Postsynthetic Annulation of Three-Dimensional Covalent Organic Frameworks for Boosting CO₂ Photoreduction

Abstract

Three-dimensional covalent organic frameworks (3D COFs), with interconnected pores and exposed functional groups, provide new opportunities for the design of advanced functional materials through postsynthetic modification. Herein, we demonstrate the successful postsynthetic annulation of 3D COFs to construct efficient CO2 reduction photocatalysts. Two 3D COFs, NJU-318 and NJU-319Fe, were initially constructed by connecting hexaphenyl-triphenylene units with pyrene- or Fe-porphyrin-based linkers. Subsequently, the hexaphenyl-triphenylene moieties within the COFs were postsynthetically transformed into π-conjugated hexabenzo-trinaphthylene (pNJU-318 and pNJU-319Fe) to enhance visible light absorption and CO2 photoreduction activity. The optimized photocatalyst, pNJU-319Fe, shows a CO yield of 688 μmol g–1, representing a 2.5-fold increase compared to that of unmodified NJU-319Fe. Notably, the direct synthesis of hexabenzo-trinaphthylene-based COF catalysts was unsuccessful due to the low solubility of conjugated linkers. This study not only provides an effective method to construct photocatalysts but also highlights the unlimited tunability of 3D COFs through structural design and postsynthetic modification.

Single-Atom Catalysts on Covalent Organic Frameworks for Energy Applications

“…Photocatalysis: (a) heteroatom COFs with dithiol units for photocatalytic CO 2 RR; (b) 3,3′,5,5′-tetraformyl-4,4′-biphenyldiol-COF with a salicylideneaniline (SA) ligand (TFBD-COF-Co-SA) with Co–N 2 O 2 sites for photocatalytic CO 2 RR; (c) metal-salen-based COF with pyrene light-harvesting units for photocatalytic HER; (d) porphyrinic pyrazine-based COF with hydrophilic group interfacial design for photocatalytic HER; (e) 3D COF via postsynthesis for photocatalytic CO 2 RR. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

“…Synthesizing COFs in 3D geometry could also be a solution to promoting the catalytic reactivity in CO 2 reduction (Figure e). Recently, Lei and co-workers synthesized NJU-318 and NJU-319Fe 3D COFs via the condensation of 6-connected 2,3,6,7,10,11-hexakis(4-formylphenyl)triphenylene (HEPTP) with 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTTA) and tetrakis(4-aminophenyl)porphyrin (TAPP) as linkers, respectively (Figure a) . Then they postmodified the COFs to extended π-conjugated networks by transforming the hexaphenyltriphenylene moiety to hexabenzotrinaphthylene (Figure b), which cannot be synthesized directly due to the low solubility of the extended π-conjugated linker.…”

“…(e) Photocatalytic performances of the NJU-318, pNJU-318, NJU-319, NJU-319Fe, and pNJU319Fe COFs. Reproduced with permission from ref . Copyright 2023 American Chemical Society.…”

Preparation of Well-Constructed and Metal-Modified Covalent Organic Framework Nanoparticles for Biosensing Design with Cascade Catalytic Capability

“…Covalent organic frameworks (COFs) have gained significant attention due to their stable covalent bonds and remarkable properties, such as high chemical stability, large specific surface area, excellent biocompatibility, and customizable constituent units. − These unique characteristics endow COFs with high versatility for various applications, including gas storage, , catalysis, , environmental remediation, ,, bioimaging, , drug delivery, , and biosensing. , Recently, significant efforts have been devoted to preparing uniform COF nanoparticles (COF NPs), and the improved tunability and bioavailability can boost the biomedical applications of COFs. , Moreover, efforts are made to make full use of the advantages of COFs in their modifiability with different functional groups, , which allows the postsynthetic modification to achieve tailored properties, including proton conductivity, , photocatalytic activity, , and fluorescence characteristic. , For instance, recent research studies have shown that postmetallized COFs can be used for electrocatalysis, , water decomposition, , and CO 2 reduction. , In these reports, metal ions were strategically modified on COFs, which could remarkably improve the performance of the materials and play important roles in enzymatic catalysis.…”

Two-Dimensional Kagome Covalent Organic Frameworks with Single Atomic Co Sites for Superior Photocatalytic CO2 Reduction

“…Covalent organic frameworks (COFs) are a class of crystalline porous material and feature many advantages, including good chemical and thermal stability, high porosity, and adjustable structure, and thus render them an ideal choice in various applications, such as heterogeneous catalysis, energy storage, drug delivery, photoelectric devices, and gas separation and storage. − To date, versatile two-dimensional (2D) and three-dimensional (3D) COFs with different topologies, such as kgd , hcb , sql , hxl , pcb , flu , and kg m , are constructed and investigated for the applications in above-mentioned fields. The kg m topology is a typical 2D COF structure that has a characteristic double-pore configuration consisting of triangular micropores and hexagonal mesopores.…”