Pore engineering in metal-organic frameworks and covalent organic frameworks: strategies and applications

Abstract

Crystalline porous materials, particularly metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have garnered significant attention for advanced applications due to their tunable pore environments and versatile functionalities. By precisely controlling factors such as size, shape, functional sites, and pore distribution, MOFs and COFs can be tailored to exhibit high selectivity for specific molecules, making them ideal for applications in gas storage and separation, catalysis, and water remediation. This review provides a background overview, beginning with an introduction to pore surface engineering strategies and the design features of MOFs and COFs. It then highlights recent advancements in three key research areas that our group has investigated in-depth over the past decade, discussing the strategies and principles involved. Finally, we outline the remaining challenges and offer our perspectives on future opportunities for pore-engineered MOFs and COFs.

Fig. 1. (a) Schematic illustration of synthesizing MM-MOF-74. (b) Combination of metal ions used to synthesize MM-MOF-74. Reproduced with permission. Copyright 2014, American Chemical Society.

Fig. 2. Construction of single-linker COFs and MTV-COFs through pure linkers or mixed linkers and the influence of solvent combinations on their synthesis. Reproduced with permission. Copyright 2023, American Chemical Society.

Fig. 3. Scheme illustrating the pore expansion strategy. (a) As-synthesized bio-MOF-101 was converted to bio-MOF-100 through ligand exchange with BPDC. (b) BPDC in bio-MOF-100 was subsequently replaced with ABDC to form bio-MOF-102, followed by the replacement of ABDC in bio-MOF-102 with NH2-TPDC to yield bio-MOF-103. (c) Light microscope images of the crystalline MOFs, with scale bars representing 0.2 mm. Reproduced with permission. Copyright 2013, American Chemical Society.

Fig. 4. (a) Precise construction of dual-pore COFs via a multiple-linking-site strategy and fabrication of triple-pore COFs through the integration of vertex-truncation design with the multiple-linking-site strategy. Reproduced with permission. Copyright 2017, American Chemical Society. (b) Structures of six functional linkers and a schematic illustration of the in situ linker exchange process for functionalizing ECOF stationary phases. Reproduced with permission. Copyright 2024, John Wiley and Sons.

Fig. 5. (a) The concept of heterogeneous concerted catalysis involving active sites on porous materials and highly flexible linear polymers. (b) Schematic representation of PPS ⊂ COF-TpBpy-Cu synthesis, along with the structures of COF-TpBpy and PPS ⊂ COF-TpBpy-Cu. Reproduced with permission. Copyright 2016, American Chemical Society.

Fig. 6. (a) Classical synthesis of salen units and (b) one-step construction of salen-COF^a. Reproduced with permission. Copyright 2016, American Chemical Society.

Fig. 7. Illustration of pore space partitioning via symmetry-matching regulated ligand insertion. (a) View along the c-axis and (b) side view of the channels, depicting the cylindrical channel before and after partitioning (green: Ni, red: O, blue: N, gray: C). Reproduced with permission. Copyright 2015, American Chemical Society.

Fig. 8. (a) Graphical representation of pore partitioning in hexagonal channels. (b) Conversion of DBAAn-BTBA-COF into DBAAn-BTBA-HAPB-COF via symmetry-matching knot insertion. Reproduced with permission. Copyright 2023, Springer Nature.

Fig. 9. Design principles for high H₂ storage through chelation of abundant transition metals in covalent organic frameworks under 0–700 bar at 298 K. Reproduced with permission. Copyright 2016, American Chemical Society.

Fig. 10. (a) The channel structure of ATC-Cu and the two primary C₂H₂ binding sites within the framework. Reproduced with permission. Copyright 2021, American Chemical Society. (b) 1D chains [Al(μ₂-OH)(COO)₂]_n and V-shaped ligands (H₂FDC, m-H₂BDC, and H₂TDC) assemble into three isostructural 3D frameworks of MIL-160, CAU-10H, and CAU-23, respectively. Hydrogen atoms are omitted for clarity. Color code, Al: pale blue; O, red and rose; C, 50% gray. Reproduced with permission. Copyright 2021, American Chemical Society.

Fig. 11. (a) Synthesis of mixed-ligand MOF 1(Zr) via PSE to obtain mixed-metal MOFs 1(Zr/Ti) and UiO-66(Zr/Ti)-NH₂. (b) Photoluminescence spectra of 1(Zr) and 1(Zr/Ti). (c) Energy band structure of 1(Zr/Ti) derived from UPS and F(R) results, showing that heterogeneous ligands create two energy levels within the MOF, potentially facilitating CO₂ catalysis. Reproduced with permission. Copyright 2015, Royal Society of Chemistry.

Fig. 12. Synthesis of Co–OAc, Co–Br, and Co–CN with different spin states of Co^II and Co^IIIvia a postsynthetic exchange strategy. Reproduced with permission. Copyright 2024, American Chemical Society.

Fig. 13. (a) The “activation” process involving a Cr₃(μ₃-O) (COO)₆(OH)(H₂O)₂ cluster in MIL-101(Cr)-FLP-H₂. Reproduced with permission. Copyright 2019, John Wiley and Sons. (b) Construction pathway of NU-1000-FLP-H₂. Reproduced with permission. Copyright 2023, American Chemical Society.

Fig. 14. (a) Schematic representation of lipase PS and porous materials used for enzyme immobilization (blue: N, gray: C, red: O, white: H, yellow: Si, purple: Na). (b) Enzyme uptake capacity of various porous materials after 6 hours of incubation in a 30 mg per mL lipase PS solution. Reproduced with permission. Copyright 2018, American Chemical Society.

Fig. 15. (a) Schematic illustration of the BS-HMT concept. Ordered HCOOH molecules in MOF-808 can be replaced by EDTA, leading to MOF-808 with an ordered EDTA arrangement, which functions as a BS-HMT for metal ion capture. (b) The removal efficiency of hard Lewis metal ions, soft Lewis metal ions, and borderline Lewis metal ions for MOF-808-EDTA. Reproduced with permission. Copyright 2018, Springer Nature.

Fig. 16. Schematic illustration of imparting superhydrophobicity on COF-V. (a) Synthetic scheme of COF-V and COF-VF. (b and c) Schematic representation of the eclipsed AA stacking structure of COF-V. (d) Schematic representation of COF-VF. Reproduced with permission. Copyright 2018, Elsevier.

Fig. 17. (a) Synthetic scheme of COF-TpDb, formed through the condensation of Tp (black) and Db (blue), followed by a chemical transformation of cyano groups into amidoxime groups, yielding COF-TpDb-AO. (b and c) Schematic representation of the eclipsed AA stacking structure of COF-TpDb (blue: N; gray: C; red: O; hydrogen omitted for clarity). (d) Schematic representation of COF-TpDb-AO (blue: N; gray: C; red: O; hydrogen omitted for clarity). Reproduced with permission. Copyright 2018, John Wiley and Sons.

Yanpei Song

Shengqian Ma