Pedro Kunihiko Kiyohara

Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids

Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA) and dodecanoic acid (DA) were synthesized and investigated through transmission electron microscopy (TEM), magnetization M, and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78%, 76%, and 65%) and the DA sample with 63% of Fe3O4. Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ∼5.5 nm. Magnetization measurements, performed in zero-field cooled (ZFC) and field cooled processes under different external magnetic fields H, exhibited a maximum at a given temperature TB in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature TB decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase in TB. The observed behavior is related to the dipolar interaction between NP, which seems to be an important mechanism ...

Catalyst Recovery and Recycling Facilitated by Magnetic Separation: Iridium and Other Metal Nanoparticles

The immobilization of metal nanoparticles in magnetic responsive solids allows the easy, fast, and clean separation of catalysts; however, the efficiency of this separation process depends on a strong metal–support interaction. This interaction can be enhanced by functionalizing the support surface with amino groups. Our catalyst support contains an inner core of magnetite that enables the magnetic separation from liquid systems and an external surface of silica suitable for further modification with organosilanes. We report herein that a magnetically recoverable amino‐functionalized support captured iridium species from liquid solutions and produced a highly active hydrogenation catalyst with negligible metal leaching. An analogous Ir0 catalyst prepared with use of a nonfunctionalized support shows a higher degree of metal leaching into the liquid products. The catalytic performance in the hydrogenation of alkenes is compared with that of Rh and Pt catalysts.

On the Stabilization of Gold Nanoparticles over Silica‐Based Magnetic Supports Modified with Organosilanes

The immobilization of gold nanoparticles (Au NPs) on silica is made possible by the functionalization of the silica surfaces with organosilanes. Au NPs could only be stabilized and firmly attached to silica-support surfaces that were previously modified with amino groups. Au NPs could not be stabilized on bare silica surfaces and most of the NPs were then found in the solution. The metal-support interactions before and after the Au NP formation, observed by X-ray absorption fine structure spectroscopy (XAFS), indicate a stronger interaction of gold(III) ions with amino-modified silica surfaces than with the silanol groups in bare silica. An amino-modified, silica-based, magnetic support was used to prepare an active Au NP catalyst for the chemoselective oxidation of alcohols, a reaction of great interest for the fine chemical industry.

Electron microscopic observations of human hair medulla

In the study of human hair, medulla is the less studied structure because it is believed that it has no influence on the fibre properties. The aim of this paper is to contribute to the better understanding of medulla morphology. Using reproducible methods for hair samples preparations allowed observing the inner fibre by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Three medulla subunits were observed in cryofractured samples. In addition, the application of plasma etching on samples allowed accessing chemical differences between them. Two kinds of medulla were identified using stereomicroscopy: thin and thick medulla. They were morphologically differentiated using TEM. These methods can be used to study systematically the effects of medulla on hair properties and to evaluate the efficiency of cosmetic products.

A record of Permian subaqueous vent activity in southeastern Brazil

The remarkable occurrence of more than 4,500 conical siliceous mounds in an area of less than 1.5 square kilometres has been reported in the Paraná basin, near Anhembi, São Paulo, in southeastern Brazil. These structures, which are up to two metres high, are thought to have been formed at the margin of a very shallow, broad but waning internal sea, and it was originally suggested that they are stromatolites. Yet their restricted occurrence, unusual abundance and nearly pure siliceous composition have never been satisfactorily explained by this hypothesis. Here we report field and laboratory observations on their shape, construction, composition and mineralogy. On the basis of our data we suggest that the conical mounds are the result of subaqueous Late Permian vent activity in southwestern Gondwana. The present siliceous cone field differs considerably from other Palaeozoic siliceous hot spring deposits, such as those at Rhynie, Scotland, and the Drummond basin, Australia, and therefore represents an unusual occurrence of vent activity.

Economically attractive route for the preparation of high quality magnetic nanoparticles by the thermal decomposition of iron(III) acetylacetonate

The thermal decomposition (TD) methods are among the most successful in obtaining magnetic nanoparticles with a high degree of control of size and narrow particle size distribution. Here we investigated the TD of iron(III) acetylacetonate in the presence of oleic acid, oleylamine, and a series of alcohols in order to disclose their role and also investigate economically attractive alternatives for the synthesis of iron oxide nanoparticles without compromising their size and shape control. We have found that some affordable and reasonably less priced alcohols, such as 1,2-octanediol and cyclohexanol, may replace the commonly used and expensive 1,2-hexadecanediol, providing an economically attractive route for the synthesis of high quality magnetic nanoparticles. The relative cost for the preparation of Fe3O4 NPs is reduced to only 21% and 9% of the original cost when using 1,2-octanediol and cyclohexanol, respectively.