Fluorene Oxidation by Coupling of Ozone, Radiation, and Semiconductors: A Mathematical Approach to the Kinetics

Abstract

The kinetics of fluorene oxidation by systems that include ozone (O3), ozonation in the presence of titanium dioxide (O3/TiO2), photolytic ozonation (O3/UV-A), titanium dioxide photocatalysis (TiO2/UV-A), and titanium dioxide photocatalytic ozonation (UV-A/O3/TiO2) has been mathematically assessed by the proposal of a mechanism based on experimental results. The conventional free-radical mechanism involved in ozone processes was the starting point to model the different systems. Single fluorene ozonation simulation suggests the existence of a hydroxyl radical source other than ozone activation through hydroxyl anions and/or the ionic form of hydrogen peroxide. Combination of O3 with TiO2 or UV-A radiation involves a negligible effect in the first case and the improvement of the fluorene removal rate in the second case. In the latter process, ozone photolysis likely entails a higher formation of hydroxyl radicals. Because fluorene does not absorb UV-A light, photocatalytic oxidation of fluorene by the system TiO2/UV-A also indicates the development of surface radical reactions. Finally, the photocatalytic ozonation of the polycyclic aromatic hydrocarbon implies a synergistic effect of the single systems.