Generalised analytical method unravels framework-dependent kinetics of adsorption-induced structural transition in flexible metal–organic frameworks

• Published in: Nature communications Vol. 14; no. 1; p. 6862
• Main Authors: Sakanaka, Yuta, Hiraide, Shotaro, Sugawara, Iori, Uematsu, Hajime, Kawaguchi, Shogo, Miyahara, Minoru T., Watanabe, Satoshi
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08-11-2023; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 639/166/898; 639/638/440/950; 639/638/898; Adsorption; Carbon dioxide; Copper; Differential pressure; Humanities and Social Sciences; Kinetics; Metal-organic frameworks; multidisciplinary; Science; Science (multidisciplinary); Separation; Separation processes; X ray powder diffraction
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-42448-3

Flexible metal–organic frameworks (MOFs) exhibiting adsorption-induced structural transition can revolutionise adsorption separation processes, including CO
2
separation, which has become increasingly important in recent years. However, the kinetics of this structural transition remains poorly understood despite being crucial to process design. Here, the CO
2
-induced gate opening of ELM-11 ([Cu(BF
4
)
2
(4,4’-bipyridine)
2
]
n
) is investigated by time-resolved in situ X-ray powder diffraction, and a theoretical kinetic model of this process is developed to gain atomistic insight into the transition dynamics. The thus-developed model consists of the differential pressure from the gate opening (indicating the ease of structural transition) and reaction model terms (indicating the transition propagation within the crystal). The reaction model of ELM-11 is an autocatalytic reaction with two pathways for CO
2
penetration of the framework. Moreover, gas adsorption analyses of two other flexible MOFs with different flexibilities indicate that the kinetics of the adsorption-induced structural transition is highly dependent on framework structure.
The kinetics of guest-induced structural transition shown by flexible metal–organic frameworks (MOFs) remain poorly understood despite being crucial for process design. Here, three MOFs are studied to reveal the framework-dependent kinetic nature.