Direct sol-gel synthesis of doped cubic mesoporous SBA-16 monoliths

Porous monoliths of a 3D cubic cage mesostructured silica (SBA-16 type) and of composites containing Co (5% wt.) and FeCo (5% wt.) nanophases dispersed in the SBA-16 type matrix were prepared following a templated-gelation method. Optically clear disk-shaped monoliths with diameter around 10 cm were obtained whose absorption spectra are tunable based on the composition. Low-angle X-ray diffraction, N₂ physisorption and transmission electron microscopy show that the ordered mesoporous structure and high surface area are preserved after calcination at 500 °C and after reduction at 800 °C, indicating a very high thermal stability. X-ray absorption spectroscopy at the Fe and Co K-edges allowed us to identify the intermediate products before and after reduction. In particular, the formation of a nanophase of layered cobalt silicate hydroxide was determined in the Co containing sample calcined at 500 °C. This compound is easily reducible giving rise to a superparamagnetic nanocomposite containing pure fcc Co nanoparticles dispersed within the 3D mesoporous silica structure. Extensive characterization points out that the proposed procedure is promising in the preparation of functional nanocomposites with adjustable magnetic and optical properties.