Focused ion beam milling and MicroED structure determination of metal-organic framework crystals

We report new advancements in the determination and high-resolution structural analysis of beam-sensitive metal organic frameworks (MOFs) using microcrystal electron diffraction (MicroED) coupled with focused ion beam milling at cryogenic temperatures (cryo-FIB). A microcrystal of the beam-sensitive MOF, ZIF-8, was ion-beam milled in a thin lamella approximately 150 nm thick. MicroED data were collected from this thin lamella using an energy filter and a direct electron detector operating in counting mode. Using this approach, we achieved a greatly improved resolution of 0.59 Å with a minimal total exposure of only 0.64 e-/A2. These innovations not only improve model statistics but also further demonstrate that ion-beam milling is compatible with beam-sensitive materials, augmenting the capabilities of electron diffraction in MOF research.

Beam-sensitive metal-organic framework structure determination by microcrystal electron diffraction

Analysis of metal-organic framework (MOF) structure by electron microscopy and electron diffraction offers an alternative to growing large single crystals for high-resolution X-ray diffraction. However, many MOFs are electron beam-sensitive, which can make structural analysis using high-resolution electron microscopy difficult. In this work we use the microcrystal electron diffraction (MicroED) method to collect high-resolution electron diffraction data from a model beam-sensitive MOF, ZIF-8. The diffraction data could be used to determine the structure of ZIF-8 to 0.87 Å from a single ZIF-8 nanocrystal, and this refined structure compares well with previously published structures of ZIF-8 determined by X-ray crystallography. This demonstrates that MicroED can be a valuable tool for the analysis of beam-sensitive MOF structures directly from nano and microcrystalline material.

Graphene oxide membranes with narrow inter-sheet galleries for enhanced hydrogen separation

This paper reports synthesis of graphene oxide (GO) membranes with narrow interlayer free spacing on scalable polyester substrates using GO sheets prepared by Brodie's method. The GO membranes show interlayer free spacing of ∼3.2 Å with significantly improved hydrogen perm-selectivity than the GO membranes with the large inter-sheet spacing reported in literature.