Visualizing the Conversion of Metal-Organic Framework Nanoparticles into Hollow Layered Double Hydroxide Nanocages

Hollow layered double hydroxide (LDH) nanostructures derived from metal-organic framework (MOF) nanoparticles (NPs) are candidate materials for applications in catalysis and energy storage. MOF NPs serve as a sacrificial template and are converted into LDH nanomaterials through two simultaneous processes: etching of the NPs and growth of LDHs on the NP surfaces. However, for these conversion processes, early reaction stages, intermediate products, and details of their reaction kinetics are still unknown. Using liquid-phase transmission electron microscopy (TEM), we show that cubic and rhombic dodecahedron (RD) ZIF-8 NPs convert into hollow LDH nanocages via the nucleation and growth of LDH nanosheets on their surface as the MOF NPs gradually etch. These direct in situ observations reveal that, in these reactions, maintaining comparable etching and growth rates is key to forming well-defined hollow nanostructures that retain the shape of the underlying MOF NP template. Our study provides a critical insight pivotal to the design and synthesis of complex MOF-derived hollow nanomaterials.