Electrocatalytic activity of palladium–polypyrrole nanocomposite in the formaldehyde oxidation reaction

Palladium–polypyrrole nanocomposite materials with high electrocatalytic activity toward formaldehyde in an alkaline solution (methylene glycolate) have been synthesized via a one-step redox route. Key factors that have an effect on the sensor properties of palladium nanoparticles have been determined. It has been demonstrated for the first time that the emergence of not only the forward but also the reverse wave of formaldehyde oxidation on palladium particles is associated with the oxidation of methylene glycolate rather than intermediate species.     

Formation and pharmacological activity of silicon—chitosan-containing glycerohydrogels obtained by biomimetic mineralization

The biomimetic sol—gel synthesis of silicon—chitosan-containing glycerohydrogels was carried out using silicon tetraglycerolate as a precursor. It was found that chitosan accelerates gel formation in weakly acidic media. In more acidic media, the kinetics of the process changes according to the curve with a maximum, which can be attributed to different mechanisms of silanol condensation before and after the isoelectric point. The investigated silicon—chitosan-containing glycerohydrogels exhibit antibacterial, anti-inflammatory, and wound healing activity. The synthesized hybrid glycerohydrogels are promising materials for biomedical applications.     

New mixed palladium—lead and palladium—tin tellurides of the NiAs type

New ternary mixed nickel arsenide-type palladium and platinum—Group 14 metal tellurides were searched for by the high-temperature ampoule synthesis combined with the X-ray powder diffraction analysis. As a result, new phases of the ternary Pd—Pb—Te and Pd—Sn—Te systems belonging to the NiAs structure type were synthesized. The crystal structure of the compound PdPb_0.304(5)Te_0.695(5) was determined by the Rietveld method (P6₃/mmc, a = 4.151(1) Å, c = 5.680(1) Å, Z = 2, R ₁ = 0.032, R _p = 0.075, wR _all = 0.025). It was shown that no ordering exists in the occupancy of the main-group atom site by lead and tellurium. In the Pd—Sn—Te system, a phase isostructural with the above-mentioned compound was found. In the latter phase, there is also no ordering in the occupancy of the main-group atom site. According to the electron diffraction data, a superstructure derived from the NiAs type exists in a narrow range of the compositions PdSn_0.3Te_0.7—PdSn_0.4Te_0.6.     

Electrochemical and electrocatalytic behaviour of platinum–palladium nanoparticle alloys

The electrochemical and electrocatalytic behaviour of Pt/Pd nanoparticles prepared in water-in-oil microemulsion was reported. The catalytic activity of the nanoparticles was studied by using the reactions of dissociative adsorption of methanol and formic acid. The use of these surface probe reactions allowed the detection of palladium at the surface of the nanoparticles. The electrochemical stability of the particles was also investigated by voltammetry and electrochemical quartz crystal microbalance (EQCM). We shown that EQCM technique may be quantitatively used to correlate mass and area modifications when the electrochemical conditions produce corrosion of the elements of the alloy.     

Surface electrochemistry of the oxidation reactions of α- and β-alanine at a platinum electrode

The electrochemical oxidation reactions of α- and β-alanine at a Pt electrode were investigated in aqueous solutions at pH 1, 7, and 13 using steady-state current-potential measurements, cyclic voltammetry, and open circuit potential decay. The capacitance behaviour and the high Tafel slopes suggest the production of free radicals at the surface of the electrode accompanied by a second reaction involving loss of CO₂ which is the rate determining step. In the surface electro-oxidation of α-alanine, it appears that the adsorbed intermediate species is either hydrolyzed anodically to acetaldehyde and ammonia, or is oxidized to a carbonium ion which is subsequently hydrolyzed to acetaldehyde and ammonia in solution, analogous to the behaviour observed for glycine [D.G. Marangoni, R.S. Smith and S.G. Roscoe, Can. J. Chem., 67 (1989) 921]. The mechanisms for β-alanine would be similar except carbonium ion formation would probably be accompanied by a hydride transfer to form acetaldehyde. No dimerized products were detected by gas chromatography. These mechanisms differ from the dimerization process typical of the radical reactions associated with the Kolbe mechanism.     

Reactivity of hydroxo palladium and platinum complexes towards N-substituted salicylaldimines and β-ketoimines

The binuclear hydroxo complexes [{M(C6F5)2(OH)}2]2–(M=PdandPt)reactwithN-substituted salicylaldimines (HSal=NR) or -ketoimines (RN=CMeCH2COR) to give the corresponding N-substituted salicylaldiminato or -ketoiminato mononuclear complexes, [M(C6F5)2(Sal=NR)]– (M=Pd or Pt; R= Me, Et, Ph, o-MeC6H4, p-MeC6H4 or p-ClC6H4) or [(C6F5)2M{N(R)C(CH3)CHC(O)R}]– (M=Pd or Pt; R=o-MeC6H4 or p-MeC6H4; R=Me or Ph), respectively. The complexes have been characterized by partial elemental analyses, conductance measurements and spectroscopic (i.r. and 1H and 19F- n.m.r.) methods.     

