Titanium dioxide sol–gel deposited over glass and its application as a photocatalyst for water decontamination

Photocatalytic degradation of water pollutants using TiO2 and solar light has been proposed as an effective alternative of treatment. Usually, TiO2 as a finely divided powder is added to polluted water forming a suspension, which is then irradiated under sunlight to conduct photochemical reactions. Although the literature frequently points out the minor efficiency of immobilized systems, it is desirable to look for a fixed catalyst to avoid wastes of time and materials during separation of the powder at the end of the treatment. This paper presents results that show the use of anatase thin films as an efficient form of deposited TiO2 for the photocatalytic degradation of 4-chlorophenol, a priority pollutant commonly used as a model in photocatalysis, and for carbaryl, a carbamic pesticide. The thin films were deposited over small cylindrical pieces of glass, using a sol–gel technique, the average thickness being 600 nm, and having a band gap of 3.28 eV. The anatase TiO2-covered glasses were used to fill a cylindrical photoreactor located at the focus of a parabolic solar collector able to concentrate up to 41 suns. Results show that the films are an effective catalyst in photodegradation, under solar irradiation, and conduct to similar values as those for TiO2 in suspension. The photoefficiency obtained is similar to that obtained using powder suspension. These results compel us to the continued pursuit of TiO2 immobilization.