Boosting photocatalysis of hydrazone-linked covalent organic frameworks through introducing electron-rich conjugated aldehyde

Hydrazone-linked COFs have shown promising potential in photocatalysis, but still face problems of limited visible-light absorption and inefficient photocarrier separation/transportation. Herein, electron-rich and conjugated benzotrithiophene (BTT) is introduced into the aldehyde monomer to get two novel BTT-based hydrazonelinked COFs (BTT-Hz-1, -2). Systematical experiments and theoretical calculations show that comparing with the benzene aldehyde-based COFs (TFB-Hz-1, -2), conjugated structure of BTT broadens the visible-light absorption range and improves the transfer efficiency of the photocarriers; electron-rich structure of BTT constructs strong built-in electric field within the COFs, therefore promotes the separation of photocarriers. As a result, BTTHz-1 shows a recorded photocatalytic H2 evolution rate for hydrazone-linked COFs of 17.27 mmol g-1h-1, 22 times than that of TFB-Hz-1, and also reveals noble metal-free CO2 photoreduction property with CO evolution rate of 774.3 & mu;mol g-1h-1. This work presents the importance of electronic structure modulation to the COFbased photocatalysis, and opens a new avenue to improve the photocatalysis performance of hydrazone-linked COFs.