In the poem "I ask you," poet An Do-hyeon asked, "Do not carelessly kick coal briquette ash with your foot/Have you ever been someone burning hot for anyone, even once?" Now we should also say, do not carelessly throw away okara, the leftover pulp from making tofu. Have you ever once captured greenhouse gases?
Scientists at the Swiss Federal Institute of Technology Zurich said on the 11th (local time) that they developed a material that directly captures carbon dioxide from the air using food waste left over from making cheese and tofu. According to the team, the efficiency of carbon dioxide capture using food waste was up to 50% better than existing technologies. The findings were published in the Proceedings of the National Academy of Sciences.
Carbon dioxide is a greenhouse gas that causes global warming. In 2015, 195 countries, including Korea, signed the Paris Agreement and agreed to reduce greenhouse gas emissions so that the global average temperature does not rise more than 1.5 degrees Celsius above the preindustrial level. The best method is to remove carbon dioxide directly from the atmosphere, but it has not been put to practical use because it consumes a lot of energy.
◇ Cheese and tofu pulp reborn as a sponge that captures carbon
A research team led by Professor Raffaele Mezzenga in the Department of Materials Science at the Swiss Federal Institute of Technology Zurich processed food waste generated during cheese and tofu production into protein beads. The protein beads efficiently bound and then released carbon dioxide with only a small amount of energy.
Whey left over from making cheese and okara, a tofu byproduct, contain a lot of protein. According to the National Standard Food Composition Table, 100 g of okara contains 4 g of protein. That is less than the 9.62 g in 100 g of tofu, but still a considerable amount. The researchers separated protein from the waste in cheese and tofu production and formed long, threadlike chains called amyloid fibrils. When they injected potassium hydroxide, beads with a diameter of 0.5–1 cm were produced.
In experiments, the protein beads extracted 0.097 g of carbon dioxide from the air per 1 g. That means with just 1 kg of protein beads, about 100 g of carbon dioxide can be separated. The team said this result was 10%–50% better than existing direct air capture (DAC) technologies.
The agent that extracts carbon dioxide from the protein beads is potassium hydroxide. Potassium hydroxide is a strong base that, when it meets the acidic oxide carbon dioxide, immediately triggers an acid-base neutralization reaction to form carbonate and water. The protein obtained from cheese and tofu waste acts as a support that holds potassium hydroxide in place so it does not run off or clump, allowing contact with air over a large surface area. Mezzenga said, "The protein beads are like a sponge that, through potassium hydroxide, absorbs large amounts of carbon dioxide."
◇ Easy carbon release, materials also recyclable
Conventional DAC methods require applying heat and a negative pressure lower than ambient pressure to the carbon-absorbing material to release carbon dioxide again. That allows carbon dioxide to be stored or converted into other substances, but the process consumes a lot of energy. In that case, the costs outweigh the benefits and the economics suffer.
Mezzenga said the carbon dioxide sorbent made from food waste also has an advantage here. At room temperature, alternating sprays of a weak acid and base onto the protein beads for about 10 minutes break the chemical bonds and allow carbon dioxide to be separated again. The team said the acid and base used at this stage, as well as the protein beads, can be reused afterward.
Zhou Dong, the first author of the paper, said, "Synthetic materials currently used for carbon dioxide capture degrade quickly, but the protein beads we developed remain stable for a long time." The team said that in the lab they repeated carbon dioxide adsorption and release 30 times without any drop in efficiency.
Of course, the protein beads must be replaced after being used thousands of times. Mezzenga said these too can be recycled. Because the composition is protein, they can be used as agricultural fertilizer or converted into biofuel, the team explained. He added that because the material is food grade and nontoxic, it causes less environmental pollution than other carbon dioxide capture methods.
The researchers are scaling up experiments to commercialize the carbon-capturing protein beads. They said they separated up to 50 g of carbon dioxide in a laboratory setting using only a few grams of protein beads. The team has not yet calculated the exact capture expense per metric ton of carbon dioxide, but expects it to be much lower than existing technologies.
References
PNAS (2026), DOI: https://doi.org/10.1073/pnas.2535689123