Loading...
Cleaving carboxyls: understanding thermally triggered hierarchical pores in the metal-organic framework MIL-121
Date
2019
Abstract
Carboxylic acid linker ligands are known to form strong metalcarboxylate bonds to afford many different variations of permanently microporous metal-organic frameworks (MOFs). A controlled approach to decarboxylation of the ligands in carboxylate-based MOFs could result in structural modifications, offering scope to improve existing properties or to unlock entirely new properties. In this work, we demonstrate that the microporous MOF MIL-121 is transformed to a hierarchically porous MOF via thermally triggered decarboxylation of its linker. Decarboxylation and the introduction of hierarchical porosity increases the surface area of this material from 13 m2/g to 908 m2/g, and enhances gas adsorption uptake for industrially relevant gases (i.e., CO2, C2H2, C2H4 and CH4). For example, CO2 uptake in hierarchically porous MIL-121 is improved 8.5 times over MIL-121, reaching 215.7 cm3/g at 195 K and 1 bar; CH4 uptake is 132.3 cm3/g at 298 K and 80 bar in hierarchically porous MIL-121 versus zero in unmodified MIL-121. The approach taken was validated using a related aluminum based MOF, ISOMIL-53. However, many specifics of the decarboxylation procedure in MOFs have yet to be unraveled and demand prompt examination. Decarboxylation, the formation of heterogeneous hierarchical pores, gas uptakes, and host-guest interactions are comprehensively investigated using variable temperature multinuclear solid-state NMR spectroscopy, Xray diffraction, electron microscopy, and gas adsorption; we propose a mechanism for decarboxylation proceeds and which local structural features are involved. Understanding the complex relationship between molecular-level MOF structure, thermal stability, and the decarboxylation process is essential to fine-tune MOF porosity, thus offering a systematic approach to the design of hierarchically porous, custom-built MOFs suited for targeted applications.
Supervisor
Description
peer-reviewed
Publisher
American Chemical Society
Citation
Journal of the American Chemical Society;141 (36), pp. 14257-14271
Collections
Files
Keywords
Funding code
Funding Information
Science Foundation Ireland (SFI), Natural Science and Engineering Research Council (NSERC), National Research Council of Canada, Natural Science Foundation of China
Sustainable Development Goals
External Link
Type
Article
Rights
https://creativecommons.org/licenses/by-nc-sa/1.0/