Iron oxide in a silica matrix prepared by the sol–gel method D. Predoi a , O. Crisan a, ⁎ , A. Jitianu b,c , M.C. Valsangiacom a , M. Raileanu c , M. Crisan c , M. Zaharescu c a National Institute for Physics of Materials, P.O. Box MG 07, Bucharest, Măgurele, Romania b Department of Materials Science and Engineering, Rutgers, The State University of NJ, 607 Taylor Road, Piscataway, NJ 08854, USA c Institute of Physical Chemistry, Romanian Academy, 202 Splaiul Independenţei, 060021 Bucharest, Romania Available online 16 January 2007 Abstract Fe x O y –SiO 2 nanocomposites were prepared by sol–gel method by using two SiO 2 sources and Fe(SO 4 ) 2 ·7H 2 O as raw materials. The amorphous gels were thermally treated up to 1000 °C. The initial gel and the thermally treated samples were characterized by thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) and infrared spectroscopy. The presence of hematite was confirmed by the obtained Mössbauer spectra which showed the characteristic sextet. The total amount and the size distributions of the hematite nanoparticles can be controlled via the initial precursors and subsequent by annealing conditions. © 2006 Elsevier B.V. All rights reserved. Keywords: Sol–gel method; Silica template; Iron oxides; Mössbauer spectrometry 1. Introduction Nanostructured magnetic materials have attracted considerable interest both from fundamental point of view as well as for their use in various technological applications [1–9]. As in small particles, a high number of atoms (as high as 40% for a nano- particle of 2 nm diameter) are located at surfaces or interfaces, having reduced coordination and exhibiting high surface anisotropy, their magnetic properties are expected to be strongly modified compared to their bulk counterparts. The composite systems containing metal oxide nanoparticles embedded in a polymeric mesoporous (silica) template represent an exciting issue in the field of nanoscience and nanotechnology, as the nanoparticle incorporation allows imparting unique properties to polymeric materials: catalytic, optical, magnetic, sensing etc. If the polymeric matrix is already nanostructured, with pores of controlled size and shapes via the sol–gel methods, before the nanoparticle formation, i.e. contains domains of different chemical nature divided by interfaces, this reflects a further degree of nanostructural organization. Normally, the presence of such nanostructures in polymer systems (presence of interfaces) allows carrying out a subtle control over nanoparticle growth, particle shapes and size distribution, and particle surface inter- actions. The above characteristics are most important in deter- mining properties of these nanomaterials and their possible applications. Nanocomposites containing iron oxide nanocrystals are intensively studied for their potential applications in magneto- optic devices [4] catalysis [5] magnetic refrigerators [6] and bioprocessing [7]. Of special importance is the use of the iron oxide nanoparticles as potential vectors for drug delivery appli- cations [8,9], magnetic resonance imaging [9], detecting and treating cancer [10]. The Fe x O y –SiO 2 nanocomposite materials can be prepared by using a large variety of methods. The sol–gel chemistry is a suitable technique as it allows to control the shape and size of pores in the silica template and thus the composition and nano- structure of the final material [6,11,12]. The nature of the silica template may give different pore nanostructures, pores that provide the sites for nucleation of the iron oxide particles, avoiding thus their aggregation [3]. There is a large variety of silica precursors used to synthesize by sol–gel method iron oxide nanoparticles as seen in a literature survey. The SiO 2 source is mainly an alkoxide: either triethoxysilane [13], or methyltriethox- ysilane [14] but most frequently tetraethoxysilane [15–22]. Concerning the iron precursor, there are also some alternatives: Thin Solid Films 515 (2007) 6319 – 6323 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: ocrisan@yahoo.com (O. Crisan). 0040-6090/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2006.11.148