Electrocatalytic effect of Ag and Cd bimetallic nanoparticles towards the reduction of nitrate and/or nitrite ions

El efecto electrocatalítico de nanopartículas bimetálicas de Cd y Ag soportadas sobre sustratos de grafito pirolítico altamente orientado (HOPG) y carbón vítreo (CV), fue evaluado para la reacción de reducción de iones nitrato y/o nitrito. Para ello, se obtuvieron inicialmente, los depósitos metálicos y bimetálicos sobre los sustratos carbonosos (SC) empleando la técnica electroquímica de simple pulso potenciostático. En el caso del par bimetálico, la cantidad de Cd fue depositada selectivamente sobre las nanopartículas de Ag previamente soportadas sobre HOPG o CV, debido a la fuerte interacción entre ambos metales, empleando diferentes tiempos de polarización. Los estudios potenciodinámicos del sistema Cd-Ag/SC, indicaron que, a tiempos de polarización relativamente grandes, es factible que los átomos de Ag y Cd formen una aleación superficial, debido a un proceso de interdifusión entre ellos, pudiendo afectar su actividad catalítica. Las partículas generadas sobre HOPG, fueron caracterizadas por AFM ex-situ y XPS, corroborando este último análisis la formación de una aleación Cd-Ag. Posteriormente, los electrodos modificados con nanopartículas metálicas y bimetálicas, y también los sustratos libres de depósitos, fueron analizados mediante voltamperometría cíclica en una solución conteniendo iones nitrato. Se detectó que los procesos de reducción de iones nitrato y/o nitrito comienzan a valores de potenciales más positivos para el caso de los depósitos bimetálicos, correspondiendo a un efecto catalítico más pronunciado debido a la presencia de Cd y Ag, los cuales pueden encontrarse aleados en la superficie, produciendo un efecto sinérgico hacia la reducción de los aniones. Incluso, se verificó un cambio en el comportamiento catalítico para mayores tiempos de polarización empleados en la deposición del Cd sobre las nanopartículas de Ag soportadas, que puede estar relacionado con la formación de dicha fase aleada. Los productos de reacción fueron analizados por colorimetría y cromatografía de intercambio iónico determinándose cantidades de nitrato, nitrito y amonio en solución.The electrocatalytic effect of Cd-Ag bimetallic nanoparticles supported on highly oriented pyrolytic graphite (HOPG) and vitreous carbon (VC) substrates was evaluated for the nitrate and/or nitrite ions reduction reaction. For this, in a first stage, the metallic and bimetallic deposits were obtained on the carbonaceous substrates (CS) using the electrochemical technique of the single potentiostatic pulse. In the case of the bimetallic pair, the amount of Cd was selectively deposited on the Ag nanoparticles previously supported on HOPG or CV, due to the strong interaction between the two metals, using different polarization times. Potentiodynamic studies of the system Cd-Ag/(CS) indicated that, for relatively large polarization times, it is feasible the formation of a surface alloy between Ag and Cd atoms, due to an interdiffusion process between them, which may affect its catalytic activity. The generated particles on HOPG, were characterized by exsitu AFM and XPS analysis, corroborating the latter the formation of a Cd-Ag alloy. Subsequently, the electrodes modified with metallic and bimetallic nanoparticles, and also the substrates free of deposits, were analysed by cyclic voltammetry in solutions containing nitrate ions. It was foundthat the reduction of nitrate and/or nitrite ions processes begin at more positive potential values in the case of bimetallic deposits, corresponding to a more pronounced catalytic effect by the presence of Cd and Ag, which could be alloyed in the surface, producing a synergistic effect for the reduction of the anions. Even, a change in the catalytic performance by using longer polarization times for the deposition of Cd on supported Ag nanoparticles was verified, that could be related with that alloyed phase. The reaction products were analyzed by colorimetry and ion exchange chromatogra-phy for determining nitrate, nitrite and ammonium amounts in solution.Fil: Ambrusi, Rubén Eduardo. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Sanchez, Miguel Dario. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Garcia, Silvana Graciela. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; Argentin

