Nurses' perceptions of aids and obstacles to the provision of optimal end of life care in ICU

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Well-Alloyed PtFe/C Nanocatalysts of Controlled Composition and Same Particle Size: Oxygen Reduction and Methanol Tolerance

A study of the effect of iron concentration on the electrocatalysis of oxygen reduction reaction (ORR) on well-alloyed carbon-supported PtFe nanocatalysts with a controlled iron content and the same particle size is presented. To obtain the catalysts for this study, PtFe nanoparticles of different compositions were first obtained in a colloidal state in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)+n-butanol/n-heptane/water microemulsions and subsequently supported in high surface area carbon powder. Transmission electron microscopy evidenced that all PtFe/C nanocatalysts prepared are monodispersed and have nearly the same average particle size. X-ray diffraction studies showed that the lattice parameter of these PtFe/C catalysts varies linearly with iron content up to 50% (in atoms), while the compositions of the alloyed phases estimated by using Vegard's law are almost identical to the nominal values, indicating a high degree of alloying. The electrocatalytic activity for ORR of these catalysts was studied using the rotating disk electrode technique in O(2) saturated 0.5 mol L(-1) H(2)SO(4) solutions, while methanol tolerance was evaluated from curves taken in acid solutions containing 0.1 mol L(-1) methanol. The results reported here reflect the dependence of the electrocatalytic activity for the ORR on iron concentration in the absence of particle size effects and metal segregation.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

The Aerosol OT + n-butanol + n-heptane + water system: Phase behavior, structure characterization, and application to Pt70Fe30 nanoparticle Synthesis

A phase diagram of the pseudo-ternary Aerosol OT (AOT) + n-butanol/n-heptane/water system, at a mass ratio of AOT/n-butanol = 2, is presented. Conductivity measurements showed that within the vast one-phase microemulsion region observed, the structural transition from water-in-oil to oil-in-water microemulsion occurs continuously without phase separation. This pseudo-ternary system was applied to the synthesis of carbon-supported Pt 70Fe30 nanoparticles, and it was found that nanoparticles prepared in microemulsions containing n-butanol have more Fe than those prepared in ternary microemulsions of AOT/n-heptane/water under similar conditions. It was verified that introducing n-butanol as a cosurfactant into the AOT/n-heptane/water system lead to complete reduction of the Fe ions that allowed obtaining alloyed PtFe nanoparticles with the desired composition, without the need of preparing functionalized surfactants and/or the use of inert atmosphere. © 2007 American Chemical Society

The Extent on the Nanoscale of Pt-Skin Effects on Oxygen Reduction and Its Influence on Fuel Cell Power

Carbon-supported PtFe nanoparticles having similar overall composition (3:1), crystallinity, and average particle diameter were prepared with and without a Pt-skin layer and used to evaluate the extent, on the nanometer scale, of Pt-skin effects on the activity for oxygen reduction. In this study, we show that when most of the relevant properties of the catalysts are kept alike, there is an increase of about 2-fold in the intrinsic activity for oxygen reduction that can be ascribed to Pt-skin effects. It is also demonstrated that the activity improvement produced by the presence of a Pt-skin surface is, however, insufficient to generate significant differences on the power density of a single proton exchange membrane fuel cell.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq