M Gharagozlou - Department of Nanotechnology, Institute for Color Science and Technology, Tehran, Iran

In this work, nanocomposites based on spinel pigments dispersed in silica matrix were successfully synthesized by a sol-gel method using silicic acid as a precursor of silica and metallic nitrates as precursors of spinel pigments. The nanocomposite samples and xerogel precursors were evaluated by powder X-ray diffraction (XRD),FT-IR spectroscopy and vibrating sample magnetometer (VSM). Also the structural and magnetic properties of the nanocomposite samples have been investigated. The XRD patterns of the nanocomposite samples show peaks assigned to pure singlephase spinel particles with a cubic system Fd3m with crystallite sizes in the range of 10-15 nm using Scherrer equation. The very broad peak observed at 2# of around 23 is attributed to the amorphous nature of silica matrix. These results indicated that spinel particles have been nucleated in the silica matrix to form nanocomposites. The well established silica matrix network provided nucleation locations for spinel nanoparticles and confining their aggregation and coarsen. FTIR spectroscopy showed changes in the matrix microstructure and the pore environment of nanocomposite samples and xerogel precursors. Strong absorptions observed at 1080, 802 and 464cm-1 indicate the formation of silica network. Thermal analyses show weight losses and exothermic peaks attributed to the loss of water, some gases adsorbed on the surface and decomposition of the organic matter which are in agreement with the infrared spectroscopy. Our results show that uniformly dispersed and size-adjustable spinel pigment nanoparticles can be prepared via this method based on the embedding particles in amorphous silica network during the nanocomposite formation.

Nanocomposite, Spinel, Pigment, Silica matrix, Xerogel precursor