Paul Boughton
A carbon dioxide capture initiative funded by both BASF and the US Department of... <p><font size="1"><p align="left">Scientists at UCLA have demonstrated that they can successfully isolate and capture carbon dioxidewhich contributes to global warmingrising sea levels and the increased acidity of oceans. Their findings could lead to power plants efficiently capturing carbon dioxide without using toxic materials.</p><p align="left">"The technical challenge of selectively removing carbon dioxide has been overcome" said OmarMYaghiUCLA’s ChristopherSFoote professor of chemistry and co-author of the Science paper in which the new work is revealed.</p><p align="left">"Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoiras 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."</p><p align="left">The carbon dioxide is captured using a new class of materials designed by Yaghi and his group called zeolitic imidazolate frameworksor ZIFs (Fig.1). These are porous and chemically robust structureswith large surface areasthat can be heated to high temperatures without decomposition and boiled in water or organic solvents for a week and still remain stable.</p><p align="left">Rahul Banerjeea UCLA postdoctoral research scholar in chemistry and Anh Phana UCLA graduate student in chemistryboth of whom work in Yaghi’s laboratorysynthesised 25ZIF crystal structures and demonstrated that three of them have high selectivity for capturing carbon dioxide (ZIF-68ZIF-69ZIF-70).</p><p align="left">"The selectivity of ZIFs to carbon dioxide is unparalleled by any other material" said Yaghiwho directs of UCLA’s Centre for Reticular Chemistry and is a member of the California NanoSystems Institute at UCLA. "Rahul and Anh were so successful at making new ZIFs thatfor the purposes of reporting the resultsI had to ask them to stop."</p><p align="left">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 casecarbon dioxide – to pass through and enter the reservoir while blocking larger molecules or molecules of different shapes (Fig.2).</p><p align="left">"We can screen and select the one type of molecule we want to capture" Phan said. "The beauty of the chemistry is that we have the freedom to choose what kind of door we want and to control what goes through the door."</p><p align="left">"The capture of carbon dioxide creates cleaner energy" Yaghi said. "ZIFs in a smokestack would trap carbon dioxide in the pores prior to its delivery to its geologic storage space."</p><p align="left">In ZIFs6869 and 70Banerjee and Phan emptied the porescreating an open framework. They then subjected the material to streams of gases – carbon dioxide and carbon monoxidefor exampleand another stream of carbon dioxide and nitrogen – and were able to capture only the carbon dioxide. They are testing other ZIFs for various applications.</p><p align="left">Carbon dioxide is killing coral reefs and marine lifedamage that will be irreversibleat least for many centuriesYaghi noted.</p><p align="left">Currentlythe process of capturing carbon dioxide emissions from power plants involves the use of toxic materials and requires 20 to 30percent of the plant’s energy outputYaghi said. By contrastZIFs 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.</p><p align="left">"For each litre of ZIFyou can hold 83litres of carbon dioxide"Banerjee said.</p><p align="left">The word ‘ZIF’Yaghi notedis used in the Bible to describe a region of splendour. It also means comeliness and brightness. This name is fitting for this new class of materialshe saidbecause its members are many and of quite beautiful constructions (Fig.3).</p><p align="left">On a fundamental levelthe invention of ZIFs has also addressed two major challenges in zeolite science. Zeolites are stableporous minerals made of aluminiumsilicon and oxygen that are employed in petroleum refining and are used in detergents and other products. Yaghi’s group has succeeded in replacing what would have been aluminium or silicon with metal ions like zinc and cobaltand the bridging oxygen with imidazolate to yield ZIF materialswhose structures can now be designed in functionality and metrics.</p><p align="left">Banerjee and Anh automated the process of synthesis. Instead of mixing the chemicals one reaction at a time and achieving perhaps several reactions per daythey were able to perform 200 reactions in less than an hour. The pair ran 9600 micro-reactions and from those reactions uncovered 25 new structures.</p><p align="left">"We keep producing new crystals of ZIFs every day" Banerjee said. "These reactions produce crystals that look as beautiful as diamonds."</p><p align="left"> </p><p align="left">n the early 1990sYaghi invented another class of materials called metal-organic frameworks (MOFs)which have been described as crystal sponges and which also have implications for cleaner energy. Yaghi can change the components of MOFs nearly at will. Like ZIFsMOFs have pores – openings on the nanoscale in which Yaghi and his colleagues can store gases that are usually difficult to store and transport.</p><p align="left">Yaghi’s laboratory has made several hundred MOFswith a variety of properties and structures. Molecules can pass in and out of them unobstructed. </p><p>OverallBASF funded the synthesis of the materialswhile the DOE funded carbon dioxide absorption and separation studies. </p></font><strong><font face="Zapf Dingbats Bold" size="1" color="#00ffd8">v</font></strong></p>"
