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 (H2) generation remains a challenge. In this work, the S-scheme heterojunction 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 prepared for photocatalytic H2 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 π–π 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 conducted. 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 π–π conjugated interface. Owing to its unique structure and optical properties, the optimal P2CNNS heterojunction photocatalyst shows excellent photocatalytic H2 generation performance, which reaches a maximum of 50.2 mmol g−1 h−1 under visible illumination.