Heptazine-based conjugated microporous polymers for enhanced light absorption and charge separation in photocatalytic hydrogen peroxide production

Abstract

The photocatalytic performance of covalent organic frameworks (COFs) is frequently constrained by inadequate light absorption and inefficient charge separation, hindering their practical application in photocatalysis. To overcome these challenges, we present a molecular design strategy centered on a heptazine core and report the solvothermal synthesis of a heptazine-based COF (Th-COF). The extended conjugation imparted by the heptazine units effectively narrows the bandgap, substantially improving visible-light absorption. Concurrently, the abundant nitrogen active sites and strengthened interlayer π−π stacking within the heptazine framework synergistically enhance the separation and transport of photogenerated charge carriers. Benefiting from these structural advantages, Th-COF exhibits remarkable activity toward visible-light-driven hydrogen peroxide (H₂O₂) production (λ ≥ 400 nm), attaining a rate of 4027 μmol g⁻¹ h⁻¹. This performance surpasses that of a conventional triazine-based COF (Tt-COF, ~893 μmol g⁻¹ h⁻¹) by more than four times. This study offers a rational molecular-engineering strategy for designing efficient COF photocatalysts and advances their potential in sustainable artificial photosynthesis and related energy-conversion technologies.