Oxide Shell (oxide + shell)

Distribution by Scientific Domains

Selected Abstracts

Surface-Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts

Qiao Zhang
Abstract Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk,shell and core,satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability of the metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework. [source]

A Multifunctional Nanodevice Capable of Imaging, Magnetically Controlling, and In Situ Monitoring Drug Release

Shang-Hsiu Hu
Abstract The multifunctional nanodevice described here integrates nanoscaled imaging, targeting, and controlled drug delivery, as well as the capability to monitor, in situ, the amount of drug released from the nanodevice with single-cell resolution. The nanodevice is composed of a polymer core/single-crystal iron oxide shell nanostructure bonded to a quantum dot. It shows outstanding release and retention characteristics via an external on/off manipulation of a high-frequency magnetic field. Upon magnetic stimulation, the single-crystal iron oxide shell demonstrates formation of nanometer-sized polycrystal domains of varying orientation. This allows a variation between retention and slow release of the drug. Further stimulation causes permanent rupturing of the shell, causing release of the drug in a burst-like manner. The quantum dot bonded to the nanodevice provides optical information for in situ monitoring of the drug release through use of a magnetic field. Remote control drug release from the nanodevice in a cancerous cell line (HeLa) was successfully accomplished using the same induction scenario. When nanodevices equipped with quantum dots are taken into cancerous cells, they are able to provide real-time drug dose information through a corresponding variation in emission spectrum. The nanodevice designed in this study has achieved its potential as a cell-based drug-delivery system for therapeutic applications. [source]

Multilayered Core/Shell Nanowires Displaying Two Distinct Magnetic Switching Events,

Yuen Tung Chong
Atomic layer deposition (ALD) and electrodeposition are combined with a porous template to create ordered arrays of nanowires in which a nickel core and an iron oxide shell are separated by a silica spacer layer. The switching of each magnetic component is distinct and occurs at a field that depends on the tunable thicknesses of the various layers. [source]

Synthesis, characterization and ESR measurements of CoNiO nanoparticles

Y. Köseo
Abstract Powders of cobalt core with a nickel (II) oxide shell (CoNiO) have been studied by Electron Spin Resonance (ESR) technique in the temperature range of 10,300 K. A strong and broad (1300 G) single ESR peak in X-, K- and Q-band spectra has been observed at all the temperature ranges. While the resonance field remains almost constant, both the ESR line intensity and the line width were seen to increase first slowly down to Tc = 160 K. And then both the resonance field and the ESR signal intensity decrease and the line width increase with decreasing temperature. Below Tc the intensity smoothly decrease down to 10 K. This kind of behavior is attributed to a typical spin-glass like behavior. Some small and relatively smooth changes at about 60 K, 90 K, 210 K, and 250 K are appeared as well. A linear dependence of resonance field to microwave frequency is observed at room temperatures and the effective g-value and internal field are theoretically found as 2,17 and 90 G, respectively. The experimental data indicate a very strong spin disorder (spin frustration) due to antiferromagnetic exchange interactions among the spins. This is attributed to the D-M anisotropy on the particle surfaces that it is expected to enhance due to increment of surface-to-volume ratio. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]