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 CO ₂ 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° 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.