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Synthesis of magnetic iron oxide/Au and iron oxide/Ag nanostructures using a simple γ-irradiation method

In this work we have used γ-irradiation as an efficient and environmentally friendly technique for the synthesis of magnetic nanoparticles. The γ-irradiation has the advantage of inducing electrons and other reducing species uniformly in the sample. The alkaline aqueous iron(III)chloride solutions were purged with nitrogen and γ-irradiated with the addition of 2-propanol. DEAE-dextran was used as a growth and stabilizing agent for MNPs in suspensions. The phase composition, stoichiometry, and morphology of MNPs were controlled by adjusting the γ-irradiation dose. Irradiation with doses of 10-36 kGy resulted in the formation of 4 nm spherical sub-stoichiometric magnetite NPs, while at higher doses (50 kGy or more) the main phase was magnetic δ-FeOOH (feroxyhyte) in the form of nanodiscs. Magnetic measurements revealed superparamagnetic behavior of magnetite NPs and exceptional intrinsic magnetic properties of δ-FeOOH nanostructures at room temperature with a Curie temperature above 300 K. Reduction of Fe3+ to Fe2+ ions was quantitatively determined using 1, 10-phenanthroline spectrophotometric method. The reduction is rapid in the initial stages of irradiation (~65% of Fe3+ is reduced up to 30 kGy), then slows down and reaches 100% at ~75 kGy. The reduction power of Fe2+ in irradiated suspensions was explored to synthesize iron oxide/Au nanostructures by adding aqueous HAuCl4 solutions to the irradiated suspensions. Microstructural and morphological analysis showed that the simultaneous oxidation of Fe(OH)2 and reduction of Au3+ led to the formation of δ-FeOOH nanodiscs decorated with small spherical Au nanoparticles. The density and size of AuNPs on the surface of nanodiscs depended on the concentration of added aqueous HAuCl4 solution. The same procedure was used for the synthesis of δ-FeOOH nanodiscs with AgNPs on the surface. The synthesized magnetic nanoparticles were tested for their SERS and catalytic activity.

feroxyhyte/Au ; ferroxyhyte/Ag ; gamma irradiation ; iron oxide nanoparticles ; SERS

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