The materials belong to a class called zeolitic imidazolate frameworks (ZIFs). They’re made of metal atoms bridged by one of a number of ring-shaped organic molecules called imidazolates. Prior to Yaghi’s research, 24 types of ZIFs had been developed over the course of 12 years. Yaghi made 25 new versions in just three months. These materials can be extremely versatile, since the metal atoms can act as powerful catalysts, and the organic molecules can serve as anchors for a number of functional molecules.
ZIF proliferation: New automated techniques allow researchers to quickly synthesize dozens of new materials called zeolitic imidazolate frameworks (ZIFs). Credit: Omar Yaghi
The new materials absorb carbon dioxide in part because they’re extremely porous, which gives them a high surface area that can come into contact with carbon dioxide molecules. The most porous of the materials that Yaghi reports in Science contain nearly 2,000 square meters of surface area packed into one gram of material. One liter of one of Yaghi’s materials can store all of the molecules of carbon dioxide that, at zero °C and at ambient pressure, would take up a volume of 82.6 liters.
While the exact mechanisms are not fully understood, Yaghi thinks that the slightly negative charge of organic molecules in his material attracts carbon dioxide molecules, which have a slightly positive charge. As a result, carbon dioxide is held in place, while other gases move through the material. This method of trapping carbon dioxide is better than some other methods because it does not involve strong covalent bonds, so it doesn’t take much energy to release the gas.
The next step for the materials is commercialization. This means scaling up production and incorporating the materials into a system at a power plant, such as by packing the materials into canisters that can be filled with pressurized exhaust gases–something that the UCLA group says could be possible in two to three years. Yaghi estimates that the materials could easily be made in large quantities, since they are similar to other materials he has developed that can now be made by the ton by BASF, the giant chemical company. “Now it’s in the hands of industry,” Yaghi says. And he has developed automated techniques that could lead to more materials that could have even better properties.