Electroless deposition of palladium nanoparticles on poly(3,4-ethylene-dioxythiophene)—role of the electrode substrate

Journal of Solid State Electrochemistry - Electroless deposition of Pd is studied comparatively on glassy carbon (GCE) and spectral graphite (SGE) electrodes modified with electrodeposited...     

Oxidation of cyclohexene and α-pinene with O2—H2 mixture in the presence of supported platinum or palladium catalysts

Oxidation of cyclohexene and -pinene with an O₂—H₂ mixture in the catalytic systems containing Pt or Pd and heteropoly compounds (HPC) was studied. The main oxidation products are epoxides, allyl alcohols, and ketones. The highest yield of the oxidation products was obtained in the presence of the platinum catalyst in combination with HPC PW₁₁ or PW₁₁Fe. The reaction mechanism was proposed. A relationship between the HPC composition and the nature of intermediates involved in oxidation was examined.     

Excitation-emission-lifetime analysis of multicomponent systems—III. Platinum,palladium and rhodium porphyrins

Excitation-emission-time matrices are obtained on five emitting systems containing platinum, palladium, and rhodium porphyrins. Two-dimensional principal component analysis provides initial guesses for the iterative least-squares refinement in three dimensions. Surprisingly good resolution is obtained in mixture A of two emitting species with spectral overlaps (0.560, 0.282, 0.997) in excitation, emission and time respectively. Excellent spectral resolution is obtained in system B of two emitting species with spectral overlaps (0.569, 0.135, 0.956). In system C, with three emitting species, the overlap between pairs of spectra was sufficiently low that the nine spectra (three species each in excitation, emission and time) are relatively well determined. In systems D and E, higher overlap between spectra produces mixing of the extracted spectra.     

Measurement of the change in partial molar volume during electrode reaction by gravity electrode—II. Examination of the accuracy of the measurement

The reliability of the measurement of the change in partial molar volume between product and reactant ions measured by gravity electrode (GE) was examined by the thermodynamic measurement of pycnometer (PM). Since the PM method requires an experimental equation of the apparent molar volume to calculate the partial molar volumes of the individual ions, the most suitable experimental equation must be first determined. As a test reaction for the experiment, oxidation of ferrocyanide (FERO) ion to ferricyanide (FERI) ion was adopted. After fitting several experimental equations to the data of the apparent molar volumes by the PM method, the calculated changes in the partial molar volume were compared with the data of the GM method. Then, it is concluded that the polynomial with a degree of 3 of the logarithm of the molality of the FERO ion suggests the most suitable equation. As a result, the reliability of the GE method was also experimentally validated.     

Comparison of the results of thermal denaturation of β-lactoglobulin obtained by DSC and UV-spectroscopy

The thermal denaturation of β-lactoglobulin in the presence of urea and alkylurea solutions were measured. In the presence of a high concentration of urea this protein shows not only heat but also cold denaturation. For studying the effect of temperature two methods were used, differential scanning calorimetry (DSC) and UV-spectroscopy. DSC provides direct model-independent determination of the transition enthalpy in comparison with UV-spectroscopy, which gives only apparent or van't Hoff enthalpy of transition. The UV-melting curves were analyzed on the basis of a two-state approximation. The apparent standard enthalpies of thermal denaturation, ΔH _app. ^o , were compared with calorimetric ones.     

Electrocatalytic interaction of nano-engineered palladium on carbon nanofibers with hydrogen peroxide and β-NADH

The growing demands for reagentless hydrogen peroxide (H₂O₂) and β-nicotinamide adenine dinucleotide (β-NADH) sensors from food, pharmaceutical, chemical, and biochemical fields have stimulated extensive research interest on nano-engineered Pd. In this paper, Pd/carbon composite nanofibers were prepared by electrodepositing Pd onto electrospun carbon nanofibers to act as a catalyst toward the electrocatalytic redox reactions of H₂O₂ and β-NADH. The morphology of nano-engineered Pd was controlled by selectively adjusting the electrodeposition time and potential. Scanning electron microscopy and transmission electron microscopy results showed that nanocactus- and nanoflower-like Pd depositions were obtained on the surface of carbon nanofibers. Electrocatalytic analysis demonstrated a high electrocatalytic activity of the composite nanofibers for the redox of H₂O₂ and oxidation of β-NADH.     

Directed cleavage of carbon—tin bonds by palladium

The ligands 8-(trimethylstannyl)methylquinoline, n-Bu₃Sn(CH₂)₃NMe₂ and Ph₃Sn(CH₂)₃,NMe₂ react with (C₆H₅CN)₂PdCl₂ to give five-membered palladium chelates. in which the nitrogen atom was able to direct palladium insertion into a specific carbon—tin bond. The X-ray crystal structure of the simple chelate [(Me₂N(CH₂)₃)PdCl]₂ is presented.     

