Ionic-liquid-assisted synthesis of uniform fluorinated B/C-codoped TiO2 nanocrystals and their enhanced visible-light photocatalytic activity

Exploiting advanced photocatalysts under visible light is of primary significance for the development of environmentally relevant photocatalytic decontamination processes. In this study, the ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate, was employed for the first time as both a structure-directing agent and a dopant for the synthesis of novel fluorinated B/C-codoped anatase TiO(2) nanocrystals (T(IL)) through hydrothermal hydrolysis of tetrabutyl titanate. These T(IL) nanocrystals feature uniform crystallite and pore sizes and are stable with respect to phase transitions, crystal ripening, and pore collapse upon calcination treatment. More significantly, these nanocrystals possess abundant localized states and strong visible-light absorption in a wide range of wavelengths. Because of synergic interactions between titania and codopants, the calcined T(IL) samples exhibited high visible-light photocatalytic activity in the presence of oxidizing Rhodamine B (RhB). In particular, 300 °C-calcined T(IL) was most photocatalytically active; its activity was much higher than that of TiO(1.98)N(0.02) and reference samples (T(W)) obtained under identical conditions in the absence of ionic liquid. Furthermore, the possible photocatalytic oxidation mechanism and the active species involved in the RhB degradation photocatalyzed by the T(IL) samples were primarily investigated experimentally by using different scavengers. It was found that both holes and electrons, as well as their derived active species, such as (·)OH, contributed to the RhB degradation occurring on the fluorinated B/C-codoped TiO(2) photocatalyst, in terms of both the photocatalytic reaction dynamics and the reaction pathway. The synthesis of the aforementioned novel photocatalyst and the identification of specific active species involved in the photodegradation of dyes could shed new light on the design and synthesis of semiconductor materials with enhanced photocatalytic activity towards organic pollutants.