| Mar 11, 2026 |
Moisture driven polymers improve efficiency of direct air carbon capture
Researchers characterized two moisture-swing polymers for direct air capture, finding that macropore structure governs CO2 sorption capacity and kinetics.
|
|
(Nanowerk News) Researchers have identified structural differences in moisture-swing polymers that could lead to better-performing materials for direct air capture of carbon dioxide. A team led by Petra Fromme at Arizona State University conducted a detailed analysis of two commercially available ion-exchange polymers used in moisture-driven direct air capture, revealing how pore structure and molecular architecture govern their ability to adsorb and release CO2.
|
Key Findings
- The polymer with larger macropores, IRA-900, demonstrated greater CO2 uptake capacity and faster initial sorption kinetics than the smaller-pored Fumasep FAA-3.
- Water sorption behavior was similar in both materials, indicating that hydration dynamics depend primarily on molecular-level ordering rather than pore size.
- Surface imaging confirmed the presence of clustering, porosity, and swelling features that directly influence carbon capture performance.
|
|
The study, published in Materials Today Chemistry ("Comprehensive structural characterization of charged polymers involved in moisture-driven direct air capture"), represents the first comprehensive structural characterization of direct air capture materials using a combined suite of techniques that includes X-ray diffraction, small- and wide-angle X-ray scattering, atomic force microscopy, focused ion beam scanning electron microscopy, and transmission electron microscopy. These imaging and diffraction methods were paired with functional sorption experiments to connect material structure to carbon capture behavior.
|
|
Atmospheric carbon dioxide concentrations have risen sharply over the past century, driving global temperature increases and contributing to disrupted weather patterns and intensified drought cycles. Direct air capture paired with permanent storage has emerged as one of several remediation strategies under investigation, alongside reforestation, soil carbon management, biomineralization, ocean fertilization, and bioenergy with carbon capture and storage. Moisture-swing direct air capture is particularly attractive because it uses changes in ambient humidity rather than high-temperature thermal energy to drive the CO2 sorption cycle, offering a potentially lower-energy pathway to atmospheric carbon removal.
|
|
"This work is so important as it shows for the first time the structural characterization of two direct air capture materials with a unique combination of techniques ranging from X-ray diffraction to electron microscopy and atomic force microscopy which we combined with functional studies on the moisture swing mechanisms of carbon dioxide binding and release," explains Fromme, who serves as Paul V. Galvin professor in ASU's School of Molecular Sciences and director of the Biodesign Institute's Center for Applied Structural Discovery.
|
|
The two polymers examined in the study, Fumasep FAA-3 and IRA-900, are both commercially available charged polymers that interact with CO2 through quaternary ammonium functional groups. The researchers subjected both materials to controlled humidity environments and measured their adsorption and desorption of both water vapor and carbon dioxide at varying moisture levels. While the two polymers exhibited nearly identical water uptake and release profiles, their CO2 capture performance diverged substantially. IRA-900, which possesses a more open macroporous architecture, captured more carbon dioxide per unit mass and did so at a faster rate during initial exposure.
|
|
Gayathri Yogaganeshan, a doctoral student in Fromme's group and first author on the paper, led the experimental work. "Our research addresses the urgent challenge of removing carbon dioxide from the atmosphere by investigating materials for low-energy, moisture-driven direct air capture," says Yogaganeshan.
|
|
The imaging techniques revealed distinct morphological features at multiple length scales. Focused ion beam scanning electron microscopy and transmission electron microscopy showed differences in internal pore networks, while atomic force microscopy captured surface-level variations including clustering and swelling behavior under hydrated conditions. Small- and wide-angle X-ray scattering provided information about molecular ordering and repeat distances within the polymer matrix. Together, these observations allowed the researchers to build a multiscale picture of how structure at every level, from molecular arrangement to macroscopic pore geometry, affects the material's carbon capture function.
|
|
"Using advanced structural characterization techniques including X-ray diffraction, SAXS/WAXS, atomic force microscopy, FIB-SEM, and TEM, combined with moisture-swing sorption experiments, we linked molecular-scale ordering, pore architecture, and hydration dynamics to CO₂ uptake and release," explains Yogaganeshan. "We found that hydration dynamics are controlled primarily by molecular structure, while CO₂ sorption kinetics and capacity are strongly influenced by macropore architecture and charge site density, with more open structures exhibiting enhanced uptake and faster initial kinetics. Surface analyses confirmed clustering, porosity, and swelling, revealing how subtle structural features govern performance. These insights provide a foundation for designing more energy-efficient materials for scalable carbon dioxide removal, with implications for advancing practical carbon capture technologies."
|
|
The research team included contributors from multiple institutions. Gayathri Yogaganeshan, Raimund Fromme, and Michele Zacks are based in ASU's School of Molecular Sciences. Rui Zhang contributed from ASU's Eyring Materials Center. Jennifer Wade and Golnaz Najaf Tomaraei are affiliated with The Steve Sanghi College of Engineering at Northern Arizona University. Sharang Sharang works at Tescan USA Inc. in Warrendale, Pennsylvania. Douglas Yates is based at the Singh Center for Nanotechnology at the University of Pennsylvania in Philadelphia. Marlene Velazco Medel contributed from ASU's Center for Negative Carbon Emissions. Martin Uher is affiliated with Tescan Group a.s. in Brno, Czech Republic. Justin Flory contributed from ASU's Walton Center for Planetary Health.
|
|
By establishing clear links between polymer structure and moisture-swing carbon capture performance, the findings offer a framework for rational material design. The identification of macropore architecture and charge site density as key determinants of CO2 sorption could guide the development of next-generation sorbents engineered for higher capacity and faster cycling, moving direct air capture closer to the efficiency levels needed for large-scale atmospheric carbon dioxide removal.
|
