Parameters affecting the homogeneous and heterogeneous degradation of quinoline solutions in light-activated processes

The light-activated degradation kinetics of quinoline were studied in detail on Hg lamp and Suntest solar-simulated irradiation. Fenton-photoassisted mineralization in homogeneous solution with a peroxide to quinoline ratio of approximately 50 (quinoline, approximately 1 mM) was complete in about 30 min on Hg lamp irradiation. Reactions activated by a solar simulator led to 80% mineralization of the same quinoline solutions within the same time period due to a lack of a strong UV component. Heterogeneous photocatalytic TiO2-mediated degradation proceeded at a slower rate than the homogeneous reaction. The influence of a number of factors, such as the substrate concentration, solution pH, gas atmosphere and dynamics of H2O2 addition, was investigated. The stoichiometry of the mineralization reaction was analysed as a function of the gas atmosphere used. Quinoline degradation was possible via dark and light-activated reactions. Quinoline did not affect the H2O2 consumption rate in the presence of Fe3+ ions. This suggests that, during degradation, the reaction of Fe3+ ions with H2O2 is the rate-determining step. Quinoline did not complex with Fe3+ ions in the dark. However, complex formation occurred during photodegradation with Fenton-like reagents, such as Cr6+ or CU2+ ions and combinations of Cu2+ + Fe3+ ions, in the presence of H2O2. The latter systems were compared with the classical Fenton reagent leading to quinoline mineralization. (C) 1997 Elsevier Science S.A.