Competitive adsorption of ofloxacin enantiomers to goethite : experiments and modelling

Qin, Xiaopeng; Zhong, Xiaofei; Du, Ping; Chen, Juan; Jia, Junfeng; He, Ying; Liu, Fei; Weng, Liping


The adsorption of ofloxacin enantiomers, namely levofloxacin (LEV) and ofloxacin (OFL), to goethite was investigated using batch experiments. Structural information of aqueous and adsorbed LEV or OFL was obtained with ultraviolet-visible (UV-Vis), three-dimensional excitation-emission matrix (EEM) and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopic methods. The results indicated that LEV molecules formed a bridging bidentate complex (≡(FeO)2-LEV) with the surface of goethite, and OFL formed a monodentate complex (≡FeO-OFL). The adsorption of OFL to goethite was stronger than that of LEV, owing to differences in their physicochemical properties and bonding modes. The adsorption of LEV and OFL to goethite in single systems was well simulated using the charge distribution multi-site complexation (CD-MUSIC) model, but their adsorption in the LEV-OFL-goethite systems was overestimated at pH ∼5.2 and high concentrations of LEV-OFL mixture (19.59 μM), in which the predicted amounts of adsorbed LEV and OFL were higher (20.0, 30.8 %) than the experimental results. Compared with the unprotonated LEV or OFL, the protonated (>99.9 %) ones were mainly adsorbed to the surface of goethite, and the single species may be used during their following modelling.