engleski

A γ-irradiation method for the synthesis of iron oxide/Au nanostructures

Magnetic iron oxide nanoparticles (MNPs) due to their unique magnetic and electrical properties have applications as sensors, contrast agents, in drug delivery, hyperthermia cancer treatments, etc. For these uses, the surface of the particles should be modified with a suitable surface coating that can easily bind the appropriate biomolecules for the selected application. Gold has become one of the favored coatings because it is non-toxic, biocompatible, chemically inert, and can protect MNPs from oxidation without significantly reducing magnetic properties. Gold enables the surface functionalization with various organic species (due to strong Au-S bond). Magnetic composite or core@shell Fe-oxide/Au nanoparticles have an advantage in the applications due to the combined magnetic properties of the core and the unique optical properties of the Au coating. However, the properties, functionality, and thus the application of magnetic iron oxide/Au NPs, depends on their size, shape, magnetic properties, and colloidal stability. In addition, the quality and homogeneity of the gold coatings significantly depend on the coating process, in this case, the radiolytic process. γ-irradiation has an advantage of inducing electrons and other reducing species homogeneously through the sample. In this work, we have used γ-irradiation as an attractive and ecologically friendly technique for the synthesis of magnetic composite nanoparticles at room temperature. We have systematically studied the influence of γ-irradiation dose. The MNPs were synthesized from N2-purged, iron(III) chloride alkaline aqueous suspensions by γ- irradiation up to doses of 130 kGy (27 kGy/h) with the addition of 2-propanol, while the composite iron oxide/Au nanostructures were synthesized by the addition of HAuCl4. DEAE-dextran was used as a growth and stabilizing agent of MNPs in suspensions. During irradiation, iron(III) reduces to iron(II) depending on the absorbed dose. This radiolytic reduction is accompanied by phase transformations of the iron oxide precursor suspension. The addition of HAuCl4 aqueous solution induced the formation of Au nanoparticles on the surface of MNPs. The phase composition, stoichiometry, and morphology of MNPs were controlled by adjusting the γ-irradiation dose. Irradiation with doses 10– 36 kGy resulted in the formation of very small 4 nm spherical superparamagnetic substoichiometric magnetite NPs, whereas at a higher dose (50 kGy or more) the major phase was magnetic δ-FeOOH (feroxyhyte) in the form of nanodiscs. The magnetic measurements showed superparamagnetic behavior of magnetite NPs and exceptional intrinsic room-temperature magnetic properties of δ-FeOOH nanostructures with the Curie temperature above 300 K. The Au nanoparticles formed were spherical ; the quantity and size of Au nanoparticles depended on the amount of initially added HAuCl4 aqueous solution. Au nanoparticle size ranged from 6 nm to 27 nm, established by UV- Vis spectroscopy and electron microscopy. In this way, it was possible to obtain magnetic spherical magnetite and spherical Au nanoparticles, and thin disc δ-FeOOH/Au nanostructures from the same starting suspension by varying just one experimental factor: the absorbed dose.

feroxyhyte/Au nanostructures ; superparamagnetic nanoparticles ; iron oxides ; gamma-irradiation ; catalytic activity ; 4-nitrophenol

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