Iron oxide based nanoparticles: synthesis and characterization / Síntese e caracterização de nanopartículas baseadas em óxidos de ferro

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Magnetic nanoparticles have importance in several areas of knowledge including physics, chemistry and biology. Obtaining nanomaterials with well defined characteristic and shapes is a great challenge for this area of research. In this work two synthetic processes for the synthesis of the magnetic nanoparticles were developed, in reversed micelles and sol-gel chemistry. Reverse micelles were used as nanoreactors with the goal of obtaining nanoparticles with controlled size and distribution. We characterized the nanoparticles in micelle solutions with small angle X-Ray scattering (SAXS) and analyzed the nanoparticles extracted from the reverse micelles after some purification steps using thermogravimetry (TG), differential scanning calorimetry (DSC), microanalysis (CHN). The structural and morphological properties were characterized by using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The magnetic properties were also investigated by using magnetization techniques (VSM and SQUID) and Mössbauer spectroscopy. The nanoparticles presented sizes ranging from 2 to 4 nanometers, with small cristallinity and impurities due to the presence of surfactants. The nanoparticles were characterized to be ferrihydrite. After heat treatment the properties of these materials were also investigated by XRD, TEM, Mössbauer spectroscopy and VSM. A transition from ferrihydrite to magnetite was characterized. In the second part of the work, we realized several synthetic co-precipitation routes of iron oxides in methanolic media, with the goal of determining the most favorable condition to create a layer of silica into the iron-oxide particle, by using the sol-gel process. The proportion of 25% methanol:base resulted in the most favorable condition to do the recovery of the nanoparticles with SiO2, by the reaction with tetraethylorthosilicate (TEOS). The TEOS amount was varied in the Si to Fe ratio, following the proportions 10, 20, 30, 50 e 70%. The structural characterization of the nanoparticles was done by X-ray diffraction, Fourier Transform Infra-Red spectroscopy (FTIR), transmission electron microscopy with energy filter, electronic imaging spectroscopy (ESI), Mössbauer spectroscopy, magnetization measurements (VSM) at room temperature. The particles with smaller concentration of silica presented cristallinity with average sizes of ~17nm. Also, the magnetic properties were preserved after the covering, and its superparamagnetic behavior was still observed with a reduction of the magnetization saturation. The FTIR analysis show the binding of the silica to the magnetic particles and the ESI images suggest that the iron oxide nanoparticles work as templates for the binding of silica.

ASSUNTO(S)

3. magnetic substance superparamagnetism 5. biochemistry. 4. substância magnética superparamagnetismo 2. física do estado sólido 3. estrutura dos sólidos 5. bioquímica. 1. nanotecnologia nanopartículas 2. solid structures 1. nanoparticules

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