Revealing the configurations and host-guest interactions of small aromatics confined in porous frameworks by electron microscopy

TL;DR

This study uses advanced electron microscopy to directly visualize and analyze the configurations and host-guest interactions of small aromatic molecules confined within porous zeolite frameworks at ambient conditions.

Contribution

The paper demonstrates the first application of integrated differential phase contrast STEM to image small aromatics in zeolites, revealing their configurations and interactions at the molecular level.

Findings

Resolved coherent aromatic configurations in MFI channels.

Quantified host-guest interaction strength through image analysis.

Revealed desorption behaviors during in-situ heating.

Abstract

Directly imaging the configurations of small molecules at the ambient temperatures will greatly promote the study of their chemical and physical properties, including the host-guest interactions of organics in porous materials during the adsorption, catalysis and energy storage. However, due to the current challenges on the small-molecule imaging by the (scanning) transmission electron microscopy ((S)TEM), we still have a lack of the molecular-level understandings on the host-guest interactions and other molecular behaviors. Here, we achieved the STEM imaging of various small aromatics confined in the MFI-type zeolite frameworks by using the integrated differential phase contrast (iDPC) technique. Due to the strong confinement effect in MFI channels, the 1D solid-like aromatic columns showed the coherent configurations, which were clearly resolved by enhancing the host-guest interactions. Then, we also evaluated the strength of host-guest interactions directly by the image analysis and revealed the desorption behaviors of confined aromatics during the in-situ heating process. These results not only helped us to reveal the configurations and host-guest interactions of small aromatics during the adsorption/desorption in porous materials, but also expanded the applications of STEM to further study other molecular behaviors in the real space.