Experimental and DFT Studies of Hybrid Silver/Cdots Nanoparticles

In this work, the combination of experimental and theoretical results was employed to confirm an interaction between Cdots and AgNPs in the silver/Cdots hybrid nanoparticles. The experimental data obtained by UV Vis, IR, zeta potential and TGA techniques were correlated and interpreted by calculations obtained by DFT. Particularly, an interaction between the -COO- functional group of the Cdots with AgNPs was revealed. As consequence of this interaction, a frequency shift and a higher absorption intensity in the IR of the –OH group in the Cdots was theoretically predicted and also observed in the experimental IR spectra. Moreover a bonding and charge distribution analysis was also carried out. These results constitute new physical insight for Ag@Cdots system. Additionally, based in this type of interaction, energy calculations explained the negative charge surrounding the AgNPs, which was detected by zeta potential measurements. This systematic methodology is not only useful for this nanoparticles system, but could also be used to analyze the interaction between the components that constitute other types of hybrid nanoparticles.Fil: Arroyave Rodriguez, Jeison Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pistonesi, Marcelo Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Centurión, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentin

Density functional theory model for carbon dot surfaces and their interaction with silver nanoparticles

Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were performed to represent carbon dots surfaces. The addition of different oxygen functional groups to the aromatic carbon core structure and the stability in the interaction with silver nanoparticles was also investigated. Adsorption energies were evaluated in order to compare the competition for adsorption sites on silver surface with D-glucose and D-gluconate ion molecules. The –COOH and –COO groups and the interaction of the latter with silver were proposed to explain some features of the UV–visible absorption spectra, which could also contribute to an explanation for the charge observed on carbon dot surfaces.Fil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Arroyave Rodriguez, Jeison Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Centurión, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Di Nezio, Maria Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Pistonesi, Marcelo Fabian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

DFT study of Rh and Ti dimers decorating N-doped pyridinic and pyrrolic graphene for molecular and dissociative hydrogen adsorption

A theoretical study using density functional theory was employed to analyze the hydrogen adsorption on Rh 2 and Ti 2 dimers decorating pyridine and pyrrolic-like nitrogen doped graphene. First, an analysis of geometry, stability, projected density of states, overlap population and charge distribution was performed to understand the interaction between Rh and Ti metal adatoms and dimers with pyridinic and pyrrolic graphene. Charge transfer occurs from metal to substrate in all cases. An investigation of H 2 adsorption on Rh and Ti metals dimers on pyridinic and pyrrolic N-doped graphene was also performed. Molecular adsorption states were observed for Ti on pyridinic graphene and for Rh on both substrates. H 2 dissociative adsorption occurs on both metal supported dimers. H 2 s states hybridize with the Rh and Ti d band, forming localized and dispersed states in concordance with the mechanisms observed for H 2 adsorption. The activation energies were calculated obtaining values smaller than 0.59 eV, indicating that the dissociation of H 2 can occur spontaneously at room temperature. HSE06 hybrid functional was used to test the accuracy of PBE-D2 functional in the activation energy calculation. Adsorption in the molecular states occurs with no barriers.Fil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Electrochemical synthesis of Cd–Ag bimetallic particles and the involved alloy formation

The formation of bimetallic Cd–Ag nanoparticles on vitreous carbon (VC) and the involved alloy formation have been studied by conventional electrochemical techniques and ex-situ atomic force microscopy (AFM). Both metals were deposited by sequential electrodeposition using single potentiostatic pulses. The AFM images of Ag deposits showed small differently sized Ag nanocrystallites uniformly distributed over the VC-substrate. This modified substrate was immersed in an electrolyte solution containing Cd2+ ions and bimetallic Cd–Ag particles were prepared by underpotential deposition (UPD) of Cd. The alloy formation phenomena observed previously during Cd UPD on massive Ag electrodes were found also in the case of Cd UPD on Ag nanoparticles. The desorption spectra in the system Cd/Ag (nanoparticles)/VC employing different polarization times, showed three desorption peaks associated with the dissolution of the Cd OPD and UPD deposits and an Ag–Cd alloy formed at low underpotentials, respectively. The electrochemical behavior of the bimetallic system was also studied applying other polarization routine designed for this purpose.Fil: Ambrusi, Rubén Eduardo. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Staikov, G.. Peter Grünberg Institut. Forschungszentrum Jülich; AlemaniaFil: Garcia, Silvana Graciela. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; Argentin

DFT study of Rh-decorated pristine, B-doped and vacancy defected graphene for hydrogen adsorption

