COF Scaffold Membrane with Gate-Lane Nanostructure for Efficient Li⁺/Mg²⁺ Separation

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Achieving efficient ion separation with high selectivity and permeability is challenging due to complex ion interactions.
• Existing membrane technologies struggle to balance ion mixing effects and separation performance.

Purpose of the Study:

• To design and fabricate a novel covalent organic framework (COF) scaffold membrane with a gate-lane nanostructure for efficient Li+/Mg2+ separation.
• To enhance ion selectivity and permeability by engineering hierarchical membrane structures.

Main Methods:

• Fabrication of a COF scaffold membrane by intercalating COF nanosheets with polyethyleneimine (PEI).
• Formation of a polyurea gating layer on the surface via reaction of PEI with 1,4-phenylene diisocyanate.
• Characterization of membrane performance for Li+/Mg2+ separation, including permeance and selectivity.

Main Results:

• The optimized COF scaffold membrane achieved a permeance of 11.5 L m-2 h-1/bar-1 and a true selectivity of 231.9 for Li+/Mg2+ separation.
• Demonstrated Li+ enrichment of 120.2% at a Mg2+/Li+ mass ratio of 50, exceeding ideal selectivity.
• Outperformed all previously reported positively charged nanofiltration membranes in Li+/Mg2+ separation.

Conclusions:

• The developed gate-lane nanostructure effectively enhances Li+/Mg2+ separation performance by controlling ion transport.
• The hierarchical membrane design successfully breaks the conventional permeability-selectivity trade-off in chemical separations.
• This work provides a new strategy for designing advanced membranes for efficient ion separation.