Interaction of the fluoroquinolone antibiotic, ofloxacin, with titanium oxide nanoparticles in water: Adsorption and breakdown

The mobility and fate of fluoroquinolone antibiotics in natural waters, soil–water systems and wastewater are controlled in part by surface interactions with nanometer (10− 9 m) metal oxide particles. Experiments were performed by mixing solutions of ofloxacin (OFL), a common, fluoroquinolone-class human and veterinary antibiotic, with 25 nm-TiO2 (anatase) nanoparticles at different pH conditions. Both sorption and degradation of OFL were observed in the drug-nanoparticle solutions with initial OFL concentrations of ~ 3 to 690 μM. Though overall isotherm behavior is logarithmic, OFL removal from the solution can be approximated by linear removal coefficients (Kr). At pH 4, Kr = 42 ± 8 L kg− 1, at pH 6 Kr = 1288 ± 217 L kg− 1, and at pH 9 Kr = 26 ± 7 L kg− 1. Rinsing of substrates at pH 4 resulted in desorption of approximately 11% of the original OFL removed from the solution by TiO2 nanoparticles. Less than 1% of the removed OFL at pH 6 was recovered by rinsing the substrate; and, at pH 9 about 39% of the OFL removed by nanoparticles during the initial mixing experiment was desorbed during rinsing.Mass spectral analysis of OFL solutions after the removal of the solid nanoparticles yielded ions that indicate the presence of de-methylated and de-carboxylated fluoroquinolone species, resulting from the degradation of OFL at the TiO2 surface.

► Experiments were done mixing ofloxacin and 25 nm-TiO2 at different pH conditions.
► Sorption and degradation of ofloxacin were observed in drug-TiO2 solutions.
► Ofloxacin degraded to de-methylated and de-carboxylated fluoroquinolone species.
► Most adsorption and degradation occurred at a pH where ofloxacin was zwitterionic.