Acid-resistant nanofiltration membrane engineered by sulfonated covalent organic framework for lithium recovery from spent lithium-ion batteries leaching solutions

Abstract

Nanofiltration (NF) represents a promising green technology for the selective separation of Li⁺ from the acid leaching solution of spent lithium-ion batteries (LIBs). However, the conventional semi-aromatic polyamide NF membrane is vulnerable to H⁺ attack, causing the severe degradation of both membrane’s structure and its separation performance. In this work, an acid-resistant NF membrane was fabricated by incorporating sulfonated covalent organic frameworks (COF-SO₃H), which served as a muti-functional combination of aqueous phase reactive monomer, diffusion regulator and charge-tunable nanofillers. During the interfacial polymerization process, COF-SO₃H contributed to form a relatively loose and conductive PA layer, which was linked by tertiary amide and sulfonamide groups. As a result, the NF membrane was endowed with outstanding antibacterial and acid-resistant properties. Under an electric field, when using a high-salinity Na₂SO₄ of 15 g·L^-1 as feed solution, the NF membrane exhibited a water permeance of 77.60 L·m⁻²·h⁻¹·MPa⁻¹. This value was an order magnitude higher than that of the pristine PA membrane, while achieving a high Na₂SO₄ rejection of 99.8 %. Even after long-term immersion in 1.0 mol·L^-1 H₂SO₄ for 14 days, it still demonstrated an uncompromising Na₂SO₄ rejection of over 96 %. In a simulated leaching solution of spend LIBs, it displayed high separation factors of S_Li+/Ni2+, S_Li+/Co2+, S_Li+/Mn2+, which reached 11.7, 12.4 and 10.8, respectively. This work paves the way for an environmentally-friendly approach to developing durable NF membranes for recycling lithium from the leaching solution of spent LIBs.