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Effects of functionalization, catenation, and variation of the metal oxide and organic linking units on the
Jesse L C Rowsell1, Omar M Yaghi
1Department of Chemistry, University of Michigan, Ann Arbor, 48109, USA.
Journal of the American Chemical Society
|January 26, 2006
Summary
Metal-organic frameworks (MOFs) show promising dihydrogen adsorption. Catenated IRMOFs offer high capacity, while MOF-74 and HKUST-1 exhibit enhanced H(2) uptake due to specific metal sites.
Area of Science:
- Materials Science
- Chemistry
- Chemical Engineering
Background:
- Metal-organic frameworks (MOFs) are porous materials with tunable structures.
- Efficient hydrogen storage is crucial for clean energy applications.
- Understanding structure-adsorption relationships in MOFs is key for optimizing hydrogen uptake.
Purpose of the Study:
- To investigate correlations between structural features of MOFs and their dihydrogen (H(2)) adsorption properties.
- To identify MOF designs that enhance H(2) storage capacity and affinity.
- To compare H(2) adsorption behavior across different MOF families, including IRMOFs, MOF-74, and HKUST-1.
Main Methods:
- Measurement of dihydrogen adsorption isotherms for eight MOFs at 77 K and up to 1 atm.
- Analysis of structural parameters, including pore volume and metal oxide units.
- Calculation of isosteric heats of adsorption to assess H(2) affinity.
Main Results:
- All MOFs exhibited Type I isotherms without hysteresis; saturation was not reached.
- Catenated IRMOFs showed the highest molar H(2) capacities (up to 9.8 H(2)/formula unit).
- MOFs with coordinatively unsaturated metal sites (MOF-74, HKUST-1) demonstrated greater H(2) uptake and affinity compared to IRMOFs.
Conclusions:
- MOF structural modifications, particularly the metal oxide units and pore dimensions, significantly influence H(2) adsorption.
- Enhanced H(2) uptake can be achieved by increasing charge gradients on metal oxide units and constricting pore sizes.
- A large pore volume remains a prerequisite for effective H(2) adsorption in MOFs.
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