Preparation and Superparamagnetism of Nano-Ni/mesoporous SiO2 Composites

Nano-Ni/mesoporous SiO2 composites were obtained by reducing Ni2+-doped SiO2 xerogels in H2, which were prepared via a sol-gel route. The average size of nano-Ni particles in mesoporous composites was estimated at 11～12nm from TEM (Transmission Electron Microscope) photographs. The results of magnetic measurements show that compared with the conventional nano-Ni particles, the Ni particles in nano-Ni/mesoporous SiO2 composites remain superparamagnetic state when their particle size is larger than the critical size of Ni calculated theoretically. Elevation of the reduction temperature promotes transformation of nano-Ni particles in mesoporous composites into the superparamagnetic state within a certain range of temperature.