Synthesis and characterization of γ-Fe2O3/SiO2 composites as possible candidates for magnetic paper manufacture

Maghemite/silica composites were prepared by a facile and effective method. First a stable magnetic fluid (MF) was obtained by dispersing in toluene the maghemite nanoparticles, prepared by coprecipitation. Afterwards, maghemite nanoparticles were coated with silica by the hydrolysis and condensation of tetraethylorthosilicate. The structural, surface and magnetic characteristics of the composites were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) and vibrating sample magnetometer (VSM) measurements. Magnetic studies indicated the superparamagnetic behavior of the samples and the decrease of the saturation magnetization with the decrease of the magnetic fluid concentration.SEM images revealed the presence of agglomerated, spherical particles and TEM images showed both separated particles and multiple maghemite particles together, covered with silica layer.The close relationship between the concentration of maghemite nanoparticles and the color of composite materials was confirmed by diffuse reflectance spectroscopy. CIEL⁎a⁎b⁎ analysis revealed the change of the composites׳ color from reddish-brown to light beige by decreasing the concentration of the maghemite nanoparticles. These results demonstrate that the maghemite/silica composites are suitable for the manufacture of magnetic paper with different degrees of whiteness that can be easily correlated with the concentration of the magnetic fluid used for their preparation.