill the empirical Frumkin isotherm with a repulsive adsorbate–adsorbate lateral interaction term. Adsorbate electrooxidation starts at about 0.65 V vs SHE. The deprotonation of hydrogen-containing thioureas yields soluble products, their electrochemical behaviour being to some extent similar to that of formamidine disulfide. For E > 0.65 V vs SHE, the oxidation of thioureas can be described as complex processes in which intermediates compete with oxide layer formation on platinum., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
2002

59. Anodisation of copper in thiourea- and formamidine disulphide-containing acid solution : Part I. Identification of products and reaction pathway

Author

Bolzán, Agustín Eduardo, Haseeb, A. S. M. A., Schilardi, Patricia Laura, Piatti, Roberto C. V., Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
Anodic copper dissolution, Corrosion inhibitor, Thiourea, Química, Ciencias Exactas
Abstract

The anodic behaviour of copper in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea or formamidine disulphide was investigated at 298 K, combining data from electrochemical polarisation, chemical analysis, UV–vis spectroscopy, XPS and EDAX analysis, and structural information on copper–thiourea complexes. The main reactions depend on the applied potential and initial thiourea concentration. In the potential range −0.30≤E≤0.075 V (versus SCE), the electro-oxidation of thiourea to formamidine disulphide, the formation of Cu(I)–thiourea soluble complexes, and Cu(I)–thiourea complex polymer-like films, are the most relevant processes. The formation of this film depends on certain critical thiourea/copper ion molar concentration ratios at the reaction interface. At low positive potentials, the former reaction is under intermediate kinetic control, with the diffusion of thiourea from the solution playing a key role. For E≥0.075 V, soluble Cu(II) ions in the solution are formed and the anodic film is gradually changed to another one consisting of copper sulphide and residual copper. The new film assists the localised electrodissolution of copper. A complex reaction pathway for copper anodisation in these media for the low and high potential range is advanced., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
2001

60. Anodisation of copper in thiourea-containing acid solution : Part II. In situ transversal imaging observations. Kinetics of anodic film growth

Author

Haseeb, A. S. M. A., Schilardi, Patricia Laura, Bolzán, Agustín Eduardo, Piatti, Roberto C. V., Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
Anodic copper dissolution, Corrosion inhibitor, Thiourea, Química, Ciencias Exactas
Abstract

The formation of anodic films during the anodisation of copper, at different applied potentials E, in aqueous 0.5 M sulphuric acid containing different amounts of dissolved thiourea was investigated following the corroding electrode profile by on line in situ imaging. For E0.07 V, the main reactions are the electro-decomposition of formamidine disulphide and Cu(I)–thiourea complexes yielding a copper sulphide-containing film (film II) and the electrodissolution of copper as aqueous Cu(II) ions through film II. The relative contribution of these processes depends on thiourea concentration in the solution, the applied electric potential and anodisation time. The growth kinetics of films I and II were determined from the evolution of the average film height〈h〉obtained from in situ imaging. The kinetics of film I fit a parabolic rate law, whereas those of film II approach a linear〈h〉versus anodisation time relationship. The rupture of film II assists the localised corrosion of copper. Likely physical mechanisms for the formation of these anodic films are discussed., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
2001

61. New insights into the chemistry of thiolate-protected palladium nanoparticles

Author

Corthey, Gaston, Rubert, Aldo, Picone, A. Lorena, Casillas, Gilberto, Giovanetti, Lisandro J, Ramallo-Lopez, Jose M, Zelaya, Eugenia, Benitez, Guillermo A, Requejo, Felix, Jose-Yacaman, Miguel, Salvarezza, Roberto, Fonticelli, Mariano H, Corthey, Gaston, Rubert, Aldo, Picone, A. Lorena, Casillas, Gilberto, Giovanetti, Lisandro J, Ramallo-Lopez, Jose M, Zelaya, Eugenia, Benitez, Guillermo A, Requejo, Felix, Jose-Yacaman, Miguel, Salvarezza, Roberto, and Fonticelli, Mariano H

