This paper describes a vapor-phase approach to the facial synthesis of cupric oxide (CuO) nanowires supported on the surfaces of various copper substrates that include grids, foils, and wires. A typical procedure simply involved the thermal oxidation of these substrates in air and within the temperature range from 400 to 700 °C. Electron microscopic studies indicated that these nanowires had a controllable diameter in the range of 30−100 nm with lengths of up to 15 μm by varying the temperature and growth time. Electron diffraction and high-resolution TEM studies implied that each CuO nanowire was a bicrystal divided by a (111) twin plane in its middle along the longitudinal axis. A possible mechanism was also proposed to account for the growth of these CuO nanowires.

This paper describes a solution-based, precursor method for the facile synthesis of uniform nanowires containing rutile SnO2 nanocrystallites. In a typical procedure, nanowires of approximately 50 nm in diameters and up to 30 mum in length were obtained as a white precipitate by refluxing SnC2O4.2H2O and poly(vinylpyrrolidone) in ethylene glycol. Structural analyses by XRD, FT-IR, and TGA indicate that these highly anisotropic nanostructures were formed in an isotropic medium through the aggregation of chainlike precursors that were, in turn, formed via polyol-mediated oligomerization. These nanowires could be further converted to polycrystalline SnO2 by calcination in air at 500 degrees C. The resultant nanowires of SnO2 were highly porous and could be used for gas sensing with improved sensitivity and reversibility under ambient conditions. We have also demonstrated that this new approach could be extended to generate polycrystalline nanowires of other metal oxides such as In2O3 and anatase TiO2.

Spherical colloids have recently been exploited by many research groups as building blocks to fabricate photonic crystals via self-assembly.[1] The majority of these studies, however, have been limited to polymer latexes and silica spheres because of the easiness in processing these materials as spherical colloids with truly monodisperse sizes and in copious quantities. Only a few demonstrations involved the synthesis and crystallization of spherical colloids made of compound semiconductors such as CdS, ZnS, and ZnS (deposited on polystyrene spheres).[2] Photonic band structures of these new systems have been shown to exhibit features different from those of conventional opals due to their higher refractive indices relative to polystyrene (~1.6) or silica (~1.5).[3] Among various inorganic semiconductors, titania has long been considered as an ideal candidate for generating photonic crystals due to its low absorption in the visible and near-infrared regions and its relatively high refractive indices (2.4 for anatase and 2.9 for rutile).[3] Unfortunately, no one has been able to prepare titania as monodispersed spherical colloids with size variations within 5 %. Because of its technological importance in various industrial applications (e.g., as pigments or paper whiteners, [4] photocatalysts, [5] and optical coatings [6] ), a large number of chemical methods have been developed for generating colloidal particles of titania. In industry, titania particles are often synthesized by digesting the ore ilmenite with sulfuric acid, followed by thermal hydrolysis of the titanium(IV) ions in a highly acidic solution and eventually dehydration of the titanium(IV) hydrous oxides. The resulting particles were often irregular in shape and exhibited broad distributions in size. Like many other ceramic oxides, titania has also been synthesized as spherical colloids by controlling the hydrolysis and condensation of an appropriate precursor. [7] For example, Matijevic  and co-workers have developed a procedure to generate titania spherical colloids with a relatively narrow distribution in size (r = 15±25 %) by reacting water vapor with a titania precursor contained in liquid aerosols. [8] They have also demonstrated that hydrolysis of TiCl 4 in the presence of sulfate ions at elevated temperatures could lead to the formation of stable aqueous dispersions of titania spheres with diameters ranging from 1 to 4 lm.[9] Barringer, Bowen, Ring, and their co-workers have prepared titania spheres 300± 700 nm in diameter by controlling the hydrolysis of titanium tetraethoxide in dilute alcoholic solutions.[10] They have also prepared fine particles of titania with relatively uniform sizes by adding hydroxypropyl cellulose (a polymeric surface stabilizer) to the sol±gel solution.[11] Because the titania spheres synthesized using these methods were not truly monodispersed (often with size variations > 10 %), it has been difficult to crystallize them into long-range ordered lattices. It has been suspected that the conventional sol±gel method...

The emergence of metal-organic frameworks (MOFs) as a new class of crystalline porous materials is attracting considerable attention in many fields such as catalysis, energy storage and conversion, sensors, and environmental remediation due to their controllable composition, structure and pore size. MOFs are versatile precursors for the preparation of various forms of nanomaterials as well as new multifunctional nanocomposites/hybrids, which exhibit superior functional properties compared to the individual components assembling the composites. This review provides an overview of recent developments achieved in the fabrication of porous MOF-derived nanostructures including carbons, metal oxides, metal chalcogenides (metal sulfides and selenides), metal carbides, metal phosphides and their composites. Finally, the challenges and future trends and prospects associated with the development of MOF-derived nanomaterials are also examined.

No abstract

Simulations of the absorption efficiency using the discrete dipole approximation (DDA) method and taking into account the real shape of gold nanorods are reported. A dominant surface plasma band corresponding to the longitudinal resonance is observed. Its maximum position lambda(max) shifts to the red as the aspect ratio increases. The transversal dipolar and multipolar mode wavelength positions are also discussed. These data are in good agreement with previous theoretical work based on classical electrostatic predictions and assuming that gold nanorods behave as ellipsoidal particles. From the experimental point of view, good agreement with the published data for gold nanorods is obtained.

International audienc

Hollow nanostructures of platinum have been synthesized by reducing PtCl2 with alcohol in the presence of selenium nanowires or colloids. The Se template could be removed by soaking the resultant Se@Pt nanostructures in hydrazine or by heating them to 200-250 degrees C. The size and wall thickness of the polycrystalline hollow nanostructures could be controlled by varying the template, reaction time, and the concentration of PtCl2.