Oxidation of oxalate ion in aqueous suspensions of TiO2 by photocatalysis and ozonation

Oxalate anion has been oxidized in aqueous alkaline solution by using ozonation and photocatalysis in the presence of TiO2. A batch annular reactor has been used for carrying out reactivity runs in the presence of air/ozone, air/ozone/near UV irradiation, air/ozone/TiO2, air/near UV-irradiated TiO2 and air/ozone/near UV-irradiated TiO2. The Langmuir–Hinshelwood kinetic model adequately describes the photocatalytic results obtained at different reaction conditions and allows determining the values of the kinetic and equilibrium adsorption constants. The contemporary presence of photocatalysis and ozonation shows a significant improvement of the process performance as the oxidation rate of oxalate anion is greatly enhanced compared with the photocatalysis or ozonation processes alone. A likely explanation of this result may be that the presence of ozone on UV-irradiated surface of TiO2 enhances both the photogeneration of hydroxyl radicals and the photoadsorption of oxalate anions, due to its higher electrophilic nature with respect to O2.