Microwave-Assisted Facile Synthesis and Microenvironment Engineering of Enaminone COFs for Efficient Photocatalytic H2O2 Production

Abstract

Covalent organic frameworks (COFs) have emerged as promising metal-free photocatalysts; however, their widespread application is often hindered by the time-consuming solvothermal preparation. Developing rapid and cost-effective routes to highly crystalline COFs is therefore essential for expanding their practical utility. In this regard, microwave-assisted synthesis offers a distinct advantage over conventional solvothermal methods by shortening reaction times from days to minutes while simultaneously improving crystallinity. Here, we report a microwave-assisted strategy for synthesizing enaminone-COFs via the Michael addition-elimination reaction, achieving >90% yields within 60 min. The developed microwave-assisted strategy demonstrated broad versatility by enabling the synthesis of six distinct enaminone COFs. Notably, the microwave-synthesized COFs exhibited physical properties similar to previously reported frameworks. Among the synthesized enaminone COFs, COF-Tz-MW and COF-Bz-MW were rationally engineered with tunable nitrogen content, creating distinct local microenvironments that modulate the acceptor–donor–acceptor (A–D–A) charge-transfer pathway for efficient photocatalytic H₂O₂ synthesis. This molecular-level variation was systematically investigated to elucidate its influence on charge distribution and photophysical properties, revealing a clear structure–reactivity correlation of enaminone-COFs in H₂O₂ photosynthesis. Notably, the COF-Bz-MW demonstrated effective charge separation and superior H₂O₂ production performance with a production rate of 8.70 mmol g^–1 h^–1 from blue LED-H₂O–O₂. Theoretical studies revealed that the enaminone moiety coupled with the benzene core amine creates an optimized A–D–A configuration, enhancing O₂-adsorption and promoting efficient photocatalytic H₂O₂ production. Our work pioneers a paradigm for facile and rapid synthesis of enaminone COFs, while demonstrating N-site microenvironment engineering as an effective strategy to advance COF-based photocatalysts for efficient photocatalytic H₂O₂ production.