Pulling Carbon Dioxide Out of the Air

Northwestern University, Evanston, IL

Even as the world slowly begins to decarbonize industrial processes, achieving lower concentrations of atmospheric carbon requires technologies that remove existing carbon dioxide from the atmosphere — rather than just prevent the creation of it.

Typical carbon capture catches CO₂ directly from the source of a carbon-intensive process. Ambient carbon capture, or “direct air capture” (DAC), on the other hand, can take carbon out of typical environmental conditions and serves as one weapon in the battle against climate change, particularly as reliance on fossil fuels begins to decrease and with it, the need for point-of-source carbon capture.

New research from Northwestern University shows a novel approach to capture carbon from ambient environmental conditions that looks at the relationship between water and carbon dioxide in systems to inform the “moisture-swing” technique, which captures CO₂ at low humidity and releases it at high humidity. The approach incorporates innovative kinetic methodologies and a diversity of ions, enabling carbon removal from virtually anywhere. The study was published in the journal Environmental Science and Technology.

“We are not only expanding and optimizing the choice of ions for carbon capture, but also helping unravel the fundamental underpinnings of complex fluid-surface interactions,” said Senior Author Vinayak P. Dravid. “This work advances our collective understanding of DAC, and our data and analyses provide a strong impetus to the community, for theorists and experimentalists alike, to further improve carbon capture under practical conditions.”

Co-First Author Benjamin Shindel said the idea behind the paper came from a desire to use ambient environmental conditions to facilitate the reaction.

“We liked moisture-swing carbon capture because it doesn’t have a defined energy cost,” Shindel said. “Even though there’s some amount of energy required to humidify a volume of air, ideally you could get humidity ’for free,’ energetically, by relying on an environment that has natural dry and wet reservoirs of air close together.”

“Not only have we doubled the number of ions that exhibit the desired humidity-dependent carbon capture, we have also discovered the highest-performing systems yet,” Co-First Author John Hegarty said.

In recent years, moisture-swing capture has taken off. Traditional carbon capture methods use sorbents to capture CO₂ at point-of-source locations, and then use heat or generated vacuums to release CO₂ from the sorbent. It comes with a high-energy cost.

“Traditional carbon capture holds onto CO₂ tightly, which means it takes significant energy to release it and reuse it,” Hegarty said.

It also doesn’t work everywhere, Shindel said. Agriculture, concrete, and steel manufacturers, for example, are major contributors to emissions but take up large footprints that make it impossible to capture carbon at a single source.

“DAC is a complex and multifaceted problem that requires an interdisciplinary approach,” Senior Author Omar Farha said. “What I appreciate about this work is the detailed and careful measurements of complex parameters. Any proposed mechanism must explain these intricate observations.”

The team believes that future experiments, coupled with computational modeling, will help better explain why certain ions are more effective than others.

Dravid’s team plans to integrate such CO_2-capturing materials with their earlier porous sponge platform, which has been developed to remove environmental toxins including oil, phosphates, and microplastics.

For more information, contact Northwestern media relations at This email address is being protected from spambots. You need JavaScript enabled to view it.; 847-491-5001.

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