[TiO2-Induced Photodegradation of Levofloxacin by Visible Light and Its Mechanism].

Levofloxacin is an emerging pollutant. Single levofloxacin and Ti O2 have no visible-light activity. However,photodegradation of levofloxacin dramatically enhanced in the presence of Ti O2 under visible light irradiation. Considering this finding,the photodegradation of levofloxacin over Ti O2 was investigated under visible light irradiation. Effects of Ti O2 dosage,levofloxacin concentration,and solution p H on levofloxacin photodegradation were examined by monitoring its concentration decay with time. The results showed that levofloxacin photodegradation fitted the Langmuir-Hinshelwood kinetic model. Solution p H,Ti O2 dose,and levofloxacin concentration had significant effects on the photodegradation rates. In addition,batch adsorption experiments revealed that adsorption of levofloxacin on Ti O2 conformed to the pseudo-second-order kinetics and the Langmuir isotherm. DRS spectrum of levofloxacin-adsorbed Ti O2 suggested that a surface complex was formed between levofloxacin and Ti O2. Addition of radical scavengers and N2-degassing affecting levofloxacin photodegradation indicated that the superoxide ion radical was mainly active species. UV-Vis spectra of a deaerated Ti O2 and levofloxacin suspensions further confirmed that the electron injection into Ti O2 conduction band took place under visible light irradiation. Based on these results,a charge-transfer mechanism initiated by photoexcitation of Ti O2/levofloxacin surface complex was proposed for levofloxacin photocatalytic degradation over Ti O2 under visible light. This study indicates that the charge-transfer-complex-mediated photocatalytic technique has promising applications in the removal of colorless organic pollutants.