γ-irradiation synthesis of magnetic iron oxide and iron oxide nanostructures decorated with Au or Ag nanoparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) due to their unique magnetic (superparamagnetism and high saturation field) and electrical properties have applications as sensor, contrast agents, in drug delivery and for hyperthermia cancer treatments. These nanoparticles (NPs) can be modified with noble metal NPs, which combines the magnetic and biocompatible properties of SPIONs and the optical properties of noble metal NPs. In this work we used -irradiation as an attractive and ecologically friendly technique for the synthesis of magnetic NPs at room temperature. -irradiation has an advantage of inducing electrons and other reducing species homogeneously through the sample. The FeCl3 alkaline aqueous solutions were purged with N2 and irradiated with addition of 2- propanol. DEAE-dextran was used as growth and stabilizing agent of MNPs. The phase composition, stoichiometry and morphology of MNPs were controlled by adjusting γ-irradiation dose and dose rate. Doses 10-36 kGy resulted in the formation of small 4 nm spherical substoichiometric magnetite NPs, whereas at higher dose (50 kGy or more) the major phase was magnetic -FeOOH (feroxyhyte) in the form of nanodiscs, as confirmed by SEM, HRTEM, XRD and electron diffraction. The magnetic measurements revealed superparamagnetic behaviour of magnetite NPs and exceptional intrinsic room-temperature properties of -FeOOH with Curie temperature above 300 K. The reduction of Fe3+ to Fe2+ ions was determined using 1, 10-phenanthroline spectrophotometric method. Reduction proceeds fast in the beginning stage of irradiation (up to 30 kGy, 65% Fe3+ reduced), slows down and reaches 100% reduction at 75 kGy. The reducing power of Fe2+ in irradiated suspensions was explored to synthesize composite nanostructures by addition of aqueous solutions of HAuCl4 or AgNO3 in irradiated suspensions. Microstructural and morphological analysis showed that simultaneous oxidation of Fe(OH)2 and reduction of Au3+ or Ag+ resulted in the formation of composite δ-FeOOH nanodiscs decorated with spherical Au or Ag nanoparticles.