Environmental (Commonwealth Union)_ Capturing and storing carbon dioxide (CO2) from the atmosphere is becoming increasingly crucial in the global effort to reduce greenhouse gas levels and mitigate the impacts of climate change. While traditional carbon capture technologies are effective at capturing emissions from concentrated sources like power plants, they struggle with low-concentration CO2 in the ambient air. Direct air capture (DAC), a technique essential for reversing the rising levels of CO2 at 426 parts per million (ppm)—a 50% increase from pre-Industrial Revolution levels—has emerged in response to this challenge. Without direct air capture (DAC), the Intergovernmental Panel on Climate Change (IPCC) set the target of limiting global warming to 1.5°C above pre-industrial averages, which may remain unattainable.
A team of chemists at the University of California, Berkeley, has developed a novel solution that could be instrumental in achieving negative emissions. COF-999, a breakthrough material, is a covalent organic framework (COF) that efficiently captures CO2 from ambient air without degrading in the presence of water or other contaminants, a common issue in existing DAC technologies. This material has the potential to address one of the most significant barriers to large-scale atmospheric carbon capture.
Omar Yaghi, the James and Neeltje Tretter Professor of Chemistry at UC Berkeley and the senior author of the study, highlighted that COF-999 could seamlessly replace existing carbon capture systems in power plants and refineries while also capturing atmospheric CO2 for underground storage. According to Zihui Zhou, a graduate student at UC Berkeley, just 200 grams of this material can absorb 20 kilograms of CO2 annually, roughly equivalent to the carbon-capturing ability of a tree.
“Flue gas capture is a way to slow down climate change by preventing CO2 emissions,” Zhou explained. “Direct air capture, on the other hand, is about taking us back to the atmospheric conditions of 100 years ago.” Zhou emphasized the importance of DAC in not just halting but reversing climate change, particularly given the steady rise in atmospheric CO2 concentrations, which could climb to 500-550 ppm without intervention.
The team at UC Berkeley has been at the forefront of this research, having developed metal-organic frameworks (MOFs) in the past that are capable of extracting water from the air. However, earlier versions of MOFs for carbon capture deteriorated after repeated use, largely due to the instability of the materials under basic conditions. Carbon capture technologies often use amines (NH2 groups), which effectively bind CO2, but they are susceptible to breakdown, particularly in energy-intensive applications.
To solve this issue, Yaghi and his team focused on developing a more robust material—COF-999. Metal ions hold MOFs together, but COFs feature covalent carbon-carbon and carbon-nitrogen double bonds. These bonds are among the strongest in nature, making COF-999 highly resilient. Amines adorn the material’s interior, capturing a greater number of CO2 molecules and significantly increasing its carbon absorption capacity.
“Trapping CO2 from the air is an extremely challenging task,” Yaghi explained. “It requires a material that has high carbon dioxide capacity, is highly selective, water-stable, and recyclable. It also needs to have a low regeneration temperature and be scalable. Meeting all these requirements is a tall order for any material, but COF-999 is up to the task.” While most current carbon capture technologies rely on liquid amines, which are energy-intensive due to the need to heat water, COF-999 requires much less energy and can withstand repeated cycles without degradation.
The team’s experiments show that when air containing 400 ppm of CO2 is passed through COF-999 at room temperature (25 °C) and 50% humidity, the material reaches half of its carbon capture capacity in just 18 minutes and becomes fully saturated in two hours. With further optimization, this time could be significantly reduced. COF-999 can then be regenerated by heating it to a relatively low temperature of 60°C (140°F), allowing the material to release the absorbed CO2 and be reused for subsequent capture cycles. Remarkably, it can withstand 100 cycles of adsorption and desorption without any loss in performance.
Although COF-999 already outperforms other solid carbon sorbents, Yaghi believes there is room for improvement. “Not all the amines in the internal polyamine chains are capturing CO2 yet,” he said, suggesting that modifying the material’s pore size could potentially double its carbon-capturing capacity.
Looking forward, Yaghi envisions the use of artificial intelligence (AI) to accelerate the discovery of new COFs and MOFs with even greater potential for carbon capture. AI could play a critical role in identifying the precise chemical conditions needed to develop these crystalline structures, opening up new avenues for large-scale DAC technologies.
As the world seeks solutions to reduce atmospheric carbon levels and slow the progress of climate change, innovations like COF-999 offer promising pathways forward. With its resilience, efficiency, and scalability, this novel material could become a key tool in the fight to achieve negative emissions and create a sustainable future for generations to come.
