Surface Characteristics
Metal nanowires attract much attention as key precursors to higher-ordered structures in nanotechnology, and they are expected to show unique physical and chemical properties owing to the quantum-size effect and low-dimensionality. In this chapter, we wil
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Metal nanowires attract much attention as key precursors to higher-ordered structures in nanotechnology, and they are expected to show unique physical and chemical properties owing to the quantum-size effect and lowdimensionality. In this chapter, we will review template syntheses and applications of metal nanowires. The metal nanowires are synthesized in templates that are recently developed porous materials such as mesoporous silica, anodic alumina membranes, and carbon nanotubes. The precursor metal ions or complexes are reduced in the mesopores by various methods: pyrolysis, hydrogen reduction, photoreduction, and electrodeposition, and in many cases small metal nanoparticles become seeds to grow nanowires in the formation mechanism. The local structure and electronic state of the nanowires are studied by physicochemical methods such as TEM, XRD, XPS, XAFS, IR, UV-visible, and gas adsorption. Some metal nanowires show unique properties in magnetism and electronic absorption resulting from the low dimensionality of the wire morphology. As an example of research into nanowires, we describe our work on template synthesis, characterization, and catalysis of Pt, Rh, Pt-Rh, and Pt-Pd nanowires in mesoporous silicas, FSM-16 and HMM-1. The morphology of the Pt nanowire in FSM-16 enhances the performances of Pt catalysts in the water-gas-shift reaction and hydrogenolysis of butane, which is due to the formation of highly active Pt sites with slight electron-deficiency at the surface of the Pt nanowires. Although many research reports have mainly focused on the synthesis and characterization of nanowires, applications of nanowires will increase in the near future.
9.1 Overview of Nanoparticles and Nanowires Now the chemistry of nanowires attracts much attention with increased interest in nanotechnology. Nanostructured metals and semiconductors are important raw substances to fabricate new materials, and they are regarded as key precursors in developing higher-ordered structures in the so-called bottom-up approach1 in nanotechnology [1]. Nanoparticles, often called colloids or clusters, are metals and metal oxides of size in the nanometer-scale and they show 1
Contrary to a top-down approach by which big substances are shaped to smaller parts as used in the semiconductor industry, atoms and molecules are self-
Y. Waseda et al. (eds.), Morphology Control of Materials and Nanoparticles © Springer-Verlag Berlin Heidelberg 2004
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A. Fukuoka, M. Ichikawa
unique magnetic, optical, electrical, mechanical, and chemical properties, and they have practical applications as cosmetics, magnetic particles, grinders, catalysts, sensors, and so on [2, 3]. However, precise control of the size and shape of nanoparticles has been a challenging topic in synthetic chemistry since the pioneering work of Faraday on gold colloids in the 19th century [4]. Nanoparticles have been prepared by a variety of methods involving thermal, photochemical, and electrochemical reductions of metal compounds in solutions or on surfaces of polymers and me
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