Visible-Light-Mediated TiO₂ Photocatalysis of Fluoroquinolone Antibacterial Agents

Abstract

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 (UV; lambda > 324 nm) or visible light (lambda > 400, > 420, or > 450 nm). Visible-light-mediated fluoroquinolone degradation is unexpected from direct photolysis or established TiO2 band gap photoexcitation mechanisms, which both require 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 band gap excitation. The process slows considerably when fluoroquinolone adsorption is inhibited. Whereas fluoroquinolone decomposition in UV-irradiated TiO2 suspensions is accompanied by mineralization, no changes in dissolved organic carbon occur during visible-light-photocatalyzed degradation. Results are consistent with a proposed charge-transfer mechanism initiated by photoexcitation 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 photoexcitation by visible light. Fluoroquinolone oxidation then occurs by electron transfer into the TiO2 conduction band, which delivers the electron to an adsorbed electron acceptor. The lack of organic carbon mineralization indicates formation of stable organic byproducts that are resistant to further degradation by visible light. In UV-irradiated TiO2 suspensions, the charge-transfer mechanism acts in parallel with the semiconductor band gap photoexcitation mechanism.

Enhanced nitrate reduction and current generation by Bacillus sp. in the presence of iron oxides

“…To avoid the interference of other inorganic anions in detection, the anaerobic NaHCO 3 -buffered (30 mM, pH 6. . The concentration of NH 4 + was measured by spectrophotometry at 420 nm after a color reaction with Nessler's reagent (Paul et al 2007). Before Nessler's reagent was added, an aliquot of the sample to be analyzed was diluted with ultrapure water.…”

Photocatalytic abatement of o-xylene using adsorption enhanced ZnO/GAC catalyst in a continuous flow reactor: Catalytic potential, Fate of o-xylene and its by-products

“…As indicated in Table 4, moreover the o-xylene as the parent compound and CS2 as the solvent, the major byproducts desorbed from GAC were methanoic acid, phenylmethanal, o-nitrop-cresol and methyl-di-phenyl-methane; whereas the main byproducts desorbed from ZnO/GAC were methanoic acid, o-xylene and methyl-di-phenyl-methane. These compounds have probably originated from inadequate reactions of active species and o-xylene in the photocatalytic process (Paul et al, 2007). These compounds have gradually filled the active sites and cause the catalyst to be deactivated (Rezaei and Soltan, 2012).…”

Occurrence and Degradation of Quinolones by Advanced Oxidation Processes

“…60 Fluoroquinolonas são resistentes a alterações de temperatura ou hidrólise, porém são sensíveis à radiação ultravioleta. 61 A fotólise depende da absorção da radiação pelo composto alvo, da sua estrutura, da sua concentração e da matriz em que o mesmo se encontra. Em amostras de rios, lagos e efluentes ETE, onde a elevada turbidez e cor dificultam a penetração da luz na solução, a fotodecomposição de poluentes orgânicos dissolvidos pode não ocorrer ou sofrer perda da eficácia.…”