Synergistic Nitrogen Binding Sites in a Metal-Organic Framework for Efficient N₂ /O₂ Separation

Area of Science:

• Materials Science
• Chemistry
• Chemical Engineering

Background:

• Porous materials with open metal sites are crucial for nitrogen (N₂) capture and N₂/O₂ separation.
• Existing materials struggle to balance adsorption capacity and selectivity.
• The d³ electronic configuration of metal sites influences adsorption properties.

Purpose of the Study:

• To develop a robust metal-organic framework (MOF) for enhanced N₂ capture and N₂/O₂ separation.
• To address the trade-off between adsorption capacity and selectivity in current adsorbents.
• To investigate the synergistic adsorption mechanisms in the novel MOF.

Main Methods:

• Synthesis and characterization of a novel chromium-based MOF, MIL-102Cr.
• Gas adsorption isotherms (N₂, O₂) measurement at 298 K and 1.0 bar.
• Breakthrough experiments for N₂/O₂ mixture separation.
• In situ infrared spectroscopy and computational modeling to elucidate adsorption mechanisms.

Main Results:

• MIL-102Cr exhibits a benchmark N₂ isosteric heat of adsorption (Qst) of 45.0 kJ/mol among Cr-based MOFs.
• Achieved a record-high volumetric N₂ uptake of 31.38 cm³/cm³.
• Demonstrated the highest N₂/O₂ selectivity of 13.11 at 298 K and 1.0 bar.
• Efficiently captured N₂ from a 79/21 N₂/O₂ mixture, yielding 99.99% pure O₂ with a productivity of 0.75 mmol/g.
• Synergistic adsorption by open Cr(III) and fluorine sites was identified as the key interaction mechanism.

Conclusions:

• MIL-102Cr is a highly effective adsorbent for N₂ capture and N₂/O₂ separation.
• The synergistic adsorption effect enhances N₂ affinity and selectivity.
• This MOF presents a promising solution for efficient gas separation challenges.