Synthesis and characterization of alkoxide-derived pt nanoparticles

Identification of the species formed during the in situ reduction of hexachloroplatinic acid by sodium ethoxide, forming a Pt sol, is made. The solution phase is shown to consist of suspended metallic Pt nanoparticles (1-3 nm in diameter), acetaldehyde, and a Pt(II) species, identified by NMR and X-ray adsorption near-edge spectroscopy (XANES) to be NaPtCl3(C2H4), a sodium analogue of Zeise's salt [KPtCl3(C2H4)]. The NaPtCl3(C2H4) product exhibits greater stability in both ethanol and air than the conventional Zeise's salt, providing a means of storing the useful Zeise's anion [PtCl3(C2H4)-]. Electrochemistry, X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses have shown that the precipitate phase formed during the synthesis is composed solely of Pt particles approximately 6 nm in diameter and NaCl. Thermal gravimetric analysis/differential scanning calorimetry (TGA/DSC) showed that the color of the precipitate is an accurate gauge of the ratio of Pt to NaCl, with the lightest to darkest precipitates containing from 1% to 40% nanoparticulate Pt by mass, respectively. A comprehensive characterization of both phases formed has allowed us to propose a mechanism for the conversion of hexachloroplatinic acid to Pt nanoparticles.     

Colloidal synthesis of pt nanoparticles: on the formation and stability of nanowires

Catalytic properties of Pt nanoparticles can significantly depend on the crystallite shape, which renders shape control an important aim in the chemical synthesis. Starting from a colloidal synthesis of quasispherical Pt nanocrystals capped with dodecylamine ligands, systematic variations of different synthesis parameters were performed in the present work in order to obtain Pt nanowires. Mechanistic investigations revealed that nanowires can form by aggregation of quasispherical particles. The process of wire formation was found to be influenced by parameters such as the concentration of the stabilizing ligands on the particle surface. Furthermore, the thermal stability of the obtained nanoparticles was examined. The nanowires were found to be stable up to approximately 140-160 degrees C. In this temperature range a structural transition to a more spherical crystallite shape occurred, which can be understood by thermodynamic considerations.     

Formate,an active intermediate for direct oxidation of methanol on pt electrode

The electro-oxidation of methanol on a Pt thin film electrode in acidic solution has been investigated by in situ surface-enhanced IR absorption spectroscopy. A new IR peak is observed at around 1320 cm-1 when the electrode potential is more positive than 0.5 V, where the bulk oxidation of MeOH occurs. This peak has been assigned to the symmetric stretching of formate species adsorbed on the Pt electrode surface. It is the first observation of formate adsorption during the electro-oxidation of methanol on a Pt surface. A near proportional relationship between the intensity of the IR band of the formate species and MeOH electro-oxidation current is observed. A new reaction scheme via non-CO pathway with formate as the active intermediate is proposed for the methanol electro-oxidation process.     

First nanoparticles of Bechgaard salts

Well-dispersed nanoparticles of the superconducting Bechgaard salts, namely (TMTSF)₂PF₆ and (TMTSF)₂ClO₄, have been electrochemically grown in organic solution in the presence of a supporting electrolyte either being an ionic liquid or a long alkyl-chains quaternary ammonium salt. Nanoparticles exhibit sizes in the 20–75 nm range. Nanoparticle powders have been characterized by infrared, Raman, visible absorption spectroscopy, and by preliminary transport measurements at room temperature.     

Influence of bi modification of pt anode catalyst in direct formic acid fuel cells

The influence of Bi modification of Pt anode catalyst on the performance of direct formic acid fuel cells was investigated. Compared with the unmodified Pt anode, the Bi modified Pt (PtBi(m)) electrode prepared by under-potential deposition (UPD) caused faster electrocatalytic oxidation of formic acid at the same value of the overpotential, and thus, PtBi(m) resulted in an increase in the power performance of direct formic acid fuel cells. Electrochemical impedance spectra helped to explain the difference of performance between the unmodified Pt and Bi modified Pt electrodes. Solution conductivity and dehydration phenomena occurring in highly concentrated formic acid solutions can also explain the higher power performance of PtBi(m).     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

Ionic liquid-assisted direct synthesis of PdO nanoparticles immobilized on boehmite nanoparticles

We demonstrated a simple route to simultaneously synthesize PdO and boehmite nanoparticles, and to directly immobilize the former on the latter using an ionic liquid (IL)-assisted one-pot solution method. PdO nanoparticles were directly immobilized on boehmite nanoparticles, and their amount and distribution were controlled by the stoichiometry of the mixture. In particular, γ-alumina nanofibers, which were topochemically transformed from boehmites, exhibited lengths of ca. 40-70 nm and diameters of ca. 1.5-3 nm, while PdO nanoparticles had diameters of ca. 2-4 nm. The nanocrystalline structures of the PdO nanoparticles immobilized on the boehmite nanoparticles were characterized by high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and (27)Al nuclear magnetic resonance (NMR). The one-step synthetic method described herein allows for the design and fabrication of host-guest systems of inorganic or metallic nanomaterials with hetero-nanostructures.     

