Study of support effects on the reduction of Ni2+ ions in aqueous hydrazine

We have studied the effect of silica of quartz-type on the reducibility of nickel acetate in aqueous hydrazine (80 degrees C, pH = 10-12) and metal particle formation. The obtained materials were characterized by X-ray diffraction, transmission electron microscopy, and thermodesorption experiments. With nickel acetate alone, the reduction was partial (45%) and a metal film at the liquid-gas interface or a powdered metal precipitate with an average particle size of 120 nm was obtained. In the presence of silica as the surfactant, the reduction of nickel acetate was total and the nickel phase deposited as a film on the support with an average particle size of 25 nm. Supported nickel acetate was also totally reduced. Crystallites of a mean particle size of about 3 nm were obtained. Decreasing the nickel content or increasing the hydrazine/nickel ratio decreased the metal particle size. Whiskers were formed for low nickel loadings. Hydrogen thermal treatment of the reduced phase showed that the organic acetate fragment, belonging to the precursor salt, still remained strongly attached to the nickel phase. The amount of the retained organic matrix depended on the metal particle size. Surface defects are suggested as active sites, which enhanced nickel ion reduction in the presence of silica as the surfactant or support. Metal-support interactions and the nucleation/ growth rate were the main factors determining the size and morphology of the supported metal particles formed. The organic matrix covered the reduced nickel phase.     

Coupled radiometric and electrochemical study of the reduction of TcO4 ions at a gold electrode in acidic medium (mechanistic aspects of Tc deposition)

The reduction of TcO₄⁻ ions at a smooth gold electrode was studied in 1 mol dm⁻³ H₂SO₄ supporting electrolyte using coupled voltammetric and volt-radiometric measurements and steady state measurements. The problems of the existence of parallel pathways leading to the formation of a Tc layer and dissolved Tc(IV) complexes are discussed. A general scheme is suggested for the interpretation of the phenomena.     

A combinatorial approach to the study of particle size effects on supported electrocatalysts: oxygen reduction on gold

A novel high-throughput technique has been developed for the investigation of the influence of supported metal particle size and the support on electrocatalytic activity. Arrays with a gradation of catalyst particle sizes are fabricated in a physical vapor deposition system that also allows selection of the support material. Simultaneous electrochemical measurements at all electrodes in the array, together with determination of the actual particle size distribution on each of the electrodes by transmission electron microscopy (TEM), then allows rapid determination of the activity as a function of catalyst center size. The procedure is illustrated using data for the reduction of oxygen on gold nanoparticles supported on both substoichiometric titanium dioxide (TiO(x)()) and carbon and the conclusions are verified using voltammetry at rotating disk electrodes. Gold centers with diameters in the range 1.4-6.3 nm were investigated and it is demonstrated that, with both supports, the catalytic activity for oxygen reduction decays rapidly for particle sizes below 3.0 nm. This may be observed as a decrease in current at constant potential or an increase in the overpotential for oxygen reduction.     

Determination of low levels of cadmium ions by the under potential deposition on a self-assembled monolayer on gold electrode

Despite the advantages of simplicity and high-throughput detection that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has over other methods, quantitative analysis of low-molecular-weight analyte is hampered by interference from matrix-derived background noise and signal fluctuation due to the inhomogeneous MALDI sample surface. Taking advantage of improved sample homogeneity through matrix-conjugated magnetic nanoparticles (matrix@MNP) and the seed-layer method, we report a new strategy for the rapid identification and quantification of drugs in urine samples, using morphine and 7-aminoflunitrazepam (7-aminoFM2) as model compounds. To our knowledge, this is the first attempt using the seed-layer method for small molecule analysis. By applying the proposed seed-layer method, which was specifically optimized for the 2,5-dihydroxybenzoic acid@MNP (DHB@MNP) matrix, homogeneous sample crystallization examined by microscopy analysis was obtained that generated reproducible MALDI signals (RSD<10.0%). For urine sample analysis, simple liquid-liquid extraction as a sample pretreatment step effectively reduced the ion suppression effect caused by the endogenous components in urine; good recoveries (82-90%) were obtained with a small ion suppression effect (<14% of signal decrease). This newly developed method demonstrated good quantitation linearity over a range of 50-2000 ng mL(-1) (R(2)>0.996) with reduced signal variation (RSD<10.0%). The detection limit is 30 ng mL(-1) with good precision (intra-day, 2.0-9.3%; inter-day, 5.0-10.0%) and accuracy (intra-day, 95.0-106.0%; inter-day, 103.0-115.5%). The nanoparticle-assisted MALDI-TOF MS combined with seed-layer surface preparation provides a rapid, efficient and accurate platform for the quantification of small molecules in urine samples.     

