In Situ Growth of Highly Dispersed TiO₂ in Covalent Organic Frameworks for Photocatalytic H₂ Evolution

Titanium dioxide (TiO₂) has the disadvantages of being difficult to excite and easily agglomerating in use. The imine-linked covalent organic frameworks (COFs) have shown various excellent properties in diverse fields, but the drawbacks such as monofunctionality and poor light-corrosion resistance are the problems that need to be improved in photocatalytic applications. In this paper, the imine-linked COF (COF-Im) was prepared and then transformed into a quinoline-based COF (COF-Qui) by an aza-Diels-Alder reaction, which successfully improved the light absorption and stability of the COFs. The COF-Qui-TiO₂ heterojunction photocatalyst was successfully prepared by in situ growth of TiO₂ in pores of COF-Qui. The highest H₂ evolution rate of COF-Qui-TiO₂ was 5373 μmol·h^-1·g^-1, and it maintained good performance and a stable structure after 5 cycles. This work provided valuable experience for the development of novel, efficient heterojunction photocatalysts.