Enhanced CO₂ Uptake in Cobalt-Based MOFs via Textural Optimization and Water-Induced Flexibility

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Developing metal-organic frameworks (MOFs) for carbon capture faces challenges in achieving high CO2 uptake, ultramicroporosity, and stability under humid conditions.
• Existing MOFs often struggle with pore accessibility and performance degradation in the presence of moisture.

Purpose of the Study:

• To develop an optimized synthetic strategy for a robust cobalt-based MOF with enhanced CO2 capture capabilities.
• To unlock latent ultramicroporosity and improve performance under realistic, humid conditions.

Main Methods:

• A rational and optimized synthetic strategy was employed to eliminate Co(OH)2 impurities in a cobalt-based MOF using Co(II) nodes and a multitopic 3,6 N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (trz2An) linker.
• Characterization involved static CO2 adsorption measurements and dynamic breakthrough experiments using CO2:N2 mixtures.

Main Results:

• The optimized MOF exhibited a 50% increase in accessible surface area with a narrow pore size distribution (3.6 Å), crucial for CO2:N2 selectivity.
• Static CO2 uptake reached 5 mmol g-1 at 0 °C. Dynamic experiments showed excellent separation performance and stability over 15 cycles.
• Notably, CO2 uptake increased by 65% under humid conditions, attributed to transient pore opening, outperforming non-optimized analogues and most CO2 adsorbents.

Conclusions:

• Targeted synthetic control can activate latent porosity in rigid ultramicroporous MOFs, leading to enhanced CO2 capture.
• The optimized cobalt-based MOF demonstrates a viable pathway for CO2 capture under realistic operating conditions, including humid environments.
• The material's unique response to humidity offers a novel approach for improving adsorbent performance.