Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads Jose ´ R. Correa a, *, Eduardo Bordallo b , Dora Canetti c , Vivian Leo ´n b , Luis C. Otero-Dı ´az d,f , Carlos Negro e , Adria ´n Go ´ mez f , Regino Sa ´ ez-Puche d a Department of General Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400, Cuba b Sugar Cane-Cellulose Research Center, Cuba-9, Quivica ´n, Cuba c Department of Inorganic Chemistry, Faculty of Chemistry, University of Havana, Zapata and G, Havana City 10400, Cuba d Department of Inorganic Chemistry-1, Complutense University of Madrid, Madrid 28040, Spain e Chemical Engineering Department, Complutense University of Madrid, Madrid 28040, Spain f Electron Microscopy Center, Complutense University of Madrid, Madrid 28040, Spain 1. Introduction The study of magnetite nanoparticles is particularly interesting because of their wide variety of technological applications in fields like recording devices, where the grains must be small and magnetically decoupled [1–4]; medicines supported by specific polymers [5–7]; pigments [8]; and biotechnology [9], they are also useful as a raw material in the synthesis of maghemite [10]. Recently, magnetite ferrofluids have become very attractive materials because they can be directed by the action of the magnetic field; they absorb electromagnetic energy with heat evolution and their physical properties may change with the application of a magnetic field [11,12]. Magnetite can be synthesized from several different paths, for example oxidation of Fe(OH) 2 precipitate via green rust [13] or through the reduction of hematite with hydrogen [14]. However, in order to obtain nanoparticles, only specific methods have been proven: iron complexes decomposition [15,16], mechanical alloy- ing [17], water/oil (w/o) microemulsion [18,19] and the Massart method [20]. Some of the reported difficulties are the wide particle size distribution and the large amount of solvent to spend [21]. The last two methods above are the most frequently employed and include Fe(II)/Fe(III) fast hydrolysis. In the original preparation reported by Massart, an aqueous mixture of ferric and ferrous chloride in hydrochloric acid is added to ammonia solution. The gelatinous precipitate is then isolated from the solution by centrifugation or magnetic decantation without washing with water. The synthesis of magnetite nanoparticles by this way has the advantages of operation simplicity, the use of economic reagents and it is still useful to study the influence of solution conditions in the size of the precipitated particles [22]. Superparamagnetic iron oxide nanoparticles (SPION) covered with a polymer have been used in medical research such as devices for cell isolation, immobilization of enzymes, controlled release systems and separation of biological materials [23]. Cellulose beads covering inorganic particles, a new kind of composite materials, can be used as organic support. Guo et al. reported the study of inorganic adsorbents inside cellulose beads in the elimination of arsenic from aqueous solutions [24]. Thus, cellulose beads could act as a column bed, suitable for liquid permeability. Materials Research Bulletin 45 (2010) 946–953 ARTICLE INFO Article history: Received 19 July 2009 Received in revised form 12 February 2010 Accepted 14 April 2010 Keywords: A. Composites A. Magnetic materials B. Chemical synthesis C. Electron microscopy D. Magnetic properties ABSTRACT Superparamagnetic magnetite nanoparticles were obtained starting from a mixture of iron(II) and iron(III) solutions in a preset total iron concentration from 0.04 to 0.8 mol l 1 with ammonia at 25 and 70 8C. The regeneration of cellulose from viscose produces micrometrical spherical cellulose beads in which synthetic magnetite were embedded. The characterization of cellulose–magnetite beads by X-ray diffraction, Scanning and Transmission Electron Microscopy and magnetic measurement is reported. X- ray diffraction patterns indicate that the higher is the total iron concentration and temperature the higher is the crystal size of the magnetite obtained. Transmission Electron Microscopy studies of cellulose–magnetite beads revealed the distribution of magnetite nanoparticles inside pores of hundred nanometers. Magnetite as well as the cellulose–magnetite composites exhibit superparamagnetic characteristics. Field cooling and zero field cooling magnetic susceptibility measurements confirm the superparamagnetic behaviour and the blocking temperature for the magnetite with a mean size of 12.5 nm, which is 200 K. ß 2010 Elsevier Ltd. All rights reserved. * Corresponding author. Fax: +53 7 873 3502. E-mail address: correa@fq.uh.cu (J.R. Correa). Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu 0025-5408/$ – see front matter ß 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2010.04.012