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Nanomaterials 2019, 9(3), 354; https://doi.org/10.3390/nano9030354

Structural Basis of CO2 Adsorption in a Flexible Metal-Organic Framework Material

1
Material Measurement Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899-8520, USA
2
AECOM Corporation, Pittsburgh, PA 15236, USA
3
National Energy Technology Laboratory (NETL), US Department of Energy, Pittsburgh, PA 15236, USA
*
Author to whom correspondence should be addressed.
Received: 3 February 2019 / Revised: 16 February 2019 / Accepted: 19 February 2019 / Published: 4 March 2019
(This article belongs to the Special Issue Nanomaterials in CO2 Capture)
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Abstract

This paper reports on the structural basis of CO2 adsorption in a representative model of flexible metal-organic framework (MOF) material, Ni(1,2-bis(4-pyridyl)ethylene)[Ni(CN)4] (NiBpene or PICNIC-60). NiBpene exhibits a CO2 sorption isotherm with characteristic hysteresis and features on the desorption branch that can be associated with discrete structural changes. Various gas adsorption effects on the structure are demonstrated for CO2 with respect to N2, CH4 and H2 under static and flowing gas pressure conditions. For this complex material, a combination of crystal structure determination and density functional theory (DFT) is needed to make any real progress in explaining the observed structural transitions during adsorption/desorption. Possible enhancements of CO2 gas adsorption under supercritical pressure conditions are considered, together with the implications for future exploitation. In situ operando small-angle neutron and X-ray scattering, neutron diffraction and X-ray diffraction under relevant gas pressure and flow conditions are discussed with respect to previous studies, including ex situ, a priori single-crystal X-ray diffraction structure determination. The results show how this flexible MOF material responds structurally during CO2 adsorption; single or dual gas flow results for structural change remain similar to the static (Sieverts) adsorption case, and supercritical CO2 adsorption results in enhanced gas uptake. Insights are drawn for this representative flexible MOF with implications for future flexible MOF sorbent design. View Full-Text
Keywords: flexible metal-organic frameworks; gate-opening effects; dual gas flow sorption; supercritical CO2 adsorption; small-angle X-ray scattering; small-angle neutron scattering; X-ray diffraction; neutron diffraction; in situ operando studies; density functional theory flexible metal-organic frameworks; gate-opening effects; dual gas flow sorption; supercritical CO2 adsorption; small-angle X-ray scattering; small-angle neutron scattering; X-ray diffraction; neutron diffraction; in situ operando studies; density functional theory
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Allen, A.J.; Wong-Ng, W.; Cockayne, E.; Culp, J.T.; Matranga, C. Structural Basis of CO2 Adsorption in a Flexible Metal-Organic Framework Material. Nanomaterials 2019, 9, 354.

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