title: Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension.
abstract: In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20mg L(-1) of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L(-1)) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L(-1) of TiO(2) favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO(2) photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.
authors.affiliation: Grupo de Diagnóstico y Control de la Contaminación, Facultad de Ingeniería, Universidad de Antioquia, Sede de Investigaciones Universitarias, SIU, A. A. 1226 Medellín, Colombia.
authors.forename: Ana L
authors.initials: AL
authors.lastname: Giraldo
authors.forename: Gustavo A
authors.initials: GA
authors.lastname: Peñuela
authors.forename: Ricardo A
authors.initials: RA
authors.lastname: Torres-Palma
authors.forename: Nancy J
authors.initials: NJ
authors.lastname: Pino
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Palominos
authors.forename: Héctor D
authors.initials: HD
authors.lastname: Mansilla
mesh_terms: D019840:2-Propanol / Q000737:chemistry; D000097:Acetonitriles / Q000737:chemistry; D000327:Adsorption / Q000187:drug effects / Q000528:radiation effects; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology / Q000633:toxicity; D002384:Catalysis / Q000187:drug effects / Q000528:radiation effects; D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli / Q000187:drug effects / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration / Q000187:drug effects / Q000528:radiation effects; D008027:Light; D013058:Mass Spectrometry; D008826:Microbial Sensitivity Tests; D010093:Oxolinic Acid / Q000737:chemistry* / Q000494:pharmacology / Q000633:toxicity; D010782:Photolysis / Q000187:drug effects / Q000528:radiation effects; D011193:Potassium Iodide / Q000737:chemistry; D012996:Solutions; D012997:Solvents / Q000737:chemistry; D013535:Suspensions; D013696:Temperature; D014025:Titanium / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D000900:Anti-Bacterial Agents; D012996:Solutions; D012997:Solvents; D013535:Suspensions; C009495:titanium dioxide; D011193:Potassium Iodide; D014025:Titanium; D010093:Oxolinic Acid; D019840:2-Propanol; C032159:acetonitrile