First direct detection of 2,3-dimethyl-2,3-diphenylcyclopropanone

3,5-dihydro-3,5-dialkyl-3,5-diaryl-4H-pyrazol-4-ones stimulate interest as potential precursors for 2,3-diarylcyclopropanones. Photoreactions of trans-3,5-dihydro-3,5-dimethyl-3,5-diphenyl-4H-pyrazol-4-one were studied by continuous-wave (CW) and pulsed laser UV photolysis revealing an intermediate that undergoes rearrangement to form cis- and trans-1,3-dimethyl-1-phenyl-2-indanones with the yield of ca. 60%. Steady-state photolysis (254 and 350 nm excitation) in different solvents produced an intermediate cyclohexadiene as evidenced by UV/vis, IR, and 1H NMR spectra. In contrast, the nanosecond laser pulsed photolysis at 355 nm produced 2,3-dimethyl-2,3-diphenylcyclopropanone along with two products of retro-1,3-dipolar addition phenylmethylketene and 1-phenyldiazoethane. These can be observed by time-resolved IR (TRIR) spectroscopy as characteristic absorption bands at 1814, 2101, and 2038 cm-1, respectively. Similar retro-1,3-dipolar addition showed 1-phenyldiazoethane formed following flash photolysis of 1-pyrazoline (trans-4,5-dihydro-3,5-dimethyl-3,5-diphenyl-3H-pyrazol-4-ol). The formation of the corresponding cyclopropanone as well the products of retro-1,3-dipolar addition during photoreaction of starting pyrazol-4-one is directly confirmed by the nanosecond TRIR spectroscopy for the first time. On the basis of the CW and pulsed laser UV photolysis, a dynamic equilibrium between cyclopropanone and intermediate 2,4-diphenyl-3-pentanone-2,4-diyl (dimethyldiphenyloxyallyl) was proposed.     

Experimental characterization of gaseous species emitted by the fast pyrolysis of biomass and polyethylene

This study aims to experimentally characterize the carbonaceous and nitrogenous species, from the flash pyrolysis of millet stalks and polyethylene plastic bags, using the device of the tubular kiln, coupled to two gas analyzers: Analyzer Fourier Transform Infrared (FTIR) and an analyzer Infrared Non-Dispersive (IRND). Gaseous products analyzed are: CH₄, C₂H₂, C₂H₄, C₃H₈, C₆H₆, CO, CO₂, NO₂, NO, N₂O, HCN and NH₃. Whatever the temperature of thermal degradation, the pyrolysis shows us that in terms of mass:

• •For the millet stalks, the gaseous compounds are formed mainly CO and CO₂ to the carbonaceous species, HCN and NH₃, for the nitrogenous species analyzed;
• •As regards the polyethylene bags, hydrocarbons for carbonaceous species and HCN, NH₃ and NO₂ for the nitrogenous species, are most abundant.

In addition, the results suppose that in our experimental conditions, the hydrocarbon which is involved primarily in the formation of CO is ethylene C₂H₄. At the end of this characterization, we determined the rate of carbon and nitrogen found in the volatile gas. With millet stalks we have about 45% of volatile carbon and 15% of the nitrogen of fuel that are found in gaseous products. The results obtained with the plastic bags give 68% carbon and 15% nitrogen found in the nitrogenous species analyzed.     

Frequency distribution of radiation emitted from excited atomic systems

General expressions for the time-dependent probability amplitudes of the quantum states of two arbitrary, interacting atoms are calculated when one atom is initially in an excited p state and the other atom is in an s ground state. The lifetimes of the excited states and the line shape of the emitted radiation are obtained as functions of both the atomic separation and the energy difference between the excited states of the two atoms. The emission line shape is shown to be doubly peaked and to agree with the line shape of the radiation scattered by a system of two interacting atoms. The expressions for the lifetimes of the excited states are found to be identical to those obtained for the radiation scattering situation.     

First direct lithiation of 2-pyridylpiperazine on solid phase

[reaction: see text] The first direct lithiation of a pyridine derivative on solid phase has been realized. Metalation of polymer-bound 2-pyridylpiperazine with the BuLi-LiDMAE reagent followed by electrophilic quenching and subsequent cleavage provided a range of new useful C-6 substituted 2-piperazinylpyridines.     

Pt fibers with stacked donut-like mesospace by assembling pt nanoparticles: guided deposition in physically confined self-assembly of surfactants

A stacked donut-like mesospace is successfully introduced into Pt fibers by assembling Pt nanoparticles with uniform particle size, by utilizing the guided deposition of Pt nanoparticles in preferentially oriented liquid crystals. We clearly demonstrate that the collaboration of both LLC templating by electrochemical processes and hard templating utilizing a confined effect can lead to the genesis of new nanostructured metals. Such a unique metal-based nanoarchitecture enhances the surface area and enables the high-mass transportation of guest species. Preferentially oriented mesochannels should contribute significantly to the fine control and transport of electronic carriers through metal fibers.     

