Morphologically controlled materials consisting of imogolite nanotubes and gold nanoparticles were prepared by electrostatic assembly. The composites consisting of imogolite nanotubes and gold nanoparticles (ca. 2 or 3. nm) were highly dispersed in water and they were subsequently used as building blocks of morphologically controlled materials. The formation of the composites was based on the electrostatic interactions between the surface carboxylato groups of gold nanoparticles and positively charged imogolite nanotubes. The composites were assembled to form free-standing films by filtration and into hollow spheres by the colloidal templating technique accompanied with the layer-by-layer technique. The free-standing films showed intense colors due to the gold nanoparticles, which makes the films useful as color filters. Hollow spheres were found to be useful as catalyst supports, because most of the gold nanoparticles retained their size as ca. 3. nm even after the heating at 500. °C. Imogolite nanotubes enabled facile morphological control of functionalized materials and are useful because of their transparency, stability, and high porosity.
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