Enhanced and suppressed effects of ionic liquid on the photocatalytic activity of TiO2

The effects of a room temperature ionic liquid, 1-butyl-3-methylimidazolium terafluoroborate ([Bmim]BF4), on the photocatalytic performance of Degussa P25 TiO2 were investigated. Also, the photocatalysis mechanism was systematically analyzed by conducting different reactive radical trapping experiments. The results showed that photogenerated electrons were the main reactive species involved in the photocatalytic degradation of methyl orange (MO), while aEuro cent OH radicals and photogenerated holes played an important role in the photocatalytic decomposition of rhodamine B (RhB). The addition of ionic liquid (IL) could slightly enhance the photocatalytic degradation rate of MO because adsorption of [Bmim](+) ions on the TiO2 surface not only enhanced traping and transfer of photogenerated electrons, but also facilitated adsorption of negatively charged MO. On the contrary, IL suppressed the degradation rate of RhB because [Bmim](+) on the TiO2 surface not only hindered the access of positively charged RhB to TiO2, but also restricted the diffusion of positively charged holes to the TiO2/solution interface.