Defect Engineering in Fluorinated Metal-Organic Frameworks Within Mixed-Matrix Membranes for Enhanced CO₂ Separation

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Developing energy-efficient membranes for CO2/CH4 separation is crucial but challenging.
• Mixed-matrix membranes (MMMs) using metal-organic frameworks (MOFs) show promise but face filler-matrix compatibility issues.
• Existing MOF-based MMMs struggle to balance permeability and selectivity.

Purpose of the Study:

• To engineer defects in fluorinated MOF ZU-61 to create high-porosity nanoparticles (HP-ZU-61).
• To fabricate and evaluate HP-ZU-61/6FDA-DAM MMMs for CO2/CH4 separation.
• To investigate the mechanism behind the enhanced separation performance.

Main Methods:

• Defect engineering of ZU-61 MOF by partial linker replacement to create HP-ZU-61 nanoparticles.
• Fabrication of HP-ZU-61/6FDA-DAM MMMs with 30 wt.% filler loading.
• Characterization of MMMs for filler dispersion, crystallinity, and gas separation performance (CO2 permeability, CO2/CH4 selectivity).
• Solution-diffusion modeling to understand gas transport mechanisms.

Main Results:

• HP-ZU-61 nanoparticles showed a 267% increase in BET surface area compared to LP-ZU-61.
• HP-ZU-61/6FDA-DAM MMMs exhibited homogeneous dispersion and preserved crystallinity.
• Achieved a CO2 permeability of 1626 barrer and CO2/CH4 selectivity of 33, exceeding the 2008 Robeson upper bound.
• Defects facilitated faster diffusion and unsaturated metal sites enhanced CO2 adsorption.

Conclusions:

• Defect engineering in fluorinated MOFs is a viable strategy to enhance nanoparticle porosity.
• HP-ZU-61/6FDA-DAM MMMs demonstrate superior CO2/CH4 separation performance by overcoming the permeability-selectivity trade-off.
• This approach offers a practical route for developing efficient membranes for CO2 capture.