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Creating hierarchical pores in metal–organic frameworks via postsynthetic reactions

Nature Protocols volume 18, pages 604–625 (2023)Cite this article

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Abstract

Metal–organic frameworks (MOFs) demonstrate promise for a multitude of applications owing to their high porosity and surface area. However, the majority of conventional MOFs possess only micropores with very limited accessibility to substances larger than 2 nm—especially functional biomacromolecules like some proteins. It is challenging to create an appropriately large pore size while avoiding framework collapse in MOFs. Herein, we present the generation of mesopores in microporous MOFs through three facile and effective techniques, namely Soxhlet washing, linker hydrolysis and linker thermolysis. These postsynthetic elimination approaches have been applied in selected MOFs, including PCN-250, PCN-160 and UiO-66, and controllably generate MOFs with hierarchical pores and high stability. Our work demonstrates reproducible and straightforward methods resulting in hierarchically porous materials that possess the benefits of mesoporosity while borrowing the robustness of a micropore framework. All the procedures can be conducted reliably at a multigram scale and operation time less than 6 h, representing a significant effort in the field of MOF synthesis. These hierarchically porous MOFs show great promise in a wide range of applications as efficient adsorbents, catalysts and drug carriers.

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Fig. 1: Schematic illustration of three methodologies introduced in this protocol, namely Soxhlet washing, linker hydrolysis and linker thermolysis.
Fig. 2: The synthesis of the carboxylic ligands utilized in this protocol, all of which can be accomplished at gram scale without column purification.
Fig. 3: Schematic illustrating the synthetic procedures of H4ABTC and PCN-250.
Fig. 4: Schematic illustrating the synthetic procedures of H2AZDC, H2CBAB, PCN-160 and PCN-160-R%.
Fig. 5: Equipment setup for the synthesis of 2.
Fig. 6: Schematic illustrating the synthesis and linker thermolysis of UiO-66-NH2-R%.
Fig. 7: Nitrogen sorption results of PCN-250 before and after Soxhlet washing.
Fig. 8: Nitrogen sorption results of PCN-160-CBAB-R% before and after linker hydrolysis.
Fig. 9: Nitrogen sorption results of UiO-66-NH2-R% before and after treatment under 350 °C.

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Data availability

All the data and figures are available at https://doi.org/10.6084/m9.figshare.c.6012310.v1.

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Acknowledgements

This work was funded by the Robert A. Welch Foundation through a Welch Endowed Chair to H.-C. Z. (A-0030) and Qatar National Research Fund under Award Number NPRP9-377-1-080. Figures 3, 4 and 6 were created with BioRender.com. The authors also appreciate the helpful discussion with G. S. Day at Framergy, Inc. and Z. Han and W. Shi at Nankai University and support from the Foresight Institute.

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Authors and Affiliations

  1. Department of Chemistry, Texas A&M University, College Station, TX, USA

    Kun-Yu Wang, Zhentao Yang, Jiaqi Zhang, Sayan Banerjee, Elizabeth A. Joseph, Yu-Chuan Hsu, Shuai Yuan, Liang Feng & Hong-Cai Zhou

  2. State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing, China

    Shuai Yuan

  3. Department of Materials Science and Engineering, Texas A&M University, College Station, TX, USA

    Hong-Cai Zhou

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Contributions

K.-Y.W. organized and revised the manuscript and drew all the scientific figures. S.Y. and L.F. designed the experiments and edited the manuscript. H.-C.Z. oversaw the whole project. Z.Y. performed the linker hydrolysis experiments. J.Z. and Y.-C.H. performed the linker thermolysis experiments. S.B. and E.A.J. conducted the Soxhlet washing experiments. All authors contributed to writing the manuscript.

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Correspondence to Shuai Yuan, Liang Feng or Hong-Cai Zhou.

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Nature Protocols thanks Banglin Chen, Hai-Long Jiang, Lin-Bing Sun and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Related Links

Key references using this protocol

Yuan, S. et al. Nat. Commun. 8, 15356 (2017): https://www.nature.com/articles/ncomms15356

Feng, L. et al. J. Am. Chem. Soc. 140, 2363–2372 (2018): https://pubs.acs.org/doi/10.1021/jacs.7b12916

Fang, Y. et al. Chem. Eur. J. 24, 16977–16982 (2018): https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.201804012

Extended data

Extended Data Fig. 1 The equipment setup to synthesize the H4ABTC ligand.

a, Initial setup for the synthesis. b, The appearance of the yellow precipitate after 12 h.

Extended Data Fig. 2 Color change of PCN-250 before and after activation.

a, The brown color of PCN-250 before activation. b, The black color of PCN-250 after 12 h activation at 240 °C.

Extended Data Fig. 3 Equipment setup for the Soxhlet washing of PCN-250.

a, Soxhlet extraction setup using a 500 ml round-bottom flask and a magnetic stir bar. b, The Soxhlet extractor with the PCN-250 and a water condenser.

Extended Data Fig. 4 Color of the mixed-linker UiO-66 before and after thermolysis.

a, The pale-yellow UiO-66-NH2-5% powder. b, The brown UiO-66-NH2-5% powder after heating at 350 °C. c, The pale-yellow UiO-66-NH2-28% powder. d, The dark-brown UiO-66-NH2-28% powder after heating at 350 °C.

Supplementary information

Supplementary Information

Supplementary Figs. 1–16, and Supplementary Table 1.

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Wang, KY., Yang, Z., Zhang, J. et al. Creating hierarchical pores in metal–organic frameworks via postsynthetic reactions. Nat Protoc 18, 604–625 (2023). https://doi.org/10.1038/s41596-022-00759-7

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