Sustainable lithium extraction enabled by responsive metal-organic frameworks with ion-sieving adsorption effects

Area of Science:

• Materials Science
• Environmental Chemistry
• Nanotechnology

Background:

• Metal-organic frameworks (MOFs) are effective ion adsorbents.
• Achieving lithium selectivity over divalent cations with MOFs is challenging due to framework flexibility and similar ion properties.
• Existing methods often lack efficiency and selectivity in complex aqueous solutions.

Purpose of the Study:

• To design sunlight-regenerable lithium adsorbents with enhanced selectivity using subnanoporous MOFs.
• To investigate the ion-sieving adsorption behavior of MOFs with varying pore sizes.
• To develop an energy-efficient method for lithium extraction from brines.

Main Methods:

• Integration of ion-sieving MOFs with light-responsive polyspiropyran (PSP) adsorption sites.
• Synthesis of PSP-MOFs with controlled pore window sizes (6.0, 8.5, and 10.0 Å).
• Evaluation of LiCl adsorption capacity, Li+/Mg2+ selectivity, and sunlight-driven regeneration.

Main Results:

• PSP-MOF adsorption capacity was inversely proportional to pore size.
• The 6.0 Å PSP-UiO-66 exhibited a high LiCl adsorption capacity (10.17 mmol g-1).
• Demonstrated Li+/Mg2+ selectivity ranging from 5.8 to 29 in synthetic brines and rapid sunlight regeneration (6 min) with 99% capacity retention over five cycles.

Conclusions:

• The developed ion-sieving adsorption approach enables selective lithium extraction using responsive subnanoporous MOFs.
• Sunlight-regenerable PSP-MOFs offer an environmentally friendly and energy-efficient solution for ion separation.
• This strategy paves the way for designing advanced materials for selective ion purification.