Photocatalytic enhanced oxidation of fluorene in water with ozone.: Comparison with other chemical oxidation methods

Fluorene, a polynuclear aromatic hydrocarbon, has been chosen as a model compound to study the synergism between ozonation and photocatalytic oxidation in water. Thus, for this purpose, different oxidation methods have been tested: single ozonation (O-3), single adsorption (TiO2), ozone photolysis (UVA/O-3) TiO2 photocatalysis (TiO2/UVA/O-3), TiO2 catalytic ozonation (TiO2/O-3), and TiO2 photocatalytic ozonation (TiO2/UVA/O-3). These processes have been carried out at two pH levels (2 and 5). In the ozone-involving cases, a positive effect of pH was observed. At a fixed pH, the reactivity order for fluorene oxidation was TiO2/UVA/O-3 > UVA/O-3 > O-3 ≈ TiO2/O-3 ≈ TiO2/UVA > TiO2. Since, after a few seconds from the start of oxidation, ozone accumulated in water, reactions of ozone developed in the slow kinetic regime, especially at pH 2. Maleic, formic, and oxalic acids were identified as intermediates or end products of oxidation. The stability and activity of the TiO2 catalyst was also studied for the TiO2/UVA/O-3 process.