CO₂ Dynamics in a Flexible Metal-Organic Framework with Gate-Opening Phenomenon

Area of Science:

• Materials Science
• Chemistry
• Chemical Engineering

Background:

• Elastic layer-structured metal-organic framework-11 (ELM-11) is a promising porous material for CO2 adsorption and storage.
• ELM-11 exhibits a unique gate-opening phenomenon, characterized by a sharp increase in CO2 uptake above a threshold pressure.

Purpose of the Study:

• To elucidate the CO2 gate-opening mechanism in ELM-11.
• To investigate the dynamics of CO2 molecules and their interactions with the framework during the gate-opening transition.

Main Methods:

• Variable-temperature 13C solid-state nuclear magnetic resonance (NMR) spectroscopy was employed to study CO2 dynamics.
• 11B, 13C, and 19F magic-angle spinning NMR, alongside in-situ XANES experiments, were used to probe CO2 adsorption sites.

Main Results:

• During gate-opening, CO2 initially adsorbs strongly at a single site with slight gate opening.
• Upon full gate opening, two distinct types of CO2 molecules were identified within the framework.
• Adsorption sites of CO2 were successfully probed using a combination of NMR techniques and XANES.

Conclusions:

• The study provides detailed insights into the CO2 gate-opening mechanism in ELM-11 at a molecular level.
• Understanding these dynamics is crucial for optimizing ELM-11 for efficient CO2 capture and storage applications.