Fully conjugated 3D covalent organic frameworks with electron donor-acceptor alternated structures for continuous-flow photosynthetic H2O2 from seawater and air.

Covalent organic frameworks (COFs) can serve as promising catalysts for photosynthesis of hydrogen peroxide (H2O2), of which the performances mostly rely on their ordered π-conjugated skeletons and electronic structures that promote the formation and separation of excitons. Designing electron donor (D)-acceptor (A) alternated structures within the fully π-conjugated frameworks has been demonstrated to be the most powerful strategy to develop high-performance photocatalysts, while most current cases are focused on two-dimensional (2D) COFs. Here we design and synthesize a series of D-A type fully conjugated 3D COFs by combining the saddle-shaped cyclooctatetrathiophene derivative with hierarchical electron donor units that consist of benzene, naphthalene and pyrene. The as-synthesized naphthalene-contained 3D COF exhibits an exceptional photocatalytic H2O2 production performance, which is almost 8 times higher than that of the non-conjugated 3D counterpart. Impressively, under the condition of actual seawater and air without sacrificial agents, it could deliver steady production over 155 h in a continuous-flow photocatalytic reactor system. Our work not only provides insight into the regulation of D-A electrical structures of 3D COFs for efficient photocatalysis, but also demonstrates that the semiconducting fully conjugated 3D COFs could be an ideal platform for green and sustainable development.