Tuning the Size of Palladium Nanoparticles in Organic and Aqueous Solutions: Influence of Aminated and Thiolated Ligands

Highly monodispersed palladium nanoparticles have been synthesized by a two-phase reduction method using two different capping agents, alkylamines and alkanethiols. The influence of ligand type in the properties of palladium nanoparticles have been analyzed in detail by means of several techniques as Infrared and Ultraviolet-Visible Spectroscopy, X-ray Diffraction and Transmission Electron Microscopy. It is shown how the size can be tuned easily between 2 and 4 nm by using alkylamines ligands with carbon chains of different lengths, while keeping up high purity and crystallinity. The transfer of these nanoparticles to water phase has been achieved by the ligand exchange process. In contrast, when alkanethiols are used as stabilizers no correlation between carbon chain length and size has been observed. This distinct chemical reactivity between palladium and mentioned ligands produces some particular electronic and magnetic properties that are analyzed by Electron Magnetic Resonance. The presence of free radicals associated with palladium and capping agent bond has been confirmed. No evidences of ferromagnetic behavior coming from Palladium nanoparticles have been found out in any of the studied samples.