Gas storage materials made easy
Fabrication and processing
March 7, 2008
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| Optical photograph of ZIF crystals (0.1–1 mm) and representations of their structures. |
Porous materials are currently used in many applications and are also crucial to next-generation technologies such as CO2 capture.
Researchers from the University of California, Los Angeles (UCLA) have used high-throughput synthesis to create a number of new and promising zeolitic imidazolate frameworks (ZIFs) [Banerjee et al., Science (2008) 319, 939].
It has been suggested that ZIFs, in which transition metal (Zn and Co atoms) replace tetrahedral linkers (Si, Al, and P atoms) and imidazolates replace bridging oxides, could form a class of materials as extensive and useful as the ubiquitous zeolites.
Traditional synthesis routes to find new ZIFs are time consuming, unpredictable, and require large amounts of reagents and solvents. Instead, the UCLA researchers took a systematic approach using high-throughput methods that are traditionally used in drug discovery but have been largely under used in the physical sciences.
“We automated the entire process of synthesis,” explains Rahul Banerjee. “Instead of mixing the chemicals one reaction at a time and achieving perhaps several reactions per day, we were able to perform 200 reactions in less than an hour.”
The approach yielded 25 ZIF crystals from 9600 microreactions, of which 16 have previously unknown compositions and structures and five have new topologies. The new ZIFs have high thermal stability (up to 390°C), chemical stability, and porosity.
Significantly, three of the porous frameworks show exceptional selectivity for CO2 capture from CO2/CO mixtures and a large capacity for storing CO2 (e.g. 1 l of ZIF-69 can store ~83 l of CO2 at 273 K).
“The selectivity of ZIFs to CO2 is unparalleled by any other material,” says lead researcher Omar M. Yaghi. “Now we have structures that can be tailored precisely to capture CO2 and store it like a reservoir.”
Such materials could be used to clean up emissions from power plants or vehicle exhausts. “ZIFs can pluck out CO2 from other gases that are emitted and can hold it,” explains Banerjee. “We are optimistic that in a year or two these materials will be ready to be tested in real power stations,” he adds.
Cordelia Sealy