Enhanced Li+/Mg2+ selectivity of two-dimensional montmorillonite membranes by end-face and interfacial layer constraint for nanosheets

Abstract

The novel two-dimensional (2D) channel membranes have great potential for effective Li+/Mg2+ separation due to the rapid ion transport and precise adjustment of their channels. However, the solution composition greatly affects the control of channel height, resulting in an unsatisfactory selectivity performance. Herein, the 2D montmorillonite membranes are used to understand the causes of channel instability and explore the effective solutions. It is found that the changes in solution component can enlarge the channel height by changing the cross-linking constraint of Fe3+ between MMT nanosheets, thus leading to a weak sieving effect. To improve the channel constraint and its Li+/Mg2+ separation, the end face and interfacial layer constraint of nanosheets are proposed. As an effective strategy to strengthen the constraint effect, glutathione can modify the end faces of nanosheets and enhance the mutual binding force between them through its oxidative transformation. Besides, the construction of an interfacial layer can also limit channel swelling by altering the membrane hydration and wetting. These strategies will also form a synergistic regulatory effect. Consequently, a superior membrane is obtained and presents an improved selectivity of 8.89 at 100:1 Mg2+/Li+ ratio. These innovative approaches offer a valuable framework for creating high-performance 2D channel membranes, which can also support their wider application in the Li+/Mg2+ separation.