Synergistic effect of size sieving, electrostatic interaction and interfacial electric field for highly-precisive Li+ separation with graphene oxide-based membrane

The sustainable and efficient lithium supply is one of the prerequisites and important supports for the transformation of global energy towards electrification and decarbonization. However, current established membrane materials for lithium recovery from salt-lake brine with high Mg/Li ratio still suffer from complex preparation process, poor stability and low selectivity. Herein, we develop a stable graphene oxide (GO)-based membrane with controllable interlayer spacing at angstrom level and positive charged surface through a facile method for highly efficient lithium separation. Specially, the interlayer spacing is precisely adjusted using dicarboxylic acids with different chain lengths through esterification reaction with GO sheets, and the poly(allylamine) (PAA) is coated on it to construct the positive charged surface. Experiments with DFT calculations demonstrate that the geometrical configuration of GO-dicarboxylic acid and the interlayer spacing with glutaric acid (GA) is most suitable for Li + separation. The synergy between crosslink of dicarboxylic acid and permeation of PAA enhances the stability of membrane. The obtained GO-GA-PAA membrane exhibits excellent Li + sieving performance with Li + /Mg 2+ selectivity up to 34.41 under the optimal operation condition, and outstanding cycling stability. The characterizations including solid zeta potential and atomic force microscope (AFM) indicate that the presence of positive charges on the surface can remarkably improve the Li + /Mg 2+ selectivity. The surface positive charge exerts stronger electrostatic repulsive towards Mg 2+ , which can also generate an interfacial electric field to induce the dehydration of Li + , ultimately promoting the transmission of Li + across the membrane. The synergistic effect of size sieving, electrostatic repulsive and interfacial electric field is proposed as the fundamental mechanism of Li + selective separation. This work opens an avenue for designing new strategies to recover lithium from salt-lake, which can also potentially be extended to the recovery of strategic metals from other complex systems.