Heterojunction and crystallinity-mediated charge separation in β-ketoenamine covalent organic frameworks for
Heng Yang1,2, Le Wang3, Yang Xia4
1Hubei Province Key Laboratory of Agricultural Waste Resource Utilization, School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Wuhan 430023, P. R. China.
Abstract:
Covalent organic frameworks (COFs), as an emerging class of metal-free organic semiconductor photocatalysts, have garnered extensive attention for their potential in photocatalytic H2 evolution. However, the weaknesses associated with low crystallinity and rapid charge recombination in single-component COFs have resulted in their low photocatalytic efficiency. To address these issues, we have developed a strategy for preparing a highly crystalline β-ketoamine-linked TpBD-COF (denoted as TpBD-COF(h)) by adjusting the reaction solvent and incorporating MoS2 nanosheets to improve surface- and bulk-carrier separation. As a result, as-prepared x-MoS2/TpBD-COF(h) composites exhibited superior visible-light-driven H2 evolution performance. In particular, the optimized 8-MoS2/TpBD-COF(h) photocatalyst achieves a maximum H2 evolution rate of 2970.0 μmol g-1 h-1, representing an enhancement of 18.3-fold, 1.5-fold, and 4.8-fold compared to TpBD-COF(h), 8-MoS2/TpBD-COF(l) (where TpBD-COF(l) denotes TpBD-COF with lower crystallinity), and Pt/TpBD-COF(h), respectively. Based on in-depth experimental characterization and theoretical studies, the significant enhancement in H2 production activity can be attributed to the improved crystallinity of the TpBD-COF, which boosts the kinetic energy of photoelectrons and increases the carrier mobility within the TpBD-COF. Moreover, the integration of MoS2 not only improves the light-harvesting ability but also dramatically stimulates the charge separation and migration efficiency in the TpBD-COF(h). This work paves the way for the further design and synthesis of efficient noble-metal-free COF-based catalysts for photocatalytic energy conversion.
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