Features Of Pt Research Articles

Shape-Controlled Platinum Nanoparticles of Different Sizes and Their Electrochemical Properties

Platinum (Pt) nanoparticles with controlled shapes and sizes were prepared from a solution of K2PtCl4 in the presence of polyacrylic acid (PAA) as a capping reagent. The effect of temperature, pH, and PAA concentration on the shape, size, and stability of the nanoparticles were investigated. Cubic Pt nanoparticles of different sizes in the range of 4.4–14 nm and cuboctahedral nanoparticles of an average size of 14 nm were obtained. The cubic and cuboctahedral Pt nanoparticles showed strong features of Pt {1 0 0} faces and Pt {1 0 0} and Pt {1 1 1} faces, respectively, on their cyclic voltammograms under argon atmosphere, respectively. Rotating ring disk electrode measurements in O2-saturated H2SO4 solution revealed that the catalytic activity for oxygen reduction reaction (ORR) of cubic Pt nanoparticles (average size 10 nm) was higher than that of cuboctahedral Pt nanoparticles (average size 14 nm). The activity for ORR of both cubic and cuboctahedral Pt nanoparticles decreased slightly after polycrystallization by repeated potential cycling in the range of 0.05 to 1.4 V.

Antiproliferative Pt(IV) complexes: synthesis, biological activity, and quantitative structure–activity relationship modeling

Several Pt(IV) complexes of the general formula [Pt(L)2(L')2(L'')2] [axial ligands L are Cl-, RCOO-, or OH-; equatorial ligands L' are two am(m)ine or one diamine; and equatorial ligands L'' are Cl- or glycolato] were rationally designed and synthesized in the attempt to develop a predictive quantitative structure-activity relationship (QSAR) model. Numerous theoretical molecular descriptors were used alongside physicochemical data (i.e., reduction peak potential, Ep, and partition coefficient, log Po/w) to obtain a validated QSAR between in vitro cytotoxicity (half maximal inhibitory concentrations, IC50, on A2780 ovarian and HCT116 colon carcinoma cell lines) and some features of Pt(IV) complexes. In the resulting best models, a lipophilic descriptor (log Po/w or the number of secondary sp3 carbon atoms) plus an electronic descriptor (Ep, the number of oxygen atoms, or the topological polar surface area expressed as the N,O polar contribution) is necessary for modeling, supporting the general finding that the biological behavior of Pt(IV) complexes can be rationalized on the basis of their cellular uptake, the Pt(IV)-->Pt(II) reduction, and the structure of the corresponding Pt(II) metabolites. Novel compounds were synthesized on the basis of their predicted cytotoxicity in the preliminary QSAR model, and were experimentally tested. A final QSAR model, based solely on theoretical molecular descriptors to ensure its general applicability, is proposed.

Cyclic-voltammetry behavior of Pt(1 1 1) in aqueous HClO 4 + C 6H 6: Influence of C 6H 6 concentration, scan rate and temperature

Pt(1 1 1) is modified with an overlayer of C 6H 6 ads by immersion in 0.05 or 0.50 M HClO 4 + 1 mM C 6H 6 and cycling in the 0.05–0.80 V vs. RHE potential range. The influence of the C 6H 6 concentration (1–20 mM), scan rate (10–100 mV s –1), and temperature (278–318 K) on cyclic-voltammetry (CV) features of Pt(1 1 1) and C 6H 6 surface excess are examined. The surface excess of C 6H 6, Γ(C 6H 6), is evaluated through its oxidative desorption. The amount of adsorbed C 6H 6 corresponds to a sub-monolayer with C 6H 6 molecules being parallel to the Pt(1 1 1) surface. As the amount of dissolved C 6H 6 increases, the surface excess of C 6H 6 increases to ca. 2 monolayers indicating that the C 6H 6 ads molecules adopt a tilted orientation on Pt(1 1 1). Increase of the scan rate from 10 to 100 mV s –1 does not result in any shift of the anodic peak but induces a shift of the cathodic peak towards lower potentials. An increase of temperature from 278 to 318 K shifts both cathodic and anodic peaks towards higher potentials, while at the same time reducing the peak current density. However, it does not modify the peaks’ charge density or the C 6H 6 surface excess. The cathodic and anodic CV peaks obtained in 0.05 or 0.50 M HClO 4 + 1 mM C 6H 6 are assigned to H UPD adsorption and desorption. Repetitive cycling of C 6H 6-modified Pt(1 1 1) in 0.05 or 0.50 M HClO 4 (free of C 6H 6) regenerates the CV profile characteristic of a well-ordered Pt(1 1 1) electrode, thus indicating that C 6H 6 adsorption and desorption does not disorder Pt(1 1 1).

