F-Serve as Surface Trapping Sites to Promote the Charge Separation and Transfer of TiO2

Abstract

Finding an effective strategy to promote the charge transfer and separation of TiO2 is urgently needed. Herein, a surface fluorination (F-)-modified TiO2 (denoted as TO-xF, where x represents the volume of HF added in the solution) catalyst has been prepared by a mild and facile post-treatment method. The changes induced by surface F- on the morphological, structural, and surface electronic features and the charge separation and transfer efficiency of TiO2 were specifically examined. Compared with pristine TO, TO-0.4F exhibits enhanced photocatalytic degradation of methyl orange and phenol, production of hydroxyl radicals, and photocurrent response. The enhanced photocatalytic activities of TO-0.4F can be attributed to the role of surface F- as surface trapping sites in effectively boosting the charge transfer and separation processes, which is verified by the steady-state and time-resolved fluorescence spectroscopy, electrochemical impedance spectroscopy, Bode plot, transient photocurrent response, and open-circuit voltage measurements. This study emphasizes the role of surface F- in promoting the charge transfer and separation and improving the photocatalytic activity of TiO2.