Isomeric Porous Cu(I) Triazolate Frameworks Showing Periodic and Aperiodic Flexibility for Efficient CO Separation

Area of Science:

• Materials Science
• Chemistry
• Chemical Engineering

Background:

• Molecule-based crystalline porous materials exhibit guest-induced transformations (periodic flexibility), but their utility in adsorptive separation remains debated.
• Aperiodic flexibility in these materials is less explored, yet potentially offers unique separation capabilities.

Purpose of the Study:

• To investigate the role of periodic versus aperiodic flexibility in carbon dioxide (CO) adsorption and separation using isomeric Cu(I) triazolate frameworks.
• To evaluate the performance of these frameworks under varying pressures and humidity conditions for CO capture applications.

Main Methods:

• Synthesis and characterization of two isomeric Cu(I) triazolate frameworks: α-[Cu(fetz)] (MAF-2Fa) and β-[Cu(fetz)] (MAF-2Fb).
• Quantitative mixture breakthrough experiments to assess CO adsorption capacity and separation efficiency.
• Evaluation of separation performance under high relative humidity conditions.

Main Results:

• MAF-2Fa (periodic flexibility) shows high CO adsorption at high pressures but significant leakage (<1 ppb) at low pressures.
• MAF-2Fb (aperiodic flexibility) exhibits lower high-pressure adsorption but negligible CO leakage (<1 ppb) at low pressures.
• Tandem connection of MAF-2Fa and MAF-2Fb enhances overall CO capture across pressure ranges.
• Both frameworks maintain performance at high humidity; MAF-2Fb shows unique coadsorption at 82% relative humidity, improving purification.

Conclusions:

• Aperiodic flexibility in MAF-2Fb is crucial for achieving highly selective CO separation with ultra-low leakage, outperforming periodic flexibility in MAF-2Fa for low-pressure applications.
• Combining frameworks with different flexibility types offers a synergistic approach for efficient CO capture.
• MAF-2Fb demonstrates potential for enhanced purification processes, particularly under humid conditions.