Binary self-assembled monolayers of alkanethiols on gold: deposition from solution versus microcontact printing and the study of surface nanobubbles

The coadsorption of alkanethiols on noble metals has been recognized for a long time as a suitable means of affording surfaces with systematically varied wettability and other properties. In this article, we report on a comparative study of the composition of the mixed self-assembled monolayers (SAMs) obtained (i) by the coadsorption of octadecanethiol (ODT) and 16-mercaptohexadecanoic acid (MHDA) from ethanol and chloroform onto gold substrates and (ii) by microcontact printing using poly(dimethyl siloxane) (PDMS) stamps. SAMs prepared by coadsorption from solution showed a preferential adsorption of ODT for both solvents, but this trend was reversed in microcontact-printed SAMs when using chloroform as a solvent, as evidenced by contact angle and Fourier transform infrared (FTIR) spectroscopy measurements. An approximately linear relationship between the static contact angle and the degree of swelling with different solvents was observed, which suggests that the surface composition can be controlled by the interaction of the solvent and the PDMS elastomer. The altered preference is attributed to the different partitioning of the two thiols into solvent-swelled PDMS, as shown by (1)H NMR spectroscopy. Finally, molecularly mixed binary SAMs on ODT and MHDA on template-stripped gold were applied to study the effect of surface nanobubbles on wettability by atomic force microscopy (AFM). With a decreasing macroscopic contact angle measured through water, the nanoscopic contact angle was found to decrease as well.     

Effect of the Zn2+ and Hg2+ ions on the structure of liquid water

The effect of ions on the structure of liquid water is still not completely understood, despite extensive experimental and theoretical studies. A combined XANES and molecular dynamics investigation on diluted Zn(2+) and Hg(2+) aqueous solutions reveals that the influence of a single ion on the bonding pattern of water molecules is strongly dependent on the nature of the ion. While the structure of water is not altered by the presence of the Zn(2+) ion, the Hg(2+) cation has a strong impact on the hydrogen-bond network of water that extends beyond the first coordination shell.     

Mechanism and kinetics of the reduction of In(III) ions at a polycrystalline gold electrode from highly concentrated ZnCl2 solutions

Summary The mechanism of the cathodic reduction of In(III) at gold has been studied by rotating disc and ring-disc voltammetry in highly concentrated aqueous ZnCl₂ solutions. At concentration of the base electrolyte higher than 7 mol dm^–3, the voltammetric curves recorded at the disc electrode split into two well-separated waves which correspond to the successive charge transfer reactions: In(III) + 2e^– In(I) and In(I) + e^– In. By the use of coulometric and potentiometric techniques, the formal potentials of the In(III)/In(I), In(III)/In and In(I)/In redox couples as well as the equilibrium constants of the reproportionation reaction In(III) + 2 In 3 In(I) has been determined and discussed. The kinetic parameters of the In(III)/In(I) electrode reaction have been also evaluated and discussed.

