From Single Molecules to Nanostructured Functional Materials: Formation of a Magnetic Foam Catalyzed by Pd@Fe_xO Heterodimers

Multicomponent nanostructures containing purely organic or inorganic as well as hybrid organic-inorganic components connected through a solid interface are, unlike conventional spherical particles, able to combine different or even incompatible properties within a single entity. They are multifunctional and resemble molecular amphiphiles, like surfactants or block copolymers, which makes them attractive for the self-assembly of complex structures, drug delivery, bioimaging, or catalysis. We have synthesized Pd@Fe_xO heterodimer nanoparticles (NPs) to fabricate a macroporous, hydrophobic, magnetically active, three-dimensional (3D), and template-free hybrid foam capable of repeatedly separating oil contaminants from water. The Pd domains in the Pd@Fe_xO heterodimers act as nanocatalysts for the hydrosilylation of polyhydrosiloxane and tetravinylsilane, while the Fe_xO component confers magnetic properties to the final functional material. Pd@Fe_xO heterodimers were synthesized by heterogeneous nucleation and growth of the iron oxide domain onto presynthesized Pd NPs at high temperatures in solution. The morphology, structure, and magnetic properties of the as-synthesized heterodimers were characterized by transmission electron microscopy (TEM), X-ray diffraction, Mössbauer spectroscopy, and a superconducting quantum interference device. The epitaxial growth of the Fe_xO domain onto Pd was confirmed by high-resolution TEM. A potential application of the 3D hydrophobic magnetic foam was exploited by demonstrating its ability to soak oil beneath a water layer, envisioning its use in oil sampling during oil prospection drilling, or to remove oil films after oil spills.