In this work we report the preparation of magnetic hematite hollow sub-micron spheres (α-Fe2O3) by colloidal suspensions of ferric nitrate nine-hydrate (Fe(NO3)3·9H2O) particles in citric acid solution by following the sol-gel method. After the gel formation, the samples were annealed at different temperatures in an oxidizing atmosphere. Annealing at 180°C resulted in an amorphous phase, without iron oxide formation. Annealing at 250°C resulted in coexisting phases of hematite, maghemite and magnetite, whereas at 400°C, only hematite and maghemite were found. Pure hematite hollow sub-micron spheres with porous shells were formed after annealing at 600°C. The characterization was performed by X-ray diffraction (XRD), Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM).
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Acknowledgements L. León and A. Bustamante thank the financial support from the Scientific Initiation Programme of the University of San Marcos (Grant No. PIC—RR 06030-07). The work in Cambridge was supported by the European Union Programme ALBAN (Grant No E06D101257PE) and the Cambridge Overseas Trust. The work in Japan was supported by the Japan Society for the Promotion of Science (JSPS grant No PE10027). The work in Japan was also partially supported by Grants-in-Aid for Scientific Research on Innovative Areas (No. 20108011, pi-Space) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), a Collaborative Research Project of the Materials and Structures Laboratory (Tokyo Institute of Technology) and the World Class University Program, at Sunchon National University, Korea.
- Mössbauer spectroscopy
- Sol-gel method