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Self-Adjusting Binding Pockets Enhance H₂ and CH₄ Adsorption in a Uranium-Based Metal–Organic Framework

preprint
submitted on 15.04.2020, 06:03 and posted on 17.04.2020, 13:36 by Dominik P. Halter, Ryan A. Klein, Michael A. Boreen, Benjamin A. Trump, Craig M. Brown, Jeffrey R. Long
A new, air-stable, permanently porous uranium(IV) metal–organic framework U(bdc)2 (1, bdc2− = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (ΔV = −7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Qst = −8.6 kJ/mol) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Qst = −24.8 kJ/mol) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal–organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.

Funding

Hydrogen Materials - Advanced Research Consortium (HyMARC), established as part of the Energy Materials Network under the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract DE-AC02-05CH11231

U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357.

Director, Office of Science, Office of Basic Energy Sciences, of the U.S. DOE under Contract No. DE-AC02-05CH11231

Feodor Lynen postdoctoral research fellowship by the Alexander von Humboldt foundation

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under Contract DE-AC36-08GO28308

History

Email Address of Submitting Author

dhalter@berkeley.edu

Institution

University of California, Berkeley

Country

United States of America

ORCID For Submitting Author

0000-0003-0733-8955

Declaration of Conflict of Interest

The authors declare no competing financial interest

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