Structure-Property relationship in β-keto-enamine-based covalent organic frameworks for highly efficient photocatalytic hydrogen production

Covalent organic frameworks (COFs), as new promising photocatalysts, have aroused great interests, but the systematic study on the structure–property relationship of COF-photocatalysts is scarcely reported. Herein, six β-keto-enamine-based COFs with different backbones and substituents have been prepared. Through systematic experiments and DFT calculation, the structure–property relationships of the composition, structure and substituents of COFs on their spectra, specific surface area, hydrophobicity, electronic structures, carrier separation and photocatalytic hydrogen production have been studied. We explore that the backbone of COFs has important influence on their band gap, spectral absorption and carrier separation. While the substituents affect the band positions, surface area and hydrophobicity of COFs. Comprehensively, TpPa-Cl2 (constructed by 1,3,5-triformylphloroglucinol and 2,5-dichloro-1,4-phenylenediamine) exhibits the best area-normalised photocatalytic performance for hydrogen production, which is about 11.73 µmol·m−2·h−1 (0.01 g catalysts) with apparent quantum efficiency of 17% at 400 nm. This work provides a new perspective for the rational design and construction of efficient COF-photocatalysts.