Alternatively, it might react with adsorbed water:
Furthermore, the increase in the scavenging rate of photoproduced electrons resulting from the presence of ozone should decrease the recombination rate of electrons and holes, and thereby augment the formation rate of hydroxyl radicals from basic OH surface groups and adsorbed water molecules.
Irrespective of the mechanism, very oxidizing species, viz. O2 and 
would thus be generated. However, similar to H2O2, O3 can act as a scavenger of hydroxyl radicals: Therefore, there is a limit to the favorable effect
As ozone is employed in various industrial processes, such as paper bleaching, TiO2 photocatalysis could be of interest in exploiting the presence of ozone to mineralize pollutants at higher rates while removing excess ozone.
When O3 is not used, the cost of its generation can be prohibitive; the interest of adding O3 will then obviously be subordinate to the particular case and the regulations.
Interferences in Photocatalytic Activity.
Effects of Inorganic Anions on Photocatalytic Water Treatment.
- Inorganic anions can significantly affect photocatalytic treatment only if they are located at the photocatalyst surface or in the Helmholtz layer.
- This location depends both on the chemical affinity of the ions for titania and on the point of zero charge (PZC) of this solid.
- At pH greater than the TiO2 PZC (between 6 and 6.5), the surface is negatively charged and anions are repelled. At pH values below the TiO2 PZC, the excess anion concentration at the surface over that in the bulk of the solution can reach very substantial values because it is proportional to the square of the surface charge density.
- Because these anions penetrate into the TiO2 inner coordination sphere. Adsorption measurements showed the following order for the amounts adsorbed on TiO2 at a pH less than the PZC:
The effect of some anions can be explained by their reaction with the photoproduced holes to give radicals (e.g., HCO3.) capable of oxidizing the pollutant, but at rates lower than those resulting either from the reaction of the pollutant with OH. radicals or from the direct interaction of the pollutant with photogenerated holes.