Tailoring sub-nanochannels of palygorskite-derived membranes for desalination and selective lithium-ion transport

Abstract Nanofiltration membranes featuring sub-1 nm channels have shown significant potential for desalination and ion separation. However, the construction of scalable membranes with tailorable one-dimensional (1D) sub-1 nm channels using a versatile and eco-friendly protocol remains a formidable challenge. In this study, we present an approach to tuning sub-1 nm channels using natural palygorskite (PAL) nanorods with carboxymethylcellulose (CMC) cross-linkers to control density and enhance stability of membrane. The sub-1 nm channels of the membrane were further regulated by an ion-imprinting technique to enable fast and selective transport of Li⁺. The resulting PAL-CMC hybrid (PCH) membranes only retained the natural 1D straight sub-1 nm channels of PAL nanorods by adjusting the CMC content, making them among 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). Notably, PCH membranes regulated by ion-imprinting technique exhibit unprecedented Li⁺ selectivity from ionic mixture solutions containing Mg²⁺, achieving a separation factor (SMg2+/ Li+) up to 32.5. Molecular dynamics simulations revealed rapid Li⁺ transport through the sub-1 nm channel of PAL. These findings position PCH membranes as next-generation candidates for desalination and Li⁺ extraction from lagoons.