Investigation of Redox-Transmetallation Process for Coating of Gold(Au)-shell on Nickel (Ni)-core Nanoparticles

Core-shell nanoparticle has created great interest among researchers due to their various unique properties. The new properties created are combination of both the core and the shell. In this work, pre-prepared Nickel (Ni) nanoparticles were coated with Gold (Au) to produce core-shell structure. Formation mechanism of the core-shell structure is investigated via UV-Vis spectrum of the as-synthesized particles and its supernatants. Ni nanoparticles were synthesized using polyol method with hydrazine as the reducing agent. Coating of Au was conducted using sodium citrate as the reducing agent and acid citric to control the pH of the mixture. UV-Vis absorption spectra analysis of as-synthesized nanoparticles and the supernatant results revealed that the coating happened via redox-transmetallation process with a very broad peak at about 540 nm and size range of 26 - 40 nm. XPS results suggest that the coating consists of Au compound.