Metal-Dependent Adsorption Mechanism in Perfluorinated MIL-140A Metal-Organic Frameworks

Area of Science:

• Materials Science
• Chemistry
• Nanotechnology

Background:

• Perfluorinated metal-organic frameworks (MOFs) are advanced porous materials with tunable properties.
• The MIL-140A topology is a known framework structure with potential applications in gas adsorption.
• Understanding metal-dependent properties is crucial for designing MOFs with specific functionalities.

Purpose of the Study:

• To investigate the metal-dependent adsorption behavior of perfluorinated MOFs with MIL-140A topology.
• To elucidate the structural factors influencing gas (CO2) and water adsorption in these MOFs.
• To compare the adsorption characteristics of cerium (CeIV) and zirconium (ZrIV) analogues.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy.
• In situ infrared (IR) spectroscopy.
• Variable temperature powder X-ray diffraction (PXRD).

Main Results:

• The CeIV analogue ([F4_MIL-140A-(Ce)]) displayed step-shaped CO2 adsorption isotherms and strong H2O affinity, linked to linker rearrangement.
• The ZrIV analogue ([F4_MIL-140A-(Zr)]) showed a type I CO2 isotherm with lower capacity and weak H2O affinity.
• Contrasting behavior is attributed to the absence of open metal sites and inability to form octacoordinated geometry in ZrIV-MOFs.

Conclusions:

• Metal identity significantly impacts adsorption properties in perfluorinated MIL-140A MOFs.
• Structural rigidity and coordination geometry around the metal center dictate metal-guest interactions.
• These findings offer insights for designing MOFs for selective gas and water adsorption applications.