S-doped C₃N₅ derived from thiadiazole for efficient photocatalytic hydrogen evolution

Graphitic carbon nitrides (g-C₃N₄) with unique physicochemical properties are promising candidates for photocatalysis applications. However, pristine g-C₃N₄ often suffers from narrow absorption ranges and high carrier recombination rates, which result in mediocre catalytic performance. In this work, we prepare novel sulfur-doped high nitrogen containing carbon nitrides, C₃N₅ (SCNs), with a combined thiadiazole, triazole, and triazine framework by facile self-assembly of 5-amino-1,3,4-thiadiazole-2-thiol (5-ATDT). Their structural, morphological, and optical properties, and photocatalytic activities are investigated in detail. From density functional theory calculations and spectroscopic characterization studies, we construct thermodynamically stable molecular structures of SCNs composed of one triazole and two triazine moieties with small ratios of thiadiazole on the edge, in which the sulfur atoms are ionically connected with carbon/nitrogen atoms and gradually detached on increasing the calcination temperatures. Remarkably, the resultant SCNs exhibit a significantly enhanced H₂-generation rate of 486 μmol g⁻¹ h⁻¹, about 60% higher than the average value derived from typical g-C₃N₄ synthesised by conventional precursors thanks to the enlarged light absorption range and enhanced charge carrier transfer rate. Our work provides a unique approach for designing novel sulfur-doped carbon nitrides with unprecedented functionalities.