Synthesis and characterization of magnetite nanoparticles from mineral magnetite Mauricio Morel a,b,n , Francisco Martínez a,nn , Edgar Mosquera b a Laboratorio de Síntesis y Polímeros, Departamento de ciencias de los Materiales, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile b Laboratorio de Materiales a Nanoescala, Departamento de ciencias de los Materiales, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Avenue Tupper 2069, Santiago, Chile article info Article history: Received 5 October 2012 Received in revised form 19 April 2013 Available online 3 May 2013 Keywords: Nanoparticle Superparamagnetic Synthesis Mineral magnetite abstract We have synthesized magnetite nanoparticles with sizes that range from 20 to 30 nm from mineral magnetite roughly 45 μm in size. The procedure consists in the dissolution of the mineral in an acidic medium and subsequent precipitation in a basic medium in the presence of oleic acid. Two experiments were conducted in different gaseous environments. The first was carried out in an environment exposed to air (M1) and the second in an N 2 (M2) environment. The x-ray diffraction results showed a slight difference, which corresponds to the surface oxidation of magnetite. The sizes of the modified nanoparticles were determined through the Scherrer equation and transmission electron microscopy. An organic material mass loss corresponding to 18% was observed through a thermogravimetric analysis. The Fourier transform infrared spectroscopic analysis provides information about the type of bond that is formed on the surface of the nanoparticle, which corresponds to a bidentate chelate. The vibrating sample magnetometer results show a superparamagnetic behavior for sample M1. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The magnetite is a ferrous–ferric oxide with an inverse spinel structure in which the oxygen is organized in a cubic close packing with iron atoms placed in tetrahedral and octahedral positions [1]. The iron ore is the principal raw material for the steel industry. It is used in many processes as sponge iron (hematite, Fe 2 O 3 ) and not as magnetite (Fe 3 O 4 ). In this process, the magnetite loses its magnetic properties. The magnetite in bulk is known as a natural magnet, due to its ferromagnetic behavior. In addition, there are a number of studies in which the nanoparticles act as water purifier to remove arsenic from contaminated drinking water [2,3,4]. Special properties are only present in a nanometric system with a strong dependence on the size, such as superplasticity in ceramic materials [5,6], plasmon absorbance in metallic particles [7], among others. On the other hand, in nanostructured magnetic materials appears the “superparamagnetism” [8]. This phenomenon is named because the presence of a similar behavior to paramagnetic materi- als is observed but with a higher magnetic moment. One way to determine qualitatively whether or not a material has superpara- magnetism is by study of hysteresis loop. If the loop has the form given by the Langevin function and the normalized remanence (Mr/Ms) is ⪡0.01 the material presents a superparamagnetic behavior [9,10]. Superparamagnetic properties are important in biological applications, especially when it is necessary to avoid the possible embolization of the capillary vessels; this is possible through a low remanence after the magnetic field is removed. In order to show superparamagnetic properties, the nanoparticles must present a minimal agglomeration, which is extremely difficult because the systems have a strong colloidal attraction among the particles, due to the van der Waals forces [11]. Besides, the attraction is favored by Ostwald ripening [12]. Carboxylic acid, amines and other reactive with chelating functional groups are incorporated in the surface of magnetic nanoparticles avoiding the agglomeration [13,14]. Iron oxides, such as magnetite [15], α-hematite [16] and γ-maghemite [17], are important because they correspond to biodegradable materials with a superparamagnetic behavior. These materials are particularly powerful because of their wide use in biomedicine, for example, in the field of magnetic resonance imaging (MRI) [18,19], and hyperthermia cancer therapy [20,21]. Nowadays, there are a number of methods for nanoparticles synthesis; among them, we can mention thermal decomposition Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2013.04.075 n Corresponding author at: Laboratorio de Síntesis y Polímeros, Departamento de ciencias de los Materiales, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Avenue Tupper 2069, Santiago, Chile. Mob.: +56 74512759 . nn Corresponding author. Tel.: +56 29784233; fax: +56 2 699 4119. E-mail addresses: mmorel@ing.uchile.cl, mauricio.morel.escobar@gmail.com (M. Morel), polimart@ing.uchile.cl (F. Martínez). Journal of Magnetism and Magnetic Materials 343 (2013) 76–81