Nanocomposites and nanomaterials

Low-energy synthesis of magnetite nanoparticles from weakly magnetic hematite using biomass  
 T.S. Antonenko, N.O. Dudchenko, V.V. Ovsienko, Yu.I. Cherevko
 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of Natl. Acad. of Sci. of Ukraine, Palladina prosp, 34, Kyiv-03142, Ukraine. 
E-mail: tetyana_savchenko@ukr.net

The aim of this work was to synthesize highly magnetic magnetite particles using weakly magnetic iron oxides (hematite) and biomass (starch) under the heating at the definite temperature. 
For magnetite synthesis, the sample of weakly magnetic hematite was thoroughly mixed with 4% starch. The resulting mixture was placed in a quartz mini-reactor with limited oxygen access and kept for 30 minutes at 650°C. Heating and cooling of the sample was carried out using the device for analysis of the magnetization of magnetic materials and ores. The Curie temperature was also determined using this device for the samples, obtained during the transformation process.
Phase composition of initial and obtained samples was determined by X-ray diffraction (X-Ray diffractometer DRON-3M). Facility for express measurement of magnetization of ores and magnetic materials was used for determination of the specific saturation magnetization. The X-ray diffraction method showed that the initial samples consisted mainly of hematite (d-spacing of hematite (Å) 3,68 Å, 2,70 Å, 2,52 Å, 1,84 Å, 1,69 Å, 1,66 Å, 1,60 Å, 1,48 ) and quartz (d-spacing of quartz (Å) 4,25 Å, 3,34 Å, 2,46 Å, 2,28 Å, 2,24 Å, 2,21 Å, 2,13 Å, 1,82 Å, 1,72 Å, 1,67 Å, 1,54 Å, 1,46 Å). Specific saturation magnetization for initial samples was ~ 1 А∙m2/кg. After the addition of starch and exposure to heating, the obtained samples consisted of magnetite, quartz and traces of hematite (d-spacing of magnetite (Å) 4,87 Å, 2,97 Å, 2,54 Å, 2,43 Å, 2,10 Å, 1,71 Å, 1,61 Å, 1,48 Å). Specific saturation magnetization of obtained samples was around 45 А∙m2/кg. Therefore, we could conclude that the specific saturation magnetization of samples increased due to magnetic minerals (magnetite) formation. Curie temperature, determined by cooling curve of obtained samples, was ~583 °C that is close to Curie temperature of pure magnetite (580 °C). We can assume, by the Curie temperature (583 °C), that the obtained samples contain magnetite or isomorphically substituted magnetite. 
The results could be used to solve the fundamental problems related to the synthesis of magnetic nanoparticles under the energy-consuming conditions.