Nitrogen-Site Engineering in Covalent Organic Frameworks for HO Photogeneration via Dual Channels of Indirect Two-Electron O Reduction.

Photocatalytic HO production is a green and sustainable route, but far from meeting the increasing demands of industrialization due to the rapid recombination of the photogenerated charge carriers and the sluggish reaction kinetics. Effective strategies for precisely regulating the photogenerated carrier behavior and catalytic activity to construct high-performance photocatalysts are urgently needed. Herein, a nitrogen-site engineering strategy, implying elaborately tuning the species and densities of nitrogen atoms, is applied for HO photogeneration performance regulation. Different nitrogen heterocycles, such as pyridine, pyrimidine, and triazine units, are polymerized with trithiophene units, and five covalent organic frameworks (COFs) with distinct nitrogen species and densities on the skeletons are obtained. Fascinatingly, they photocatalyzed HO production via dominated two-electron O reduction processes, including O-O -HO and O-O -O -HO dual pathways. Just in the air and pure water, the multicomponent TTA-TF-COF with the maximum nitrogen densities triazine nitrogen densities exhibited the highest HO production rate of 3343 µmol g h, higher than most of other reported COFs. The theoretical calculation revealed the higher activity is due to the easy formation of O and O in different catalytic process. This study gives a new insight into designing photocatalysis at atomic level.