“The underlying chemistry is really the same as what happens with hydroxide solutions in water. But by doing it in these sponge-like materials, you gain a lot of advantages. The carbon-dioxide capture is very fast, it can have a very high capacity and it may be very stable to oxygen.”Phillip Milner, Cornell University
One promising strategy for helping to tackle the growing climate crisis is the development of materials that can capture the carbon dioxide released by a range of industrial facilities. A big hitch is the sheer volume of carbon-capture material that would be required to make an impact, and the equally high price tag that would come with manufacturing it. On top of that, many of the leading contenders for carbon capture degrade quickly from oxidation.
Now, an international collaboration led by Phillip Milner, assistant professor of chemical and chemical biology at Cornell University, has developed porous, sponge-like materials that can trap carbon dioxide in their cavities while allowing other gases such as nitrogen to pass through. The materials are made from sugar and low-cost alkali metal salts, making them inexpensive enough for large-scale deployment, and could prove particularly effective for limiting the environmental damage of coal-fired power plants. The researchers describe the novel material in a paper in Angewandte Chemie.
For the past 100 years, the leading method for carbon capture in chemistry has been a process known as amine scrubbing. Amines are organic, ammonia-derived compounds that contain nitrogen; in an aqueous solution, they are able to selectively remove carbon dioxide from gas mixtures. However, oxygen degrades the amines every time they’re used, requiring more and more of the material to be produced, which drives up the cost of carbon capture.
Rather than trying to figure out how to overcome the oxidation problem in amines, Milner’s lab has been experimenting with a different family of materials and designing them specifically for capturing carbon dioxide.
This latest project focuses on sponge-like materials containing hydroxide sites in their pores. Typically, solutions of hydroxide salts reversibly react with carbon dioxide to form bicarbonate salts such as baking soda, thereby trapping the carbon dioxide. But in order to regenerate the hydroxide salt, the material needs to be heated up to 500–800°C – no easy feat, and not a cheap one either.
Lead author Mary Zick, a doctoral student at Cornell, found that by boiling bundles of sugar molecules called cyclodextrins with alkali metal salts in water, she could create a sponge-like material that is riddled with cavities in which carbon dioxide binds strongly, but other gases such as nitrogen pass easily through.
“We expose the material to mixtures of carbon dioxide and nitrogen and see if they can absorb the carbon dioxide and ignore the nitrogen, which is the major component of air and emission streams,” Milner said. “The underlying chemistry is really the same as what happens with hydroxide solutions in water. But by doing it in these sponge-like materials, you gain a lot of advantages. The carbon-dioxide capture is very fast, it can have a very high capacity and it may be very stable to oxygen.”
The reversible reactions allow carbon dioxide to be released at relatively low temperatures of 80–120°C. And the material’s tunability could make it useful for an array of other applications, from drug delivery to catalysis to gas storage.
“Coal emissions are still the No. 1 anthropogenic contributor to carbon dioxide emissions in the world,” Milner said. “What’s nice about this work is that Mary not only found a material that’s useful for carbon dioxide capture from coal flue gas, but she outlined the structure-property relationships that will allow us to design materials for other applications, like capturing carbon dioxide from natural-gas-fired power plants, as well as maybe even from air, which is one of the really big challenges of our time.”
An additional bonus of the project is the instrumentation that Zick custom-built to analyze if a gas mixture could be separated in a solid material – a capability that wasn’t previously available at the university. Now Milner’s group is using this modular apparatus to test samples from other Cornell researchers.
“We’ve got people coming out of the woodwork to do these experiments,” Milner said. “We have a little hub now. If somebody brings us some material, in a week or two Mary can tell you if it’s promising for carbon dioxide capture.”
This story is adapted from material from Cornell University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.