Reliability of the direct ICP-MS analysis of volcanic ash nanoparticles

In the present work, major and trace element concentrations in suspensions of volcanic ash nanoparticles were determined by ICP-MS after either the acid digestion of the suspensions or the direct analysis of these suspensions. The results obtained were compared. Since the acid digestion can be accompanied by an important dilution or can consist in different steps of evaporation and dilution, the determination of some trace element concentrations became limited because of the limit of detection of the analytical instrument. Therefore, analysis after acid digestion of suspensions and direct analysis after acidification of these suspensions were carried out and compared. The concentration of Al, Fe, Y, La, Ce, Pr, Gd, Ho, Cu, Tl and Pb determined by both preparation procedures were in agreement. The values of relative standard deviation are in the range from 1% to 14%. These results prove the reliability of the direct ICP-MS analysis and the possibility of its further application in hyphenated systems for the dimensional and elemental characterisation of natural mineral nanoparticles.     

Translational and rotational dynamics of colloidal rods by direct visualization with confocal microscopy

We report an experimental method to characterize the dynamics of colloidal rods by measuring their rotation and translation in three dimensions with confocal microscopy. The method relies on solvent viscosification to retard dynamics to time scales that are compatible with 3D confocal optical microscopy. Because the method yields a full three-dimensional characterization of rod displacement and orientation, it is applicable to situations in which complex, anisotropic dynamics emerge. Examples include behavior in liquid crystal phases with both orientational and positional order, suspensions subjected to applied fields such as shear flow or sedimentation, and the emerging area of anisotropic particle dynamics. We demonstrate the performance of the method by quantifying the Brownian motion of fluorescent poly(methyl methacrylate) rods (aspect ratio, L/D=3.1 and 7.0) grafted with poly(dimethylsiloxane) stabilizer. The rods are dispersed at dilute concentration in a solvent mixture of viscosity 2.0 Pa s. Rod translational and rotational diffusivities are extracted from the measured translational mean square displacement of the centroid positions and of the rod unit vector u(t), respectively. Rod orientational dynamics are characterized relative to both their azimuthal and polar angles. Probability distributions for the translation and rotation in the frame of rod are computed from the measurements. Experimental values obtained agree well with theory available for the dynamics of isolated rods.     

城市生活垃圾焚烧产物中二噁英检测方法

为研究城市生活垃圾焚烧产生的二噁英污染检测问题,介绍了垃圾焚烧过程中二噁英类的生成机理及其检测方法。色谱法、免疫法、生物法、激光质谱法是目前检测二噁英类的主要手段,其中高分辨气相色谱-高分辨质谱（HRGC-HRMS）法、虫荧光素酶报告基因（CALUX）法及酶免役分析（EIA）法等在实践中取得了很好的检测效果,但各种方法适应范围有很大差别。色谱法可有效分离各种二噁英类成分,但对仪器精度和操作水平要求较高,测试周期较长,费用较高,适于准确对各种成分定量检测,不需计算总量的场合;生物法测试周期短,可平行测试大量样品,适于快速、大规模样品的筛选,但只能测定总毒性当量;激光质谱法具有高选择性、高灵敏度、多组分测定、可实现在线检测等优势,但需要预先了解污染物的光谱结构。     

Study of electronic X-rays emitted from pionic and muonic atoms

The electronic X-ray energies of muonic atoms were precisely measured. The atomic number (Z) dependence of the energy difference between electronic X-rays of muonic atoms and Z-1 atoms (energy shift) was systematically investigated. The energy shifts in the low-Z region were compared with those of the high-Z region that had been obtained experimentally and theoretically in previous work. An obvious difference between these two regions was found in the atomic-number dependence of the energy shift. We also compared the energy shifts of muonic atoms with those of pionic atoms.     

New SPME fibre for analysis of mequinol emitted from DVDs

A piece of fused-silica fibre coated with silica modified with ketamine-groups was used as a solidphase microextraction (SPME) fibre and its efficiency in the qualitative and quantitative analysis of volatile organic compounds released from coloured overprinting on DVDs was evaluated. The effect of the parameters that can affect the SPME procedure, such as extraction time, extraction temperature, desorption temperature, was investigated to determine the analytical performance of this novel fibre in the qualitative and quantitative analyses of organic compounds. The optimised procedure was applied to the qualitative and quantitative analyses of organic compounds released from coloured overprinting on DVDs. The limit of detection of 4-methoxyphenol (mequinol) was 88 × 10⁻³ μg mL⁻¹, while the limit of quantification (LOQ) was calculated as ten times the baseline noise, i.e. 3.1 × 10⁻¹ μg mL⁻¹. The proposed fibre was used successfully for preconcentration of the volatile organic compounds from the gaseous phase of DVD samples.