Different reaction routes in electrocatalytic nitrate/nitrite reduction using an H+-conducting solid polymer electrolyte

Electrocatalytic reduction of NO3-/NO2- in an aqueous solution was carried out over several bimetallic cathodes, which were deposited on a Nafion-117 H+-conducting polymer membrane. The reactivity and selectivity were largely dependent on metallic compositions of the cathode. In contrast to the inactive feature of Pt alone, the activity was significantly improved by the deposition of Ni, Cu, Ag and/or Rh onto Pt. Although the activity was enhanced mostly by Cu or Ag, their reaction mechanisms are quite different, i.e., the catalytic hydrogenation of nitrate (H2- NO3- reaction) occurs on the Cu–Pt cathode, whereas the Ag–Pt cathode exhibits an electrochemical route of nitrate reduction.

Preparation of Cubic Platinum Nanoparticles of Different Sizes and Their Electrochemical Propeties

Pt nanoparticles with controlled shapes and sizes would be useful for fundamental researches on the catalytic activity for oxygen reduction reaction. In the present study, cubic Pt nanoparticles were prepared from a solution of K2PtCl4 in the presence of polyacrylic acid (PAA) as a capping reagent. The effect of temperature, pH, and PAA concentration on the shape, size, and stability of the nanoparticles were investigated, and cubic Pt nanoparticles of different sizes in the range of 4.4-10 nm were obtained. The cubic nanoparticles showed strong features of Pt {1 0 0} faces on their cyclic voltammogram under argon atmosphere. Rotating ring disk electrode measurements in O2-saturated H2SO4 solution revealed that the cubic nanoparticles have a high catalytic activity for ORR.

High activity PtPd-WC/C electrocatalyst for hydrogen evolution reaction

Pd modified Pt over a novel support of tungsten carbide nanocrystals (the catalyst denotes as PtPd-WC/C) have been prepared by using an intermittent microwave heating (IMH) method. The as-prepared electrocatalysts are characterized by using the techniques of XRD, SEM, TEM, linear sweeping voltammetry and tested for the hydrogen evolution reaction (HER) in the acidic media. It shows a better performance for the HER on PtPd-WC/C electrocatalyst than that on Pt-WC/C electrocatalyst. In addition, these effects on the catalytic activity by changing environmental temperature and electrolyte concentration were taken into account. Kinetic study shows that the HER on the PtPd-WC/C electrocatalyst gives higher exchange current density in H 2SO 4 solution with high concentration, leading to a lower overpotential and facile kinetics. XRD, SEM and TEM images of PtPd-WC/C show the crystalline features of Pt, Pd and tungsten carbides and indicated the coexistence of these components.

Assembly and Electrochemical Characterization of Nanometer-Scale Electrode|Solid Electrolyte Interfaces

A technique is herein described for the assembly and characterization of nanometer-scale metal electrode|solid electrolyte interfaces of variable dimensions. The specific system examined in this work involves a sharp Pt tip attached to the piezo-driven head of a scanning tunneling microscope (STM) allowing the tip to be inserted into (or retrieved from) a Nafion membrane placed normal to the direction of tip travel. The actual Pt|Nafion area of contact was determined by coulometric analysis of the characteristic voltammetric features of Pt, using the tip as the working electrode and a much larger Pt gauze attached to the other side of the Nafion as a counter-reference electrode, yielding for some of the interfaces examined values equivalent to as low as 35 000 Pt surface atoms. This rather versatile arrangement allows experiments to be performed in both inert (Ar) and reactive atmospheres, such as oxygen or hydrogen on either or both sides of the membrane, under controlled humidity conditions, and thus sheds light into such phenomena as changes in the overall faradaic currents induced by plastic deformations of the Nafion as well as fundamental aspects of mass transport at reactant gas|Pt|Nafion three-boundary interfaces of relevance to polymer electrolyte fuel cells (PEFCs).

