Enhancing Ion Selectivity of Nanofiltration Membranes via Heterogeneous Charge Distribution

Area of Science:

• Materials Science
• Chemical Engineering
• Separation Science

Background:

• Nanofiltration is crucial for separating ions like lithium (Li) and magnesium (Mg) during extraction from salt lakes.
• Understanding membrane spatial charge distribution is key to improving ion selectivity.
• Existing technologies face challenges in precisely separating monovalent and multivalent ions.

Purpose of the Study:

• To investigate the impact of membrane spatial charge distribution on ion-selective separation.
• To develop and evaluate novel mixed-charge membranes for enhanced Li/Mg separation.
• To elucidate the mechanisms governing ion selectivity in charge-mosaic membranes.

Main Methods:

• Synthesis of two types of mixed-charge membranes with varied charge distributions.
• Characterization of membrane properties, including pore size and charge distribution.
• Performance evaluation using nanofiltration experiments for ion fractionation.
• Application of mathematical modeling and machine learning to analyze selectivity.

Main Results:

• A novel charge-mosaic membrane achieved high water permeance (15.4 LMH/bar) and exceptional Li/Mg selectivity (108).
• Spatial charge distribution was identified as the dominant factor determining ion selectivity.
• The charge-mosaic structure effectively enhanced selectivity via localized Donnan effects.
• Performance remained stable despite variations in feedwater concentration.

Conclusions:

• Charge-mosaic membranes offer a promising approach for precise ion separation in nanofiltration.
• This technology has significant implications for lithium extraction, water treatment, and energy storage.
• The findings highlight the critical role of membrane design in achieving high ion selectivity.