An all-organic S-scheme heterojunction containing donor-acceptor type conjugated polymer and C3N4 nanosheets assembled via π-π interaction for photocatalytic H2 generation

Designing an excellent photocatalyst with high space separation efficiency of photogenerated carriers to boost the rate of photocatalytic hydrogen (H-2) generation remains a challenge. In this work, the S-scheme hetero-junction containing a donor-acceptor (D-A) type conjugated polymer of PyDTDO-3 and a two-dimensional (2D) -layered conjugated polymer of C3N4 nanosheets with conjugated heptazine units (denoted as PCNNS) was pre-pared for photocatalytic H-2 production. It is found that the recombination rate of photogenerated electron-hole pairs is decreased by the S-scheme heterojunction structure through establishing an intimate pi-pi conjugated heterointerface between PyDTDO-3 and C3N4 NS. To clarify the potential photocatalytic mechanism, diversified characterization techniques were employed and the density functional theory (DFT) calculations were con-ducted. As a result of the difference in the work function, a Fermi level gap is formed between PyDTDO-3 and C3N4, which eventually leads to the band edge bent upward/downward and the presence of the built-in electric field causing the spontaneous interfacial charge transfer from C3N4 NS to PyDTDO-3 at the pi-pi conjugated interface. Owing to its unique structure and optical properties, the optimal P2CNNS heterojunction photocatalyst shows excellent photocatalytic H-2 generation performance, which reaches a maximum of 50.2 mmol g(-1) h(-1) under visible illumination.