Synthesis of magnetite (Fe 3 O 4 ) nanoparticles without surfactants at room temperature I. Martínez-Mera a,b , M.E. Espinosa-Pesqueira a , R. Pérez-Hernández a , J. Arenas-Alatorre c, ⁎ a Instituto Nacional de Investigaciones Nucleares (ININ), Km. 36.5 Carr. México Toluca, La Marquesa, Municipio de Ocoyoacac, Edo. de México, C. P. 52750, Mexico b Facultad de Química-UAEM, Paseo Colón Esq. Paseo Tollocan, Toluca, Edo. de México, C.P. 50120, Mexico c Departamento de Materia Condensada, Instituto de Física, Universidad Nacional Autónoma de México, México, D.F., C.P. 04510, Mexico Received 8 August 2005; accepted 9 February 2007 Available online 15 February 2007 Abstract Iron oxide nanoparticles in the interval of 4–43 nm were synthesized by a colloidal method at room temperature, without use of surfactants and using precursors like FeCl 3 ·6H 2 O and FeCl 2 ·4H 2 O; deionizated water free of dissolved oxygen and ammonia solution (29% vol.) and using several aging times (2, 5 and 10 min). A detailed study by X- ray diffraction (XRD), Conventional Transmission Electron Microscopy (CTEM), High-Resolution Transmission Electron Microscopy (HRTEM) and electron diffraction patterns showed that with a reaction time less than 5 min nanoparticles of magnetite phase (Fe 3 O 4 ) were synthesized, and with a bigger time of reaction the lepidocrocite phase (FeO(OH)) was identified. The minor particle average size measured was 6 nm in the sample, 0.0125 M with 2 min of aging time (0.0125M2 m). In addition it was possible to obtain a narrow nanoparticle size dispersion from 4 to 10 nm for small aging times. © 2007 Elsevier B.V. All rights reserved. Keywords: Magnetite nanoparticles; Magnetic materials; Microstructure; Nanomaterials; HRTEM; XRD 1. Introduction Advances in nanoscience and nanotechnology are centered in the control of the size and shape of nanoparticles, as well as obtainment of the extended arrangement of nanoparticles in 1D, 2D and 3D. Their physical properties depend on these variables and their anisotropy from which it may be possible to find new nanostructured systems with novel and specific properties [1]. New optimized methods of synthesis are necessary to allow for the control of the shape and size distribution of nanoparticles. In particular, systems made of iron oxides nanoparticles, have an enormous potential towards applications in several areas such as magnetic recording technology, pigments, catalysis, photocatalysis and medical uses. In medicine, these systems have been applied as part of cancer therapy, as well as in diagnosis, where the magnetite nanoparticles are used as contrast agent for studies of nuclear magnetic resonance (NMR) [2]. Commercial products in the market for these medical treatments exist in the market nowadays. However, they have wide size distributions (120– 180 nm) and their particle size is bigger than the extracellular space (b 50 nm) [3]. Hence it is necessary to obtain magnetic nanoparticles with smaller and narrower size distribution than the ones manipulated with external magnetic fields. Another potential application of these nanoparticles is their use as tertiary treatment of residual waters acting as powerful reducer agents of organic and inorganic material, with the advantage that it could be possible to recycle and separate the magnetite particles by an external magnetic field [4]. Concerning the synthesis of magnetite, Gribanov et al. [5] have used a colloidal method with NH 4 OH as hydrolyzing agent in substitution of NaOH or KOH. They obtained a high saturation of magnetization and avoided impurities as α- FeOOH and other iron compounds. They report that a the temperature of 20 °C is ideal for magnetite formation and suggest the use of an excess of alkali and iron salts concentration of about 0.1 M. On the other hand, Murray et al. [6] synthesized Materials Letters 61 (2007) 4447 – 4451 www.elsevier.com/locate/matlet ⁎ Corresponding author. Instituto de Física, UNAM, Apdo. Postal 20–364, C.P. 01000, México, D.F., Mexico. Tel.: +52 55 56225163; fax: +52 55 56225009. E-mail address: jarenas@fisica.unam.mx (J. Arenas-Alatorre). 0167-577X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2007.02.018