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Mechanismus und Kinetik der Reduktion von In(III)-Ionen an der Goldelektrode in hochkonzentrierten wäßrigen ZnCl₂-Lösungen

Zusammenfassung Es wird der Mechanismus der Reduktion von In(III)-Ionen in hochkonzentrierten ZnCl₂ Lösungen mittels der Scheiben- und Ring-Scheiben-Elektrode aus Gold untersucht. Wenn die Konzentration des Grundelektrolyten 7 mol dm^–3 übersteigt, verteilen sich die erhaltenen Stromspannungskurven auf zwei gut gestaltete Stufen, die den konsekutiven Durchtrittsreaktionen In(III) + 2e^– In(I) und In(I) + e^– In entsprechen. Aufgrund der coulometrischen und potentiometrischen Messungen werden die Formal-Standardpotentiale der In(III)/In(I)-, In(III)/In-und In(I)/In-Redoxpaare, die Gleichgewichtskonstanten der Reproportionierungsreaktion In(III) + 2 In 3 In ermittelt. Die kinetischen Parameter der Durchtrittsreaktion In(III)/In(I) werden bestimmt und diskutiert.

     

Remarks on the reactions of a tetracarboxylic porphyrin with gold and silver ions: A spectrophotometric,TEM and SEM study

The coproporphyrin-I (CPI) behaves as a reducing agent for silver and gold metal ions and as stabilizing agent for the formed colloidal metallic nanoparticles. The peculiarity of silver and gold nanoparticles obtained in the reactions of monomeric form of CPI with their metal ions has been studied. The optical properties of the colloidal forms of these metals have been investigated by UV–Vis spectrophotometry, and their morphology by TEM and SEM measurements. The structures and the size distributions of Ag and Au particles have been characterized and determined by computerized TEM images.     

Theoretical study of phase transitions and underpotential deposition on a liquid|solid interface

The underpotential deposition of metals on a single crystal electrode in the presence of anions has been studied in the framework of a triangular lattice gas model with pair- and three particle lateral interactions. Interactions between the adsorbed species cause the formation of the ordered (√3 × √3) structures in accordance with the symmetry of the lattice of adsorption sites. Using the mathematical equivalence between the lattice gas model and Ising and Blume-Emery-Griffiths spin models, we apply the method of the real space renormalization group for investigation the phase diagram of the system and the processes of deposition and desorption of the ions. It is shown that the phase transitions, occurring in the system, influence the underpotential deposition of metal ions strongly and are observed as sharp peaks in the voltammograms. We calculate coulometric and voltammetric curves and estimate the order of the lateral interaction magnitude between the adsorbed ions.     

Non-isothermal reduction of silica-supported nickel catalyst precursors in hydrogen atmosphere: a kinetic study and statistical interpretation

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature-programmed reduction at four different heating rates (2, 5, 10 and 20 °C min^?1), in a hydrogen atmosphere. Kinetic parameters (E _a, A) were determined using Friedman isoconversional method. It was found that for all mole ratios, apparent activation energy is practically constant in conversion range of α = 30–70 %. In considered conversion range, the following values of apparent activation energy were found: E _a = 129.5 kJ mol^?1 (SiO₂/Ni = 0.20), E _a = 133.8 kJ mol^?1 (SiO₂/Ni = 0.80) and E _a = 125.0 kJ mol^?1 (SiO₂/Ni = 1.15). Using two special functions (y(α) and z(α)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO₂/Ni mole ratios is a complex process and can be described by two-parameter ?esták–Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the experimental data, in the wide range of conversions (α = 5–95 %). Based on obtained values of Weibull shape parameter (θ), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.     

Synthesis of a stable gold hydrosol by the reduction of chloroaurate ions by the amino acid, aspartic acid

Development of reliable protocols for the synthesis of nanoparticles of well-defined sizes and good monodispersity is an important aspect of nanotechnology. In this paper, we present details of the synthesis of gold nanoparticles of good monodispersity by the reduction of aqueous chloroaurate ions by the amino acid, aspartic acid. The colloidal gold solution thus formed is extremely stable in time, indicating electrostatic stabilization via nanoparticle surface-bound amino acid molecules. This observation has been used to modulate the size of the gold nanoparticles in solution by varying the molar ratio of chloroaurate ions to aspartic acid in the reaction medium. Characterization of the aspartic acid-reduced gold nanoparticles was carried out by UV-visible spectroscopy, thermogravimetric analysis and transmission electron microscopy. The use of amino acids in the synthesis and stabilization of gold nanoparticle in water has important implications in the development of new protocols for generation of bioconjugate materials.     

