Constructing robust NGO-grafted polyamide membranes for efficient Mg2+/Li+ separation from salt-lake brines

Achieving high permselectivity and strong tolerance is crucial for Mg 2+ /Li + separation membranes in salt lake lithium extraction. This study proposes an innovative strategy to covalently graft nitrogen-functionalized graphene oxide (NGO) onto the polyamide membrane surface. NGO was prepared by modifying GO with PEI. The polyamide membrane was synthesized via interfacial polymerization of PEI and TMC. PEI modification increases GO interlayer spacing to suppress aggregation, while GO rigidity facilitates PEI chain extension to enhance the positive charge density, whereas residual carboxyl groups from NGO provide specific ion transport channels. Simultaneously, covalent reaction ensures NGO uniform and stable grafting and prevents acyl chloride hydrolysis, constructing a robust outer barrier layer. This strategy enhances membrane stability, acid-resistance, and antibacterial properties. Consequently, the membrane flux reaches 62.7 L·m −2 ·h −1 , and the Mg 2+ /Li + separation factor is 43.12. A two-stage separation factor reaches 170.21. This membrane technology holds significant application potential in lithium extraction from salt lakes.