Scalable Production and Covalent Functionalization of WS₂ Nanosheets for Membrane Fabrication and Ion Separation

Transition metal dichalcogenide (TMD) membranes offer a promising solution to freshwater scarcity by desalinating seawater through ion blocking. However, research has largely focused on MoS₂ due to its efficient exfoliation via n-butyl lithium intercalation, unlike other TMDs. Here, we report scalable production of WS₂ nanosheets by increasing the Li⁺ intercalation driving force (increasing current density up to 10 mA g^-1 and decreasing cutoff voltage down to 0.7 V) of the electrochemical intercalation method. WS₂ membranes were then fabricated by organohalide functionalization followed by vacuum filtration. The resulting membranes exhibit a high rejection rate of up to 90% for divalent and trivalent cations. The selectivity for monovalent/divalent and monovalent/trivalent cations reaches up to 8.7 and 9.9, respectively, in both single and binary cation solutions. Theoretical calculations reveal that the improved rejection rates of divalent and trivalent cations compared to those of monovalent cations originate from the stronger binding preferences of monovalent cations with functionalized WS₂ membranes.