TiO_2诱导下左旋氧氟沙星的可见光降解及其机制

TiO_2-Induced Photodegradation of Levofloxacin by Visible Light and Its Mechanism

左旋氧氟沙星是一种新型污染物.单一的左旋氧氟沙星(LFV)和Ti O2无可见光响应,但二者共存下左旋氧氟沙星能发生显著的可见光降解.为此研究Ti O2用量、溶液p H以及左旋氧氟沙星浓度对Ti O2/Vis(可见光)降解左旋氧氟沙星的影响及机制.结果表明,左旋氧氟沙星能吸附在Ti O2表面,吸附服从准二级吸附动力学和Langmuir吸附等温线.吸附左旋氧氟沙星的Ti O2漫反射UV-Vis光谱进一步表明二者形成表面复合物.左旋氧氟沙星的Ti O2/Vis降解动力学符合LangmuirHinshelwood方程.合适的Ti O2浓度和中性p H有利于光解过程的进行.自由抑制实验、N2保护下左旋氧氟沙星的Ti O2/Vis降解实验揭示·O-2是该过程中的主要活性物种.同时,无氧左旋氧氟沙星-Ti O2悬浮液光照不同时间的UV-Vis光谱证明体系中存在电子向Ti O2导带的注入.依据实验结果提出吸附在Ti O2表面的左旋氧氟沙星与Ti O2形成表面复合物,在可见光照下发生电子迁移,从而引发左旋氧氟沙星降解.本研究表明利用污染与Ti O2形成表面复合物诱导其可见光降解可用来去除水中某些有机污染物.

Levofloxacin is an emerging pollutant. Single levofloxacin and TiO2 have no visible-light activity. However, photodegradation of levofloxacin dramatically enhanced in the presence of TiO2 under visible light irradiation. Considering this finding, the photodegradation of levofloxacin over TiO2 was investigated under visible light irradiation. Effects of TiO2 dosage, levofloxacin concentration, and solution pH 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 pH, TiO2 dose, and levofloxacin concentration had significant effects on the photodegradation rates. In addition, batch adsorption experiments revealed that adsorption of levofloxacin on TiO2 conformed to the pseudo-second-order kinetics and the Langmuir isotherm. DRS spectrum of levofloxacin-adsorbed TiO2 suggested that a surface complex was formed between levofloxacin and TiO2 . 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 TiO2 and levofloxacin suspensions further confirmed that the electron injection into TiO2 conduction band took place under visible light irradiation. Based on these results, a charge-transfer mechanism initiated by photoexcitation of TiO2 /levofloxacin surface complex was proposed for levofloxacin photocatalytic degradation over TiO2 under visible light. This study indicates that the charge-transfer-complex-mediated photocatalytic technique has promising applications in the removal of colorless organic pollutants.