Xuchuan Jiang

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.

A simple and convenient method has been demonstrated for large-scale synthesis of metal oxide (including TiO2, SnO2, In2O3, and PbO) nanowires with diameters around 50 nm and lengths up to 30 µm. In a typical procedure, tetraalkoxyltitanium, Ti(OR)4 (with R = –C2H5, –iso-C3H7, or –n-C4H9), was added to ethylene glycol and heated to 170 °C for 2 h under vigorous stirring. The alkoxide was transformed into a chain-like, glycolate complex that subsequently crystallized into uniform nanowires. Similarly, nanowires made of tin glycolate were synthesized by refluxing SnC2O4·2H2O in ethylene glycol at 195 °C for 2 h, and nanowires consisting of indium and lead glycolates were prepared by adding In(OOCC7H15)(OiPr)2 and Pb(CH3COO)2 to ethylene glycol, followed by heating at 170 °C for 2 h. The nanowires could be readily collected as precipitates after the reaction solutions had been cooled down to room temperature. By calcining at elevated temperatures, each glycolate precursor could be transformed into the corresponding metal oxide without changing the wire-like morphology. Electron microscopic and XRD powder diffraction studies were used to characterize the morphology, crystallinity, and structure of these nanowires before and after calcination at various temperatures. A plausible mechanism was also proposed to account for the one-dimensional growth of such nanostructures in a highly isotropic medium. This mechanism was supported by XRD, FT-IR, solid state 13C-NMR, and TGA measurements. As a demonstration of potential applications, the polycrystalline nanowires made of SnO2 were used as functional components to fabricate sensors that could detect combustible gases (CO and H2) with greatly enhanced sensitivity under ambient conditions.

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.