The study of photocatalytic activities of titania and titania-silica aerogels

Titania and titania-silica aerogels have been prepared by sol-gel method. The pH of their point of zero charge (pH(PZC)), S-BET, volumes of the micro- and mesopores were determined. Considering titania-silica aerogels FTIR analyses were carried out. Three phenol para-derivatives (p-chlorophenol, p-nitrophenol, 4-hydroxybenzoic acid) were chosen as model compounds in photodegradation processes. All aerogels indicated photocatalytic activity. However, titania aerogels were more efficient photocatalysts comparing to titania-silica aerogels. The results can be explained by the percentage content of two phases (5, 10 and 20 wt.% SiO2 in TiO2). The ratio of SiO2:TiO2 results in the presence of two separated phases that hinders photocatalytic processes. The identified by-products of p-chlorophenol and p-nitrophenol degradation are hydroquinone, benzoquinone as well as chloride ions and nitrate ions, respectively. The pH(PZC) of all catalysts changed between 6.2 and 6.7. Between the pH(PZC) and photoactivity there was no direct correlation. The course of the photodegradation did not depend on surface area and pores volumes of the catalysts but on the kind of pollutant. (C) 2003 Elsevier B.V. All rights reserved.