Benzothiadiazole and its derivative-based sp2 carbon-conjugated covalent organic frameworks for photocatalytic hydrogen generation

Designing crystalline porous materials with efficient hydrogen evolution is a promising strategy to obtain green energy. Covalent organic frameworks have been regarded as outstanding photocatalysts for solar-to-hydrogen conversion. In particular, sp2 carbon-conjugated covalent organic frameworks (sp2c-COFs), via carbon–carbon double bond linkage, have good chemical and physical stability, which has attracted great attention in recent years. Herein, we design and synthesize two series of benzothiadiazole and its derivative-based isoreticular sp2c-COFs (HIAM-0001 to HIAM-0006) for photocatalytic hydrogen generation. The experimental results show that benzothiadiazole-based COFs exhibit much higher photocatalytic activity compared with its derivative-based ones possessing much broader light-harvesting ranges. The average hydrogen evolution rates of HIAM-0001 and HIAM-0004 are up to 1410 μmol g−1 h−1 and 1526 μmol g−1 h−1 under visible-light illumination (λ > 420 nm), respectively. This work presents the relevant background for the study of the structure–property relationship in benzothiadiazole and its derivative-based sp2c-COFs, and also provides a new guidance for the rational design and development of efficient photocatalysts for hydrogen generation.