Two-dimensional/two-dimensional Z-scheme photocatalyst of graphitic carbon nitride/bismuth vanadate for visible-light-driven photocatalytic synthesis of imines

As an environmentally friendly strategy, photocatalytic synthesis of imines via selective oxidation of amines has inspired numerous interests. In comparison to conventional type-II heterojunction, the photogenerated electrons and holes on a Z-scheme photocatalyst has strong redox ability. Herein, we prepared a two-dimensional/two-dimensional (2D/2D) Z-scheme photocatalyst of graphitic carbon nitride nanosheet/bismuth vanadate (CNNS/BVO) with a large two-phase interface, which is favorable for the transfer and separation of photoexcited charge carriers. For selective oxidation of benzylamine to N-benzylidenebenzylamine under oxygen atmosphere and visible light irradiation, the CNNS/BVO showed much higher activity than the single CNNS and BVO. The optimized nanocomposite photocatalyst with a 50% CNNS/BVO mass ratio presented a high conversion (~96%) and selectivity (~99%) in 6 h oxidative coupling reaction of benzylamine. More importantly, this 2D/2D CNNS/BVO photocatalyst has good cycling stability, as well as universality for different benzylamine derivatives. Based on the experimental results, a Z-scheme mechanism was determined, where photoinduced electrons were accumulated on the conduction band (CB) of CNNS that is higher than that of BVO and holes were collected on the valence band (VB) of BVO that is lower than that of CNNS. Further, superoxide radicals and photogenerated holes are examined to the mainly active species for selective oxidation of benzylamine, and a possible reaction pathway was therefore proposed. This study demonstrates that the Z-scheme 2D/2D CNNS/BVO with high redox ability is an efficient photocatalyst for the imine synthesis.