Abstract
© 2016 the Owner Societies. Experimental sorption measurements, inelastic neutron scattering (INS), and theoretical studies of H2 sorption were performed in α-[Mg3(O2CH)6], a metal-organic framework (MOF) that consists of a network of Mg2+ ions coordinated to formate ligands. The experimental H2 uptake at 77 K and 1.0 atm was observed to be 0.96 wt%, which is quite impressive for a Mg2+-based MOF that has a BET surface area of only 150 m2 g-1. Due to the presence of small pore sizes in the MOF, the isosteric heat of adsorption (Qst) 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 H2 in α-[Mg3(O2CH)6] is very unusual for a porous material, as there exist several different peaks that occur below 10 meV. Simulations of H2 sorption in α-[Mg3(O2CH)6] revealed that the H2 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 H2 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 H2 sorbed at the most favorable site in α-[Mg3(O2CH)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 H2 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 H2 in a MOF with small pore sizes.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1786-1796 |
| Number of pages | 11 |
| Journal | Phys. Chem. Chem. Phys. |
| Volume | 18 |
| Issue number | 3 |
| DOIs | |
| State | Published - 2016 |
| Externally published | Yes |
Bibliographical note
KAUST Repository Item: Exported on 2020-10-01Acknowledged KAUST grant number(s): FIC/2010/06
Acknowledgements: The authors would like to thank A. K. Cheetham and Z. Hulvey for helpful discussions, and R. Ziegler and N. de Souza for help with the experiment at IPNS. This work was funded in part by the Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DE-FC36-50GO15004). B.S. acknowledges the National Science Foundation (Award No. CHE-1152362), the computational resources that were made available by a XSEDE Grant (No. TG-DMR090028), and the use of the services provided by Research Computing at the University of South Florida. This publication is also based on work supported by Award No. FIC/2010/06, made by King Abdullah University of Science and Technology (KAUST).
This publication acknowledges KAUST support, but has no KAUST affiliated authors.