Synthesis and characterization of composite SiO2–Al2O3–Fe2O3 core–shell microspheres

The aim of this study was the synthesis and structural characterization of SiO2–Al2O3 microspheres with SiO2 core and (100 − x)Al2O3·xFe2O3 (x = 0, 5, and 10 mol%) shell. Smooth spherical silica particles of uniform size around 1 μm have been synthesized as core material based on the Stöber method. In order to enhance the specific surface area, the silica particles were coated with a thin nanostructurated shell, about 15 nm, of aluminum and iron oxides (100 − x)Al2O3·xFe2O3 (x = 0, 5, and 10 mol%). The embedding of iron oxide in the covering shell was related to potential applications of these composite biomaterials for contrast enhancement in magnetic resonance imaging (MRI) and at the same time for local treatments of cancer by hyperthermia. The XRD results point out the amorphous structure of the obtained core–shell particles. The TEM images evidence continuous shell coating of silica spherical microparticles and the XPS analysis of the surfaces prove the occurrence of iron oxide on the outermost layer of the microspheres. Both FTIR and XPS results evidence the formation of Al–O–Si linkage proving that Al2O3 and SiO2 are chemically bonded in the investigated core–shell microspheres.