New Study Could Help Develop More Efficient Ways to Capture CO2 from Air

A research team has successfully visualized how carbon dioxide (CO₂) acts in an ionic liquid that selectively absorbs CO₂. The study results are likely to help create more efficient techniques to trap CO₂ in the atmosphere, one of the key factors triggering global warming.

Each year, the levels of CO₂ in the air—a key factor in global warming—continuously increase, leading to serious concerns about the Earth’s future. Industrial societies should take steps to reduce CO₂ emissions to mitigate global warming.

One method is to isolate and collect CO₂ before it is emitted into the air. While this is, in part, already happening, it has not been very successful. Thus, there is a pressing need to build technology that can isolate and collect CO₂ more effectively, not only to safeguard the environment but also to boost the recycling of CO₂ as a resource.

The use of ion liquids to efficiently absorb CO₂ has been the topic of vigorous research. However, further exploration of the behavior of CO₂ absorbed in ionic liquids is necessary to enhance the materials used in the CO₂ separation and collection process. Ionic liquids are fluids without any standard structure, and thus it has been hard to directly note the state of CO₂ absorbed in them.

In the current research, the focus of the research team, including Professors Shin-ichiro Noro and Takayoshi Nakamura, both of Hokkaido University’s Graduate School of Environmental Science, was on a soft crystal, a material that has both the regularity of a crystal and the softness of a liquid. They produced a soft crystal comprising components of an ionic liquid that absorbed CO₂.

As expected, the soft crystal preserved its regularity even after absorbing CO₂, rendering it feasible to carry out X-ray diffraction analysis.

The examination revealed that the absorbed CO₂ interacts with both fluorine and oxygen atoms of the bis(trifluoromethylsulfonyl)imide anion, a component of the ionic liquid. Moreover, the researchers’ theoretical analysis indicated that dispersion and electrostatic interactions occur between CO₂ and the framework, thereby producing the force that binds CO₂ to the anion.

The study results would help design and develop ionic liquids that can efficiently separate and collect CO₂ and will possibly hasten practical applications of such liquids, which is a crucial step in eliminating the negative impacts of global warming.

The focus of Shin-ichiro Noro is on the creation of porous materials to facilitate environmental restoration and conservation, while the focus of Takayoshi Nakamura’s work is on the development of molecular devices for a broad range of applications.

Journal Reference:

Zheng, X., et al. (2020) Understanding the interactions between the bis(trifluoromethylsulfonyl)imide anion and absorbed CO₂ using X-ray diffraction analysis of a soft crystal surrogate. Communications Chemistry. doi.org/10.1038/s42004-020-00390-1.