Hollow sp²-conjugated covalent organic framework encapsulating thiophene-based photosensitizer for enhanced visible-light-driven hydrogen evolution

Vinylene-linked sp(2)-conjugated covalent organic frameworks (COFs) have gained increasing attention for photocatalytic hydrogen evolution owing to their high degree of in-plane pi-conjugation and exceptional stability. However, the photocatalytic activity of vinylene-linked COFs is restricted due to the low exciton dissociation efficiency and wide band gap. Herein, a novel Z-scheme heterostructure g(2)T-T@HCOFs was fabricated through the hybridization of vinylene-linked sp(2) conjugated COFs with a hollow structure and thiophene-based photosensitizer (g(2)T-T) using a template method and post-encapsulating modification. The hollow-structured HCOFs enabled uniform encapsulation of the g(2)T-T both within their channels and on their surfaces, which facilitates the formation of a firm and stable interface between n-type HCOF and p-type g(2)T-T. Therefore, the encapsulation of g(2)T-T enables the realization of a Z-scheme pathway for efficient charge separation and transfer, leading to enhanced electron accumulation within the HCOFs during water splitting. Consequently, the obtained Z-scheme heterostructure g(2)T-T@HCOFs exhibited a remarkable 5.5-fold enhancement in their visible-light-induced hydrogen evolution activity compared to the pristine COF and long-term stability arising from their stable double carbon bonds and hollow spherical structure. This work provides a successful strategy to construct morphology-controllable sp(2)-conjugated COFs and hollow shell-core Z-scheme photocatalysts for high-performance water splitting.