Eco-friendly synthesis of imine-based COFs for efficient photocatalytic H2O2 production

Abstract

Covalent organic frameworks (COFs) are crystalline porous polymers with precise structural tunability, offering unique advantages in photocatalysis due to their well-ordered pore structures, tunable π-conjugated systems, and exceptional chemical stability. However, traditional solvothermal synthesis of imine-linked COFs faces major challenges, including harsh reaction conditions, high costs with low yields, toxic organic solvents, prolonged reaction times at elevated temperatures, and complex procedures, all of which significantly hinder their industrial application. To overcome these challenges, alternative COF synthesis methods have rapidly advanced, with growing interest in green and sustainable approaches. This study presents a straightforward approach to synthesize imine-linked COFs at moderate temperature and ambient pressure in gram level yields based on a green solvent system, utilizing 2,4,6-triformyl triazine (TFPT) as the key electron-accepting building block. Among various COFs synthesized with donor units such as TAPA, TAPB, and TAPT, COF-NC achieves the highest H₂O₂ yield (5535.65 μmol g⁻¹ h⁻¹). Detailed characterization confirms that such superior performance is attributed to the higher crystallinity and efficient separation of photogenerated carriers on this well-designed COF structure combined with the eco-friendly synthesis strategy, which utilizes a combination of indirect 2e⁻ ORR pathways in photocatalytic H₂O₂ production. This study not only introduces a novel green synthesis strategy for COFs but also provides valuable theoretical insights into designing efficient photocatalytic materials based on the discovered structure–performance relationship.