| Research Abstract |
Mono- and bimetallic nanowires were synthesized in mesoporous silica materials such as FSM-16 and organic-inorganic hybrid HMM (pore diameter 3 nm). The formation mechanism, large-scale synthesis, and separation of nanowires were studied. It is revealed that, when migration of metal ions is faster than photoreduction, nanowires are formed in the mesoporous voids. In contrast, nanoparticles are formed when migration is slower than reduction. By considering this mechanism, we have discovered an effective and versatile method to synthesize nanowires in large-scale, in which water vapor is added to hydrogen flow at high temperature. To date we have synthesized nanowires of platinum, palladium, rhodium, and platinum-gold. By dissolving silica matrix with diluted hydrofluoric acid, the metal nanowires were separated and isolated. In TEM and STM observations, the diameter of wires is 3 nm and the length is up to 25 μm (aspect ratio 8300). The nanowires have a necklace-structure. We have also studied the preparation of metal nanoparticle catalysts by usuing supercritical fluids. After the impregnation of mesoporous silica with step metal salts such as Rh and Rh/Pt, the samples were terated with supercritical carbon dioxide. The treated samples have high dispersion of metal particles inside the voids, and the resulting RhPt catalysts shows high yields of ethane in butane hydrogenolysis.
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