How does precursor solution concentration influence growth of metal-organic frameworks around metal nanoparticles?

Guoming Lin and Utkur Mirsaidov from the National University of Singapore have used the Hummingbird Scientific Gen IV TEM liquid flow sample holder to visualize the formation of metal nanoparticle@metal−organic framework (NP@MOF) hybrid nanostructures. As zeolitic imidazolate framework-8 (ZIF-8) shells encapsulated gold nanoparticles, the speed and shape of shell formation were observed to understand how the crystallization pathways can be controlled by manipulation of MOF precursor concentration.

a) Schematic illustrating MOF shell formation on Au NPs to create Au@ZIF-8 nanostructures. Low precursor concentrations are more likely to yield a single cuboidal shell, while higher concentrations promote multi-site nucleation, forming multiple shells around the NP. b) In-situ TEM image series showing the encapsulation of Au NPs by ZIF-8 shells in an aqueous solution containing a low concentration of MOF precursor, in a liquid cell at room temperature. c) Enlarged view of in-situ TEM image series showing the encapsulation of Au NPs by multiple ZIF-8 shells in an aqueous solution with a higher MOF precursor concentration, in a liquid cell at room temperature. d) STEM and EDX images of a Au@ZIF-8 nanostructure on the SiNx window of a liquid cell after the in-situ growth in a low concentration of MOF precursor. e) STEM and corresponding EDX images of a Au@ZIF-8 nanostructure on the SiNx window of a liquid cell after the in-situ growth in a higher concentration of MOF precursor. Copyright © 2025 Guoming Lin, Utkur Mirsaidov, Advanced Science Published by Wiley-VCH GmbH

Ultra-low electron-flux in situ liquid phase TEM was used to achieve the resolution necessary to observe crystallization, without damaging the metal-organic frameworks. Observation showed that at low concentrations of MOF precursor, NPs are typically encapsulated within well-defined single-crystalline MOF shells, while at high concentrations, MOFs tend to nucleate and grow much faster, often from multiple sites on the NP surface. This resulted in irregularly shaped polycrystalline MOF shells at high concentrations. Uniformity of synthesized hybrid nanostructures is important applications in catalysis, underscoring the importance of understanding how MOF precursor concentration can be used to optimize of the speed and shape of crystallization.

Guoming Lin, Utkur Mirsaidov, Encapsulation of Metal Nanoparticles by Metal–Organic Framework Imaged with In Situ Liquid Phase Transmission Electron Microscopy. Adv. Sci. 2025, 12, 2500984. DOI: 10.1002/advs.202500984

Full paper Copyright © 2025 Guoming Lin, Utkur Mirsaidov, Advanced Science Published by Wiley-VCH GmbH

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