Covalent organic frameworks (COFs) are promising photocatalysts for hydrogen peroxide (H2O2) synthesis. However, the nature of organic polymers makes the balance between high activity and stability challenging. We demonstrate that the linkage position matters in the design of robust COF photocatalysts with durable high activity without sacrificial reagents. COFs with ortho- and para-linkages (o-COFs and p-COFs) were constructed by 1,3,5-triformylphloroglucinol with benzene-, pyridine-, pyrazine-orthodiamines and paradiamines. The pyrzaine-containing o-COFs with two pyridinic nitrogen atoms exhibited a H2O2 production rate of 4396 μmol g-1 h-1 together with long-time continuous H2O2 photosynthesis performance in pure water (48 h), superior to the corresponding p-COFs. A four-step reaction mechanism is proposed by density function calculations. Moreover, the active sites and origin of stability enhancement for o-COFs are clarified. This work provides a simple and effective molecular design strategy in the design of robust COF photocatalysts for artificial H2O2 photosynthesis.
Keywords: covalent organic frameworks; hydrogen peroxide; linkage position; photocatalyst; stability.
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