Determination of main species involved in the first steps of TiO2 photocatalytic degradation of organics with the use of scavengers: The case of ofloxacin

With the aid of different scavengers species involved in the first steps of TiO2/UVA (black light) photocatalytic elimination of ofloxacin (OFX) in water have been investigated. The effect of the presence of scavengers of hydroxyl radicals in bulk water (t-butanol), oxidant holes (h(+)) (2-propanol, iodide and oxalate), singlet oxygen (azide), electrons (oxygen) and superoxide ion radical (p-benzoquinone and tiron) has been checked at pH 7 with 0.03 M HClO4/ClO4- aerated media. The main elimination pathway leads to the formation of OFX center dot+ and takes place through an electronic transfer between the antibiotic and the catalyst surface. OFX center dot+ further reacts with O-2(center dot-) leading to the reductive demethylation of OFX and generates 1 mole of hydrogen peroxide and similar to 1 mole of formaldehyde per mole of OFX eliminated. The presence of phosphate promotes a change in the pathway degradation, possibly favoring the generation of HO radicals as well as the participation of this species on the oxidative demethylation of OFX and therefore reduces the production of H2O2. Therefore, OFX can be photocatalytically reduced and/or oxidized depending on the experimental conditions. (C) 2014 Elsevier B.V. All rights reserved.