Supramolecular-Based Ion Separation Membranes for Direct Separation of Concentrated Mixed-Salt Solutions

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Efficient ion separation from concentrated brines is crucial for water sustainability and resource recovery.
• Conventional ion-selective membranes (ISMs) struggle with concentrated solutions due to weak interactions or high diffusion barriers.
• Existing ISMs are limited to dilute solutions, hindering applications in water treatment and resource management.

Purpose of the Study:

• To develop a supramolecular ion-selective membrane (ISM) capable of efficient ion separation from concentrated brines.
• To overcome the trade-off between ion binding affinity and transport kinetics in membrane design.
• To create a dual-channel architecture for selective cation and anion transport.

Main Methods:

• Integration of 18-crown-6 (18C6) macrocycles into the nanochannels of covalent organic frameworks (COFs).
• Formation of a dual-channel architecture with supramolecular pathways for cations and macrocycle-separated channels for anions.
• Experimental characterization and simulation studies to evaluate membrane performance and ion transport mechanisms.

Main Results:

• The 18C6-COF membrane demonstrated high selectivity (S_K⁺/Mg²⁺ = 254.7) and fast permeation (P_K⁺ = 2403 mmol m^-2 h^-1) in concentrated solutions.
• Monovalent cations exhibited rapid transport through the 1D 18C6 channels via a knock-on-like process, even with strong ion-pore interactions.
• The membrane design effectively minimized ion interference and outperformed state-of-the-art ISMs.

Conclusions:

• The developed supramolecular ISM overcomes traditional limitations, enabling efficient ion separation in concentrated brines.
• The dual-channel architecture and strong ion-channel interactions facilitate rapid ion transport without compromising selectivity.
• This research provides a foundation for advanced membranes designed for high-concentration mixed-salt separation and resource recovery.