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Double-walled oxide nanotube structures are interesting for a wide range of applications, from photocatalysis to drug delivery. In this work, a progressive oxidation method to fabricate double-walled nanotube structures is reported in detail. The approach is based on the electrodeposition of metallic iron nanowires, in porous alumina templates, followed by a selective chemical etching, nanoscale Kirkendall effect, a fast oxidation and out-diffusion of the metallic core structure during thermal annealing. To validate the formation mechanism of such core-shell structure, chemical composition and atomic structure were assessed. The resulting hematite nanotubes have a high degree of uniformity, along several microns, and a nanoscopic double-walled structure.

We report an easy synthesis strategy for the incorporation of carbon-coated Ni nanoparticles within the pores of a highly porous carbon matrix. An advantageous feature of this process is that it is able to provide large amounts of magnetic Ni composite by means of an easy-to-follow one-pot reaction. While a typical chemical route based on a conventional pyrolysis procedure gives rise to NPs with Ni@NiO (core@shell structure), the addition of sucrose to the synthesis mixture and its subsequent transformation to carbon endows the Ni-NPs with an effective protection via the formation of a thin carbon layer around the metallic nanoparticles. This protective shell stabilizes the inserted metallic particles by preventing the aerial oxidation of Ni-NPs (i.e., NiO) and their dissolution in an aqueous acid environment. The macroscopic magnetization values of these nanocomposites (up to 6 emu/g) and their superparamagnetic behavior at room temperature allow them to be easily manipulated with conventional magnets. This makes them ideal candidates for use in applications that involve magnetic separation (i.e., heterogeneous catalysis, adsorption of contaminants in aqueous media, etc.). © 2011 American Chemical Society.

We report unusual cooling field dependence of the exchange bias in oxide-coated cobalt nanoparticles embedded within the nanopores of a carbon matrix. The size-distribution of the nanoparticles and the exchange bias coupling observed up to about 200 K between the Co-oxide shell (--3–4 nm) and the ferromagnetic Co-cores (--4–6 nm) are the key to understand the magnetic properties of this system. The estimated values of the effective anisotropy constant and saturation magnetization obtained from the fit of the zero-field cooling and field cooling magnetization vs. temperature curves agree quite well with those of the bulk fcc-Co.