Covalent Organic Framework Photocatalysts: Decoding Linkage Chemistry in Hydrogen Peroxide Synthesis From Air and Water.

Covalent organic frameworks (COFs) provide a polymer platform for exploring covalent linkages to design ordered skeletal and porous architectures. However, the role of linkages in controlling structural and functional evolutions remains to be well explored. In this study, we reported hexaphenyltriphenylene COF photocatalysts constructed with ketazine or azine linkages that differ by a single pinpoint methyl substituent, enabling a controlled interrogation of linkage chemistry. Unexpectedly, the ketazine linkage enhances water uptake, accelerates transport, and directs water confinement within trigonal pores. Simultaneously, it modulates the π-electronic structure through hyperconjugation and inductive/resonance effects, extends light absorption, lowers exciton binding energy, prolongs charge-separated lifetimes, and promotes balanced charge transport. These synergistic structural and electronic evolutions translate into exceptional photocatalysis for hydrogen peroxide production from air and water under ambient conditions. Ketazine-HPTP-COF achieves a production rate of 8.17 mmol g-1 h-1 with an apparent quantum yield of 15.1% at 420 nm, outperforming azine-linked, amorphous, and other photocatalysts. The system operates under sunlight, enabling scalable production, and maintains activity across tap water, rainwater, and seawater. Mechanistic studies reveal dense yet spatially resolved photocatalytic sites, where linkage sites mediate oxygen reduction and knot units drive water oxidation, promoting photosynthesis through efficient charge and mass transport.