麻豆淫院

As industries seek innovative solutions for carbon capture, scientists have turned to advanced materials that efficiently trap and store carbon dioxide (CO鈧�) from industrial emissions.

A recent study by a team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden University of Technology (TUD), and Maria Curie-Sk艂odowska University in Lublin (Poland) sheds light on the gas adsorption physics of so-called Calgary Framework 20 (CALF-20), a zinc-based metal-organic framework (MOF). The research highlights how CALF-20 efficiently captures CO鈧� while resisting interference from water鈥攁 common issue in carbon capture materials.

The work is in the journal Small.

CO鈧� capture technologies rely on materials that can selectively trap the greenhouse gas from gas streams while minimizing energy consumption. Traditional adsorbents, such as activated carbons and zeolites, often suffer from high-energy demands or poor selectivity in humid environments.

In contrast, CALF-20 stands out due to its high CO鈧� uptake and its mild heat of adsorption and regeneration. It maintains a high selectivity by preferentially adsorbing CO鈧� over water in moderately humid conditions. CALF-20 captures CO鈧� more effectively and absorbs less water in such conditions, when compared to other widely studied similar compounds.

All those MOFs are highly porous and made of metal-oxygen clusters, which are connected in a structured manner by pillars of organic chemicals. This three-dimensional arrangement leads to networks of cavities reminiscent of the pores of a kitchen sponge.

"In this study, we employed a multifaceted approach to investigate CALF-20's CO鈧� adsorption behavior. Using a combination of positron annihilation lifetime spectroscopy (PALS), in situ powder X-ray diffraction (PXRD), as well as gas adsorption experiments, we were able to visualize the interaction between CO鈧� molecules and the material's internal structure under different temperatures and humidity levels," explains Dr. Ahmed Attallah from the Institute of Radiation 麻豆淫院ics at HZDR.

"These insights provide important information for optimizing CO鈧� capture technologies in real-world industrial settings."

A deep dive into adsorption mechanisms

"PALS plays a critical role in analyzing how gases interact with porous materials. This technique measures the lifetime of positronium, a bound state of an electron and a positron, which is sensitive to local free volumes. In porous materials like CALF-20, positronium lifetimes indicate empty spaces, their size, and how they change when gas molecules start to fill the pores," says Prof. Rados艂aw Zaleski from the Maria Curie-Sk艂odowska University, Lublin.

Through PALS, researchers observed that CO鈧� initially gathers at the center of CALF-20's nanopores, forming a structured arrangement before adhering to the pore walls. This progression correlates with increasing CO鈧� pressure, confirming that PALS can track molecular adsorption steps in real time. The method also revealed that even after CO鈧� fills the pores, small free volumes persist, which may be critical for enhancing adsorption efficiency.

PALS was particularly useful in distinguishing how CO鈧� and water interact within the material. Under humid conditions, PALS data showed that water forms isolated clusters at low humidity, but at higher humidity levels, it forms interconnected networks.

"These structural changes affect pore accessibility, yet CALF-20 maintains its significant CO鈧� adsorption capacity at a relative humidity below 40%. Conventional gas adsorption methods alone would struggle to resolve these fine structural variations, demonstrating the unique value of PALS in analyzing dynamic gas-material interactions," TUD's Prof. Stefan Kaskel adds.

The impact of humidity: A key challenge in CO鈧� capture

In industrial applications, CO鈧� is rarely captured from dry gas streams鈥攎oisture is almost always present. This poses a challenge for many materials, as water molecules often compete with CO鈧� for adsorption sites, reducing efficiency.

Through in situ humidity-controlled experiments, the team discovered that CALF-20 maintains a robust CO鈧� adsorption performance even in the presence of water, where the level of relative humidity defines this robustness. At low humidity, water molecules remain isolated within the framework. This network formation alters the material's free volume, but CO鈧� still finds available adsorption sites, demonstrating CALF-20's resilience under humid conditions. At increasingly higher humidity levels, they form interconnected hydrogen-bonded networks, allowing water uptake to dominate.

By integrating PALS with other characterization techniques, this study provides a comprehensive understanding of how CALF-20 captures CO鈧� under diverse environmental conditions. The results suggest that CALF-20 could serve as a scalable and energy-efficient solution for industrial CO鈧� capture, particularly in settings where humidity poses a challenge. Developed by researchers at the University of Calgary, CALF-20 has already been scaled up to multi-kilogram production, making it a strong candidate for real-world applications.

The implications extend beyond fundamental science鈥攖hese insights could pave the way for optimizing next-generation MOFs for large-scale deployment in carbon capture and storage (CCS) applications. Further research will focus on long-term stability and process integration, moving closer to the implementation of CALF-20 in industrial CO鈧� mitigation strategies.