Boosting photocatalytic hydrogen evolution by in-situ loading and photo-induced transformation of metal salts to efficient cocatalysts in covalent organic frameworks

Uniform and controllable loading of cocatalysts in covalent organic framework (COF) photocatalysts are still highly desirable for efficient photocatalytic hydrogen evolution. Herein, we achieve this goal by in-situ loading and photo-induced transformation of metal salts to their efficient cocatalysts in Tp-Pa-2-COF. Based on this, a series of M-based (M = Ni, Cu and Co) cocatalysts/Tp-Pa-2-COF photocatalysts with highly integrated systems are successfully prepared. The formation of highly dispersed cocatalysts can be attributed to the uniform loading of metal salts and the subsequent photo-induced process. As a result, all the M-based/Tp-Pa-2-COF photocatalysts exhibit excellent performance and the best variant is the 3 % Ni-based/Tp-Pa-2-COF, which achieves a hydrogen production of 2.89 mmol g-1 h-1 even after 32 h. In addition, the photo-induced transformation and catalytic mechanism of the M-based/Tp-Pa-2-COF photocatalysts are also elucidated through monitoring the cocatalyst formation process along with hydrogen evolution performance changes during photo-illumination. This study provides a potential pathway for uniform and controllable loading of cocatalysts in COF photocatalysts.