Rh adatom stability on graphene, with and without defects has been investigated by density functional theory (DFT) calculations to evaluate the feasibility to achieve a uniform dispersion of the metallic atom. Different defects introduced include B dopants, single vacancies and double 585 and 555-777 type vacancies. An energetic analysis of the hydrogen adsorption capacity for the different Rh decorated graphene structures was also performed. Dispersion force contribution to the adsorption energy was determined in order to obtain a quantitative method to know whether H2 molecules adsorbed chemically or the adsorption on the Rh decorated graphene supports is controlled by van der Waals forces. Partial density of states (PDOS) for the different systems, were obtained to understand the Rh-C, H2-Rh (adsorbed) and H-H interactions and magnetic effects, before and after Rh and H2 adsorption. When H2 molecules bind to Rh adatoms, an electrostatic interaction occurs due to a charge transfer from the metal to the graphene surfaces after adsorption. Bonding and Bader charge analysis are also included.Fil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Luna, Carla Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Underpotential deposition and involved alloy formation of cadmium on silver particles modified HOPG substrates

Cadmium underpotential deposition (UPD) on Ag particles modified highly ordered pyrolytic graphite (HOPG) surfaces, and the involved alloy formation were studied by conventional electrochemical techniques. Voltammetric results indicated that the Cd UPD followed an adsorption behavior different from that observed for massive Ag electrodes and Ag particles supported on vitreous carbon. Nanometer-sized bimetallic Cd–Ag particles were characterized by ex situ atomic force microscopy (AFM). Initially, AFM images show Ag deposits of similar size distributed preferably on HOPG step edges. No remarkable morphological changes are observed on the surface after the subsequent Cd deposition, suggesting that the Cd particles are deposited selectively over the Ag crystals. From the analysis of desorption spectra, employing different polarization times, and density functional theory (DFT) calculations, the formation of a Cd–Ag surface alloy could be inferred.Fil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Garcia, Silvana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; Argentin

Formation of Ag nanowires on graphite stepped surfaces: A DFT study

We investigate the feasibility of obtaining silver nanowires on graphite stepped surfaces theoretically, using density functional theory calculations. Three layer slabs are used to model graphite surfaces with and without defects. Adsorption energies for Ag atoms on graphite surfaces were calculated showing the preference of Ag adatoms to locate on the steps, forming linear structures like nanowires. An analysis of the charge densities and projected densities of states for different structures is also performed.Fil: Ambrusi, Rubén Eduardo. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; ArgentinaFil: Garcia, Silvana Graciela. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin

Interaction between cetyltrimetylammonium tosylate and two poly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers studied by cyclic voltammetry

Mixtures of hexadecyltrimetylammonium tosylate (hexadecyltrimethylammonium p-toluene sulfonate or cetyltrimethylammonium tosylate, CTAT) with two Pluronic block copolymers, F127 and F68, were studied using cyclic voltammetry. The hydrodynamic radii of aggregates were analyzed in light of the aggregate composition. It was confirmed that the mixtures CTAT-F127 and CTAT-F68 have different behaviors. This corroborates that the interaction between different Pluronics and the same conventional surfactant depends on the kind of copolymer surfactant and also that differences in the size of the hydrophobic and the hydrophilic parts of the molecule may cause different behaviors. The penetration of CTAT into the micelle core may be more or less hindered by the size and structure of the hydrophilic shell. However, once the conventional surfactant has penetrated the corona and reached the polyoxypropylene core in a cooperative manner, the aggregates tend to disappear, thus being replaced by smaller structures, which are probably complexes having a finite number of CTAT molecules per copolymer molecule.Fil: Schulz, Eduardo Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Garcia, Silvana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Brigante, Maximiliano Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentin

DFT study of the formation of Cd-Ag surface alloys on Ag surfaces

We investigate the feasibility of forming a surface alloy between Ag and Cd on Ag surfaces, employing Density Functional Theory calculations. Six layers slabs are used to model surface alloy systems. Adsorption energies for Cd atoms and a monolayer on Ag(1 1 1) and Ag(1 0 0) surfaces are calculated, and compared with surface alloy formation energies, verifying the energetic preference of Ag and Cd to stay in alloyed form on the surface, as found in different electrochemical experiences for this system. This means that there is an electronic effect which favors this type of phenomenon. An analysis of the charge densities and projected densities of states for the different structures proposed is also performed.Fil: Ambrusi, Rubén Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Garcia, Silvana Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química; Argentina. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin