Gabriela I. Lacconi

Influence of thiourea on silver deposition: Spectroscopic investigation

Abstract The interfacial behaviour of thiourea (TU) in perchloric acid solutions on glassy carbon electrodes during silver electrodeposition has been studied using surface enhanced Raman spectroscopy (SERS). The spectroscopic results are compared with those obtained on electrochemically activated silver electrodes. Potential-dependent thiourea adsorption (occurring via sulphur) and ClO4− coadsorption are observed. No evidence for the adsorption of solution silver–thiourea complexes regardless of TU concentration was found. The time evolution of the TU SERS signals during the electroreduction of silver is a function of the crystallite formation (nucleation) and stabilization.

Enhancement of the rate of the hydrogen evolution reaction on polycrystalline silver in alkaline solutions

The changes produced by electrochemical treatments on the voltammograms, mainly those related to the enhancement of the rate of the hydrogen evolution reaction on silver in alkaline solutions are described. Voltammograms do not yield a steady profile, at least up to 7 h of cycling. The current enhancements are analysed in terms of a minor contribution due to a roughness factor increase and of a major contribution involving highly reactive silver centres. The apparent +1 reaction order with respect to OH− ions for the hydrogen evolution reaction is interpreted through the participation of (OH−)ad in the reaction pathway.

Study of thiourea adsorption onto polycrystalline gold electrodes

Abstract Cyclic voltammetry, differential capacity determinations and chronocoulometry have been employed for quantitative study of thiourea (TU) adsorption at polycrystalline gold/aqueous KClO 4 solution interface. The film pressure and the Gibbs surface excess are determined as functions of potential. The thermodynamic data suggest that the adsorbed TU exhibits distinct surface states which appear when the TU concentration is increased and the potential is more positive.

Nicotinic acid as brightener agent in copper electrodeposition

Copper electrodeposition on platinum electrodes from slightly acidic solutions of copper sulphate containing nicotinic acid (NA) is studied. The electrochemical results indicate that NA produces an inhibition of the copper deposition, probably related to the additive adsorption. Also, complex species formation between NA and cuprous ions occur at the interface. Nicotinic acid acts as a very effective brightener producing highly uniform and smooth surfaces of copper deposits. Surface morphology, brightness and adherence depend on the potential at which the deposition is performed.

Electrochemical study of thiourea in relation to the silver electrodeposition process

Abstract The electrodeposition of silver from solutions containing thiourea (TU) was investigated using cyclic voltammetry and potential step measurements. The voltammetric results for different amounts of TU with respect to Ag + revealed retardation of silver nucleation, showing separate waves for the deposition coming from Ag + , Ag(TU) + or AG(TU) + 2 species. SEM microphotographs, revealed that crystal growth takes place through the strongly adsorbed TU layer, the size and amount of crystallites being dependent on the species involved in the deposition.

Electrochemical synthesis of palladium nanoparticles in PVP solutions and their catalytic activity in Suzuki and Heck reactions in aqueous medium

Fil: Uberman, Paula Marina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Cordoba. Instituto de Investigaciones en Fisico-quimica de Cordoba. Universidad Nacional de Cordoba. Facultad de Ciencias Quimicas. Instituto de Investigaciones en Fisico-quimica de Cordoba; Argentina

Ellipsometric characterization of copper deposits

The growth of copper layers electrodeposited from acidic solutions is investigated by in situ ellipsometry. The effect of nicotinic acid on the properties of the copper deposits is also reported. Refractive indices and extinction coefficients of films formed under diferent conditions were obtained by the use of optical models. The ellipsometric results can be interpreted using an anisotropic single layer model for the copper coatings which is related to the morphology of the deposits. The optical constants are strongly dependent on the deposition potential. The presence of the additive modifies slightly the optical properties of the electrodeposited copper layers.

Synthesis and Performance of Nickel/Reduced Graphene Oxide Hybrid for Hydrogen Evolution Reaction.

AbstractIn this work, a simple and reproducible method for the syntheses of hybrid nickel/reduced graphene oxide electrodes is presented. This method consists in a direct modification of a conventional nickel electrodeposition bath, making the synthesis industrially scalable. The synthesized catalyst is structural and electrochemically characterized and compared to the traditional electrodeposited nickel. The kinetics of hydrogen evolution reaction (HER) is studied on both conventional nickel watts (Ni-watts) and nickel/reduced graphene oxide hybrid (NirGO). An increment in the catalytic activity is observed along with the absence of nickel hydrides. Thus, the NirGO catalyst presents a higher catalytic activity towards HER, and the presence of graphene in the Ni matrix inhibits the nickel hidruration. Graphical Abstractᅟ

A spectroscopic sensing platform for MARCKS protein monolayers

We developed a highly sensitive silicon platform, suitable to assess the molecular organization of protein samples. Prototype platforms were obtained using different electrochemical protocols for the electrodeposition of Ag-nanoparticles onto the hydrogenated silicon surface. A platform with high Surface Enhanced Raman Scattering efficiency was selected based on the surface coverage and the number density of particles size distribution. The performance of the platform was determined by studying the interaction of Myristoylated Alanine-Rich C Kinase Substrate (MARCKS) protein with the substrate according to its molecular organization. The chemical and structural characteristics of MARCKS molecules were examined under two configurations: i) a disordered distribution given by a MARCKS solution drop deposited onto the platform and, ii) a compact monolayer transferred to the platform by the Langmuir-Blodgett method. Raman spectra show vibrational bands of Phenylalanine and Lysine residues specific for the protein effector domain, and evidence the presence of alpha helix structure in both configurations. Moreover, we distinguished the supramolecular order between the compact monolayer and random molecular distribution. The platforms containing Ag-nanoparticles are suitable for studies of protein structure and interactions, advancing a methodological strategy for our long term goal, which is to explore the interaction of proteins with model membranes.