The photocatalytic activites of several TiO2 materials have been compared studying the degradation of an aliphatic and an aromatic model compound under optimized experimental conditions (e.g., c(TiO2), pH of the solution). For dichloroacetic acid (DCA) a new anatase catalyst, i.e., Hombikat UV100, yielded significantly higher photonic efficiencies (ζ=15%) than almost all the other materials, especially in comparison to rutiles. For 4-chlorophenol (4-CP) the discrepancies were relatively small and the degradation was generally slower (ζ<1%); in this case the formation of intermediates has to be considered, too. While for DCA the addition of CuNO3 (1–10mM) or a platinization of the catalyst lead to a significant raise in ζ, this had almost no effect on the degradation of 4-CP. For this model compound ζ could be accelerated strongly by the addition of bromate (3mM KBrO3); the photocatalytic nature of the process could be demonstrated. The addition of other oxidants had no beneficial effect, in some cases an inhibition was observed. The stability and long time activity of standard and platinized TiO2 materials could be demonstrated.