Electron Beam-Assisted Synthesis of Superparamagnetic Iron Oxide Nanoparticles: Reaction Kinetics and Structural-Magnetic Properties

Energetic electron-induced radiolysis constitutes a highly versatile approach for tailored synthesis and modification of nano- and biomaterials. In doing so, one-step protocols are highly desirable, as they allow for efficient synthesis and combinations of these materials classes in hybrid materials. With this motivation, the formation of iron oxide nanoparticles by electron beam radiolysis was investigated in detail. Particles with an average size of approximate to 6 nm were synthesized by irradiating microemulsions containing Fe3+ ions with 10 MeV electrons. The mechanistic and kinetic details of formation were revealed by pulse radiolysis, and the structural-magnetic properties of the resulting nanoparticles were characterized using high-resolution transmission electron microscopy, selective area diffraction, and vibrating sample magnetometry. The formation of nanoparticles with superparamagnetic properties was observed when microemulsions were irradiated with doses of 50 kGy and above. While the particles obtained from irradiation with just 50 kGy are partially characterized by an amorphous nature, the crystallinity in the magnetite/maghemite phases increases with increasing irradiation dose, as observed via a selective area electron diffraction pattern. This is also reflected in an increasing saturation magnetization.