Evolution of water structures in metal-organic frameworks for improved atmospheric water harvesting

• Published in: Science (American Association for the Advancement of Science) Vol. 374; no. 6566; pp. 454 - 459
• Main Authors: Hanikel, Nikita, Pei, Xiaokun, Chheda, Saumil, Lyu, Hao, Jeong, WooSeok, Sauer, Joachim, Gagliardi, Laura, Yaghi, Omar M.
• Format: Journal Article
• Language: English
• Published: United States The American Association for the Advancement of Science 22.10.2021; AAAS
• Subjects: Air temperature; Atmospheric water; Clusters; Crystals; Density functional theory; Enthalpy; Evolution; Metal-organic frameworks; Pores; Porous materials; Regeneration; Science & Technology - Other Topics; Single crystals; Water; Water chemistry; Water harvesting; Water uptake; X-ray diffraction
• ISSN: 0036-8075; 1095-9203; 1095-9203
• DOI: 10.1126/science.abj0890

Although the locations of water molecules in some porous materials have been determined with diffraction techniques, determining the filling sequence of water sites has been challenging. Hanikel et al . used single-crystal x-ray diffraction to locate all of the water molecules in pores of the metal-organic framework MOF-303 at different water loadings (see the Perspective by Öhrström and Amombo Noa). They used this information on the water molecule adsorption sequence to modify the linkers of this MOF and control the water-harvesting properties from humid air for different temperature regimes. —PDS The water uptake mechanism in a metal-organic framework informed optimization to improve uptake from humid air. Although the positions of water guests in porous crystals can be identified, determination of their filling sequence remains challenging. We deciphered the water-filling mechanism for the state-of-the-art water-harvesting metal-organic framework MOF-303 by performing an extensive series of single-crystal x-ray diffraction measurements and density functional theory calculations. The first water molecules strongly bind to the polar organic linkers; they are followed by additional water molecules forming isolated clusters, then chains of clusters, and finally a water network. This evolution of water structures led us to modify the pores by the multivariate approach, thereby precisely modulating the binding strength of the first water molecules and deliberately shaping the water uptake behavior. This resulted in higher water productivity, as well as tunability of regeneration temperature and enthalpy, without compromising capacity and stability.