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New Porous Solids for Krypton and Xenon Capture without Cryogenics

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Project #: 22-030 | Year 1 of 2

Mark Morey,a Douglas Hunter,b Marc Schrier,c Mark Phillips,d Bill Harrisone

aSpecial Technologies Lab; bSavannah River National Laboratory, cCalchemist, dPleasanton Ridge Research Corp., LLC., eUniversity Of Aberdeen, Scotland

Executive Summary

Noble gas collection and isotopic analysis are regularly conducted for treaty verification and nonproliferation studies related to the nuclear fuel cycle. This project aims to use newly reported, microporous metal-organic framework (MOF) solids to trap the gases and bypass traditional cryogenic infrastructure.

Description

We have reproduced the synthesis of two recently reported MOF compounds and confirmed their structures with x-ray diffraction and surface area analysis. The micropores of these two MOFs are the ideal diameter to trap noble gases of interest for monitoring events in the nuclear fuel cycle. Traditionally, cryogenic units collect and liquify large volumes of air to later separate the target gases through distillation. This approach is naturally limited by size, weight, power, and access issues, hindering its effectiveness for persistent monitoring. The high affinity and specificity of these newly reported MOFs could enable the collection and possible detection of these noble gases at standard temperatures and atmospheric pressure. In this first year, we prepared a chemistry laboratory by procuring chemicals and special high-pressure reaction vessels for the synthesis. The first round of work was performed at Calchemist laboratory in San Francisco to overcome chemical purchasing setbacks. This first attempt produced sample crystals of the two compounds, calcium and cobalt squarate, respectively. Following this early success, work has continued on optimizing the challenging and fickle cobalt squarate synthesis for scaling up into larger batches. Samples of the two crystals shown in the figure were then sent to Pleasanton Ridge Research in Albuquerque, NM for x-ray and surface area analysis. Results of this x-ray work confirmed the identity of the two target compounds. Work continues to refine the protocol for removing water molecules from within the pore network with heat and high vacuum. This step is required prior to surface area analysis and noble gas uptake studies.

A) Calcium squarate Ca(C4O4) •3H2O MOF made in bulk (left), scanning electron microscope (SEM) picture (middle), and x-ray powder diffraction matched to literature (right). B) Cobalt squarate [Co3(C4O4)2(OH)2] •3H2O crystals 0.1-1 mm under an optical microscope (left, middle), with x-ray powder diffraction matched to literature.
A) Calcium squarate Ca(C4O4) •3H2O MOF made in bulk (left), scanning electron microscope (SEM) picture (middle), and x-ray powder diffraction matched to literature (right). B) Cobalt squarate [Co3(C4O4)2(OH)2] •3H2O crystals 0.1-1 mm under an optical microscope (left, middle), with x-ray powder diffraction matched to literature.

Conclusion

We have successfully reproduced two literature syntheses of microporous MOF materials and confirmed their structure by x-ray diffraction. While the calcium squarate recipe can be easily made in large (0.1-1 kg) quantities, the cobalt squarate MOF material is vastly more challenging. A number of activities are planned for the second year. During the course of studying the cobalt squarate synthesis, two additional compounds were observed with well-defined crystal structure seen under a microscope. One is a non-porous cobalt squarate compound, and the other is a related but possibly new compound and will be studied further by single crystal x-ray diffraction by a new collaborator, Bill Harrison, at the University of Aberdeen, Scotland. Surface area and pore size determination is done by adsorbing gas molecules within the pores at low temperatures. This is made more complex as the pore sizes determined in literature by x-ray are on the scale of the gas molecule itself. Conducting this study with gases other than traditional nitrogen will be emphasized. Once a protocol for water removal from the pores is established and resultant void pore volume is measured, work will be done to determine efficacy for noble gas sequestration. Quantities required for later isotopic analysis will be determined and dictate specifications for future fieldable devices containing these MOFs. Finally, during the past year, yet another MOF article was published detailing a new compound with even higher specificity and affinity for noble gases of interest. Chemical reagents have been procured and this new synthesis will be attempted in October.

Mission Benefit

The field of nuclear non-proliferation is an important, multi-faceted “arms race” between obfuscation and discovery. Progress is made by expanding capabilities to overcome an increasingly clever and expanding roster of motivated adversaries. The first year of this project is on track to move the field of atmospheric sampling forward by overcoming the drawbacks of the current cryogenic process. This work on these new MOFs establishes a route to incorporating these materials in a system for gas collection and preconcentration in the field. We have a current sponsor of a related effort that is fully aware of our progress and would likely be a recipient and user of such a device.

Publications, Technology Abstracts, Presentations/Posters

We have prepared a draft invention disclosure for a device to collect noble gas in the field and measure any resultant beta decay from radioactive isotopes.

References

Li, L., L. Guo, Z. Zhang, Q. Yang, Y. Yang, Z. Bao, Q. Ren, J. Li. 2019. “A Robust Squarate-Based Metal-Organic Framework Demonstrates Record-High Affinity and Selectivity for Xenon over Krypton.” J. Am. Chem. Soc.141(23): 9358-9364. https://doi.org/10.1021/jacs.9b03422.

Pei, J., X.-W. Gu, C.-C. Liang, B. Chen, B. Li, G. Qian. 2022. “Robust and Radiation-Resistant Hofmann-Type Metal−Organic Frameworks for Record Xenon/Krypton Separation.” J. Am. Chem. Soc.,144(7): 3200−3209. https://doi.org/10.1021/jacs.1c12873.

Xiong, X., G. Chen, S. Xiao, Y. Ouyang, H. Li, Q. Wang. 2020. “New Discovery of Metal–Organic Framework UTSA-280: Ultrahigh Adsorption Selectivity of Krypton over Xenon.” J. Phys. Chem. C,124(27): 14603-14612. https://doi.org/10.1021/acs.jpcc.0c02280.

This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy. DOE/NV/03624–1596.

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