In order to achieve the Paris Agreement’s goal of limiting the global temperature increase to 1.5-2 degrees compared to the level of 1990, it is necessary to develop and implement new technologies to limit – and even better remove – some of the greenhouse gases emitted in the atmosphere through time.

This process is called CO₂ capture and storage (CCS). The technique most used so far is the collection of flue gases from, for example, coal-fired power plants. Now researchers from the American research institute Sandia National Laboratories have presented an alternative form of CO₂ capture and storage.

Clay can collect CO₂ like a sponge

In the scientific article in the journal The Journal of Physical Chemistry Letters, a team of researchers presents clay as a bid for a material that has the potential to contribute to solving global warming.

Tuan Ho, a chemical engineer and leader of the research team, and his colleagues have used powerful computer models in conjunction with laboratory experiments to investigate how a particular type of clay can absorb CO₂ like a sponge and store it.

“These fundamental results have the potential to capture CO₂ directly from the air – this is what we are working towards. Clay is really cheap and is found in abundance in nature. It should enable us to significantly reduce the cost of CO₂ capture in the air if this high-risk, high-reward project ultimately leads to a technology,” says Ho, lead author of the paper.

Converts carbon dioxide (CO₂) to carbonic acid (H 2 CO 3 ) in clay

Tuan Ho envisions a device based on clay that acts like a sponge and absorbs carbon dioxide from the air. The collected CO₂ can then be “squeezed” out of the sponge and pumped into the underground.

The device will differ from existing technologies by being cheap, and at the same time clay is widely used and also has stable properties with a large surface area. This is because clay consists of many microscopic particles with cracks and fissures, which are about a hundred thousand times smaller than the diameter of a human hair – also called nanopores.

The researchers have made use of a type of computer simulation called molecular dynamics , where the interaction and movements between atoms and molecules are examined on a nanoscale. With the simulations, the researchers have found that CO₂ is stored much more stably in nanopores in wet clay compared to pure water. When carbon dioxide dissolves in water, carbonic acid (H 2 CO 3 ) is formed. However, the conversion of CO₂ to carbonic acid in the nanopores is even more efficient than in pure water, it says.

Similarly, researchers from Purdue University have also recently found that water enclosed in nanopores of clay absorbs more CO₂ than ordinary water does.

“This tells us so far that clay is a good material for capturing CO₂ and turning it into another molecule. And we understand why that is so that the synthesis scientists and engineers can change the material to improve it. The simulations can also be helpful in testing new hypotheses.”

Will develop clay based unit over three years

The next step for the researchers is to use the molecular dynamics simulations and experiments to find out how to get CO₂ out of the nanopores. Within the project’s three-year term, Tuan Ho hopes to have developed a clay-based device that can capture CO₂ from the air.

And if all goes well, it could prove to be an important tool in the fight against global warming.


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