Donor-Acceptor structural polymeric carbon nitride with in-plane electric field accelerating charge separation for efficient photocatalytic hydrogen evolution

Abstract

The realization of efficient photocatalytic hydrogen evolution based on polymeric carbon nitride (PCN) is severely hampered by the insufficient separation of photogenerated electrons and holes. Herein, we successfully introduced Benzo[b]thiophene-2-carboxylic acid (BTH) as donor parts through supramolecular self-assembly into the framework of PCN to form D-A structure to promote the photoexciton separation efficiency. The SCN-BTH structure shows the improved separation efficiency of charge carriers and shorter diffusion path resulting in hydrogen evolution rate up to 3950 μmol/g/h, which is 13.3 times higher than that of bulk carbon nitride (BCN) under visible light irradiation (λ > 420 nm). Further density functional theory (DFT) calculation reveals that SCN-BTH structure exhibits strong spatial separation of lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) compared to that of BCN with the even distribution. In addition, electrostatic potential diagram indicates the in-plane polarized electric field in SCN-BTH embedded with the D-A structure can drive the photo-generated electrons and holes toward reverse direction, thereby accelerating the separation of carriers. All those factors synergistically facilitated the charge separation and transport process which are responsible for the improved photocatalytic performance.