Exploring cation distribution in ion-exchanged Al,Ga-containing metal-organic frameworks using 17O NMR spectroscopy

Zachary H. Davis, Russell E. Morris*, Sharon E. Ashbrook*

*Corresponding author for this work

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Abstract

A mixed-metal metal–organic framework, (Al,Ga)-MIL-53, synthesised by post-synthetic ion exchange has been investigated using solid-state nuclear magnetic resonance (NMR) spectroscopy, microscopy and energy dispersive X-ray (EDX) spectroscopy. 17O enrichment during the ion-exchange process enables site specific information on the metal distribution to be obtained. Within this work two ion-exchange processes have been explored. In the first approach (exchange of metals in the framework with dissolved metal salts), 17O NMR spectroscopy reveals the formation of crystallites with a core–shell structure, where the cation exchange takes place on the surface of these materials forming a shell with a roughly equal ratio of Al3+ and Ga3+. For the second approach (exchange of metals between two frameworks), no core–shell structure is observed, and instead crystallites containing a majority of Al3+ are obtained with lower levels of Ga3+. Noticeably, these particles show little variation in the metal cation distribution between crystallites, a result not previously observed for bulk (Al,Ga)-MIL-53 materials. In all cases where ion exchange has taken place NMR spectroscopy reveals a slight preference for clustering of like cations.
Original languageEnglish
Pages (from-to)20267-20280
Number of pages14
JournalPhysical Chemistry Chemical Physics
Volume25
Issue number30
Early online date18 Jul 2023
DOIs
Publication statusPublished - 14 Aug 2023

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