Preparation of Zirconia Aerogels

Zirconia aerogels were among the first to be prepared by controlled hydrolysis of zirconium alkoxides in nonaqueous media followed by SCD [18] (Chap. 1). Later this method became a standard and was extended to many other metal oxides [19, 20]. 

In fact, zirconia aerogels with very high surface areas exceeding 500 m /g were prepared by Bedilo et al. [21], using a sol-gel method with high-temperature SCD. 

The synthesis of zirconia nanomaterials by a one-step sol-gel route under supercritical C02(l) drying using zirconium alkoxides and acetic acid was reported by Sui et al. [24]. Their materials exhibited high surface areas (up to 399 m /g) and porosity, while the calcined materials demonstrated tetragonal and/or monoclinic nanocrystallites. Either a translucent or opaque monolith was obtained. Investigation by electron microscopy showed that the translucent monolithic Z1O2 exhibited a well-defined mesoporous structure, while the opaque monolith, formed using added alcohol as a co-solvent, was composed of loosely compacted nanospherical particles with a diameter of approximately 20 nm. 

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