Exceptional H 2 sorption characteristics in a Mg 2+ -based metal–organic framework with small pores: insights from experimental and theoretical studies
Experimental sorption measurements, inelastic neutron scattering (INS), and theoretical studies of H 2 sorption were performed in α-[Mg 3 (O 2 CH) 6 ], a metal–organic framework (MOF) that consists of a network of Mg 2+ ions coordinated to formate ligands. The experimental H 2 uptake at 77 K and 1.0...
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| Published in | Physical chemistry chemical physics : PCCP Vol. 18; no. 3; pp. 1786 - 1796 |
|---|---|
| Main Authors | , , , , |
| Format | Journal Article |
| Language | English |
| Published |
2016
|
| Online Access | Get full text |
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| Summary: | Experimental sorption measurements, inelastic neutron scattering (INS), and theoretical studies of H
2
sorption were performed in α-[Mg
3
(O
2
CH)
6
], a metal–organic framework (MOF) that consists of a network of Mg
2+
ions coordinated to formate ligands. The experimental H
2
uptake at 77 K and 1.0 atm was observed to be 0.96 wt%, which is quite impressive for a Mg
2+
-based MOF that has a BET surface area of only 150 m
2
g
−1
. Due to the presence of small pore sizes in the MOF, the isosteric heat of adsorption (
Q
st
) value was observed to be reasonably high for a material with no open-metal sites (
ca.
7.0 kJ mol
−1
). The INS spectra for H
2
in α-[Mg
3
(O
2
CH)
6
] is very unusual for a porous material, as there exist several different peaks that occur below 10 meV. Simulations of H
2
sorption in α-[Mg
3
(O
2
CH)
6
] revealed that the H
2
molecules sorbed at three principal locations within the small pores of the framework. It was discovered through the simulations and two-dimensional quantum rotation calculations that different groups of peaks correspond to particular sorption sites in the material. However, for H
2
sorbed at a specific site, it was observed that differences in the positions and angular orientations led to distinctions in the rotational tunnelling transitions; this led to a total of eight identified sites. An extremely high rotational barrier was calculated for H
2
sorbed at the most favorable site in α-[Mg
3
(O
2
CH)
6
] (81.59 meV); this value is in close agreement to that determined using an empirical phenomenological model (75.71 meV). This rotational barrier for H
2
exceeds those for various MOFs that contain open-metal sites and is currently the highest yet for a neutral MOF. This study highlights the synergy between experiment and theory to extract useful and important atomic level details on the remarkable sorption mechanism for H
2
in a MOF with small pore sizes. |
|---|---|
| ISSN: | 1463-9076 1463-9084 |
| DOI: | 10.1039/C5CP05906B |