The effect of Co2+ on the structure and colour of silica gel derived materials

Undoped and doped Co2+ silica gel-derived materials were prepared from hydrolysis and condensation of tetraethylorthosilicate (TEOS). In order to better understand the structural evolution of these samples, with the heat-treatment temperature, ultra-violet (UV), visible (VIS) and near-infrared (NIR) spectrophotometry, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used. The spectroscopic behaviour of Co2+ allows us to obtain information about the ability of this ion to act as a network-former and/or as a network-modifier. Above 800 degreesC the samples are opaque and show crystalline phases. (C) 2001 Kluwer Academic Publishers.