Surface characteristics

Abstract

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 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.