Thermal route for the synthesis of maghemite/hematite core/shell nanowires

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Nowadays, iron oxide-based nanostructures are key materials in many technological areas. Their physical and chemical properties can be tailored by tuning the morphology. In particular, the possibility of increasing the specific surface area has turned iron oxide nanowires (NWs) into promising functional materials in many applications. Among the different possible iron oxide NWs that can be fabricated, maghemite/hematite iron oxide core/shell structures have particular importance since they combine the magnetism of the inner maghemite core with the interesting properties of hematite in different technological fields ranging from green energy to biomedical applications. However, the study of these iron oxide structures is normally difficult due to the structural and chemical similarities between both iron oxide polymorphs. In this work, we propose a route for the synthesis of maghemite/hematite NWs based on the thermal oxidation of previously electrodeposited iron NWs. A detailed spectroscopic analysis based on Raman, Mossbauer, and X-ray absorption shows that the ratio of both oxides can be controlled during fabrication. Transmission electron microscopy has been used to check the core/shell structure of the NWs. The biocompatibility and capability of internalization of these NWs have also been proven to show the potential of these NWs in biomedical applications.
© Amer Chemical Soc. This work was funded by Spanish MINECO under projects MAT2013-48009-C4-1-P, MAT2014- 52477-C5-2-P and MAT2015-64110-C2-1-P. We acknowledge the European Synchrotron Radiation Facility (ESRF), MINECO and CSIC for provision of synchrotron radiation facilites and the financial support for the beam line (PIE-2010-OE-013-200014). We would like to thank the BM25-SpLine staff for the technical support beyond their duties. We also acknowledge the use of the XRD facilities of the ISOM-UPM and thank A. Prados for her help during the XRD experiments. We also thank G. Pieplow for his help with the analysis using the FSD method. Belén Cortés acknowledges MINECO (FPI program) for her pre-doctoral fellowship.