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.