UCLA scientists have demonstrated that they can successfully isolate and capture carbon dioxide, which contributes to global warming, rising sea levels and the increased acidity of oceans. Their findings could lead to power plants efficiently capturing carbon dioxide without using toxic materials.
The carbon dioxide is captured using a new class of materials designed by Omar M. Yaghi, UCLA's Christopher S. Foote Professor of Chemistry and his group, shown above, called zeolitic imidazolate frameworks, or ZIFs. These are porous and chemically robust structures, with large surface areas, that can be heated to high temperatures without decomposition and boiled in water or organic solvents for a week and still remain stable.
"Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoir, as we have demonstrated. No carbon dioxide escapes. Nothing escapes — unless you want it to do so. We believe this to be a turning point in capturing carbon dioxide before it reaches the atmosphere."
-- Omar M. Yaghi
Currently, the process of capturing carbon dioxide emissions from power plants involves the use of toxic materials and requires 20 to 30 percent of the plant's energy output, Yaghi said. By contrast, ZIFs can pluck carbon dioxide from other gases that are emitted and can store five times more carbon dioxide than the porous carbon materials that represent the current state-of-art.
Graduate students synthesized 25 ZIF crystal structures and demonstrated that three of them have high selectivity for capturing carbon dioxide (ZIF-68, ZIF-69, ZIF-70).
The inside of a ZIF can store gas molecules. Flaps that behave like the chemical equivalent of a revolving door allow certain molecules — in this case, carbon dioxide — to pass through and enter the reservoir while blocking larger molecules or molecules of different shapes.
In ZIFs 68, 69 and 70, Banerjee and Phan emptied the pores, creating an open framework. They then subjected the material to streams of gases -- carbon dioxide and carbon monoxide, for example, and another stream of carbon dioxide and nitrogen — and were able to capture only the carbon dioxide.