Effects of surface fluoride modification on TiO2 for the photocatalytic oxidation of toluene

In the present study, we investigated the influence of surface fluorine (F) on TiO 2 for the photocatalytic oxidation (PCO) of toluene. TiO 2 modified with different F content was prepared and tested. It was found that with the increasing of F content, the toluene conversion rate first increased and then decreased. However, CO 2 mineralization efficiency showed the opposite trend. Based on the characterizations, we revealed that F substitutes the surface hydroxyl of TiO 2 to form the structure of Ti-F. The presence of the appropriate amount of surface Ti-F on TiO 2 greatly enhanced the separation of photogenerated carriers, which facilitated the generation of ·OH and promoted the activity for the PCO of toluene. It was further revealed that the increase of only ·OH promoted the conversion of toluene to ring-opening containing intermediates, causing the accumulation of intermediates and then conversely inhibited the ·OH generation, which led to the decrease of the CO 2 mineralization efficiency. The above results could provide guidance for the rational design of photocatalysts for toluene oxidation.