ORIGINAL PAPER Microwave-assisted one-step hydrothermal synthesis of pure iron oxide nanoparticles: magnetite, maghemite and hematite Ling Hu • Aurelien Percheron • Denis Chaumont • Claire-Helene Brachais Received: 18 April 2011 / Accepted: 5 September 2011 / Published online: 24 September 2011 Ó Springer Science+Business Media, LLC 2011 Abstract A simple, rapid, one-step synthesis way of pure iron oxide nanoparticles: magnetite (Fe 3 O 4 ), maghemite (c-Fe 2 O 3 ) and hematite (a-Fe 2 O 3 ) was investigated. Nano- particles were prepared by microwave synthesis, from eth- anol/water solutions of chloride salts of iron (FeCl 2 and FeCl 3 ) in the presence of sodium hydroxide NaOH. X-ray powder diffraction (XRD), Transmission Electron Micros- copy (TEM), Fourier transform infrared (FTIR) spectros- copy and X-ray photoelectron spectroscopy (XPS) were used to characterize these nanoparticles. Keywords Iron oxides Á Nanoparticles Á Microwave heating Á XRD Á TEM Á FTIR Á XPS 1 Introduction The development of major iron oxide particles: magnetite (Fe 3 O 4 ), maghemite (c-Fe 2 O 3 ) and hematite (a-Fe 2 O 3 ) in uniform nanometer size has been widely pursued because of their technological importance [1]. Hematite crystallizes in the rhombohedral system and shows weak ferromagnetism at room temperature [2]. It is extensively used in catalysis [3, 4], pigments [5], gas sensors [6], optical devices [7] and medicine applications [8]. Magnetite and maghemite crystallize in the cubic crystal system. At room temperature, they are ferromag- netic. Due to their magnetic properties, these oxides have been exploited in a broad range of applications including information storage [9], sensors [10], refrigeration [11] and coil cores [10], as well as in contrast agent for magnetic resonance imaging [12, 13] and potential mediator for magnetic hyperthermia [14]. Chemical composition, morphology and size controls of nanoparticles appear to be crucial for these applications. These characteristics are strongly dependent on the method of preparation. Various techniques have been used to syn- thesize these iron oxides: co-precipitation, sol–gel methods, thermal decomposition, micro emulsion and hydrothermal methods. Formation and stabilization of super paramagnetic iron oxide nanoparticles prepared by alkaline co-precipita- tion of ferric and ferrous chlorides in aqueous solution require careful pH adjustment of the reaction medium [15–17], and it is difficult to control particle sizes and size distributions. In sol–gel methods, the hydrolysis and con- densation of metal alkoxides or alkoxide precursors lead to dispersion of oxide particles in a ‘‘sol’’ [18–20]. The main disadvantages of these methods are the possible contami- nation from by-products of reactions and the need for post- treatment like thermal treatment of the products [18]. High quality monodisperse iron oxide nanoparticles could be produced by the thermal decomposition of organometallic precursors such as Fe(CO) 5 [21], iron acetylacetonate [22, 23] and iron-oleate complexes [24] in organic solvents. The particle size can be tuned by the choice of precursor and reaction temperature [24]. Hydrophobic surfactant coating is generally used to facilitate stabilization in organic solvents, however, this reduces their stability in aqueous biological environment [25]. Iron oxide nanoparticles could also be produced in water/oil (w/o) micro emulsion systems by L. Hu (&) Á A. Percheron Á D. Chaumont Laboratoire Interdisciplinaire Carnot de Bourgogne, Universite ´ de Bourgogne, CNRS UMR 5209, 9 Avenue Alain Savary, 21078 Dijon Cedex, France e-mail: ling.hu@univ-lyon1.fr C.-H. Brachais Institut de Chimie Mole ´culaire de l’Universite ´ de Bourgogne, Universite ´ de Bourgogne, CNRS UMR 5260, 9 Avenue Alain Savary, 21078 Dijon Cedex, France 123 J Sol-Gel Sci Technol (2011) 60:198–205 DOI 10.1007/s10971-011-2579-4