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The stability of metal-organic frameworks (MOFs) in water affects their ability to function as chemical catalysts, their capacity as adsorbents for separations in water vapor presence, and their usefulness as recyclable water harvesters. Here, we have examined water stability of four node-modified variants of the mesoporous MOF, NU-1000, namely formate-, Acac-, TFacac-, and Facac-NU-1000, comparing these with node-accessible NU-1000. These NU-1000 variants present ligands grafted to NU-1000's hexa-Zr(iv)-oxy nodes by displacing terminal aqua and hydroxo ligands. Facac-NU-1000, containing the most hydrophobic ligands, showed the greatest water stability, being able to undergo at least 20 water adsorption/desorption cycles without loss of water uptake capacity. Computational studies revealed dual salutary functions of installed Facac ligands: (1) enhancement of framework mechanical stability due to electrostatic interactions; and (2) transformation and shielding of the otherwise highly hydrophilic nodes from H-bonding interactions with free water, presumably leading to weaker channel-stressing capillary forces during water evacuation - consistent with trends in free energies of dehydration across the NU-1000 variants. Water harvesting and hydrolysis of chemical warfare agent simulants were examined to gauge the functional consequences of modification and mechanical stabilization of NU-1000 by Facac ligands. The studies revealed a harvesting capacity of ∼1.1 L of water vapor per gram of Facac-NU-1000 per sorption cycle. They also revealed retention of catalytic MOF activity following 20 water uptake and release cycles. This study provides insights into the basis for node-ligand-engendered stabilization of wide-channel MOFs against collapse during water removal.
|Original language||English (US)|
|Number of pages||10|
|Journal||Journal of Materials Chemistry A|
|State||Published - Aug 8 2022|
Bibliographical noteFunding Information:
J. T. H. gratefully acknowledges support from the National Science Foundation via grant number DMREF-2119433 and from Northwestern University. For studies of catalytic hydrolysis he gratefully acknowledges the Defense Threat Reduction Agency via grant number HDTRA1-19-1-0010. D. A. G.-G. gratefully acknowledges funding from the NSF through CAREER Award CBET-1846707. T. R. S. gratefully acknowledges support from a National Defense Science and Engineering Graduate Fellowship. Mechanical testing described in this work was primarily supported by the MRSEC Program of the National Science Foundation under Award Number DMR-2011401. Parts of this work were carried out in the Characterization Facility, University of Minnesota, which receives partial support from NSF through the MRSEC program. K. M. S. and N. A. M. acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper. This work made use of the J. B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University. This work made use of the EPIC and Keck-II facilities of the NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. The REACT Facility of the Northwestern University Center for Catalysis and Surface Science is supported by a grant from the DOE (DE-SC0001329).
© 2022 The Royal Society of Chemistry.
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University of Minnesota Materials Research Science and Engineering Center (DMR-2011401)
9/1/20 → 8/31/26
Project: Research project
MRSEC SEED Projects DMR-2011401
9/1/20 → 8/31/26
Project: Research project