Controlled growth and shape formation of platinum nanoparticles and their electrochemical properties

Cubic Pt nanoparticles were prepared from a solution of K 2PtCl 4 containing sodium polyacrylate as a capping reagent. The effects of the Pt/polymer molar ratio, the average molecular weight ( M w) of the polymer, and reaction temperature on the shape and size were investigated. When the polymer of M w = 5100 was added at a molar ratio of Pt/polymer = 1/12, cubic platinum nanoparticles of an average size of 10.3 nm were predominantly formed (ca. 50% in number) at 25 °C. The electron diffraction pattern of the cubic nanoparticles revealed that they are single crystals with Pt {1 0 0} faces on the surface. The cubic nanoparticles were electrochemically active, and showed strong features of Pt {1 0 0} faces on cyclic voltammogram under argon atmosphere. After repeated potential cycling in the range 0.05–1.4 V, the features of Pt {1 0 0} were gradually lost, and changed to those of polycrystalline Pt. Rotating ring disk electrode measurements in O 2-saturated H 2SO 4 solution revealed that the cubic nanoparticles had a high catalytic activity for oxygen reduction reaction (ORR). After polycrystallization by repeated potential cycling, the activity for ORR and hydrogen peroxide formation decreased slightly, which were attributed to the surface structural change from Pt {1 0 0} to polycrystalline.

Enantioselective Hydrogenation on Palladium: Limitations of Continuous Fixed-Bed Reactor Operation

The palladium-catalyzed continuous enantioselective hydrogenation of 4-methoxy-6-methyl-2-pyrone 1 to the corresponding 5,6-dihydropyrone 2 was studied in a fixed-bed reactor. Steady-state enantiodifferentiation was achieved by feeding the chiral modifier (cinchonine). The influence of reaction conditions on the rate and enantiomeric excess (ee) was investigated under differential and integral reactor conditions. Optimization of the enantioselectivity afforded 84.5% ee to ( R)- 2 at 1% conversion and 100% chemoselectivity. The attempt to produce high yield of ( R)- 2 failed since increasing conversion resulted in further hydrogenation of 2 to the tetrahydropyrone derivative 3, and a rapid loss of ee due to hydrogenation of cinchonidine. The poor chemo- and enantioselectivities at higher conversion are attributed to the high Pd/ 1 and Pd/cinchonine ratios in the fixed-bed reactor. It seems to be a general feature of Pt- and Pd-catalyzed enantioselective hydrogenations that the necessary cinchona alkaloid/reactant ratio is remarkably higher in a continuous reactor than in a slurry reactor.

Size and composition effects in polymer-protected ultrafine bimetallicPtxRu1−x(0<x<1)particles

Ultrafine ${\mathrm{Pt}}_{x}{\mathrm{Ru}}_{1\ensuremath{-}x}$ particles (with $0<~x<~1),$ synthesized by decomposition of organometallic precursors in the presence of a stabilizing polymer, are studied using both high-resolution transmission electron microscopy and wide-angle x-ray scattering techniques. In this paper, we focus on the influence of the size and the composition on the atomic organization and structural features of Pt, Ru, and Pt-Ru particles. It is shown that the pure Pt and Ru particles crystallize in the same structure as in the bulk, i.e., face centered cubic (fcc) for platinum and hexagonal close packed (hcp) for ruthenium. A modification of the cell parameters due to size reduction is observed. In particular, evidence is given for the change of the $c/a$ ratio in Ru particles. The alloy particles are also crystalline, whatever the composition. The role of the composition in the structural transition from the fcc structure to the hcp one in nanoscaled particles is demonstrated. The mechanism of structural transition is fully described.