Abstract

This paper establishes the chemical nature of Pd nanoparticles protected by alkanethiolates that were prepared through a ligand placeexchange approach and the two-phase method, first developed for Au nanoparticles by Brust and Schiffrin. After 10 years since the first study on this kind of Pd nanoparticles was published, the surface composition of the particles is a matter of debate in the literature and it has not been unambiguously assessed. The nanoparticles were studied by means of several techniques: UV−visible spectroscopy, scanning transmission electron microscopy, Fourier-transform infrared spectroscopy, extended X-ray absorption fine structure, and X-ray photoelectron spectroscopy. The experimental data, obtained for the 3 nm diameter Pd particles, prepared by both synthetic routes, are consistent with nanoparticles composed by Pd(0) cores surrounded by a submonolayer of sulfide species, which are protected by alkanethiolates. Also, we unambiguously demonstrate that the chemical nature of these particles is very similar to that experimentally found for alkanethiolate-modified bulk Pd. The results from this paper are important not only for handling thiolate-protected Pd nanoparticles in catalysis and sensing, but also for the basic comprehension of metallic nanoparticles and the relation of their surface structure with the synthesis method.

Published
2012

62. The electrodeposition of mercury from aqueous Hg2+2 ion-containing acid solutions on smooth and columnar-structured platinum electrodes

Author

Martins, María Elisa, Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
Platinum electrode topography, Mercury underpotential electrodeposition, Columnar-structured electrode, Química, Mercury electrodeposition, Mercury penetration into platinum, Ciencias Exactas
Abstract

The electrodeposition of Hg on polycrystalline smooth and columnar structured Pt (cs-Pt) substrates was comparatively studied in acid solution at 298 K applying potentiodynamic techniques. The topography of both types of Pt electrodes was characterized by scanning tunneling microscopy. The use of cs-Pt substrates provides information about surface processes which are not easily detected on conventional smooth Pt. At moderate and high potential scan rates Hg electrodeposition under mass transport control on cs-Pt yields a non-equilibrium complex deposit consisting of 2d and 3d Hg domains, and Pt-Hg alloy coexisting with bare Pt domains at intercolumnar voids. The dynamics of these domains approaching equilibrium can be followed by conventional voltammetry. The kinetics of Hg penetration into bulk Pt results from a Hg atom shift to a position underlying the first layer of Pt atoms followed by a diffusion-controlled penetration into bulk Pt. The Hg atom diffusion coefficient into bulk Pt results in D≅2×10−17 cm2 s−1, Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
1998

71. In situ sequential STM imaging of structural changes resulting from the electrodissolution of silver crystal surfaces in aqueous perchloric acid : The roughening kinetics

Author

Vela, María Elena, Andreasen, Gustavo, Salvarezza, Roberto Carlos, Hernández Creus, A., and Arvia, Alejandro Jorge

Subjects
Kinetics, Química, Silver crystal surfaces, Scanning tunneling microscopy, Ciencias Exactas
Abstract

Structural changes of silver terrace domains in aqueous perchloric acid solution at constant anodic current density (j) and room temperature were followed by in situ scanning tunneling microscopy sequential imaging. For j-2 silver electrodissolution proceeds at step edges without roughening. Conversely, for j-2 the silver surface becomes progressively rougher to attain, after a certain critical time, a steady roughness. In this case, the dynamic scaling theory applied to STM images indicates that the dissolving silver surface can be described as a self-affine fractal surface with a static roughening exponent α50.9060.06, and a dynamic roughening exponent β50.3660.08. The value of a is consistent with the relevant role played by surface diffusion in the silver electrodissolution mechanism, whereas the value of b is slightly higher than those derived from growth models incorporating surface diffusion. The difference in the value of β would reflect the influence of either the electric field or energetic barriers at step edges on the rate of roughness development., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
1996

74. New Insights into the Chemistry of Thiolate-Protected Palladium Nanoparticles

Author

Corthey, Gastón, primary, Rubert, Aldo A., additional, Picone, A. Lorena, additional, Casillas, Gilberto, additional, Giovanetti, Lisandro J., additional, Ramallo-López, José M., additional, Zelaya, Eugenia, additional, Benitez, Guillermo A., additional, Requejo, Félix G., additional, José-Yacamán, Miguel, additional, Salvarezza, Roberto C., additional, and Fonticelli, Mariano H., additional

Published
2012
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81. From Single to Multiple Ag-Layer Modification of Au Nanocavity Substrates: A Tunable Probe of the Chemical Surface-Enhanced Raman Scattering Mechanism

