Hierarchical Porosity

Sufficient pore size, appropriate stability, and hierarchical porosity are three prerequisites for open extended frameworks designed for drug delivery, enzyme immobilization, and catalysis involving large molecules. Although many approaches have been attempted to increase the pore size of MOF materials, it is still a challenge to construct MOFs with precisely customized pore apertures for specific applications. Linker instability, usually an undesirable trait of MOFs, was exploited to create mesopores by generating crystal defects throughout a microporous mixed-linker MOF crystal via thermolysis. Beside thermolysis, hydrolysis of chemically labile sites such as dynamic covalent bonds were investigated in MOFs. A sequential linker labilization and reinstallation method, linker reinstallation, was used to expand the unit cell dimensions of MOFs while manipulating the framework structure and interpenetration. In addition to the abovementioned examples based on labile covalent bonds in MOFs, Liang conducted more studies that demonstrate the role of the lability of coordination bonds in switching porosity insides MOFs. Linker migration triggered by desorption has been observed recently accompanied with a cascade lattice rearrangement in a defective Al-MOF. The system transforms from a disordered MOF with low porosity to a highly porous and crystalline isomer within 40 s following activation (solvent exchange and desolvation), resulting in a substantial increase in surface area and pore size. This disordered–crystalline switch between two topological distinct MOFs is shown to be reversible over four cycles through activation and reimmersion in polar solvents.

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Further reading:

  • Lo, S.-H.‡; Feng, L.‡; Tan, K.; Huang, Z.; Yuan, S.; Wang, K.; Li, B.-H.; Liu, W.-L.; Day, G. S.; Tao, S.; Yang, C.-C.; Luo, T.-T.; Lin, C.-H.; Wang, S.-L.; Billinge, S.; Lu, K.-L.; Chabal, Y.-J.; Zou, X.; Zhou, H.-C., Nat. Chem. 2020, 12, 90–97.

  • Feng, L.; Wang, K.-Y.; Day, G. S.; Ryder, M.; Zhou, H.-C., Chem. Rev. 2020, 120, 13087–13133.

  • Kirchon, A.‡; Feng, L.‡; Drake, H. F. ‡; Joseph, E. A.; Zhou, H.-C., Chem. Soc. Rev. 2018, 47, 8611–8638.

  • Feng, L.; Yuan, S.; Zhang, L.-L.; Tan, K.; Li, J.-L.; Kirchon, A.; Liu, L.-M., Zhang, P.; Han, Y.; Chabal, Y. J.; Zhou, H.-C., J. Am. Chem. Soc. 2018, 140, 2363–2372.

  • Feng, L.; Yuan, S.; Qin, J.-S.; Wang, Y.; Kirchon, A.; Qiu, D.; Cheng, L.; Madrahimov, S.; Zhou, H.-C., Matter, 2019, 1, 156–167.

  • Feng, L.‡; Lo, S.-H.‡; Tan, K.; Li, B.-H.; Yuan, S.; Lin, Y.-F.; Lin, C.-H.; Wang, S.-L.; Lu, K.-L.; Zhou, H.-C., Matter, 2020, 2, 988–999.

  • Feng, L.; Wang, K.-Y.; Lv, X.-L.; Yan, T.-H.; Zhou, H.-C., Nat. Sci. Rev. 2020, 7, 1743-1758.