Degradation of antibiotic norfloxacin in aqueous solution by visible-light-mediated C-TiO2 photocatalysis

A visible-light-mediated C-TiO2 photocatalytic process (Vis/C-TiO2) was employed to degrade antibiotic norfloxacin. The influences of catalyst dosage, initial probe compound concentration and solution pH levels on the decay performance and reaction kinetics were investigated and optimized. Based on the experimental results, an equation was established to predict the observed rate constant under neutral pH. In addition, the decay rate was accelerated under weak alkali in the presence of moderate OH- anions. Hydroxyl radical was confirmed to play a major role in the Vis/TiO2 process, where in the presence of (OH)-O-center dot quencher and electron acceptor, retardation and improvement were found respectively. Furthermore, an original schematic diagram describing the surface property of C-TiO2 was built and further verified, in which, NH4+ cations normally served as hole scavengers showed a negligible effect because the adsorbed OH- formed a barrier for NH4+ ions to approach the holes, and the F- anions presented a significant suppression on norfloxacin decay due to the formation of hydrogen bond (O-H center dot center dot center dot F) around the C-TiO2 surface. Besides, the recycling and sedimentation tests justified that the Vis/C-TiO2 process is a cost-effective and feasible way for wastewater treatment. (C) 2012 Elsevier B.V. All rights reserved.