Charge transfer between layers of polymeric carbon nitride driven by surface grafting phosphotungstic polyanions toward efficient photocatalytic hydrogen evolution

Abstract

It is a challenging issue to achieve efficient charge transfer between layers for the layered polymer photocatalysts, because the photogenerated carriers would prefer random migration within layers and thus have high reverse recombination rate due to their inherent anisotropy and high exciton binding energy. Herein, an innovative surface grafting strategy is developed to modify the layered polymeric carbon nitride (PCN) making use of phosphotungstic (PWO) polyanions. The surface coupling effect of PWO on PCN effectively improves reduction ability and utility rate of luminous energy through shifting the conduction band (CB) upward and broadening light absorption range to cover near infrared region up to 1000 nm, respectively. In especial, the strong electron-withdrawing effect of surface PWO moieties can reduce layer spacing to shorten electron transfer path and attract the photogenerated electrons transfer from PCN matrix to surface, thus conquering the charge transfer restriction between layers to improve the carrier separation efficiency. As a result, the photocatalytic hydrogen evolution (PHE) performance is dramatically enhanced. The optimal PWO-PCN-1% sample achieves an average PHE rate of 9.6 times that of PCN, stable operation for a total of 28 h on 7 cycles, and an AQY up to 22.3% at 400 nm. This contribution affords a viable modification avenue to overcome the limitation of charge transfer between layers for layered polymer photocatalysts.