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Title: The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials

For applications of metal–organic frameworks (MOFs) such as gas storage and separation, flexibility is often seen as a parameter that can tune material performance. In this work we aim to determine the optimal flexibility for the shape selective separation of similarly sized molecules (e.g., Xe/Kr mixtures). To obtain systematic insight into how the flexibility impacts this type of separation, we develop a simple analytical model that predicts a material’s Henry regime adsorption and selectivity as a function of flexibility. We elucidate the complex dependence of selectivity on a framework’s intrinsic flexibility whereby performance is either improved or reduced with increasing flexibility, depending on the material’s pore size characteristics. However, the selectivity of a material with the pore size and chemistry that already maximizes selectivity in the rigid approximation is continuously diminished with increasing flexibility, demonstrating that the globally optimal separation exists within an entirely rigid pore. Molecular simulations show that our simple model predicts performance trends that are observed when screening the adsorption behavior of flexible MOFs. These flexible simulations provide better agreement with experimental adsorption data in a high-performance material that is not captured when modeling this framework as rigid, an approximation typically made in high-throughput screening studies. Wemore » conclude that, for shape selective adsorption applications, the globally optimal material will have the optimal pore size/chemistry and minimal intrinsic flexibility even though other nonoptimal materials’ selectivity can actually be improved by flexibility. In conclusion, equally important, we find that flexible simulations can be critical for correctly modeling adsorption in these types of systems.« less
Authors:
ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [1] ; ORCiD logo [3] ;  [4] ;  [2] ; ORCiD logo [5]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering
  2. King's College London (United Kingdom). Dept. of Chemistry
  3. Ecole Polytechnique Federale Lausanne (Switzlerland). Inst. of Chemical Sciences and Engineering, Lab. of Molecular Simulation
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division; IMDEA Materials Inst., Madrid (Spain)
  5. Univ. of California, Berkeley, CA (United States). Dept. of Chemical and Biomolecular Engineering; Ecole Polytechnique Federale Lausanne (Switzlerland). Inst. of Chemical Sciences and Engineering, Lab. of Molecular Simulation
Publication Date:
Grant/Contract Number:
SC0001015; EP/K039296/1; EP/K038400/1; 666983; AC02-05CH11231
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 15; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE
OSTI Identifier:
1350787
Alternate Identifier(s):
OSTI ID: 1352568; OSTI ID: 1408429

Witman, Matthew, Ling, Sanliang, Jawahery, Sudi, Boyd, Peter G., Haranczyk, Maciej, Slater, Ben, and Smit, Berend. The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials. United States: N. p., Web. doi:10.1021/jacs.7b01688.
Witman, Matthew, Ling, Sanliang, Jawahery, Sudi, Boyd, Peter G., Haranczyk, Maciej, Slater, Ben, & Smit, Berend. The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials. United States. doi:10.1021/jacs.7b01688.
Witman, Matthew, Ling, Sanliang, Jawahery, Sudi, Boyd, Peter G., Haranczyk, Maciej, Slater, Ben, and Smit, Berend. 2017. "The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials". United States. doi:10.1021/jacs.7b01688.
@article{osti_1350787,
title = {The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials},
author = {Witman, Matthew and Ling, Sanliang and Jawahery, Sudi and Boyd, Peter G. and Haranczyk, Maciej and Slater, Ben and Smit, Berend},
abstractNote = {For applications of metal–organic frameworks (MOFs) such as gas storage and separation, flexibility is often seen as a parameter that can tune material performance. In this work we aim to determine the optimal flexibility for the shape selective separation of similarly sized molecules (e.g., Xe/Kr mixtures). To obtain systematic insight into how the flexibility impacts this type of separation, we develop a simple analytical model that predicts a material’s Henry regime adsorption and selectivity as a function of flexibility. We elucidate the complex dependence of selectivity on a framework’s intrinsic flexibility whereby performance is either improved or reduced with increasing flexibility, depending on the material’s pore size characteristics. However, the selectivity of a material with the pore size and chemistry that already maximizes selectivity in the rigid approximation is continuously diminished with increasing flexibility, demonstrating that the globally optimal separation exists within an entirely rigid pore. Molecular simulations show that our simple model predicts performance trends that are observed when screening the adsorption behavior of flexible MOFs. These flexible simulations provide better agreement with experimental adsorption data in a high-performance material that is not captured when modeling this framework as rigid, an approximation typically made in high-throughput screening studies. We conclude that, for shape selective adsorption applications, the globally optimal material will have the optimal pore size/chemistry and minimal intrinsic flexibility even though other nonoptimal materials’ selectivity can actually be improved by flexibility. In conclusion, equally important, we find that flexible simulations can be critical for correctly modeling adsorption in these types of systems.},
doi = {10.1021/jacs.7b01688},
journal = {Journal of the American Chemical Society},
number = 15,
volume = 139,
place = {United States},
year = {2017},
month = {3}
}