Understanding the adsorption process in ZIF-8 using high pressure crystallography and computational modelling

Area of Science:

• Materials Science
• Chemistry
• Crystallography

Background:

• Porous crystalline solids, such as metal-organic frameworks (MOFs), exhibit structural changes upon guest molecule inclusion.
• Understanding framework-guest interactions is crucial for optimizing MOF applications.

Purpose of the Study:

• To investigate gas uptake mechanisms and framework-guest interactions in ZIF-8 MOFs.
• To characterize structural and energetic changes during gas adsorption at high pressures.

Main Methods:

• Cryogenic high-pressure loading of liquefied gases into ZIF-8.
• High-pressure single-crystal X-ray diffraction.
• Grand canonical Monte Carlo (GCMC) simulations.
• Periodic Density Functional Theory (DFT) calculations.

Main Results:

• Identification of six distinct, symmetry-independent gas adsorption sites within the ZIF-8 framework.
• Observation of a structural phase transition to a high-pressure phase.
• Classification of adsorption sites based on interaction energies derived from GCMC simulations.
• Determination of the energy barrier for the high-pressure phase transition via DFT.

Conclusions:

• The integrated experimental and computational approach provides atomistic insights into gas adsorption in MOFs.
• The cryogenic high-pressure loading method is effective for detailed characterization.
• This study offers a holistic understanding of adsorption-induced structural and energetic modifications in porous materials.