Author

Tognalli, Nicolás G., primary, Cortés, Emiliano, additional, Hernández-Nieves, Alexander D., additional, Carro, Pilar, additional, Usaj, Gonzalo, additional, Balseiro, Carlos A., additional, Vela, María E., additional, Salvarezza, Roberto C., additional, and Fainstein, Alejandro, additional

Published
2011
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82. Surface functionalization of electro-deposited nickel

Author

Sadler, James E., primary, Szumski, Doug S., additional, Kierzkowska, Agnieska, additional, Catarelli, Samantha R., additional, Stella, Kevin, additional, Nichols, Richard J., additional, Fonticelli, Mariano H., additional, Benitez, Guillermo, additional, Blum, Bárbara, additional, Salvarezza, Roberto C., additional, and Schwarzacher, Walther, additional

Published
2011
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90. Synergistic Effects in the Inhibition of Copper Corrosion

Author

González, S., Laz, M. M., Souto, R. M., Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
benzotriazole, potassium ethylxanthate, Química, synergistic inhibiting effects, thiourea, Ciencias Exactas, copper pitting
Abstract

Benzotriazole (BTA), thiourea (TU), and potassium ethylxanthate (KEX), behave as copper (Cu) corrosion inhibitors under certain conditions. These chemicals have been investigated to establish whether they provide synergistic effects. The Cu corrosion inhibition was followed through changes in electrochemical characteristics. Cu specimens were tested at 25°C in two aggressive media, 0.1 M NaCl and 1 M NaClO4, using the linear potential sweep technique at 0.001 V s–1 and by scanning electron microscopy of Cu specimens subjected to potentiodynamic and potentiostatic routines. A comparative behavior of the different substances for Cu was presented in the 6.6 ≤ pH ≤ 11 range. For KEX-BTA mixtures, synergistic inhibition effects were found in 0.1 M NaCl (7 ≤ pH ≤ 11). The apparent synergistic inhibition was explained tentatively by an increase in the compactness of the polymer-like passivating layer of KEX-Cu, which formed in the presence of BTA and Cl– ions., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
1993

91. A mechanistic approach to the electroformation of anodic layers on copper and their electroreduction in aqueous solutions containing NaHCO3 and Na2 CO3

Author

Pérez Sánchez, M., Souto, R. M., Barrera, M., González, S., Salvarezza, Roberto Carlos, and Arvia, Alejandro Jorge

Subjects
Cu passivation, Cu anodic layers, Solution composition, Química, Cu corrosion, Ciencias Exactas, Nucleation and growth processes
Abstract

The electrochemical behaviour of Cu in solutions containing Na2CO3 + NaHCO3 (8.8 < pH < 11 .1) has been studied using potentiodynamic and potentiostatic techniques complemented by Scanning Electron Microscopy. The initial stages of the anodic layer formation involve the electroformation of a thin inner Cu2O layer followed by the growth of a CuO/Cu(OH)2-Cu(HO)3 complex outer layer. Soluble Cu(II) species were detected in the entire anodization potential range . Kinetic models devised for phase change electrochemical processes have been applied to explain the characteristics of anodic and cathodic current transients., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Published
1993

93. Self-Assembly of Alkanedithiols on Au(111) from Solution: Effect of Chain Length and Self-Assembly Conditions

Author

Millone, María Antonieta Daza, primary, Hamoudi, Hicham, additional, Rodríguez, Luis, additional, Rubert, Aldo, additional, Benítez, Guillermo A., additional, Vela, María Elena, additional, Salvarezza, Roberto C., additional, Gayone, J. Esteban, additional, Sánchez, Esteban A., additional, Grizzi, Oscar, additional, Dablemont, Céline, additional, and Esaulov, Vladimir A., additional

Published
2009
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94. Oxygen Reduction on Iron−Melanin Granular Surfaces

Author

Orive, Alejandro González, primary, Creus, Alberto Hernández, additional, Grumelli, Doris, additional, Benitez, Guillermo A., additional, Andrini, Leandro, additional, Requejo, Felix G., additional, Bonazzola, Cecilia, additional, and Salvarezza, Roberto C., additional

Published
2009
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