Preparation and characterization of bimetallic core-shell nanoparticles

New fields of research in chemistry and physics require improved synthetic techniques for colloidal metal particles. This work reports two novel techniques for synthesising bimetallic core-shell nanoparticles. The first technique is the chemical deposition of transition metal salts onto gold nanoparticle seeds. The transition metals used were platinum, palladium and rhodium. Gold nanoparticle seeds were produced using published methods. The gold nanoparticles were stabilised with either citrate or thiol-based stabilisers and the effects of the different stabilisers were studied. The gold nanoparticle seeds and the bimetallic core-shell nanoparticles were characterised using UV-vis spectroscopy, HAADF imaging, AFM imaging and with cyclic voltammetry. The citrate-stabilised gold nanoparticle seeds provided a better starting material for the bimetallic core-shell nanoparticles, however this route had problems with aggregation and morphology. The thiol-stabilised gold nanoparticles had a better morphology, but the thiol-stabilisation meant that it was difficult to coat the gold nanoparticles. The second technique studied was the use of galvanic replacement technique for producing bimetallic core-shell nanoparticles, which provides a novel and rapid technique for coating gold nanoparticle seeds with platinum. The Au(core)-Pd(shell) bimetallic nanoparticle system stabilised with citrate was the most successful of the three bimetallic systems studied, producing core-shell particles of approximately 5 nm in diameter