Core/Shell Magnetite/Bismuth Oxide Nanocrystals with Tunable Size, Colloidal, and Magnetic Properties

New inorganic hybrid nanoparticles integrating different materials in a core/shell structure of iron and bismuth oxides have been synthesized by a simple aqueous route. The method is based on the precipitation of an Fe(II) salt in the presence of bismuth(III) cations in a mild oxidant and leads to highly uniform and crystalline magnetic nanoparticles with sizes in the range between 8 and 30 nm. Bismuth in proportions between 1 and 20% atomic ratio of Bi to Fe acts as surfactant being accumulated at the nanoparticle surface, controlling particle size and colloidal properties. Evidence of a core/shell structure is revealed by X-ray photoelectron spectroscopy analysis with bismuth enrichment in an outer shell. This robust material with very long chemical stability and resistance to degradation, good magnetic properties, and high density due to the presence of bismuth ions is expected to have important applications in diagnosis as a new double contrast agent for both magnetic resonance imaging and computed tomography.