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Hollow Nanostructures (hollow + nanostructure)
Selected AbstractsA Closer Look Inside Nanotubes: Pore Structure Evaluation of Anodized Alumina Templated Carbon Nanotube Membranes Through Adsorption and Permeability StudiesADVANCED FUNCTIONAL MATERIALS, Issue 15 2010Georgios Pilatos Abstract Although hollow nanostructures, such as nanotubes, represent a major portion of nanoscaled materials with a tremendously large application range, a detailed evaluation of their internal characteristics still remains elusive. Transmission electron microscopy is the most common analytical technique to examine the internal configuration of these structures, yet it can only provide evidence of a minimal portion of the overall material, thus, it cannot be accurately generalized. In the present paper, in addition to electron microscopy and other spot-size analysis methods (X-ray diffraction, Raman spectroscopy, etc.), a combination of techniques including adsorption, permeability, and relative permeability are employed in order to provide important insights into various crucial details of the overall internal surface and hollow-space characteristics of carbon nanotube (CNT) arrays and membranes. The CNT arrays are fabricated using anodized alumina as a template in a flow-through chemical vapor deposition (CVD) reactor. This is the first systematic approach for investigating the internal configuration of template-based CNT arrays in detail. Key findings are made for the customized optimization of the resulting nanotube membranes for a variety of applications, including separations, nanofluidics and nanoreactors, biological capturing and purification, and controlled drug delivery and release. [source] Cover Picture: Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 11 2006Mater. Abstract Hollow nanocrystals have been synthesized through a mechanism analogous to the Kirkendall Effect. When a cobalt nanocrystal reacts with sulfur in solution, the outward diffusion of cobalt atoms is faster than the inward diffusion of sulfur atoms through the sulfide shell. The dominating outward diffusion of cobalt cations produces vacancies that can condense into a single void in the center of the nanocrystal at high temperatures. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds and is described in the Full Paper by A.,P. Alivisatos and co-workers on p.,1389. Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at >,120,°C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature-dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell-size statistics and transmission electron microscopy images of as-grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system. [source] Synthesis and Characterization of Noble-Metal Nanostructures Containing Gold Nanorods in the CenterADVANCED MATERIALS, Issue 6 2010Eun Chul Cho Noble-metal nanostructures containing gold (Au) nanorods in the center were synthesized by employing Au nanorods as templates for epitaxial growth of silver (Ag). The immediate products, Au@Ag core,shell nanocrystals with an octahedral shape, were transformed into noble-metal (Au, Pd, and Pt) hollow nanostructures containing Au nanorods in the center, via galvanic replacement reactions (see figure). [source] A General Method for the Rapid Synthesis of Hollow Metallic or Bimetallic Nanoelectrocatalysts with Urchinlike MorphologyCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2008Shaojun Guo Abstract We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100,°C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile. Most importantly, the hollow bimetallic nanospheres (Au/Pt and Pd/Pt) obtained here exhibit an area of greater electrochemical activity than other Pt hollow or solid nanospheres. In addition, the ,6,nm hollow urchinlike Pt nanospheres can achieve a potential of up to 0.57,V for oxygen reduction, which is about 200,mV more positive than that obtained by using a ,6,nm Pt nanoparticle modified glassy carbon (GC) electrode. Rotating ring-disk electrode (RRDE) voltammetry demonstrates that ,6,nm hollow Pt nanospheres can catalyze an almost four-electron reduction of O2 to H2O in air-saturated H2SO4 (0.5,M). Finally, compared to the ,6,nm Pt nanoparticle catalyst, the ,6,nm hollow urchinlike Pt nanosphere catalyst exhibits a superior electrocatalytic activity toward the methanol oxidation reaction at the same Pt loadings. [source] General and Facile Syntheses of Metal Silicate Porous Hollow NanostructuresCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2010Jun Zheng Abstract Porous hollow nanostructures have attracted intensive interest owing to their unique structure and promising applications in various fields. A facile hydrothermal synthesis has been developed to prepare porous hollow nanostructures of silicate materials through a sacrificial-templating process. The key factors, such as the concentration of the free metal cation and the alkalinity of the solution, are discussed. Porous hollow nanostructures of magnesium silicate, nickel silicate, and iron silicate have been successfully prepared by using SiO2 spheres as the template, as well as a silicon source. Several yolk,shell structures have also been fabricated by a similar process that uses silica-coated composite particles as a template. As-prepared mesoporous magnesium silicate hollow spheres showed an excellent ability to remove Pb2+ ions in water treatment owing to their large specific surface and unique structures. [source] | |||||||||||||