Advanced Materials
1 Dec 2021

Metal-organic Framework Materials (MOFs) as Passive Systems for Long Duration Space Missions

Fig. 1: Example of a cubic molecular unit cell structure (8 cells) in MOF-5. Yellow and orange spheres represent the internal pore volume contained in each pocket. Zinc atoms visible at nodes with organic linkers forming the edges. Source: Wikimedia
Fig. 1: Example of a cubic molecular unit cell structure (8 cells) in MOF-5. Yellow and orange spheres represent the internal pore volume contained in each pocket. Zinc atoms visible at nodes with organic linkers forming the edges. Source: Wikimedia

Metal-organic frameworks (MOFs) are functional materials with the potential to replace complex devices for performing crucial mission operations. These include e.g. gas capture; separation and storage; water splitting; enhanced catalysis; and when augmented with organic plant matter, even enhanced photosynthesis.

Their incredible properties are due to their highly ordered nanoporosity. Pores are arranged in a crystalline, cage-like molecular structure made up of repeating “pockets” bounded by organic-inorganic hybrid bonds (Fig. 1). The combination of metal nodes and organic linkers creates highly configurable cage topologies, with experimental active surface area up to >7000 m2/g being reported [1]. Contrary to other nanoporous materials, MOFs offer unparalleled tunability, by which researchers can swap metal atoms and organic chains to tailor the pocket size and composition to the absorption of specific gasses.

In addition to rapidly growing applications on earth, these crystalline materials could prove especially useful during long duration space missions, since they reduce reliance on mechanical devices with complex mechanisms prone to failure and repair. The prospect of high-volume gas storage in a nanoporous medium is a particularly attractive multifunctional solution, addressing challenges in fuel sequestration and transport, but also delivering protection from the harsh radiation environment in space. The latter will be a focus of this work.

Project overview

The high volumetric gas adsorption capacity in MOFs promotes the incorporation of immense volumes of e.g. hydrogen and methane; gasses composed largely of low-Z elements well-suited for inhibiting neutron collisions when properly contained [2]. MOFs may thus help address the major challenge of protecting spacecraft and astronauts from neutron radiation. We hypothesize that H-filled MOFs could provide similar protection to water-filled spacecraft "hulls", but in much thinner and lighter form factor.

This project seeks to synthesize MOFs in-house and asses their viability in the space environment. To this end, their stability under exposure to vacuum, UV, cosmic radiation, etc. is tested in collaboration with the Materials and Electrical Components Laboratory at ESTEC. From there, manufacturability and performance are assessed. While MOFs are conventionally synthesized as fine powders, this poses a great challenge to handling and storage. To improve their practical utility for space applications, we are instead creating MOF-laden gels tailored for 3D-printing of robust, monolithic structures [3-5]. We hereby improve handling in-situ, and drastically increase scalability of the material deposition.

Finally, a later stage of the project will apply newly gained knowledge from the above to a computational inverse design framework. Its goal will be to predict optimal, mission-specific MOFs with targeted composition for space-relevant tasks. Inspired by the work of [6], the idea is to use machine learning to scan the immense molecular landscape (90,000 unique MOF combinations to date) and propose novel archictures that consider space environmental and manufacturing constraints.

References:

[1] O. K. Farha et al., “Metal–Organic Framework Materials with Ultrahigh Surface Areas: Is the Sky the Limit?,” J. Am. Chem. Soc., vol. 134, no. 36, pp. 15016–15021, Sep. 2012, doi: 10.1021/ja3055639.

[2] K. Rojdev and W. Atwell, “Hydrogen- and Methane-Loaded Shielding Materials for Mitigation of Galactic Cosmic Rays and Solar Particle Events,” Gravitational and Space Research, vol. 3, p. 24, 2015.

[3] G. J. H. Lim et al., “3D-Printing of Pure Metal–Organic Framework Monoliths,” ACS Mater. Lett., vol. 1, no. 1, pp. 147–153, Jul. 2019, doi: 10.1021/acsmaterialslett.9b00069.

[4] H. Thakkar, S. Eastman, Q. Al-Naddaf, and F. Rezaei, “3D-Printed Metal-Organic Framework Monoliths for Gas Adsorption Processes,” ACS Appl. Mater. Interfaces, vol. 9, Sep. 2017, doi: 10.1021/acsami.7b11626.

[5] S. Lawson, A.-A. Alwakwak, A. A. Rownaghi, and F. Rezaei, “Gel–Print–Grow: A New Way of 3D Printing Metal–Organic Frameworks,” ACS Appl. Mater. Interfaces, vol. 12, no. 50, pp. 56108–56117, Dec. 2020, doi: 10.1021/acsami.0c18720.

[6] Z. Yao et al., “Inverse design of nanoporous crystalline reticular materials with deep generative models,” Nat Mach Intell, vol. 3, no. 1, Art. no. 1, Jan. 2021, doi: 10.1038/s42256-020-00271-1.

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Advanced Concepts Team