Hydrophobic magnetic nanocomposites silica aerogel/maghemite

P. MENDOZA ZÉLIS; M. B. FERNÁNDEZ VAN RAAP; L. M. SOCOLOVSKY; A. G. LEYVA; F. H. SÁNCHEZ

Manizales

Workshop; IX Latin American Workshop on Magnetism, Magnetic Materials and Their Applications; 2010

Universidad Nacional de Colombia in Manizales

p { margin-bottom: 0.21cm; } Silica aerogels are the lightest solid materials that find applications in several areas. Particularly, magnetic hydrophobic aerogels present novel applications. These magnetic materials are iron oxide nanoparticles hosted in hydrophobic silica aerogel. In this work, we discussed on the preparation and characterization of this kind of material. The aim of this work is to investigate the interrelation between porosity and magnetic nanostructure in these porous nanocomposites. Silica aerogel/iron oxide nanocomposites have been synthetized by sol-gel process followed by supercritical drying. The gel have been synthesized from tetraethylorthosilicate (TEOS) and methytrimethoxysilane (MTMS) with a molar ratio MTMS/TEOS= 0.5. The later was added to achieve the hydrophobic property by surface modification. Iron nitrate had been incorporated as Fe oxide precursor. Molar ratios alcohol/TEOS= 2.3, H2O/TEOS=1.8 were hold fixed while iron concentration was varied to achive mFe/mSi=0.083, 0.207 and 0.330. The structural and magnetic properties of Fe2O3−SiO2 nanocomposite porous aerogels were systematically investigated by XRD, Mössbauer Spectroscopy, TEM, SQUID magnetometry and with SAXS and XAF by using synchrotron radiation at LNLS. These materials exhibit an accessible internal porous structure, both in the meso and in the micro scale. Porosity structure was studied by SAXS and displays the typical fractal power law behaviors with primary particle radius of 20 nm.  Field cooled and zero field cooled magnetization curves indicates that the composites behave as an assembly of non-interacting superparamagnetic nanoparticles for the three compositions studied. The samples become blocked at a temperature TB between 27 and 40K.Direct magnetic particle size determination is not an easy task because these materials exhibit low crystallinity and low constrast for TEM. Hydrophobicity allows the aerogel to be loaded with an organic liquid. Loaded aerogeles were also studied by SAXS in an attempt to lower the silica/porous constrast. Contrast studies and the feasibility of a direct determination of magnetic structure from the scattering data is discussed. The results provide new insights into innovative materials and on the relation between the compositional and microstructural features, and the properties of magnetic nanocomposite.