Multiple Li+ extraction mechanisms of sulfate saline by graphene nanopores: Effects of ion association under electric fields

Abstract

In this work, the extraction of Li+ from sulfate solution by functionalized nanopores under various electric fields was investigated by molecular dynamics simulation. It was found that the dynamics of ion association and dissociation near nanopores play an important role in regulating the ion selectivity mechanism. When a strong electric field is applied (1.4 V nm−1), the ion transport can be affected by ion association enhanced near nanopore and the following dissociation near nanopore. Mg2+ is affected more apparently by ion association characteristics near nanopores than Li+, and thus rendering Li+ selectivity. Good separation of Mg2+ and Li+ can also be achieved by large nanopores of 3.5 nm, which is beneficial for the reverse migration of Mg2+ included in negatively charged structures. Alternatively, the strong association of Mg2+ with the COO− groups of nanopores may also be an important factor of Li+ selectivity under a relatively weaker electric field (0.6 V nm−1) for smaller nanopores (∼1.2 nm) and a dilute solution. Our results provide inspiration for the practical separation and purification of Li+ from sulfate-type saline.