Porous framework materials

3 min read · References ↓

Porous frameworks, such as metal–organic frameworks, hold small molecules inside pores only a few ångströms wide. By choosing the size and chemistry of those pores, a framework can be made to store a gas or to take up one gas and reject another, which makes these materials candidates for capturing CO2, separating air and hydrocarbons, and storing hydrogen at moderate pressures. Our first-principles calculations, working alongside adsorption, diffraction and spectroscopy measurements by our collaborators, show where the molecules bind and why a framework prefers one gas over another.

Aluminum formate (ALF). Much of our recent work concerns Al(HCOO)3, a framework made cheaply from commodity chemicals. ALF removes CO2 from N2-rich gas streams by a size-selective separation that rests on the small difference between the two molecules’ kinetic diameters,1 and its hydrogen-lined pore cavities recognize CO2 while rejecting hydrocarbons, including acetylene and methane.2 The same material adsorbs O2 from air near dry-ice temperatures, without cryogenic distillation,3 and stores hydrogen competitively at 120–160 K and 10–20 bar.4 We have also traced its temperature-regulated gating, which lets temperature alone switch the separation of one gas from another, to the motion of the formate linkers that frame the windows between its cavities.5

This builds on our earlier first-principles work on metal–organic frameworks, carried out with experimental collaborators, which spans the main questions a porous framework raises.

How molecules move and bind. We have identified how H2, CO2 and H2O diffuse through the channels of MOF-74-Mg,6 screened the adsorption of H2, CO2, CH4 and H2O in MOF-74 made with 25 different metals,7 and developed a continuum model that predicts gas uptake in porous materials directly from first-principles gas–framework interaction energies, far faster than grand canonical Monte Carlo simulations.8

Selective separation. In a flexible framework, we found that hydrocarbons are separated by the different pressures at which each one opens the framework’s gates, depending on chain length and on how each gas interacts with the framework.9

Stability in real gas streams. Frameworks must survive water and acid gases. We have shown how water reacts with paddle-wheel frameworks M(bdc)(ted)0.5, depending on the metal,10 and dissociates at the open metal sites of MOF-74;11 how SO2 is taken up by paddle-wheel frameworks,12 and how NO2 decomposes in MOF-74 while SO2 binds intact,13 which bears on poisoning by the minor components of flue gases.

Responses to guests. Water forms clusters in the hydrophobic cavities of a fluorinated framework while methane is adsorbed,14 and loading MOF-74-Zn with H2, CO2, CH4 or H2O changes its structural, elastic, thermal and electronic properties in ways specific to each molecule, pointing to frameworks as gas sensors.15

Relevant references

  1. H. A. Evans, D. Mullangi, Z. Deng, Y. Wang, S. B. Peh, F. Wei, J. Wang, C. M. Brown, D. Zhao, P. Canepa, and A. K. Cheetham; Sci. Adv. 8, eade1473 (2022).
  2. Z. Zhang, Z. Deng, H. A. Evans, D. Mullangi, C. Kang, S. B. Peh, Y. Wang, C. M. Brown, J. Wang, P. Canepa, A. Cheetham, and D. Zhao; J. Am. Chem. Soc. 145, 11643 (2023).
  3. D. Mullangi, H. A. Evans, T. Yildirim, Y. Wang, Z. Deng, Z. Zhang, T. T. Mai, F. Wei, J. Wang, A. R. Hight Walker, C. M. Brown, D. Zhao, P. Canepa, and A. Cheetham; J. Am. Chem. Soc. 145, 9850 (2023).
  4. H. A. Evans, T. Yildirim, P. Peng, Y. Cheng, Z. Deng, Q. Zhang, D. Mullangi, D. Zhao, P. Canepa, H. M. Breunig, A. K. Cheetham, and C. M. Brown; J. Am. Chem. Soc. 145, 22150 (2023).
  5. H. A. Evans, T. Yildirim, G. A. McCarver, T. T. Mai, Y. Cheng, Z. Deng, R. A. Klein, D. Zhao, P. Canepa, A. R. Hight Walker, A. K. Cheetham, and C. M. Brown; Chem. Mater. 37, 7102–7114 (2025).
  6. P. Canepa, N. Nijem, Y. J. Chabal, and T. Thonhauser; Phys. Rev. Lett. 110, 026102 (2013).
  7. P. Canepa, C. A. Arter, E. M. Conwill, D. H. Johnson, B. A. Shoemaker, K. Z. Soliman, and T. Thonhauser; J. Mater. Chem. A 1, 13597–13604 (2013).
  8. Y. Ihm, V. R. Cooper, L. Vlcek, P. Canepa, T. Thonhauser, J. H. Shim, and J. R. Morris; J. Phys. Chem. C 121, 17625–17632 (2017).
  9. N. Nijem, H. Wu, P. Canepa, A. Marti, K. J. Balkus, T. Thonhauser, J. Li, and Y. J. Chabal; J. Am. Chem. Soc. 134, 15201–15204 (2012).
  10. K. Tan, N. Nijem, P. Canepa, Q. Gong, J. Li, T. Thonhauser, and Y. J. Chabal; Chem. Mater. 24, 3153–3167 (2012).
  11. K. Tan, S. Zuluaga, Q. Gong, P. Canepa, H. Wang, J. Li, T. Thonhauser, and Y. J. Chabal; Chem. Mater. 26, 6886–6895 (2014).
  12. K. Tan, P. Canepa, Q. Gong, J. Liu, D. H. Johnson, A. Dyevoich, P. K. Thallapally, T. Thonhauser, J. Li, and Y. J. Chabal; Chem. Mater. 25, 4653–4662 (2013).
  13. K. Tan, S. Zuluaga, H. Wang, P. Canepa, K. Soliman, J. Cure, J. Li, T. Thonhauser, and Y. J. Chabal; Chem. Mater. 29, 4227–4235 (2017).
  14. N. Nijem, P. Canepa, T. Thonhauser, and Y. J. Chabal; J. Am. Chem. Soc. 135, 12615–12626 (2013).
  15. P. Canepa, K. Tan, Y. Du, H. Lu, Y. J. Chabal, and T. Thonhauser; J. Mater. Chem. A 3, 986–995 (2015).

All our papers on porous frameworks (19) →