Structure, morphology and magnetic properties of Au/Fe3O4 nanocomposites fabricated by a soft aqueous route

Magnetic Fe3O4 (magnetite) nanoparticles are synthesized via a chemical precipitation route in different alkaline environments (NH3 or NaOH) and subsequently functionalized with a (propynylcarbamate)triethoxysilane moiety, with the aim of promoting the nucleation and subsequent stabilization of gold nanoparticles. The propynylcarbamate group is able to capture the gold precursor (HAuCl4), spontaneously reduce it, and stabilize the resulting Au nanoaggregates. The obtained results show that though the dimensions of the starting magnetite substrate depend on the base used in the preparation, they remain unaltered upon the subsequent modification. Conversely, the average Au nanoparticle dimensions can be conveniently tailored as a function of the base used in Fe3O4 preparation and the presence/absence of the organic functionalization. The smallest dimensions (15 nm) are obtained for AuNP supported on propynylcarbamate-functionalized Fe3O4 prepared in the presence of ammonia. Magnetization measurements highlight that all the Au/Fe3O4 nanocomposites display a superparamagnetic behavior and those obtained using ammonia showed consistently smaller Hc and Mr values (av. values of 7.4 Oe and 0.8 emu/g) than those prepared with sodium hydroxide (av. values of 28 Oe and 2.8 emu/g).