Fast three-dimensional nanoimaging of electron-beam-sensitive metal-organic frameworks-encapsulated materials

Abstract

Understanding the three-dimensional (3D) micro-arrangement of active phases in metal-organic frameworks (MOFs) is paramount for the rational design of MOFs-based encapsulation materials. While electron tomography (ET) enables 3D reconstruction of real-space microstructures with high spatial resolution, conventional ET is time-consuming and dose-intensive, which sacrifices characterization efficiency and introduces the risk of sample damage. Herein we develop a pre-calibration fast ET acquisition method that reduces ET series acquisition time from 1 h 20 min to 9 min 54 s and decreases the cumulative electronic dose by 88.9%. The fast ET delivers detailed 3D information of metal nanoparticles encapsulated within zeolitic imidazolate framework-8 (MNPs@ZIF-8). Unlike ambiguous qualitative assessment in two-dimensional (2D) projections, we precisely quantify the encapsulation efficiency, aggregation ratio, radial distribution and nearest-neighbor distance (NND) of MNPs based on the 3D reconstruction. These unique analyses reveal that MNPs’ encapsulation exhibits two modes: saturated adsorption and adsorption decay, which can be regulated by altering the relative abundance between MNPs and adsorption active sites. It is also found that MNPs exhibit unbiased isotropic dispersion characteristics, which is evidenced by the NND following a single-peaked Gaussian distribution. This work achieves a leap from 2D qualitative to 3D quantitative analysis of MOFs-encapsulated materials, thereby paving the way to structure-oriented rational design.

Keywords

Metal-organic frameworks / transmission electron microscopy / fast electron tomography / metal nanoparticles / encapsulation / electron-beam-sensitive materials

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