A new route to air-stable Cu(0) nanoparticles

Abstract

Cu nanoparticles (NPs) can offer plasmonic properties in the near infrared region of the electromagnetic spectrum while boasting substantially greater abundance than group 11 counterparts Au or Ag and reduced cytotoxicity compared to the latter. To maintain plasmonic responsiveness, the NPs metallic character must be conserved, meaning resistance to environmental oxidation is required. Core@shell Cu@Fe₃O₄ NPs are synthesized here by decomposing Fe(CO)₅ onto preformed Cu seeds made in the presence of oleic acid (OA) and oleylamine (OAm). Variation of the OA:OAm ratio induces seeds to transition from pseudospheres to cubes and then rods. Facile coating succeeds irrespective of seed morphology and is proved for non-magnetic seeds for, as far as we know, the first time. Imaging reveals a continuous, ∼2.5 nm wide Fe₃O₄ shell encapsulating Cu in each morphology. Samples can be redispersed in undried organic media or stored under air as solids for many months without core oxidation, and this is attributed to the coating of the Cu core with an uninterrupted magnetite shell. Treatment with meso-2,3-dimercaptosuccinic acid results in surface ligand exchange without morphological changes. The resulting Cu@Fe₃O₄ NPs can then be dispersed in polar organic solvents or water.