ENVR 89 |
| This study reports on the photocatalytic transformation of fluoroquinolone antibacterial agents (ciprofloxacin, enrofloxacin, norfloxacin and flumequine) in aqueous titanium dioxide (TiO2) suspensions irradiated with ultraviolet (λ>324 nm) or visible light (λ>400, >420 or >450 nm). Visible light-mediated fluoroquinolone degradation is unexpected from direct photolysis or established TiO2 bandgap photo-excitation mechanisms, which both require ultraviolet (UV) light. Visible light-mediated photocatalysis requires an appropriate conduction band electron acceptor (e.g., O2, BrO3-), but is not dependent upon hydroxyl radical, superoxide or other reactive oxygen species generated upon TiO2 bandgap excitation. The process slows considerably when fluoroquinolone adsorption is inhibited. Fluoroquinolone decomposition in UV-irradiated TiO2 suspensions is accompanied by mineralization, whereas no changes in dissolved organic carbon occur during visible light photocatalyzed degradation. Results are consistent with a mechanism initiated by photo-excitation of surface-complexed fluoroquinolone molecules. Complexation to the TiO2 surface causes a red shift in the fluoroquinolone absorption spectrum (via ligand-to-metal charge transfer), enabling photo-excitation at longer wavelengths. Fluoroquinolone oxidation then occurs by electron transfer into the TiO2 conduction band, which can deliver the electron to an adsorbed electron acceptor. The lack of organic carbon mineralization indicates that stable organic by-products are formed that are resistant to further degradation by visible light. |
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The C. Ellen Gonter Environmental Chemistry Awards
1:30 PM-4:35 PM, Tuesday, August 21, 2007 Boston Park Plaza -- Beacon Hill Rm, Oral
Division of Environmental Chemistry |