The effects of hydrolysis level on structural properties of titania aerogels

In this paper seven titania aerogels with different hydrolysis levels from 3.75 to 9 were prepared by sol-gel method and subsequent drying by supercritical CO2 dynamic extraction at 75 °C and 220 atm. The effects of the amount of water as hydrolysis agent was considered by observing the destruction of the gels during the aging period and investigating the porosity, specific surface area and pore volume of the aerogels. Besides a portion of some of the samples were calcined up to 450 °C to achieve anatase crystalline phase which formation was examined by XRD and Raman spectroscopy measurements. The observations showed that the gels with lower hydrolysis levels (3.75 and 4) were not stable enough and dissolved during the aging period. From the physical stability of the gels and the structural characterizations of the prepared aerogels, an optimum hydrolysis level equal to 7.35 was chosen. The aerogel prepared with this hydrolysis level has a specific surface area of 639 m2 g− 1, and its anatase phase (after the calcination of the aerogel up to 450 °C) has a specific surface area of 157 m2 g− 1.