Functionalization of Covalent Organic Frameworks with Thiazole Rings and Hydroxyl Groups for Improved Photocatalytic Water Splitting Performance

Photocatalytic water splitting for hydrogen production holds considerable potential for simultaneously addressing fuel production and carbon neutrality, although increasing photocatalyst activity and enhancing exciton dissociation continue to be very difficult tasks. Covalent organic frameworks (COFs) with predesignable structures and customizable functionalities are promising candidates for photocatalysis. In this study, we present the design and synthesis of these COFs using thiazole rings as linkage units. Three COFs (denoted as COF-S-OH-1, COF-S-OH-2, and COF-S-OH-3) were prepared based on aldehyde ligands with varying numbers of hydroxyl groups (2-hydroxybenzene-1,3,5-tricarbaldehyde, 2,4-dihydroxybenzene-1,3,5-tricarbaldehyde, and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde, respectively). The results demonstrate that COFs constructed with thiazole linkages exhibit superior stability and conjugation compared to those linked solely by imine bonds, ultimately achieving enhanced electronic conductivity. The tight interaction between donor and acceptor groups in this donor-acceptor (D-A) system facilitates an improved photocatalytic hydrogen evolution performance. Furthermore, increasing the number of hydroxyl groups (electron-donating groups) significantly enhances the photocatalytic efficiency of the resulting COFs.