Span80 induced orderly diffusion of monomer for the construction of small pore volume polyamide nanofiltration membrane with high Li/Mg separation ratio

The key to lithium extraction from brine lies in achieving efficient Li + /Mg 2+ separation, which imposes stringent requirements on the precision and efficiency of separation technologies. Among existing techniques, nanofiltration (NF) membranes stand out as a critical approach due to their superior ion-sieving capabilities, yet conventional NF membranes still face challenges in improving Li + /Mg 2+ separation ratios. In this study, the nonionic surfactant, Sorbitan monooleate dehydrate (Span80) was introduced to regulate the diffusion behavior of piperazine (PIP) molecules by reducing interfacial tension. Results from molecular dynamics simulations, ultraviolet spectroscopy experiments, and positron annihilation lifetime spectroscopy analysis revealed that Span80 enhances the uniform diffusion of PIP molecules at the interface, optimizes the membrane pore size distribution, and significantly improves Li + /Mg 2+ separation performance. The fabricated NF membrane achieved a Li + /Mg 2+ separation ratio of 94.28 under a Mg 2+ /Li + mass ratio of 100:1. This study introduces an innovative strategy for tailoring interfacial reactions via surfactant modulation, providing new insights into the design of high-performance NF membranes for lithium extraction from brine.