Porous material exceeds expectations
Porous materials
February 8, 2008
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| Three-dimensional framework of PCN-14 as cuboctahedral net. |
The search is on for alternative fuels to replace gasoline and diesel for vehicles. One of the most widely available options is methane but there is currently no effective, economic, or safe on-board storage system available.
The US Department of Energy (DOE) has set a target for methane storage to promote the adoption of methane as a fuel. Until now, though, this target has remained elusive.
Now researchers from the Universities of Miami and Pennsylvania, together with the National Institute of Standards and Technology, believe they have broken the DOE target with a new microporous metal-organic framework (MOF) [Ma et al., J. Am. Chem. Soc. (2008) 130, 1012].
The new MOF, PCN-14 (porous coordination network), is based on an anthracene derivative, 5,5’-(9,10-anthracenediyl)di-isophthalate (H4adip).
It crystallizes in the R-3c space group, different from other MOFs (which are typically R-3m), and comprises nanoscale cuboctahedral cages (or intersecting hexagons).
Crucially, PCN-14 is very porous – the solvent accessible volume for desolvated PCN-14 is 63.5%, the estimated Langmuir surface area is 2176 m2/g, and the estimated pore volume is 0.87 cm3/g – slightly higher than MOF-505 (but slightly lower than some other isophthalate-derivative MOFs).
When the researchers analyzed the methane adsorption of PCN-14 at 290 K and 35 bar (the DOE target conditions), they found an absolute methane-adsorption capacity of 230 v/v – smashing the DOE target (of 180 v/v) by 28%.
The result is very promising for methane storage applications. “This material… gives the highest mass loadings of any MOF to date,” comments Neil McKeown of Cardiff University. “Indeed, the amount of methane adsorbed by PCN-14 is comparable with the best performing carbons under practical storage conditions.”
The researchers believe that their strategy of adding more aromatic rings and incorporating nanoscopic cages to framework could lead to even higher methane affinities. Already PCN-14 has achieved a record high for methane-storage materials.
Cordelia Sealy