As hurricanes, droughts, and wildfires get more intense, it is increasingly clear that combating climate change will need every tool we have in our belt. One of those is capturing carbon dioxide (CO₂) from air.

But technologies that nab CO₂ directly from air remain expensive, and it takes a lot of energy to release that captured CO₂ for burial or use.

Researchers at the University of California, Berkeley now report a material that releases carbon dioxide at low temperature. The porous material is also unaffected by water or other contaminants. This makes the material stable and reusable, a key advantage over previous materials and one that could bring down carbon capture costs.

In laboratory tests, just 200 grams of the material could absorb up to 20 kilograms of CO₂ per year. That’s as much as a mature tree will capture in that timeframe.

The new material reported in the journal Nature belongs to a family of porous polymers called covalent organic frameworks (COFs), which were invented by Omar Yaghi, a chemistry professor at UC Berkeley and co-author of the paper. COFs have rigid, highly ordered crystalline structures with regularly spaced internal pores that provide a large surface area for gases to stick.

For this particular material, which the team has dubbed COF-999, the Berkeley team attached amine polymers to the material’s hexagonal pores. When air flows through the pores, the amine, which is basic, captures the CO₂, which is acidic. Amine solutions are commonly used right now for direct carbon capture, but heating them up takes a lot of energy. Other solid materials that are being used today degrade after a few uses.

But COF-999 is stable, and the material’s high porosity allows a lot of air through and provides a large surface area to pin CO₂. The material captures the greenhouse gas at a rate at least ten times faster than other carbon capture materials. But since the gas is attached to the surface, it is easily removed at a temperature about half that conventional materials need.

To test COF-999’s abilities, the researchers packed the powder into a stainless steel tube about the size of a straw and kept it outside in the Berkeley air for 20 days. They could reuse the material 100 times without any decline in performance.

“This COF has a strong chemically and thermally stable backbone, it requires less energy, and we have shown it can withstand 100 cycles with no loss of capacity,” Yaghi said in a press release. “No other material has been shown to perform like that. It’s basically the best material out there for direct air capture.”

Source: Zihui Zhou et al. Carbon dioxide capture from open air using covalent organic frameworks. Nature, 2024.

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