Metallic nanorings
have attracted much attention of researchers owing to their unique
optical, electrical, and magnetic properties, and now, simple and
large-scale synthesis methods must be developed for their practical
application in various fields. Here, we report the one-pot synthesis
of ultrathin Pd nanorings through a simple and novel soft-template
approach based on wet-chemical synthesis. A spindle-shaped assembly
of a long-chain amidoamine derivative (C18AA) served as the soft template
of Pd nanorings that were prepared in an aqueous solution containing
the Pd precursor and a suitable amount of C18AA and toluene, and the
chemical reduction of the Pd precursor in the aqueous solution produced
an array of almost circular Pd nanorings covering the assembly. Pd
nanorings that were parallel to the amine group, which is the head
group of C18AA, appeared on the assembly surface. The amount of toluene
strongly affected the formation of the spindle-shaped assembly and
Pd nanorings. Furthermore, transmission electron microscope images
were obtained at several points in time during the reaction; they
revealed that the Pd nanorings were produced by the fusion of Pd nanoparticles
formed on the spindle-shaped molecular assembly during an early stage
of the reaction. The Pd nanorings were also found to have high structural
stability against organic solvents, high temperatures, and high and
low pH.