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An investigation into the adsorption mechanism of n-butanol by ZIF-8: a combined experimental and ab initio molecular dynamics approach

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The zeolitic imidazolate framework, ZIF-8, has been shown by experimental methods to have a maximum saturation adsorption capacity of 0.36 g g−1 for n-butanol from aqueous solution, equivalent to a loading of 14 butanol molecules per unit cell or 7 molecules per sodalite β-cage. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) shows the presence of hydrogen bonding between adsorbed butanol molecules within the cage; the presence of three different O–H stretching modes indicates the formation of butanol clusters of varying size. Ab initio molecular dynamics simulations show the formation of intermolecular hydrogen bonding between the butanol molecules, with an average hydrogen-bond coordination number of 0.9 after 15 ps simulation time. The simulations also uniquely demonstrate the presence of weaker interactions between the alcohol O–H group and the π-orbital of the imidazole ring on the internal surface of the cage during early stages of adsorption. The calculated adsorption energy per butanol molecule is −33.7 kJ mol−1, confirming that the butanol is only weakly bound, driven primarily by the hydrogen bonding. Solid-state MAS NMR spectra suggest that the adsorbed butanol molecules possess a reasonable degree of mobility in their adsorbed state, rather than being rigidly held in specific sites. 2D 13C–1H heteronuclear correlation (HETCOR) experiments show interactions between the butanol aliphatic chain and the ZIF-8 framework experimentally, suggesting that O–H interactions with the π-orbital are only short lived. The insight gained from these results will allow the design of more efficient ways of recovering and isolating n-butanol, an important biofuel, from low-concentration solutions.

Funding

DTP 2016-2017 Loughborough University

Engineering and Physical Sciences Research Council

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DTP 2018-19 Loughborough University

Engineering and Physical Sciences Research Council

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DTP 2020-2021 Loughborough University

Engineering and Physical Sciences Research Council

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Sydney Andrew Scholarship

Sulis: An EPSRC platform for ensemble computing delivered by HPC Midlands+

Engineering and Physical Sciences Research Council

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History

School

  • Aeronautical, Automotive, Chemical and Materials Engineering
  • Science

Department

  • Chemical Engineering
  • Chemistry
  • Materials

Published in

Physical Chemistry Chemical Physics

Volume

25

Issue

29

Pages

19911-19922

Publisher

Royal Society of Chemistry (RSC)

Version

  • VoR (Version of Record)

Rights holder

© The Authors

Publisher statement

This is an Open Access Article. It is published by the Royal Society of Chemistry under the Creative Commons Attribution 3.0 Unported Licence (CC BY). Full details of this licence are available at: https://creativecommons.org/licenses/by/3.0/

Acceptance date

2023-07-10

Publication date

2023-07-11

Copyright date

2023

ISSN

1463-9076

eISSN

1463-9084

Language

  • en

Depositor

Prof Sandie Dann. Deposit date: 12 July 2023

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