Electron Beam-Assisted Synthesis of Superparamagnetic\nIron Oxide Nanoparticles: Reaction Kinetics and Structural–Magnetic\nProperties

Energetic electron-induced\nradiolysis constitutes a highly versatile\napproach for tailored synthesis and modification of nano- and biomaterials.\nIn doing so, one-step protocols are highly desirable, as they allow\nfor efficient synthesis and combinations of these materials classes\nin hybrid materials. With this motivation, the formation of iron oxide\nnanoparticles by electron beam radiolysis was investigated in detail.\nParticles with an average size of ≈6 nm were synthesized by\nirradiating microemulsions containing Fe<sup>3+</sup> ions with 10\nMeV electrons. The mechanistic and kinetic details of formation were\nrevealed by pulse radiolysis, and the structural–magnetic properties\nof the resulting nanoparticles were characterized using high-resolution\ntransmission electron microscopy, selective area diffraction, and\nvibrating sample magnetometry. The formation of nanoparticles with\nsuperparamagnetic properties was observed when microemulsions were\nirradiated with doses of 50 kGy and above. While the particles obtained\nfrom irradiation with just 50 kGy are partially characterized by an\namorphous nature, the crystallinity in the magnetite/maghemite phases\nincreases with increasing irradiation dose, as observed via a selective\narea electron diffraction pattern. This is also reflected in an increasing\nsaturation magnetization.