Metal-Hydroxide-Porphin Framework Membrane for Almost Perfectly Selective Li⁺ Retention

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Membrane separation is crucial for green direct lithium extraction from brines.
• Efficiently separating lithium ions (Li+) from competing alkaline ions remains a challenge.

Purpose of the Study:

• To develop a metal-hydroxide-porphin framework membrane for selective lithium ion (Li+) separation.
• To investigate the membrane's ability to retain Li+ while allowing passage of other cations.

Main Methods:

• Fabrication of a crystalline metal-hydroxide-porphin framework membrane.
• Utilizing density functional theory (DFT) calculations to understand ion-porphin interactions.
• Conducting ion transport experiments under low external voltage.

Main Results:

• The membrane selectively retains Li+ while allowing Na+, K+, Ca2+, and Mg2+ to pass.
• Porphin molecules within the membrane exhibit strong interactions with Li+, preventing its translocation.
• Complete rejection of Li+ transport observed for monovalent cations, with passage of divalent ions under low voltage.

Conclusions:

• Metal-hydroxide-porphin framework membranes show promise for selective ion sieving.
• This technology offers a versatile platform for direct lithium extraction and ion separation applications.