Tailoring sub-nanochannels and ion-imprinted functionality of palygorskite nanofiltration membranes for desalination and lithium-ion transport

Nanofiltration membranes featuring sub-1-nm channels have demonstrated considerable potential for desalination and ion separation. However, the construction of both high selectivity and permeance membranes with tailorable one-dimensional (1D) sub-1-nm channels using a versatile and eco-friendly protocol remains a formidable challenge. Here, high selectivity PAL-CMC hybrid (PCH) nanofiltration membranes were successfully prepared based on the coordination-driven self-assembly between natural Palygorskite (PAL) nanorods and carboxymethylcellulose (CMC) in water. We first discovered the ion-imprinting adsorption feature of Mg²⁺ on PAL. By adjusting the coordination ratio, the PCH membrane retains only the natural 1D straight sub-1-nm channels of PAL nanorods, rendering it one of the few membranes capable of ultra-fast water transport (> 25 L m^-2 h^-1 bar^-1) and exceptional salt retention (97.4% for Na₂SO₄ and 86.2% for NaCl). Through applying ion imprinting technology, Mg²⁺-imprinting sites enable the membrane to transport Li⁺ rapidly and selectively in mixture solutions containing Mg²⁺, achieving a Li⁺/Mg²⁺ selectivity of up to 175. Molecular dynamics simulations indicate that water and lithium ions can be transported rapidly through the intrinsic and tailored sub-1-nm channels of PAL nanorods, respectively. These findings establish PCH membranes as prospective candidates for desalination and lithium extraction from lagoons.