Intramolecular π-conjugated channel expansion achieved by doping cross-linked dopants into carbon nitride frameworks for propelling photocatalytic hydrogen evolution and mechanism insight

Developing modified carbon nitride (CN) with a multi-bonding mode remains a pivotal challenge for high-efficiency photocatalytic hydrogen evolution (PHE). Here, we fabricate a PYM-CN photocatalyst by doping pyrimethamine (PYM) in CN by a facile one-step polymerization method, which shows remarkably enhanced PHE performance in contrast with pure CN, because PYM as a cross-linked bridge in CN frameworks via a multi-bonding mode broadens the visible-light absorption range and expedites the transfer and separation of intramolecular photoproduced electron–hole pairs by π-conjugated channel expansion. Density functional theory (DFT) calculations reveal that this significant improvement is attributed to the orbital hybridization and delocalization effects resulting from the unique intramolecular cross-linked structure in PYM-CN. As expected, the PHE rate over the optimal PYM100-CN sample is about 11.6 times that of pure CN and the AQE value reaches up to 17.7% at 420 nm. Hence, this work provides a representative paradigm to exploit intramolecular cross-linked polymer photocatalysts with a multi-bonding mode for the high-efficiency PHE reaction or other photocatalytic application fields.