Abstract
In this study, we have used a simple seed-mediated synthesis process to prepare uniform Pd nanorods with average lengths of ~ 200 and 300 nm and display a penta-twinned structure through the addition of 50–100 □L of 0.004 M Cu(OAc)2 solution into the growth solution for the first time. These long nanorods settle nicely to the bottom of the growth vial to form a precipitate, and can easily be separated from the faceted particles. The nanorods have an average diameter of ~ 20 nm, so they have high aspect ratios of 10–15 or more. By increasing the volume of Cu(OAc)2 solution added to 250 □L, extensively branched Pd nanocrystals were synthesized. The growth mechanism was studied and showed that a mixture of short Pd rods and faceted particles were formed first, and elongated into long rods or branched nanocrystals with the assistance of copper atom deposition. A lower reduction potential of copper than that of palladium leads to reduction and reoxitation of copper ions on the growing rods and faceted particles. UV–vis spectra of the Pd nanorods showed that the longitudinal band of the Pd nanorods with high aspect ratios red-shifts to longer wavelengths in the near-infrared region. Both the nanorods and branched nanocrystals were tested for the application as catalysts for Suzuki coupling reactions. They were found to be highly efficient and recyclable catalysts. These crystals are also thermally stable under the reflux condition and can be easily removed from the product solution.