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Magnetic nanoparticles have been extensively studied because of the increasing interest in applications as different as high-density magnetic recording media and drug delivery systems. The effective use of a magnetic nanoparticle for a given application is primarily based on its physical and physico-chemical characteristics, such as morphological and compositional, and surface characteristics. Further, tailored surfaces play a key role in the development of superparamagnetic iron oxide nanoparticle (SPIO) based systems. Among SPIO, maghemite (γ-Fe2O3) nanoparticles are commonly used because of their stability and simple synthesis. In this work γ-Fe2O3 nanoparticles capped with oleic acid (OA) have been synthesized in different conditions. Nanosized maghemite were obtained via oxidation of magnetite nanoparticles, the latter synthesized via co-precipitation of Fe (II) and Fe (III) ions in alkaline medium. The magnetite oxidation was performed using two different routes, by bubbling O2 into a magnetite aqueous suspension and via treatment with ferric nitrate solution producing γ-Fe2O3. Alkaline aqueous suspension of maghemite nanoparticles was used to perform the OA grafting procedures. The amount of OA adsorbed on the surface of nanoparticles was estimated from the carbon content obtained from elemental analysis. The effect of the maghemite oxidation conditions on the adsorption process of OA macromolecules on the nanoparticle surface has been investigated by XRD, micro Raman, Infrared, TG/DTA and Mössbauer spectroscopy. From XRD analysis we had found an average particle size in the range from 5.2 nm to 6.2 nm for maghemite nanoparticles. Mössbauer measurements reveal that only γ-Fe2O3 is present. Raman data of oleic acid coated γ-Fe2O3 nanoparticles show the presence of peaks at 300, 506, 1395 cm-1, confirming maghemite characteristics and also at 2895 cm-1characteristic of OA. The infrared features at 600 cm-1 region change as the degree of oxidation increases, the magnetite band at 600 cm-1 became two broad maximum at around 630 and 595 cm-1, revealing the presence of maghemite after 5 hours of exposing on O2. Our results show that the functionalization efficiency of maghemite nanoparticles using oleic acid depends on the magnetite oxidation conditions. |