1 Diagnosis and classification of erythrocytoses and thrombocytoses

An erythrocytosis describes an increased peripheral blood packed cell volume (PCV) and is deemed to be absolute or apparent depending on whether or not the measured red cell mass (RCM) is above the reference range. This reference range must be related to the individual's height and weight to avoid erroneous interpretations using ml/kg total body weight expressions in obesity. Absolute erythrocytoses are divided into primary, where the erythropoietic compartment is intrinsically abnormal, secondary, where the erythropoietic compartment is normal but is responding to external pathological events leading to an increased erythropoietin drive, and idiopathic, where neither a primary nor a secondary erythrocytosis can be established. Both primary and secondary erythrocytoses have congenital and acquired forms. The only form of primary acquired erythrocytosis that has been defined is the clonal myeloproliferative disorder, polycythaemia vera (PV). Modified diagnostic markers for PV are proposed. Thrombocytoses can be classified into primary, where megakaryopoiesis is intrinsically abnormal, secondary, where megakaryopoiesis is normal but increased platelet production is a reaction to some other unrelated pathology, and finally idiopathic. This latter new group would be used for patients not satisfying the criteria for primary or secondary thrombocytoses, if these were more precise and rigidly used than currently is the case. While theoretically congenital and acquired forms of primary and secondary thrombocytoses might exist, only one cause of secondary congenital thrombocytosis has been established, and primary congenital thrombocytosis has not yet been precisely defined. Primary (essential) thrombocythaemia (PT) is one of the forms of primary acquired thrombocytoses. The diagnostic criteria of PT traditionally involve the exclusion of secondary thrombocytoses and other myeloproliferative disorders but marrow histology could hold a key positive diagnostic role if objective histological features of PT were agreed.

Electrochemical behaviour of platinum in alkaline and acidic solutions of heavy and regular water☆

The behaviour of Pt as an electrode for hydrogen (protium and deuterium) and oxygen evolution in both alkaline and acidic, heavy and regular water solutions has been investigated primarily by cyclic voltammetry. The main features, such as adsorption and underpotential deposition of hydrogen (both protium and deuterium), as well as the specific charge capacity for monolayer oxide growth with successive increase in oxygen content (preceding hydrogen and oxygen evolution, respectively, with characteristic desorption peaks), were more or less marked in both electrolytes. Some distinctly different behaviour, however, has been observed, revealing that heavy and regular water behave almost as different solvent ambients. The hydrogen evolution reaction (HER) particularly in alkaline heavy water occurs at substantially more negative potentials, while oxygen evolution becomes shifted to considerably more positive potential values. Hydrogen absorption, besides adsorption, of both protium and deuterium, has been marked clearly by the continuously growing charge capacity of the diffusional desorption peak, whose extent depends on the evolving rate and contact time of hydrogen evolution and distinctly exceeds both one-to-one hydrogen to platinum (H/Pt or D/Pt) atom coverage on the exposed electrode surface, and relative to the corresponding reversible adsorption wave charge area for its underpotential deposition. In addition, the hydrogen oxidation peak immediately following its desorption (in particular from acidic heavy water) has also been clearly marked on voltammograms. A distinct merging and melding together of two initial deuterium reversible desorption peaks into the diffusional desorption peak in acidic heavy water has been discernibly scanned, too. Oxide formation usually starts at more anodic potentials together with deuterium oxidation and, specifically in acidic media, proceeds vigorously with higher and continuously growing rates and merging together with evolving molecular oxygen, while the prevailing oxygen evolution thereby becomes shifted to more positive potential values. These features reveal that, owing to its distinctly different steric factor, heavy water (in particular in acidic media) behaves as a stronger oxidizing agent than regular water. Some discernible properties of the interplay between hydrogen and oxygen on the Pt electrode in both electrolytes along the potential axis have been clearly marked and pointed out. The Rowland or EDTA effect on the potentiodynamic features of Pt has also been scanned and displayed.

Interpretation of the Structure of LEED Intensity Spectra in τ-Matrix Approximation for the Platinum (100) Surface

Abstract LEED intensity spectra of the clean (00 and ⅕ 0 beams) and cesium covered (½ 0 beam) Pt(100) surface at normal or nearly normal incidence are compared with a double diffraction approach developed for the scattering process. A second order scattering approach is always restricted to cases where strong attenuation or weak scattering of the propagating electrons can be assumed. The comparison shows that many (but not all) intensity features of Pt(100) can be attributed to first and second order scattering processes only. Some of the maxima are likely to represent resonances. For proper assignment an effective inner potential is chosen that accounts for slowly varying dynamical effects as well as distortions of the crystal. The approach reveals only interpretations rather than predictions. However, it needs nearly no computational effort.