Structure-Property Relation of Mechanochemically Synthesized β-Ketoenamine-Linked COFs in Photocatalytic Hydrogen...

Covalent organic frameworks (COFs) are promising photocatalysts for solar-driven hydrogen evolution due to their tunable structures and intrinsic porosity. In this work, a series of Tp-Pa-based COFs bearing different electron-withdrawing groups was synthesized via a scalable mechanochemical route to examine the impact of framework functionalization on their structural, electronic, and photocatalytic properties. Spectroscopic analyses (solid-state ^{1 3}C CP-MAS NMR and FT-IR) confirmed the formation of β-ketoenamine linkages, while PXRD revealed higher crystallinity for pristine Tp-Pa compared to its functionalized analogues. Electrochemical studies indicated n-type semiconducting behavior, with pristine Tp-Pa exhibiting more efficient charge separation and lower charge-transfer resistance. Under visible-light irradiation, Tp-Pa showed the highest hydrogen evolution rate (25,717 µmol g^{- 1} h^{- 1}), whereas functionalized derivatives displayed reduced activity, with Tp-Pa-NO₂ being nearly inactive. Notably, Tp-Pa also demonstrated excellent performance in simulated seawater (33,331 µmol g^{- 1} h^{- 1}). These findings highlight the critical role of functionalization and synthesis strategy in governing crystallinity, charge transport, and photocatalytic efficiency, offering design guidelines for scalable COF-based hydrogen evolution systems.