Exotic Powder Pulls Carbon Dioxide from the Air at a Record Rate

Exotic Powder Pulls Carbon Dioxide from the Air at a Record Rate

By Alec Luhn

This story was produced in partnership with the Pulitzer Center’s Ocean Reporting Network.

Scientists and engineers are developing big machines to suck carbon dioxide out of the atmosphere, but the technology sucks up a lot of energy and money as well—as much as $1,000 per metric ton of captured CO₂. Chemists at the University of California, Berkeley, have created a yellow powder they claim could boost this field by absorbing CO₂ much more efficiently.

Detailed climate projections indicate the world will need to remove far more CO₂ than it is doing now to achieve climate targets. The U.S. is investing billions of dollars in start-ups developing direct air capture (DAC) technology, which uses fans to blow air through alkaline materials that bond with the slightly acidic CO₂. Along with lye and crushed limestone, a popular alkaline material is an amine, a compound that is typically manufactured from ammonia.

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Graduate student Zihui Zhou and professor Omar Yaghi, both at U.C. Berkeley, embedded amines in a crystalline compound known as a covalent organic framework, which has extensive surface area. The resulting powder, which they named COF-999, is a microscopic scaffolding of hydrocarbons held together by superstrong carbon-nitrogen and carbon-carbon bonds, such as those found in diamonds. The amines sit in the scaffolding’s open spaces, ready to snag CO₂ molecules passing by. When Zhou and Yaghi pumped air through a tube packed with the powder, it captured CO₂ at the greatest rate ever measured, they wrote in a recent Nature study in October. We were scrubbing the CO₂ out of the air entirely,” Yaghi says.

Besides equipment, the biggest cost for DAC is often energy to heat the absorbent material so it releases the captured CO₂, which is collected in tanks and later injected underground or sold to industry. The powder released CO₂ when heated to 60 degrees Celsius—much less than the more than 100 degrees C needed at current DAC plants. The powder was deployed again to grab CO₂ from the air. After more than 100 catch-and-release cycles, it showed no significant decline in capacity, according to the study.

The COF-999 compound might also compete with liquid amines used in carbon capture and storage scrubbers on refinery and power plant smokestacks, Yaghi says. It’s light enough—200 grams can draw down as much CO₂ in a year as a large tree—that it could potentially strip carbon from the exhaust onboard ships, too.

Companies already manufacture a similar material, metal organic frameworks, to capture CO₂ from smokestacks, as well as for gas masks to protect against hazardous chemicals. In these crystalline structures, the superstrong bonds are formed between metal compounds rather than hydrocarbons. But Yaghi, who owns a company that produces both types of materials, says COF-999 can be more durable, water-resistant and efficient at removing CO₂ than leading metal organic frameworks. A Nature Communications study published in September reported that another covalent organic framework based on phosphate bonds also had potential for carbon capture.

The COF-999 powder hasn’t yet been tested for real-life applications, notes Jennifer Wilcox, a University of Pennsylvania chemical engineer who formerly worked on carbon removal at the U.S. Department of Energy. For example, if it restricts airflow too much when coated on a filter or formed into pellets, that could increase energy consumption by the fans. These kinds of engineering properties, Wilcox says, “will ultimately dictate costs.”