A sol-gel route to synthesize monolithic zinc oxide aerogels

The epoxide addition sol-gel process is a relatively new route to synthesize transition and main group metal oxide aerogels. Zinc oxide monoliths were obtained by sol-gel processing of an alcoholic zinc nitrate solution with propylene oxide as the gelation initiator. The alcogels were dried either by supercritical CO2 fluid extraction (aerogel) or by ambient temperature slow evaporation (xerogel). The resulting materials were characterized using powder X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM), nitrogen adsorption/desorption analysis, and photoluminescence (PL). Annealing of the aerogel at low temperatures (below 250 degrees C) yields a highly crystalline material which exhibits a significant increase in photoluminescence while retaining the inherent characteristics of the original aerogel, including high surface area ( > 100 m(2)/g) and porosity.