Uniform Covalent Polymerization of Zirconium-Organic Cages for High-Loading CO₂ Separation Membranes

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Metal-organic cages (MOCs) offer potential for gas separation membranes due to their defined structures and porosity.
• Conventional blending methods lead to MOC aggregation, hindering membrane performance at high loadings.

Purpose of the Study:

• To develop a strategy for fabricating uniform, high-loading, and selective membranes for CO2 separation using MOCs.
• To overcome the aggregation issue of MOCs in membrane applications.

Main Methods:

• Synthesized an amino-functionalized zirconium MOC (ZrTNH2) as a building block.
• Polymerized ZrTNH2 with poly(ethylene glycol)diisocyanate (NCO-PEG-NCO) via nucleophilic addition.
• Fabricated mixed-matrix membranes with high MOC loading.

Main Results:

• Achieved remarkable MOC loading up to 75 wt % while maintaining discrete MOC structures.
• The ZrTNH2-PEG membrane demonstrated high CO2 permeability (577 Barrer) and CO2/N2 selectivity (50) at 2 bar and 298 K.
• Exceeded the performance of previously reported MOC-based membranes.

Conclusions:

• Site-specific polymerization is an effective strategy for creating advanced MOC-based membranes.
• This approach significantly advances the mixed-matrix membrane concept for gas separations.
• The developed membranes represent a new generation of materials for efficient CO2 separation.