Effect of dissolved ozone or ferric ions on photodegradation of thiacloprid in presence of different TiO2 catalysts

Combining TiO2 photocatalysis with inorganic oxidants (such as O3 and H2O2) or transition metal ions (Fe3+, Cu2+ and Ag+) often leads to a synergic effect. Electron transfer between TiO2 and the oxidant is usually involved. Accordingly, the degree of synergy could be influenced by TiO2 surface area. With this in mind, the disappearance of thiacloprid, a neonicotinoid insecticide, was studied applying various photochemical AOPs and different TiO2 photocatalysts. In photocatalytic ozonation experiments, synergic effect of three different TiO2 photocatalysts was quantified. Higher surface area resulted in a more pronounced synergic effect but an increasing amount of TiO2 did not influence the degree of the synergy. This supports the theory that the synergy is a consequence of adsorption of ozone on the TiO2 surface. No synergy was observed in photocatalytic degradation of thiacloprid in the presence of dissolved iron(III) species performed under varied experimental conditions (concentration, age of iron(III) solution, different TiO2 films, usage of TiO2 slurries). This goes against the literature for different organic compounds (i.e., monuron). It indicates different roles of iron(III) in the photodegradation of different organic molecules. Moreover, TiO2 surface area did not affect photodegradation efficiency in iron(III)-based experiments which could confirm absence of electron transfer between TiO2 photocatalyst and iron(III).