COF Scaffold Membrane with Gate‑lane Nanostructure for Efficient Li+/Mg2+ Separation

Why It Matters

The breakthrough lifts the long‑standing permeability‑selectivity trade‑off, enabling energy‑efficient lithium extraction from high‑Mg brines and accelerating the supply chain for electric‑vehicle batteries.

Key Takeaways

• True Li+/Mg2+ selectivity reaches 231.9
• Li+ flux 11.5 L·m⁻²·h⁻¹·bar⁻¹
• Membrane rejects >99% Mg2+ for 7 days
• Gate‑lane architecture creates separate Li+ and Cl- lanes
• Roll‑to‑roll fabrication enables scalable spiral‑wound modules

Pulse Analysis

The surge in electric‑vehicle production has intensified demand for lithium, yet traditional brine extraction struggles with the “permeability‑selectivity” dilemma: membranes that let lithium through often allow magnesium to slip through, inflating processing costs. Brine sources such as the Salar de Atacama contain Mg²⁺ concentrations up to 50 times higher than Li⁺, making selective separation a critical bottleneck for sustainable supply chains. Emerging nanofiltration platforms aim to address this gap, but most fall short on either flux or rejection, limiting commercial viability.

The newly reported COF scaffold membrane tackles the problem with a dual‑layer gate‑lane architecture. A 20 nm polyurea gating layer, densely charged positively, acts as a Mg²⁺ barrier, while an underlying COF/PEI scaffold forms parallel nano‑lanes that preferentially conduct Li⁺ and Cl⁻ ions. Molecular dynamics and DFT simulations confirm spatial segregation of charge carriers, translating into a true selectivity of 231.9—far above the ideal benchmark of 80.5. Coupled with a water permeance of 11.5 L m⁻² h⁻¹ bar⁻¹, the membrane delivers high throughput with minimal energy input, and maintains >99% Mg²⁺ rejection across a broad pH range for a week.

Beyond laboratory metrics, the membrane’s thin 135 nm profile and vacuum‑filtration roll‑to‑roll production align with existing spiral‑wound module manufacturing lines, smoothing the path to scale‑up. Its robustness against fouling and chemical attack positions it for direct integration into lithium‑brine plants, seawater pretreatment, and battery‑electrolyte purification. Future work will explore anti‑scaling surface treatments and cost‑effective COF synthesis, while the gate‑lane concept could be adapted for other divalent/monovalent separations such as K⁺/Ca²⁺. By converting ion‑mixing penalties into separation bonuses, this technology could reshape the economics of lithium recovery and support the broader clean‑energy transition.