PHOTOCATALYTIC ACTIVITY AND SELECTIVITY OF TITANIA COLLOIDS AND PARTICLES PREPARED BY THE SOL-GEL TECHNIQUE - PHOTOOXIDATION OF PHENOL AND ATRAZINE

The photocatalyzed degradation of phenol and atrazine has been reexami ned under AM1 simulated solar light irradiation of TiO2 catalysts in a queous acid media to explore the photocatalytic activity and selectivi ty of titania colloids and titania specimens prepared by the sol-gel m ethod yielding particles from nanometer size powders to millimeter sph erical beads. In the photooxidation of phenol, the different TiO2 mate rials show small but significant variations in activity; there is no e vidence for variations in selectivity with phenol because of the rathe r similar nature of the intermediates formed (hydroquinone, catechol, benzoquinone) and the rather analogous interaction(s) of these with th e active oxidizing species (.OH radicals). By contrast, when atrazine is the test probe, there is a dramatic and significant variation in ac tivity and selectivity in the differently prepared titania samples, as witnessed by the variations in the temporal distribution of intermedi ate species and product formed. This is a consequence of the three dif ferent degradation pathways and the modes of interaction between the p robe and the catalyst: (i) dehalogenation, (ii) dealkylation, and (iii ) deamination, affording a relevant different sensitivity to the oxidi zing active oxygen species. Particular attention is focused on the act ivity of millimeter sized TiO2 beads in the light of their potential u sefulness in photochemical reactors.