Adsorption Contraction Mechanics: Understanding Breathing Energetics in Isoreticular Metal-Organic Frameworks

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are advanced porous materials with tunable structures.
• Understanding MOF flexibility and gas adsorption is crucial for applications like gas storage and energy absorption.
• DUT-48 and DUT-49 are isoreticular MOFs with distinct structural and adsorption properties.

Purpose of the Study:

• To investigate the mechanical flexibility and adsorption-induced behavior of DUT-48 and DUT-49.
• To explain the differences in adsorption-induced structural transitions between DUT-48 and DUT-49.
• To evaluate the potential of these MOFs as shock-absorbing materials.

Main Methods:

• Synthesis and characterization of DUT-48.
• High-pressure methane adsorption measurements.
• Adsorption microcalorimetry.
• Molecular simulations (Monte Carlo and molecular dynamics).
• Mercury porosimetry experiments.
• Hydrostatic compression studies.

Main Results:

• DUT-48 exhibits a high surface area (4560 m²·g⁻¹) and methane storage capacity (0.27 g·g⁻¹ at 6.5 MPa).
• Both DUT-48 and DUT-49 contract under mechanical pressure.
• Only DUT-49 shows adsorption-induced structural transitions and negative gas adsorption for n-butane and nitrogen.
• DUT-48's lower adsorption enthalpy difference and higher framework stiffness prevent adsorption-induced breathing.
• Both MOFs demonstrate significant volume changes under hydrostatic compression, indicating potential as shock absorbers.

Conclusions:

• DUT-48's inherent properties limit its adsorption-induced flexibility, unlike DUT-49.
• The differing adsorption behaviors are attributed to variations in adsorption enthalpy and framework stiffness.
• DUT-48 and DUT-49 show promise as high-performance shock-absorbing materials due to their mechanical compressibility.