One approach receiving growing attention is direct air capture (DAC), a process that removes CO₂ directly from the air. Companies and research teams have spent years developing DAC systems, and ETH Zurich spin-off Climeworks, founded in 2009, was among the first to bring the technology to market. Despite this progress, capturing carbon from the atmosphere remains expensive and requires large amounts of energy.

Protein Beads Made From Food Industry Waste

Researchers at ETH Zurich have now developed a new carbon capture material made from an unexpected source: waste products from dairy and tofu manufacturing.

In a study published in PNAS, a team led by materials scientist Raffaele Mezzenga, a professor in ETH Zurich's Department of Health Sciences and Technology, describes a method that uses whey and byproducts from tofu production to absorb CO₂.

Large amounts of protein-rich liquid are generated during dairy and tofu production. Only a portion is reused in food manufacturing, while much of the remainder is discarded. The researchers extracted proteins from this waste stream and assembled them into long thread-like structures known as amyloid fibrils.

These fibrils were then combined with potassium hydroxide and formed into porous beads measuring about half a centimeter to one centimeter in diameter.

"The resulting material is like a sponge that can absorb large quantities of CO₂ via the potassium hydroxide," Mezzenga explains.

Carbon Capture Performance Exceeds Existing Methods

When exposed to air, the potassium hydroxide inside the beads reacts with CO₂, producing hydrogen carbonate, a salt of carbonic acid. This reaction effectively removes carbon dioxide from the atmosphere.

"In our tests with ambient air, we were able to extract 97 milligrams of CO₂ with one gram of material," explains Zhou Dong, a postdoctoral researcher in Mezzenga's group and lead author of the study.

According to Dong, that performance is exceptionally strong, exceeding the capacity of conventional DAC technologies by 10 to 50 percent. He estimates that one kilogram of the protein beads could theoretically capture and isolate about 100 grams of CO₂ during a single operating cycle.

Lower Energy Carbon Removal

Traditional direct air capture systems typically rely on heat and negative pressure to release captured CO₂ from the materials that hold it. The recovered carbon dioxide can then be stored or converted into other products, keeping it out of the atmosphere over the long term.

Because this process consumes significant amounts of energy, DAC facilities are generally most practical in locations with abundant renewable energy resources.

The ETH Zurich team developed a different approach. To release the captured CO₂, the researchers alternately spray the protein beads with a mild acid and a mild base for roughly 10 minutes at room temperature. This process breaks the chemical bonds holding the CO₂, allowing it to be collected.

Reusable Beads Support a Circular Economy

The acid, base, and protein beads can all be reused.

"The synthetic materials that are used to capture CO₂ today decompose quickly," says Dong. "By contrast, our protein beads remain stable for a long time."

Laboratory tests showed that the material maintained its performance through 30 cycles of carbon capture and release, with no major loss of efficiency.

Over time, the adsorption capacity would eventually decline. Mezzenga estimates that replacement might be necessary after several thousand cycles. However, because the beads are entirely organic, they could then be repurposed as agricultural fertilizer or converted into biofuel.

Their biodegradable nature could allow the technology to fit into a broader circular economy model, reducing waste while continuing to provide value after the beads are retired from carbon capture use.

"The materials we use for this process are non-toxic and are food-grade," Mezzenga points out.

The team also conducted a life cycle analysis and found that the new approach creates less environmental pollution over its full lifespan than existing DAC technologies.

Can the Technology Scale Up?

Although the results are promising, additional testing will be needed to determine whether the technology can operate effectively on an industrial scale while maintaining its high carbon capture capacity.

For the current study, researchers worked in a controlled laboratory setting using only a few grams of material and captured roughly 50 grams of CO₂.

Mezzenga remains optimistic about the technology's future. He has spent nearly two decades studying amyloid fibrils and has previously used them to develop biodegradable plastic alternatives and water purification technologies.

"We're confident that the technology is scalable," he says.

According to Mezzenga, the spray-based system used to release CO₂ is compatible with industrial techniques that are already widely used. Dong will continue investigating how the process performs at larger scales.

The researchers have not yet calculated the exact cost of capturing a ton of CO₂ using the new material. Even so, Mezzenga expects it to be substantially less expensive than conventional direct air capture systems.

"Our technology is cheaper and more sustainable because it requires little energy and is based on a widely available waste product," he says. "That could be a game changer for the future of removing CO₂ from the air."