Simultaneous Electrochemical Exfoliation and Covalent Functionalization of MoS₂ Membrane for Ion Sieving

Transition metal dichalcogenide membranes exhibit good antiswelling properties but poor water desalination property. Here, a one-step covalent functionalization of MoS₂ nanosheets for membrane fabrication is reported, which is accomplished by simultaneous exfoliating and grafting the lithium-ion-intercalated MoS₂ in organic iodide water solution. The lithium intercalation amount in MoS₂ is optimized so that the quality of the produced 2D nanosheets is improved with homogeneous size distribution. The lamellar MoS₂ membranes are tested in reverse osmosis (RO), and the functionalized MoS₂ membrane exhibits rejection rates of >90% and >80% for various dyes (Rhodamine B, Crystal Violet, Acid Fuchsin, Methyl Orange, and Evans Blue) and NaCl, respectively. The excellent ion-sieving performance and good water permeability of the functionalized MoS₂ membranes are attributed to the suitable channel widths that are tuned by iodoacetamide. Furthermore, the stability of the functionalized MoS₂ membranes in NaCl and dye solutions is also confirmed by RO tests. Molecular dynamics simulation shows that water molecules tend to form a single layer between the amide-functionalized MoS₂ layers but a double layer between the ethanol-functionalized MoS₂ (MoS₂ -ethanol) layers, which indicates that a less packed structure of water between the MoS₂ -ethanol layers leads to lower hydrodynamic resistance and higher permeation.