Adsorption properties of acetylene, ethylene and ethane in UiO-66 with linker defects and NO2 functionalization

H. Pandey; T. Barrett; M. D. Gross; T. Thonhauser

doi:10.1039/D0MA00722F

Adsorption properties of acetylene, ethylene and ethane in UiO-66 with linker defects and NO₂ functionalization†

H. Pandey,

^ab T. Barrett,^bc M. D. Gross^bd and T. Thonhauser

*^ab

Author affiliations

* Corresponding authors

^a Department of Physics, Wake Forest University, Winston-Salem, NC 27109, USA
E-mail: thonhauser@wfu.edu

^b Center for Functional Materials, Wake Forest University, Winston-Salem, NC 27109, USA

^c Department of Chemistry, Wake Forest University, Winston-Salem, NC 27109, USA

^d Department of Engineering, Wake Forest University, Winston-Salem, NC 27109, USA

Abstract

Separation of small hydrocarbon gases is crucial for many industrial processes, but the high energy demand of current separation techniques encourages exploration of alternative sorption-based approaches. Here, we investigate the metal organic framework UiO-66(Zr) as possible solid adsorbent with a focus on the fundamental sorption mechanisms of C₂ hydrocarbons in the presence of linker defects and NO₂ functionalization. To this end, we directly measure heats of adsorption with calorimetry and correlate our results with ab initio calculations. In particular, we study adsorption of C₂H₂, C₂H₄ and C₂H₆ at 293 K and 195 K. At 293 K, the measured low-coverage enthalpy is found to be an average enthalpy of multiple adsorption sites. However, at 195 K, the low-coverage enthalpy corresponded to the strongest binding site, i.e. the linker defect site. We find that C₂H₂ exhibits the highest adsorption enthalpy with a significant gap of ∼6 kJ mol⁻¹ to C₂H₄ and ∼9 kJ mol⁻¹ to C₂H₆. Our ab initio calculations show excellent agreement with our experiments and are crucial to uncover the mechanisms that lead to the observed differences in binding affinity as a function of coverage. We also find that binding enthalpies increase for all three gases by adding –NO₂ functional groups, which even further increase the gap to ∼9 kJ mol⁻¹ and ∼10 kJ mol⁻¹ for C₂H₄ and C₂H₆, respectively. Our findings provide mechanistic insight that suggests that linker defects in UiO-66(Zr) have promise to improve its effectiveness as a solid adsorbent in C₂H₂, C₂H₄ and C₂H₆ applications and that functionalization may be used to increase specificity.

This article is part of the themed collection: Celebrating materials science in the United States of America

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DOI: https://doi.org/10.1039/D0MA00722F
Article type: Paper
Submitted: 21 Sep 2020
Accepted: 05 Dec 2020
First published: 07 Dec 2020
This article is Open Access

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Mater. Adv., 2021,2, 426-433

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Adsorption properties of acetylene, ethylene and ethane in UiO-66 with linker defects and NO₂ functionalization

H. Pandey, T. Barrett, M. D. Gross and T. Thonhauser, Mater. Adv., 2021, 2, 426 DOI: 10.1039/D0MA00722F

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