A method to capture carbon dioxide directly from ambient air offers a new option for carbon capture and storage strategies to combat global warming.

Using X-ray diffraction, the molecular structure of the simple guanidine compound was analyzed. Carbonate, a crystal that forms when carbon dioxide from air reacts with water, was discovered.

In studying methods to remove environmental contaminants such as sulfate, chromate, or phosphate from water, researchers synthesized a simple compound known as guanidine designed to bind strongly to the contaminants and form insoluble crystals that are easily separated from water. In the process, they discovered a method to capture and release carbon dioxide that requires minimal energy and chemical input.

When an aqueous solution of the guanidine was left open to air, prism-like crystals began to form. It was determined that the crystals contained carbonate, which forms when carbon dioxide from air reacts with water.

Decades of research have led to the development of carbon capture and long-term storage strategies to lessen the output or remove power plants’ emissions of carbon dioxide, a heat-trapping greenhouse gas contributing to a global rise in temperatures. Carbon capture and storage strategies comprise an integrated system of technologies that collect carbon dioxide from the point of release or directly from the air, then transport and store it at designated locations.

A less traditional method that absorbs carbon dioxide already present in the atmosphere, called direct air capture, could also be used at the point where carbon dioxide is emitted. Once carbon dioxide is captured, it needs to be released from the compound so the gas can be transported, usually through a pipeline, and injected deep underground for storage. Traditional direct air capture materials must be heated up to 900 °C to release the gas — a process that often emits more carbon dioxide than initially removed. The new guanidine material offers a less energy-intensive alternative.

Using the process, the bound carbon dioxide was released by heating the crystals at 80-120 °C, which is relatively mild when compared with current methods. After heating, the crystals reverted to the original guanidine material. The recovered compound was recycled through three consecutive carbon capture and release cycles.

The process needs to be further developed and aggressively implemented to be effective in combating global warming. Researchers need to gain a better understanding of the guanidine material and how it could benefit existing and future carbon capture and storage applications.

The team is studying the material's crystalline structure and properties. By analyzing carbonate binding in the crystals, they hope to better understand the molecular mechanism of carbon dioxide capture and release, and help design the next generation of sorbents. The team also plans to evaluate the use of solar energy as a sustainable heat source to release the bound carbon dioxide from the crystals.

For more information, contact Sara Shoemaker at This email address is being protected from spambots. You need JavaScript enabled to view it.; 865-576-9219.

Tech Briefs Magazine

This article first appeared in the July, 2018 issue of Tech Briefs Magazine.

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