Phase diagrams of liquid-phase mixing in multi-component metal-organic framework glasses constructed by quantitative elemental nano-tomography

Abstract

Several distinct mixing processes and resulting microstructures have recently been reported in multicomponent glasses prepared from multiple metal-organic frameworks. Here, two illustrative examples of multicomponent zeolitic imidazolate framework (ZIF) glasses, the (a T ZIF-4-Co) 0.5 (agZIF-62) 0.5 blend and the ag[(ZIF-67) 0.2 (ZIF-62) 0.8 ] flux melted glass, are studied. These materials are characterized by quantitative X-ray energy dispersive spectroscopy in the scanning transmission electron microscope. By advancing a partial ionization cross section methodology using standards of arbitrary morphology, quantitative nanoscale elemental analysis throughout the glass volume is achieved. In turn, phase diagrams describing the mixing states are presented, offering mechanistic insight into the formation of the observed microstructures. Significant miscibility was observed in ag[(ZIF-67) 0.2 (ZIF-62) 0.8 ]. These findings establish phase-segregation and interdiffusion as two processes in multicomponent glass formation, which explains the different outcomes observed in blending and flux melting.

A new route to porous metal–organic framework crystal–glass composites

“…To highlight the advantages of this method of preparation, ZIF-67 (the isostructural cobalt(II) analogue of ZIF-8), and UiO-66 were chosen as the crystalline components. The former has been reported to undergo ux-melting within the liquid state of ZIF-62, 26,27 whilst the latter undergoes partial decomposition. 25 Thus far, stable MOF crystal-glass composites have therefore not been formed from either ZIF-67 or UiO-66.…”

Extraction of 3D quantitative maps using EDS-STEM tomography and HAADF-EDS bimodal tomography

“…Therefore, prior to this normalization, a thresholding was performed in order to define the voxels within the particle, that any intensities smaller than the threshold were set to zero based on the summation of all the elemental maps of 𝑿 𝐴,𝑗 /𝑓 𝐴 . The exact threshold value was determined using a modified edge spread function (ESF) fitting approach [21]. The approach calculates the particle volume for a series of threshold values, and the variation of the threshold relative to the particle volume can be fitted using the ESF.…”

“…The subscripts, 0.2 and 0.8, refer to the weight fraction of each component, and ag refers to melt quenched glass. For additional details of the synthesis and previous EDS tomography analysis of this sample, refer to [20] and [21],…”

“…described in previous reports [20,21]. Here we look specifically at the implementation and results from the quantified HEBT reconstruction.…”

Functional Group Mapping by Electron Beam Vibrational Spectroscopy from Nanoscale Volumes

“…Here, the core loss analysis provides crucial evidence that the functional group signature of the ligands is not eliminated by electron beam induced damage. In addition to this validation experiment, no volume contraction associated with electron beam damage of MOFs 33 was recorded after vibrational and core loss STEM-EELS experiments (see also SI). EEL spectra at N and O K edges and the corresponding maps, shown in Figure 4(b), further illustrate the chemical domain structure inferred from the STEM-EDS analyses, but with enhanced detail highlighting, for example, the bright N π* peak consistent with imidazolate species.…”