Investigation of entrance and exit effects on liquid transport through a cylindrical nanopore

The entrance and exit effects on liquid transport through a nano-sized cylindrical pore under different solid wall-liquid interactions were studied by comparing molecular dynamics (MD) results of a finite length nanopore in a membrane with those of an infinite length one. The liquid transport through a finite length nanopore in a membrane was carried out by using a pressure-driven non-equilibrium molecular dynamics (NEMD) method proposed by Huang et al. [C. Huang, K. Nandakumar, P. Choi and L. W. Kostiuk, J. Chem. Phys., 2006, 124, 234701]. The fluid motion through an infinite length nanopore, which had the same cross-stream dimension as the finite length channel in the membrane, but with periodic boundary conditions in the stream-wise direction, was carried out by using the external-field driven NEMD approach [J. Koplik, J. R. Bavanar and J. F. Willemsen, Phys. Rev. Lett., 1988, 60, 1282]. The NEMD results show that the pressure and density distributions averaged over the channel in the radial direction in both finite and infinite length channels are similar, but the radial distributions of the stream-wise velocity were significantly different when the solid wall was repulsive. The entrance and exit effects lead to a decrease in flow rate at about 39% for the repulsive wall and 6% for the neutral-like wall.     

Oligopyridine ligands derived from amino acid precursors: their Zn2+ complexation and effects on hepatic stellate cell functions

A series of oligopyridine ligands were derived from amino acid amides in which amide oxygen and ternary nitrogen atoms were combined with pyridine moieties. 1H NMR and circular dichroism spectroscopic characterizations revealed that they formed stable Zn2+ complexes in neutral aqueous solutions and caused Zn2+ deficiency in the hepatic stellate cell systems. Since collagen synthesis was effectively promoted in the cells, the present oligopyridine derivatives worked as biocompatible ligands for Zn2+ complexation and cell activation.     

On the adsorption of cadmium(II) ions on a HMDE from KF + thiourea aqueous solutions: A chronocoulometric study

The adsorption of cadmium(II) ions from thiourea aqueous solutions has been studied by double potential step chronocoulometry (DPSSC). The adsorption is strong on mercury electrodes and it has been studied as a function of thiourea concentration, cadmium(II) concentration and potential. A discrepancy between the double-layer charge values from either blank solutions or solutions containing reactant obtained by this technique has been found.     

Ruthenocene and cyclopentadienyl pyrrolyl ruthenium as precursors for ruthenium atomic layer deposition: a comparative study of dissociation enthalpies

RuCp₂ (ruthenocene) and RuCpPy (cyclopentadienyl pyrrolyl ruthenium) complexes are used in ruthenium (Ru) atomic layer deposition (ALD) but exhibit a markedly different reactivity with respect to the substrate and co-reactant. In search of an explanation, we report here the results of a comparative study of the heterolytic and homolytic dissociation enthalpy of these two ruthenium complexes, making use of either density functional theory (DFT) or multiconfigurational perturbation theory (CASPT2). While both methods predict distinctly different absolute dissociation enthalpies, they agree on the relative values between both molecules. A reduced heterolytic dissociation enthalpy is obtained for RuCpPy compared to RuCp₂, although the difference obtained from CASPT2 (19.9?kcal/mol) is slightly larger than the one obtained with any of the DFT functionals (around 17?kcal/mol). Both methods also agree on the more pronounced stability of the Cp^? ligand in RuCpPy than in RuCp₂ (by around 9?kcal/mol with DFT and by 6?kcal/mol with CASPT2).