Formation of Ni/NiO Nanoparticles in Supermicroporous Silica-Based SiO2-Al2O3-NiO Materials: Structural and Magnetic Studies

Microporous silica-based materials SiO₂-Al₂O₃-NiO with a predominant pore size in the range 8-20 Aring, prepared by the sol-gel method by variation in Ni²⁺ concentrations from 0 to 30 weight %, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy. The nature of the nickel centers has been studied by magnetic susceptibility measurements supported by the XPS and X-ray experiments. It has been shown that these centers represent NiO and Ni⁰ (observed at high nickel loadings) aggregated into nanoparticles. The Ni⁰ nanoparticles are responsible for the room-temperature ferromagnetic behavior of the materials prepared with high nickel loadings.