Local structural effects of Gd3+ ions incorporation in shell of nanostructured silica core – alumina rich shell microspheres

Abstract

Non-crystalline nanostructured silica core – alumina rich shell microspheres, with Gd ions in the shell were obtained by sol-gel procedure following a synthesis route based on the Stöber method. The samples were characterized by DTA/TGA, XRD, SEM and TEM, EPR, solid-state NMR and XPS techniques. The effect of increasing Gd ions content on the local structure in alumina rich shell and at its interface with silica core was investigated. It was also found that increasing the concentration of the paramagnetic ions leads to a modification of the local magnetic field at sites of neighboring aluminum and silicon ions. Gadolinium ions are distributed in the aluminum sites from alumina rich shell. As result of increasing the gadolinium incorporation at the core-shell interface the diffusion of aluminum in the silica network, as well as the migration of the silicon in the alumina rich shell, are enhanced. Therefore, Si-O-Al bridges are formed at the interface, leading to stable non-crystalline structures, with Gd ions on the external layer of the shell, as proved by XPS, having potential application as contrast agents for magnetic resonance imaging (MRI).