Fe@FeOxide magnetic nanomaterials with core@shell structure produced by reduction of magnetite nanoparticles

Abstract

Magnetic materials in nanoscale, specially nanoparticles (NP), show unique magnetic properties in comparison to their bulk counterparts. These properties have been exploited to obtain new functionalities and applications in many areas of knowledge, including biomedicine. Biomedical applications of magnetic NP require NP with chemical and colloidal stability in physiological medium, high magnetic emanation and superparamagnetic behavior at room temperature. Magnetic Iron oxides (e.g. magnetite and maghemite), beyond the features mentioned above, have low biotoxicity, which make these materials strong candidates to application in biomedicine. Superparamagnetic iron oxide nanoparticles presents saturation magnetization (MS) values about 50-80 emu/g, low blocking temperatures and a wide versatility in the functionalization of their surface with polymers, surfactants and biomolecules. However, the coating of the NP surface with diamagnetic compounds during the functionalization process results in MS decrease. Despite having MS values around 200 emu/g, metallic-based magnetic NP as Fe and Co presents low chemical stability and tend to oxidize in aqueous medium, which is a barrier to direct application of metallic NP in biomedicine. In this context, this project, which is linked to the regular PhD project (FAPESP grants No. 2011/12210-4), proposes to obtain superparamagnetic iron oxide-coated iron NP (Fe@FeOxide) in a core@shell structure. The intension is combining the high magnetic emanation of the metallic core with the low toxicity and wide versatility in the surface functionalization of the oxide shell. This material will be prepared by hydrogen reduction of magnetite NP at high temperatures followed by the controlled oxidation of the NP surface in order to obtain an iron oxide layer. These magnetite NP will be prepared by using two different methods: thermal decomposition of metal complexes and coprecipitation in aqueous medium. The thermal decomposition method is well known due to produce NP with great size and shape control and is widely used in our group in Brazil. , but results in hydrophobic NP, which is undesirable for biomedical applications. Recently, researchers from the Materials Science Institute of Madrid (ICMM) have been studying modifications of coprecipitation methods in order to produce magnetite NP with good size and shape control. As it is an unusual method for our group in Brazil, but of great interest, we decided to include this method within this project. We believe the study of this coprecipitation method will assist not only the development of the regular PhD project, but also the development of other currently projects in our group. Core@shell Fe@FeOxide NP are composed by two distinct magnetic phases, which can result in different couplings in the interface between then. So, this project also aim combine the wide equipment set available in ICMM for magnetic characterization of materials and the solid knowledge of the ICMM researchers in this area in order to study the magnetic properties of Fe@FeOxide system, considering that different magnetic coupling between distinct magnetic phases can results in unique magnetic phenomena, as reported in the literature for other magnetic core/shell systems. We believe this study will give fundamental knowledge for the study of magnetic properties presented by FePt@Fe3O4, FeCo@Fe3O4, FeAg@Fe3O4 and Co@Fe3O4 core@shell systems, which are currently been studied in the regular PhD project in Brazil. (AU)