Structure, Magnetic and Photochemical Properties of Fe–TiO2 Nanoparticles Stabilized in Al2O3 Matrix

Resumo

Fe–TiO₂ nanoparticles with Fe concentration from 0.24 to 5 wt % were synthesized in a Al₂O₃ matrix through multiple impregnations from organic solutions of Ti n-butoxide and Fe acetylacetonate. Microstructure, morphology and magnetic properties of the composites were studied using X-ray analysis, transmission electron microscopy, energy-dispersive analysis, Mössbauer spectroscopy and magnetic susceptibility. It was shown that the deposition of the solution with low concentration of Ti n-butoxide leads to the formation of mostly extensive Fe–TiO₂ films with a small fraction of individual Fe–TiO₂ nanoparticles. On the contrary, the increase of Ti n-butoxide concentration results in the formation of a great number of individual Fe–TiO₂ nanoparticles on Al₂O₃. The size of these particles increases from 2–3 nm to 5–8 nm with the increase of Fe content in the samples from 0.24 to 1.0 (wt %). Mössbauer spectroscopy revealed two types of magnetic ions. The first type of paramagnetic Fe³⁺ demonstrate spin–lattice relaxation properties while another one substitutes Ti⁴⁺ in the TiO₂ structure thus forming Fe–TiO₂ stabilized particles in the matrix. According to the magnetic data antiferromagnetic and ferromagnetic types of exchange spin coupling occur in Fe–TiO₂/Al₂O₃ composites. The increase of Fe concentration in the composites from 1 to 5 wt % results in the narrowing of the TiO₂ band gap from 3.2 to 2.7 eV and shifting the absorption edge in visual spectrum from 350–400 to 450–500 nm.