Urchin-Like Covalent Organic Frameworks with Facilitated Charge Separation and Transfer for NADH-Dependent Photoenzyme-Coupled CO ₂ Fixation

Enzyme encapsulation with covalent organic frameworks (COFs) has garnered great potential for green biomanufacturing of pharmaceuticals, fuels, and carbon sequestration. However, a functional enzyme@COF photobiocatalyst with rationally designed molecular topology and unique strange morphology has recently been developed. Herein, an urchin-like COF (UCOF) with uniform dimensions was successfully developed from 1,3,5-tris(4-aminophenyl)benzene and 3,3′-bipyridine-6,6′-dicarbaldehyde, which possesses an iminopyridyl moiety and hierarchical hexagonal pores for the coordination of a rhodium-based electron mediator and formate dehydrogenase (FDH) enzyme encapsulation, respectively. Under light illumination, a photogenerated electron generated from the Cp*Rhx-UCOF structure was transferred to the electron mediator center (Cp*Rh complex) for NAD+ reduction into NADH, whereas holes left on the UCOF skeleton were consumed by the sacrificial agent triethanolamine. The separated donor–acceptor (D–A) pair along the UCOF skeletons enables the smooth separation and migration of charge carriers for improved NADH photogeneration because of the low polarized phenylene linkages. Besides, due to the facilitated substrate transfer pathways, the encapsulated FDH enzyme embedded in the mesoporous pores can improve the formic acid generation from CO2 with a 435 μmol·g–1·h–1 conversion rate. Such a design will provide a feasible pathway for constructing photoenzyme-coupled catalytic systems for valuable chemicals and pharmaceuticals with high demands.