Boosting the visible-light-induced toluene oxidation via synergistic effect between nanoparticulate Pd/BiVO4 photocatalyst and a cyclic nitroxyl redox mediator

Selective organic conversion using semiconductor photocatalysts has been focused on the viewpoint of sustainable synthesis processes. Especially, C-H activation is one of the most attractive reactions. We recently reported photo-oxidation of toluene to benzaldehyde over visible-light responsible Pd-loaded BiVO4 (Pd/BiVO4) photocatalyst. However, it remains challenging due to its low efficiency. Herein, we introduce a novel strategy to apply a cyclic nitroxide compound as an efficient redox mediator along with Pd/BiVO4 for toluene oxidation. Including N-hydroxyphthalimide (NHPI) could significantly expedite the activity of benzaldehyde production up to ca. 28 times compared to without NHPI under blue-to-green light irradiation. The sustainable conditions realized a conversion in high efficiency (apparent quantum yield = 10.8 and 5.4 %@420 and 520 nm, respectively) and with excellent selectivity (>99 %). The excellent efficiency was realized by the synergistic effect between the presence of NHPI and the use of nanoparticulate Pd/BiVO4 with a relatively large surface area.