Restoring Porosity and Uncovering Flexibility in Pillared 3D-Linker Metal-Organic Frameworks

Area of Science:

• Materials Science
• Chemistry
• Chemical Engineering

Background:

• Porous adsorbents are crucial for carbon capture, with pressure-swing regeneration being more energy-efficient than temperature-swing methods.
• Flexible metal-organic frameworks (MOFs) with pillared linkers can adjust pore sizes for optimal guest interactions.
• A significant challenge with pillared MOFs is their tendency to collapse after activation, compromising porosity.

Purpose of the Study:

• To develop a novel approach for constructing pillared MOFs that maintain porosity after activation.
• To investigate the structural dynamics and gas adsorption properties of these new MOFs.
• To understand the mechanisms governing the flexibility and phase transformations in these materials.

Main Methods:

• Synthesis of two new pillared MOFs, [Zn2(trz)2(cdc)] and [Zn2(trz)2(Br-cdc)], using cubane-1,4-dicarboxylate (cdc) linkers.
• In situ X-ray powder diffraction coupled with gas adsorption experiments to study structural transformations.
• Advanced characterization techniques and in silico calculations to analyze framework dynamics and coordination flexibility.

Main Results:

• The synthesized MOFs successfully retained their porosity upon activation, exhibiting flexibility.
• Reversible structural transformations between narrow and open pore phases were observed during gas adsorption.
• The new MOFs demonstrated a high enthalpy of CO2 adsorption, attributed to network flexibility.
• Phase transformations were linked to local coordination flexibility around open-metal sites.

Conclusions:

• A new strategy for creating robust, flexible pillared MOFs with retained porosity has been demonstrated.
• These MOFs show promising selective gas adsorption capabilities and high CO2 uptake.
• The findings provide insights into MOF design for efficient carbon capture applications.