Functional Chain Engineering in MOFs: Balancing Pore Size and Affinity for Noble Gas Separation

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Efficient separation of xenon (Xe) from krypton (Kr) is critical for various applications.
• Adsorbent materials with tailored pore environments are needed to enhance Xe adsorption via van der Waals interactions.
• Metal-organic frameworks (MOFs) offer tunable structures for gas separation challenges.

Purpose of the Study:

• To synthesize and investigate a series of mixed-ligand MOFs for selective Xe/Kr separation.
• To optimize pore size and environment within MOFs for enhanced Xe adsorption.
• To evaluate the performance of ML-80C8 as a selective adsorbent for Xe/Kr mixtures.

Main Methods:

• A mixed-ligand strategy was employed to synthesize five MOFs based on the IRMOF-1 framework.
• Varying ratios of terephthalic acid (BDC) and 2,5-bis(octyloxy)-1,4-benzenedicarboxylic acid (C8BDC) were used to tune pore size.
• Gas adsorption isotherms and dynamic mixture separation experiments were conducted to assess performance.

Main Results:

• Increasing C8BDC content progressively reduced MOF pore size, with ML-80C8 (80% C8BDC) showing optimal pore characteristics.
• ML-80C8 achieved a high Xe uptake of 0.96 mmol g⁻¹ and a Xe/Kr selectivity of 12.1.
• The material demonstrated excellent separation performance under dynamic conditions, stability, and regenerability.

Conclusions:

• Mixed-ligand MOFs provide a viable route for designing tailored pore environments for selective noble gas separation.
• ML-80C8 exhibits superior Xe/Kr separation performance, comparable to benchmark MOFs.
• This study highlights the potential of MOFs in advancing Xe/Kr separation technologies.