Tunable activity in electrochemical reduction of oxygen by gold–polyaniline porous nanocomposites

Oxygen electrochemical reduction on gold–polyaniline (Au–PANI) porous nanocomposite-modified glassy carbon electrode in basic media was described. The as-prepared Au–PANI porous nanocomposite showed superior tunable activity for electrochemical reduction of oxygen. The specific surface area of Au–PANI porous nanocomposites was evaluated to be about 11.3 m² g⁻¹ through a convenient voltammetric approach. Rotating ring-disk electrode experiments further demonstrated the number of electrons exchanged in oxygen reduction increased from 2e to 4e with increasing the trigger potential from 300, to 500, 700 mV. The tunable activity in electrochemical reduction of oxygen was achieved as a result of positive potential-induced formation and reduction of Au surface oxide. However, the tunable oxygen reduction reaction is fit for applying potential in a linear positive-going potential sweep. Irreversible ORR tunability was found after a more active surface formed at 700 mV. To optimize the applied potential window on these Au-based porous materials has potential applications such as in electrochemical sensing, fuel cells, or getting rid of the interference from the coexisted substances.     

The Peltier heat and the standard electrode potential of ferro-ferricyanide couple at 298.15 K determined by electrochemical–calorimetry

An experiment was done on electrochemical–calorimetry to identify the Peltier heats of the ferro-ferricyanide reversible electrode reaction over the concentration range of 0.075–0.3 mol dm⁻³ at 298.15 K. A new approach has been developed to obtain the standard potential of this electrode, which was identified as (+0.3580 ± 0.0030) volt at 298.15 K and compared with previously reported values. An equation derived from the approach is also applied to several standard couples, such as Fe(CN)₆⁻³/Fe(CN)₆⁻⁴, H⁺/H₂, Cu²⁺/Cu, Cl⁻/Hg₂Cl₂,Hg, Fe³⁺/Fe²⁺, and Cl⁻/Cl₂ to determine their respective reaction heats with satisfying results.     

Electrocatalytic oxidation and determination of norepinephrine in the presence of ascorbic and uric acids at a poly (Evans Blue)—modified glassy carbon electrode

A sensitive and selective electrochemical method for the determination of norepinephrine using a poly (Evans Blue) film-modified glassy carbon electrode was developed. The polymer film-modified electrode shows excellent electrocatalytic activity toward the oxidation of norepinephrine (NE) in phosphate buffer solution (pH 5.0). The linear range of 5.0 × 10⁻⁷–1.8 × 10⁻⁵ M and detection limit of 3.5 × 10⁻⁸ M were observed for the determination of NE in pH 5.0 phosphate buffer solutions. The interference studies showed that the modified electrode had excellent selectivity for the determination of NE in the presence of large excess of ascorbic acid (AA) and uric acid (UA). The differences of the oxidation peak potentials for NE-AA and NE-UA were about 175 and 172 mV, respectively. The resolution is large enough to determine AA, NE and UA individually. This work provides a simple and easy approach to selective detection of NE in the presence of AA and UA in physiological samples. The article is published in the original.     

445 — Reaction of the purine and pyrimidine derivatives with the electrode mercury

The electrochemical behaviour of 30 purine and pyrimidine derivatives and of a further 12 derivatives containing sulphur or halogens was studied. It was demonstrated that most of these substances react with the electrode mercury and form sparingly soluble compounds; this phenomenon can be exploited for the determination of purine and pyrimidine derivatives at low concentrations. The relation between the structural formulae of the substances and their ability to yield anodic polarographic currents conditioned by formation of sparingly soluble compounds with mercury was found. The behaviour of adenine and 8-oxyadenine was studied in greater detail by means of differential (DPP) and normal pulse polarography (NPP), d.c. polarography and cathodic stripping voltammetry (CSV). Both substances can be determined with the aid of the CSV at concentrations of the order of magnitude of 10⁻⁹M, while DPP may be used at concentrations three to four orders of magnitude higher. Interactions of some purine and pyrimidine derivatives with Hg(II) ions in homogeneous aqueous solutions were investigated. On the one hand, a correlation was found between the ability of these substances to react with mercury in solution and form precipitates, and, on the other hand, to yield anodic polarographic currents.     

Measurement of the change in the partial molar volume during electrode reaction by gravity electrode—I. Theoretical examination

Gravity electrode is an electrode system, which is operated in a high gravity field arising from centrifugal force, and allows us to measure the change in the partial molar volume between product and reactant ions in an electrode reaction. In this paper, in the presence of a large amount of supporting electrolyte, the partial molar volume of each active ion in equilibrium state is first formulated on the basis of thermodynamics. Then, the change in the partial molar volume applicable to gravity electrode is derived. Therefore, it is possible to validate the equation obtained for gravity electrode by the thermodynamic measurement.     

Oxidation of L-sorbose and 2,3;4,6-di-O-isopropylidene-α-L-sorbose over supported platinum and palladium catalysts

Oxidation of L-sorbose and 2,3;4,6-di-O-isopropylidene--L-sorbose by oxygen (air) has been studied over supported Pt and Pd catalysts. The results indicate that the activity and stability of these catalysts are greatly dependent on their composition and preparation conditions.

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L- 2,3;4,6--O---L- () . , .