Cheap transition metal reinforced donor–acceptor covalent organic frameworks for CO2 photoreduction

Artificial photoreduction of CO2 is considered an attractive solution for simultaneously achieving carbon neutrality goals and solving the energy shortage crisis. In this study, a donor–acceptor (D–A) covalent organic framework (COF), COF-BT, comprising (1,1′-biphenyl)-3,3′,5,5′-tetracarbaldehyde and 4,4′-(2,1,3-benzothiadiazole-4,7-diyl)bis[benzenamine] was prepared, and cheap CoO was introduced into COF-BT via a two-step impregnation-calcination process to obtain Co-COF-BT with immobilized transition metals. Photoelectrochemical experimental and theoretical results indicate that the D–A structure of Co-COF-BT reduces the band gap, enhances visible light absorption, inhibits electron–hole recombination, and prolongs the life of photogenerated carriers. The introduction of CoO provides additional active sites, and the Co-S bond in Co-COF-BT provides an additional channel for ultrafast electron migration from the COF-BT unit to the CoO active center, which increases charge mobility and reduces the energy barrier formed by *COOH intermediates. Thus, the excellent photocatalytic CO2 reduction activity of Co-COF-BT is achieved with a CO yield of 2423 μmol g−1h−1 and selectivity > 99% under visible light. The superior photocatalytic performance is attributed to the synergistic effect of D–A moieties and CoO in Co-COF-BT. This study not only presents a novel COF-based photocatalyst with high charge transfer efficiency and high catalytic activity in CO2 reduction but also provides a potential strategy to fine-tune photoelectronic properties by adjusting the functional building blocks and additional metal active sites.